## cairo_t cairo_t — The cairo drawing context |

## Synopsis

    typedef             cairo_t;
    cairo_t *           cairo_create                        (cairo_surface_t *target);
    cairo_t *           cairo_reference                     (cairo_t *cr);
    void                cairo_destroy                       (cairo_t *cr);
    cairo_status_t      cairo_status                        (cairo_t *cr);
    void                cairo_save                          (cairo_t *cr);
    void                cairo_restore                       (cairo_t *cr);
    cairo_surface_t *   cairo_get_target                    (cairo_t *cr);
    void                cairo_push_group                    (cairo_t *cr);
    void                cairo_push_group_with_content       (cairo_t *cr,
                                                             cairo_content_t content);
    cairo_pattern_t *   cairo_pop_group                     (cairo_t *cr);
    void                cairo_pop_group_to_source           (cairo_t *cr);
    cairo_surface_t *   cairo_get_group_target              (cairo_t *cr);
    void                cairo_set_source_rgb                (cairo_t *cr,
                                                             double red,
                                                             double green,
                                                             double blue);
    void                cairo_set_source_rgba               (cairo_t *cr,
                                                             double red,
                                                             double green,
                                                             double blue,
                                                             double alpha);
    void                cairo_set_source                    (cairo_t *cr,
                                                             cairo_pattern_t *source);
    void                cairo_set_source_surface            (cairo_t *cr,
                                                             cairo_surface_t *surface,
                                                             double x,
                                                             double y);
    cairo_pattern_t *   cairo_get_source                    (cairo_t *cr);
    enum                cairo_antialias_t;
    void                cairo_set_antialias                 (cairo_t *cr,
                                                             cairo_antialias_t antialias);
    cairo_antialias_t   cairo_get_antialias                 (cairo_t *cr);
    void                cairo_set_dash                      (cairo_t *cr,
                                                             const double *dashes,
                                                             int num_dashes,
                                                             double offset);
    int                 cairo_get_dash_count                (cairo_t *cr);
    void                cairo_get_dash                      (cairo_t *cr,
                                                             double *dashes,
                                                             double *offset);
    enum                cairo_fill_rule_t;
    void                cairo_set_fill_rule                 (cairo_t *cr,
                                                             cairo_fill_rule_t fill_rule);
    cairo_fill_rule_t   cairo_get_fill_rule                 (cairo_t *cr);
    enum                cairo_line_cap_t;
    void                cairo_set_line_cap                  (cairo_t *cr,
                                                             cairo_line_cap_t line_cap);
    cairo_line_cap_t    cairo_get_line_cap                  (cairo_t *cr);
    enum                cairo_line_join_t;
    void                cairo_set_line_join                 (cairo_t *cr,
                                                             cairo_line_join_t line_join);
    cairo_line_join_t   cairo_get_line_join                 (cairo_t *cr);
    void                cairo_set_line_width                (cairo_t *cr,
                                                             double width);
    double              cairo_get_line_width                (cairo_t *cr);
    void                cairo_set_miter_limit               (cairo_t *cr,
                                                             double limit);
    double              cairo_get_miter_limit               (cairo_t *cr);
    enum                cairo_operator_t;
    void                cairo_set_operator                  (cairo_t *cr,
                                                             cairo_operator_t op);
    cairo_operator_t    cairo_get_operator                  (cairo_t *cr);
    void                cairo_set_tolerance                 (cairo_t *cr,
                                                             double tolerance);
    double              cairo_get_tolerance                 (cairo_t *cr);
    void                cairo_clip                          (cairo_t *cr);
    void                cairo_clip_preserve                 (cairo_t *cr);
    void                cairo_clip_extents                  (cairo_t *cr,
                                                             double *x1,
                                                             double *y1,
                                                             double *x2,
                                                             double *y2);
    cairo_bool_t        cairo_in_clip                       (cairo_t *cr,
                                                             double x,
                                                             double y);
    void                cairo_reset_clip                    (cairo_t *cr);
                        cairo_rectangle_t;
                        cairo_rectangle_list_t;
    void                cairo_rectangle_list_destroy        (cairo_rectangle_list_t *rectangle_list);
    cairo_rectangle_list_t * cairo_copy_clip_rectangle_list (cairo_t *cr);
    void                cairo_fill                          (cairo_t *cr);
    void                cairo_fill_preserve                 (cairo_t *cr);
    void                cairo_fill_extents                  (cairo_t *cr,
                                                             double *x1,
                                                             double *y1,
                                                             double *x2,
                                                             double *y2);
    cairo_bool_t        cairo_in_fill                       (cairo_t *cr,
                                                             double x,
                                                             double y);
    void                cairo_mask                          (cairo_t *cr,
                                                             cairo_pattern_t *pattern);
    void                cairo_mask_surface                  (cairo_t *cr,
                                                             cairo_surface_t *surface,
                                                             double surface_x,
                                                             double surface_y);
    void                cairo_paint                         (cairo_t *cr);
    void                cairo_paint_with_alpha              (cairo_t *cr,
                                                             double alpha);
    void                cairo_stroke                        (cairo_t *cr);
    void                cairo_stroke_preserve               (cairo_t *cr);
    void                cairo_stroke_extents                (cairo_t *cr,
                                                             double *x1,
                                                             double *y1,
                                                             double *x2,
                                                             double *y2);
    cairo_bool_t        cairo_in_stroke                     (cairo_t *cr,
                                                             double x,
                                                             double y);
    void                cairo_copy_page                     (cairo_t *cr);
    void                cairo_show_page                     (cairo_t *cr);
    unsigned int        cairo_get_reference_count           (cairo_t *cr);
    cairo_status_t      cairo_set_user_data                 (cairo_t *cr,
                                                             const cairo_user_data_key_t *key,
                                                             void *user_data,
                                                             cairo_destroy_func_t destroy);
    void *              cairo_get_user_data                 (cairo_t *cr,
                                                             const cairo_user_data_key_t *key);

## Description

cairo_t is the main object used when drawing with cairo. To draw with cairo, you create a cairo_t, set the target surface, and drawing options for the cairo_t, create shapes with functions like `cairo_move_to()` and `cairo_line_to()`, and then draw shapes with `cairo_stroke()` or `cairo_fill()`.

cairo_t's can be pushed to a stack via `cairo_save()`. They may then safely be changed, without loosing the current state. Use `cairo_restore()` to restore to the saved state.

## Details

### cairo_t

    typedef struct _cairo cairo_t;

A cairo_t contains the current state of the rendering device, including coordinates of yet to be drawn shapes.

Cairo contexts, as cairo_t objects are named, are central to cairo and all drawing with cairo is always done to a cairo_t object.

Memory management of cairo_t is done with `cairo_reference()` and `cairo_destroy()`.

### cairo_create ()

    cairo_t *           cairo_create                        (cairo_surface_t *target);

Creates a new cairo_t with all graphics state parameters set to default values and with `target` as a target surface. The target surface should be constructed with a backend-specific function such as `cairo_image_surface_create()` (or any other cairo_backend`_surface_create()` variant).

This function references `target`, so you can immediately call `cairo_surface_destroy()` on it if you don't need to maintain a separate reference to it.

`target` : | target surface for the context
Returns : | a newly allocated cairo_t with a reference count of 1. The initial reference count should be released with `cairo_destroy()` when you are done using the cairo_t. This function never returns `NULL`. If memory cannot be allocated, a special cairo_t object will be returned on which `cairo_status()` returns `CAIRO_STATUS_NO_MEMORY`. You can use this object normally, but no drawing will be done.

### cairo_reference ()

    cairo_t *           cairo_reference                     (cairo_t *cr);

Increases the reference count on `cr` by one. This prevents `cr` from being destroyed until a matching call to `cairo_destroy()` is made.

The number of references to a cairo_t can be get using `cairo_get_reference_count()`.

`cr` : | a cairo_t
Returns : | the referenced cairo_t.

### cairo_destroy ()

    void                cairo_destroy                       (cairo_t *cr);

Decreases the reference count on `cr` by one. If the result is zero, then `cr` and all associated resources are freed. See `cairo_reference()`.

`cr` : | a cairo_t

### cairo_status ()

    cairo_status_t      cairo_status                        (cairo_t *cr);

Checks whether an error has previously occurred for this context.

`cr` : | a cairo context
Returns : | the current status of this context, see cairo_status_t

### cairo_save ()

    void                cairo_save                          (cairo_t *cr);

Makes a copy of the current state of `cr` and saves it on an internal stack of saved states for `cr`. When `cairo_restore()` is called, `cr` will be restored to the saved state. Multiple calls to `cairo_save()` and `cairo_restore()` can be nested; each call to `cairo_restore()` restores the state from the matching paired `cairo_save()`.

It isn't necessary to clear all saved states before a cairo_t is freed. If the reference count of a cairo_t drops to zero in response to a call to `cairo_destroy()`, any saved states will be freed along with the cairo_t.

`cr` : | a cairo_t

### cairo_restore ()

    void                cairo_restore                       (cairo_t *cr);

Restores `cr` to the state saved by a preceding call to `cairo_save()` and removes that state from the stack of saved states.

`cr` : | a cairo_t

### cairo_get_target ()

    cairo_surface_t *   cairo_get_target                    (cairo_t *cr);

Gets the target surface for the cairo context as passed to `cairo_create()`.

This function will always return a valid pointer, but the result can be a "nil" surface if `cr` is already in an error state, (ie. `cairo_status()` `!=` `CAIRO_STATUS_SUCCESS`). A nil surface is indicated by `cairo_surface_status()` `!=` `CAIRO_STATUS_SUCCESS`.

`cr` : | a cairo context
Returns : | the target surface. This object is owned by cairo. To keep a reference to it, you must call `cairo_surface_reference()`.

### cairo_push_group ()

    void                cairo_push_group                    (cairo_t *cr);

Temporarily redirects drawing to an intermediate surface known as a group. The redirection lasts until the group is completed by a call to `cairo_pop_group()` or `cairo_pop_group_to_source()`. These calls provide the result of any drawing to the group as a pattern, (either as an explicit object, or set as the source pattern).

This group functionality can be convenient for performing intermediate compositing. One common use of a group is to render objects as opaque within the group, (so that they occlude each other), and then blend the result with translucence onto the destination.

Groups can be nested arbitrarily deep by making balanced calls to `cairo_push_group()`/`cairo_pop_group()`. Each call pushes/pops the new target group onto/from a stack.

The `cairo_push_group()` function calls `cairo_save()` so that any changes to the graphics state will not be visible outside the group, (the pop_group functions call `cairo_restore()`).

By default the intermediate group will have a content type of `CAIRO_CONTENT_COLOR_ALPHA`. Other content types can be chosen for the group by using `cairo_push_group_with_content()` instead.

As an example, here is how one might fill and stroke a path with translucence, but without any portion of the fill being visible under the stroke:

    1
    2
    3
    4
    5
    6
    7
    cairo_push_group (cr);
    cairo_set_source (cr, fill_pattern);
    cairo_fill_preserve (cr);
    cairo_set_source (cr, stroke_pattern);
    cairo_stroke (cr);
    cairo_pop_group_to_source (cr);
    cairo_paint_with_alpha (cr, alpha);

`cr` : | a cairo context

Since 1.2

### cairo_push_group_with_content ()

    void                cairo_push_group_with_content       (cairo_t *cr,
                                                             cairo_content_t content);

Temporarily redirects drawing to an intermediate surface known as a group. The redirection lasts until the group is completed by a call to `cairo_pop_group()` or `cairo_pop_group_to_source()`. These calls provide the result of any drawing to the group as a pattern, (either as an explicit object, or set as the source pattern).

The group will have a content type of `content`. The ability to control this content type is the only distinction between this function and `cairo_push_group()` which you should see for a more detailed description of group rendering.

`cr` : | a cairo context
`content` : | a cairo_content_t indicating the type of group that will be created

Since 1.2

### cairo_pop_group ()

    cairo_pattern_t *   cairo_pop_group                     (cairo_t *cr);

Terminates the redirection begun by a call to `cairo_push_group()` or `cairo_push_group_with_content()` and returns a new pattern containing the results of all drawing operations performed to the group.

The `cairo_pop_group()` function calls `cairo_restore()`, (balancing a call to `cairo_save()` by the push_group function), so that any changes to the graphics state will not be visible outside the group.

`cr` : | a cairo context
Returns : | a newly created (surface) pattern containing the results of all drawing operations performed to the group. The caller owns the returned object and should call `cairo_pattern_destroy()` when finished with it.

Since 1.2

### cairo_pop_group_to_source ()

    void                cairo_pop_group_to_source           (cairo_t *cr);

Terminates the redirection begun by a call to `cairo_push_group()` or `cairo_push_group_with_content()` and installs the resulting pattern as the source pattern in the given cairo context.

The behavior of this function is equivalent to the sequence of operations:

    1
    2
    3
    <a class="link" href="cairo-cairo-pattern-t.html#cairo-pattern-t" title="cairo_pattern_t">cairo_pattern_t</a> *group = cairo_pop_group (cr);
    cairo_set_source (cr, group);
    cairo_pattern_destroy (group);

but is more convenient as their is no need for a variable to store the short-lived pointer to the pattern.

The `cairo_pop_group()` function calls `cairo_restore()`, (balancing a call to `cairo_save()` by the push_group function), so that any changes to the graphics state will not be visible outside the group.

`cr` : | a cairo context

Since 1.2

### cairo_get_group_target ()

    cairo_surface_t *   cairo_get_group_target              (cairo_t *cr);

Gets the current destination surface for the context. This is either the original target surface as passed to `cairo_create()` or the target surface for the current group as started by the most recent call to `cairo_push_group()` or `cairo_push_group_with_content()`.

This function will always return a valid pointer, but the result can be a "nil" surface if `cr` is already in an error state, (ie. `cairo_status()` `!=` `CAIRO_STATUS_SUCCESS`). A nil surface is indicated by `cairo_surface_status()` `!=` `CAIRO_STATUS_SUCCESS`.

`cr` : | a cairo context
Returns : | the target surface. This object is owned by cairo. To keep a reference to it, you must call `cairo_surface_reference()`.

Since 1.2

### cairo_set_source_rgb ()

    void                cairo_set_source_rgb                (cairo_t *cr,
                                                             double red,
                                                             double green,
                                                             double blue);

Sets the source pattern within `cr` to an opaque color. This opaque color will then be used for any subsequent drawing operation until a new source pattern is set.

The color components are floating point numbers in the range 0 to 1. If the values passed in are outside that range, they will be clamped.

The default source pattern is opaque black, (that is, it is equivalent to cairo_set_source_rgb(cr, 0.0, 0.0, 0.0)).

`cr` : | a cairo context
`red` : | red component of color
`green` : | green component of color
`blue` : | blue component of color

### cairo_set_source_rgba ()

    void                cairo_set_source_rgba               (cairo_t *cr,
                                                             double red,
                                                             double green,
                                                             double blue,
                                                             double alpha);

Sets the source pattern within `cr` to a translucent color. This color will then be used for any subsequent drawing operation until a new source pattern is set.

The color and alpha components are floating point numbers in the range 0 to 1. If the values passed in are outside that range, they will be clamped.

The default source pattern is opaque black, (that is, it is equivalent to cairo_set_source_rgba(cr, 0.0, 0.0, 0.0, 1.0)).

`cr` : | a cairo context
`red` : | red component of color
`green` : | green component of color
`blue` : | blue component of color
`alpha` : | alpha component of color

### cairo_set_source ()

    void                cairo_set_source                    (cairo_t *cr,
                                                             cairo_pattern_t *source);

Sets the source pattern within `cr` to `source`. This pattern will then be used for any subsequent drawing operation until a new source pattern is set.

Note: The pattern's transformation matrix will be locked to the user space in effect at the time of `cairo_set_source()`. This means that further modifications of the current transformation matrix will not affect the source pattern. See `cairo_pattern_set_matrix()`.

The default source pattern is a solid pattern that is opaque black, (that is, it is equivalent to cairo_set_source_rgb(cr, 0.0, 0.0, 0.0)).

`cr` : | a cairo context
`source` : | a cairo_pattern_t to be used as the source for subsequent drawing operations.

### cairo_set_source_surface ()

    void                cairo_set_source_surface            (cairo_t *cr,
                                                             cairo_surface_t *surface,
                                                             double x,
                                                             double y);

This is a convenience function for creating a pattern from `surface` and setting it as the source in `cr` with `cairo_set_source()`.

The `x` and `y` parameters give the user-space coordinate at which the surface origin should appear. (The surface origin is its upper-left corner before any transformation has been applied.) The `x` and `y` patterns are negated and then set as translation values in the pattern matrix.

Other than the initial translation pattern matrix, as described above, all other pattern attributes, (such as its extend mode), are set to the default values as in `cairo_pattern_create_for_surface()`. The resulting pattern can be queried with `cairo_get_source()` so that these attributes can be modified if desired, (eg. to create a repeating pattern with `cairo_pattern_set_extend()`).

`cr` : | a cairo context
`surface` : | a surface to be used to set the source pattern
`x` : | User-space X coordinate for surface origin
`y` : | User-space Y coordinate for surface origin

### cairo_get_source ()

    cairo_pattern_t *   cairo_get_source                    (cairo_t *cr);

Gets the current source pattern for `cr`.

`cr` : | a cairo context
Returns : | the current source pattern. This object is owned by cairo. To keep a reference to it, you must call `cairo_pattern_reference()`.

### enum cairo_antialias_t

    typedef enum _cairo_antialias {
        CAIRO_ANTIALIAS_DEFAULT,
        CAIRO_ANTIALIAS_NONE,
        CAIRO_ANTIALIAS_GRAY,
        CAIRO_ANTIALIAS_SUBPIXEL
    } cairo_antialias_t;

Specifies the type of antialiasing to do when rendering text or shapes.

`CAIRO_ANTIALIAS_DEFAULT` | Use the default antialiasing for the subsystem and target device
`CAIRO_ANTIALIAS_NONE` | Use a bilevel alpha mask
`CAIRO_ANTIALIAS_GRAY` | Perform single-color antialiasing (using shades of gray for black text on a white background, for example).
`CAIRO_ANTIALIAS_SUBPIXEL` | Perform antialiasing by taking advantage of the order of subpixel elements on devices such as LCD panels

### cairo_set_antialias ()

    void                cairo_set_antialias                 (cairo_t *cr,
                                                             cairo_antialias_t antialias);

Set the antialiasing mode of the rasterizer used for drawing shapes. This value is a hint, and a particular backend may or may not support a particular value. At the current time, no backend supports `CAIRO_ANTIALIAS_SUBPIXEL` when drawing shapes.

Note that this option does not affect text rendering, instead see `cairo_font_options_set_antialias()`.

`cr` : | a cairo_t
`antialias` : | the new antialiasing mode

### cairo_get_antialias ()

    cairo_antialias_t   cairo_get_antialias                 (cairo_t *cr);

Gets the current shape antialiasing mode, as set by `cairo_set_shape_antialias()`.

`cr` : | a cairo context
Returns : | the current shape antialiasing mode.

### cairo_set_dash ()

    void                cairo_set_dash                      (cairo_t *cr,
                                                             const double *dashes,
                                                             int num_dashes,
                                                             double offset);

Sets the dash pattern to be used by `cairo_stroke()`. A dash pattern is specified by `dashes`, an array of positive values. Each value provides the length of alternate "on" and "off" portions of the stroke. The `offset` specifies an offset into the pattern at which the stroke begins.

Each "on" segment will have caps applied as if the segment were a separate sub-path. In particular, it is valid to use an "on" length of 0.0 with `CAIRO_LINE_CAP_ROUND` or `CAIRO_LINE_CAP_SQUARE` in order to distributed dots or squares along a path.

Note: The length values are in user-space units as evaluated at the time of stroking. This is not necessarily the same as the user space at the time of `cairo_set_dash()`.

If `num_dashes` is 0 dashing is disabled.

If `num_dashes` is 1 a symmetric pattern is assumed with alternating on and off portions of the size specified by the single value in `dashes`.

If any value in `dashes` is negative, or if all values are 0, then `cr` will be put into an error state with a status of `CAIRO_STATUS_INVALID_DASH`.

`cr` : | a cairo context
`dashes` : | an array specifying alternate lengths of on and off stroke portions
`num_dashes` : | the length of the dashes array
`offset` : | an offset into the dash pattern at which the stroke should start

### cairo_get_dash_count ()

    int                 cairo_get_dash_count                (cairo_t *cr);

This function returns the length of the dash array in `cr` (0 if dashing is not currently in effect).

See also `cairo_set_dash()` and `cairo_get_dash()`.

`cr` : | a cairo_t
Returns : | the length of the dash array, or 0 if no dash array set.

Since 1.4

### cairo_get_dash ()

    void                cairo_get_dash                      (cairo_t *cr,
                                                             double *dashes,
                                                             double *offset);

Gets the current dash array. If not `NULL`, `dashes` should be big enough to hold at least the number of values returned by `cairo_get_dash_count()`.

`cr` : | a cairo_t
`dashes` : | return value for the dash array, or `NULL`
`offset` : | return value for the current dash offset, or `NULL`

Since 1.4

### enum cairo_fill_rule_t

    typedef enum _cairo_fill_rule {
        CAIRO_FILL_RULE_WINDING,
        CAIRO_FILL_RULE_EVEN_ODD
    } cairo_fill_rule_t;

cairo_fill_rule_t is used to select how paths are filled. For both fill rules, whether or not a point is included in the fill is determined by taking a ray from that point to infinity and looking at intersections with the path. The ray can be in any direction, as long as it doesn't pass through the end point of a segment or have a tricky intersection such as intersecting tangent to the path. (Note that filling is not actually implemented in this way. This is just a description of the rule that is applied.)

The default fill rule is `CAIRO_FILL_RULE_WINDING`.

New entries may be added in future versions.

`CAIRO_FILL_RULE_WINDING` | If the path crosses the ray from left-to-right, counts +1. If the path crosses the ray from right to left, counts -1. (Left and right are determined from the perspective of looking along the ray from the starting point.) If the total count is non-zero, the point will be filled.
`CAIRO_FILL_RULE_EVEN_ODD` | Counts the total number of intersections, without regard to the orientation of the contour. If the total number of intersections is odd, the point will be filled.

### cairo_set_fill_rule ()

    void                cairo_set_fill_rule                 (cairo_t *cr,
                                                             cairo_fill_rule_t fill_rule);

Set the current fill rule within the cairo context. The fill rule is used to determine which regions are inside or outside a complex (potentially self-intersecting) path. The current fill rule affects both `cairo_fill()` and `cairo_clip()`. See cairo_fill_rule_t for details on the semantics of each available fill rule.

The default fill rule is `CAIRO_FILL_RULE_WINDING`.

`cr` : | a cairo_t
`fill_rule` : | a fill rule, specified as a cairo_fill_rule_t

### cairo_get_fill_rule ()

    cairo_fill_rule_t   cairo_get_fill_rule                 (cairo_t *cr);

Gets the current fill rule, as set by `cairo_set_fill_rule()`.

`cr` : | a cairo context
Returns : | the current fill rule.

### enum cairo_line_cap_t

    typedef enum _cairo_line_cap {
        CAIRO_LINE_CAP_BUTT,
        CAIRO_LINE_CAP_ROUND,
        CAIRO_LINE_CAP_SQUARE
    } cairo_line_cap_t;

Specifies how to render the endpoints of the path when stroking.

The default line cap style is `CAIRO_LINE_CAP_BUTT`.

`CAIRO_LINE_CAP_BUTT` | start(stop) the line exactly at the start(end) point
`CAIRO_LINE_CAP_ROUND` | use a round ending, the center of the circle is the end point
`CAIRO_LINE_CAP_SQUARE` | use squared ending, the center of the square is the end point

### cairo_set_line_cap ()

    void                cairo_set_line_cap                  (cairo_t *cr,
                                                             cairo_line_cap_t line_cap);

Sets the current line cap style within the cairo context. See cairo_line_cap_t for details about how the available line cap styles are drawn.

As with the other stroke parameters, the current line cap style is examined by `cairo_stroke()`, `cairo_stroke_extents()`, and `cairo_stroke_to_path()`, but does not have any effect during path construction.

The default line cap style is `CAIRO_LINE_CAP_BUTT`.

`cr` : | a cairo context
`line_cap` : | a line cap style

### cairo_get_line_cap ()

    cairo_line_cap_t    cairo_get_line_cap                  (cairo_t *cr);

Gets the current line cap style, as set by `cairo_set_line_cap()`.

`cr` : | a cairo context
Returns : | the current line cap style.

### enum cairo_line_join_t

    typedef enum _cairo_line_join {
        CAIRO_LINE_JOIN_MITER,
        CAIRO_LINE_JOIN_ROUND,
        CAIRO_LINE_JOIN_BEVEL
    } cairo_line_join_t;

Specifies how to render the junction of two lines when stroking.

The default line join style is `CAIRO_LINE_JOIN_MITER`.

`CAIRO_LINE_JOIN_MITER` | use a sharp (angled) corner, see `cairo_set_miter_limit()`
`CAIRO_LINE_JOIN_ROUND` | use a rounded join, the center of the circle is the joint point
`CAIRO_LINE_JOIN_BEVEL` | use a cut-off join, the join is cut off at half the line width from the joint point

### cairo_set_line_join ()

    void                cairo_set_line_join                 (cairo_t *cr,
                                                             cairo_line_join_t line_join);

Sets the current line join style within the cairo context. See cairo_line_join_t for details about how the available line join styles are drawn.

As with the other stroke parameters, the current line join style is examined by `cairo_stroke()`, `cairo_stroke_extents()`, and `cairo_stroke_to_path()`, but does not have any effect during path construction.

The default line join style is `CAIRO_LINE_JOIN_MITER`.

`cr` : | a cairo context
`line_join` : | a line join style

### cairo_get_line_join ()

    cairo_line_join_t   cairo_get_line_join                 (cairo_t *cr);

Gets the current line join style, as set by `cairo_set_line_join()`.

`cr` : | a cairo context
Returns : | the current line join style.

### cairo_set_line_width ()

    void                cairo_set_line_width                (cairo_t *cr,
                                                             double width);

Sets the current line width within the cairo context. The line width value specifies the diameter of a pen that is circular in user space, (though device-space pen may be an ellipse in general due to scaling/shear/rotation of the CTM).

Note: When the description above refers to user space and CTM it refers to the user space and CTM in effect at the time of the stroking operation, not the user space and CTM in effect at the time of the call to `cairo_set_line_width()`. The simplest usage makes both of these spaces identical. That is, if there is no change to the CTM between a call to `cairo_set_line_width()` and the stroking operation, then one can just pass user-space values to `cairo_set_line_width()` and ignore this note.

As with the other stroke parameters, the current line width is examined by `cairo_stroke()`, `cairo_stroke_extents()`, and `cairo_stroke_to_path()`, but does not have any effect during path construction.

The default line width value is 2.0.

`cr` : | a cairo_t
`width` : | a line width

### cairo_get_line_width ()

    double              cairo_get_line_width                (cairo_t *cr);

This function returns the current line width value exactly as set by `cairo_set_line_width()`. Note that the value is unchanged even if the CTM has changed between the calls to `cairo_set_line_width()` and `cairo_get_line_width()`.

`cr` : | a cairo context
Returns : | the current line width.

### cairo_set_miter_limit ()

    void                cairo_set_miter_limit               (cairo_t *cr,
                                                             double limit);

Sets the current miter limit within the cairo context.

If the current line join style is set to `CAIRO_LINE_JOIN_MITER` (see `cairo_set_line_join()`), the miter limit is used to determine whether the lines should be joined with a bevel instead of a miter. Cairo divides the length of the miter by the line width. If the result is greater than the miter limit, the style is converted to a bevel.

As with the other stroke parameters, the current line miter limit is examined by `cairo_stroke()`, `cairo_stroke_extents()`, and `cairo_stroke_to_path()`, but does not have any effect during path construction.

The default miter limit value is 10.0, which will convert joins with interior angles less than 11 degrees to bevels instead of miters. For reference, a miter limit of 2.0 makes the miter cutoff at 60 degrees, and a miter limit of 1.414 makes the cutoff at 90 degrees.

A miter limit for a desired angle can be computed as: miter limit = 1/sin(angle/2)

`cr` : | a cairo context
`limit` : | miter limit to set

### cairo_get_miter_limit ()

    double              cairo_get_miter_limit               (cairo_t *cr);

Gets the current miter limit, as set by `cairo_set_miter_limit()`.

`cr` : | a cairo context
Returns : | the current miter limit.

### enum cairo_operator_t

    typedef enum _cairo_operator {
        CAIRO_OPERATOR_CLEAR,

        CAIRO_OPERATOR_SOURCE,
        CAIRO_OPERATOR_OVER,
        CAIRO_OPERATOR_IN,
        CAIRO_OPERATOR_OUT,
        CAIRO_OPERATOR_ATOP,

        CAIRO_OPERATOR_DEST,
        CAIRO_OPERATOR_DEST_OVER,
        CAIRO_OPERATOR_DEST_IN,
        CAIRO_OPERATOR_DEST_OUT,
        CAIRO_OPERATOR_DEST_ATOP,

        CAIRO_OPERATOR_XOR,
        CAIRO_OPERATOR_ADD,
        CAIRO_OPERATOR_SATURATE,

        CAIRO_OPERATOR_MULTIPLY,
        CAIRO_OPERATOR_SCREEN,
        CAIRO_OPERATOR_OVERLAY,
        CAIRO_OPERATOR_DARKEN,
        CAIRO_OPERATOR_LIGHTEN,
        CAIRO_OPERATOR_COLOR_DODGE,
        CAIRO_OPERATOR_COLOR_BURN,
        CAIRO_OPERATOR_HARD_LIGHT,
        CAIRO_OPERATOR_SOFT_LIGHT,
        CAIRO_OPERATOR_DIFFERENCE,
        CAIRO_OPERATOR_EXCLUSION,
        CAIRO_OPERATOR_HSL_HUE,
        CAIRO_OPERATOR_HSL_SATURATION,
        CAIRO_OPERATOR_HSL_COLOR,
        CAIRO_OPERATOR_HSL_LUMINOSITY
    } cairo_operator_t;

cairo_operator_t is used to set the compositing operator for all cairo drawing operations.

The default operator is `CAIRO_OPERATOR_OVER`.

The operators marked as unbounded modify their destination even outside of the mask layer (that is, their effect is not bound by the mask layer). However, their effect can still be limited by way of clipping.

To keep things simple, the operator descriptions here document the behavior for when both source and destination are either fully transparent or fully opaque. The actual implementation works for translucent layers too. For a more detailed explanation of the effects of each operator, including the mathematical definitions, see http://cairographics.org/operators/.

`CAIRO_OPERATOR_CLEAR` | clear destination layer (bounded)
`CAIRO_OPERATOR_SOURCE` | replace destination layer (bounded)
`CAIRO_OPERATOR_OVER` | draw source layer on top of destination layer (bounded)
`CAIRO_OPERATOR_IN` | draw source where there was destination content (unbounded)
`CAIRO_OPERATOR_OUT` | draw source where there was no destination content (unbounded)
`CAIRO_OPERATOR_ATOP` | draw source on top of destination content and only there
`CAIRO_OPERATOR_DEST` | ignore the source
`CAIRO_OPERATOR_DEST_OVER` | draw destination on top of source
`CAIRO_OPERATOR_DEST_IN` | leave destination only where there was source content (unbounded)
`CAIRO_OPERATOR_DEST_OUT` | leave destination only where there was no source content
`CAIRO_OPERATOR_DEST_ATOP` | leave destination on top of source content and only there (unbounded)
`CAIRO_OPERATOR_XOR` | source and destination are shown where there is only one of them
`CAIRO_OPERATOR_ADD` | source and destination layers are accumulated
`CAIRO_OPERATOR_SATURATE` | like over, but assuming source and dest are disjoint geometries
`CAIRO_OPERATOR_MULTIPLY` | source and destination layers are multiplied. This causes the result to be at least as dark as the darker inputs.
`CAIRO_OPERATOR_SCREEN` | source and destination are complemented and multiplied. This causes the result to be at least as light as the lighter inputs.
`CAIRO_OPERATOR_OVERLAY` | multiplies or screens, depending on the lightness of the destination color.
`CAIRO_OPERATOR_DARKEN` | replaces the destination with the source if it is darker, otherwise keeps the source.
`CAIRO_OPERATOR_LIGHTEN` | replaces the destination with the source if it is lighter, otherwise keeps the source.
`CAIRO_OPERATOR_COLOR_DODGE` | brightens the destination color to reflect the source color.
`CAIRO_OPERATOR_COLOR_BURN` | darkens the destination color to reflect the source color.
`CAIRO_OPERATOR_HARD_LIGHT` | Multiplies or screens, dependant on source color.
`CAIRO_OPERATOR_SOFT_LIGHT` | Darkens or lightens, dependant on source color.
`CAIRO_OPERATOR_DIFFERENCE` | Takes the difference of the source and destination color.
`CAIRO_OPERATOR_EXCLUSION` | Produces an effect similar to difference, but with lower contrast.
`CAIRO_OPERATOR_HSL_HUE` | Creates a color with the hue of the source and the saturation and luminosity of the target.
`CAIRO_OPERATOR_HSL_SATURATION` | Creates a color with the saturation of the source and the hue and luminosity of the target. Painting with this mode onto a gray area prduces no change.
`CAIRO_OPERATOR_HSL_COLOR` | Creates a color with the hue and saturation of the source and the luminosity of the target. This preserves the gray levels of the target and is useful for coloring monochrome images or tinting color images.
`CAIRO_OPERATOR_HSL_LUMINOSITY` | Creates a color with the luminosity of the source and the hue and saturation of the target. This produces an inverse effect to `CAIRO_OPERATOR_HSL_COLOR`.

### cairo_set_operator ()

    void                cairo_set_operator                  (cairo_t *cr,
                                                             cairo_operator_t op);

Sets the compositing operator to be used for all drawing operations. See cairo_operator_t for details on the semantics of each available compositing operator.

The default operator is `CAIRO_OPERATOR_OVER`.

`cr` : | a cairo_t
`op` : | a compositing operator, specified as a cairo_operator_t

### cairo_get_operator ()

    cairo_operator_t    cairo_get_operator                  (cairo_t *cr);

Gets the current compositing operator for a cairo context.

`cr` : | a cairo context
Returns : | the current compositing operator.

### cairo_set_tolerance ()

    void                cairo_set_tolerance                 (cairo_t *cr,
                                                             double tolerance);

Sets the tolerance used when converting paths into trapezoids. Curved segments of the path will be subdivided until the maximum deviation between the original path and the polygonal approximation is less than `tolerance`. The default value is 0.1. A larger value will give better performance, a smaller value, better appearance. (Reducing the value from the default value of 0.1 is unlikely to improve appearance significantly.) The accuracy of paths within Cairo is limited by the precision of its internal arithmetic, and the prescribed `tolerance` is restricted to the smallest representable internal value.

`cr` : | a cairo_t
`tolerance` : | the tolerance, in device units (typically pixels)

### cairo_get_tolerance ()

    double              cairo_get_tolerance                 (cairo_t *cr);

Gets the current tolerance value, as set by `cairo_set_tolerance()`.

`cr` : | a cairo context
Returns : | the current tolerance value.

### cairo_clip ()

    void                cairo_clip                          (cairo_t *cr);

Establishes a new clip region by intersecting the current clip region with the current path as it would be filled by `cairo_fill()` and according to the current fill rule (see `cairo_set_fill_rule()`).

After `cairo_clip()`, the current path will be cleared from the cairo context.

The current clip region affects all drawing operations by effectively masking out any changes to the surface that are outside the current clip region.

Calling `cairo_clip()` can only make the clip region smaller, never larger. But the current clip is part of the graphics state, so a temporary restriction of the clip region can be achieved by calling `cairo_clip()` within a `cairo_save()`/`cairo_restore()` pair. The only other means of increasing the size of the clip region is `cairo_reset_clip()`.

`cr` : | a cairo context

### cairo_clip_preserve ()

    void                cairo_clip_preserve                 (cairo_t *cr);

Establishes a new clip region by intersecting the current clip region with the current path as it would be filled by `cairo_fill()` and according to the current fill rule (see `cairo_set_fill_rule()`).

Unlike `cairo_clip()`, `cairo_clip_preserve()` preserves the path within the cairo context.

The current clip region affects all drawing operations by effectively masking out any changes to the surface that are outside the current clip region.

Calling `cairo_clip_preserve()` can only make the clip region smaller, never larger. But the current clip is part of the graphics state, so a temporary restriction of the clip region can be achieved by calling `cairo_clip_preserve()` within a `cairo_save()`/`cairo_restore()` pair. The only other means of increasing the size of the clip region is `cairo_reset_clip()`.

`cr` : | a cairo context

### cairo_clip_extents ()

    void                cairo_clip_extents                  (cairo_t *cr,
                                                             double *x1,
                                                             double *y1,
                                                             double *x2,
                                                             double *y2);

Computes a bounding box in user coordinates covering the area inside the current clip.

`cr` : | a cairo context
`x1` : | left of the resulting extents
`y1` : | top of the resulting extents
`x2` : | right of the resulting extents
`y2` : | bottom of the resulting extents

Since 1.4

### cairo_in_clip ()

    cairo_bool_t        cairo_in_clip                       (cairo_t *cr,
                                                             double x,
                                                             double y);

Tests whether the given point is inside the area that would be visible through the current clip, i.e. the area that would be filled by a `cairo_paint()` operation.

See `cairo_clip()`, and `cairo_clip_preserve()`.

`cr` : | a cairo context
`x` : | X coordinate of the point to test
`y` : | Y coordinate of the point to test
Returns : | A non-zero value if the point is inside, or zero if outside.

Since 1.10

### cairo_reset_clip ()

    void                cairo_reset_clip                    (cairo_t *cr);

Reset the current clip region to its original, unrestricted state. That is, set the clip region to an infinitely large shape containing the target surface. Equivalently, if infinity is too hard to grasp, one can imagine the clip region being reset to the exact bounds of the target surface.

Note that code meant to be reusable should not call `cairo_reset_clip()` as it will cause results unexpected by higher-level code which calls `cairo_clip()`. Consider using `cairo_save()` and `cairo_restore()` around `cairo_clip()` as a more robust means of temporarily restricting the clip region.

`cr` : | a cairo context

### cairo_rectangle_t

    typedef struct {
        double x, y, width, height;
    } cairo_rectangle_t;

A data structure for holding a rectangle.

double `x`; | X coordinate of the left side of the rectangle
double `y`; | Y coordinate of the the top side of the rectangle
double `width`; | width of the rectangle
double `height`; | height of the rectangle

Since 1.4

### cairo_rectangle_list_t

    typedef struct {
        cairo_status_t     status;
        cairo_rectangle_t *rectangles;
        int                num_rectangles;
    } cairo_rectangle_list_t;

A data structure for holding a dynamically allocated array of rectangles.

cairo_status_t `status`; | Error status of the rectangle list
cairo_rectangle_t *`rectangles`; | Array containing the rectangles
int `num_rectangles`; | Number of rectangles in this list

Since 1.4

### cairo_rectangle_list_destroy ()

    void                cairo_rectangle_list_destroy        (cairo_rectangle_list_t *rectangle_list);

Unconditionally frees `rectangle_list` and all associated references. After this call, the `rectangle_list` pointer must not be dereferenced.

`rectangle_list` : | a rectangle list, as obtained from `cairo_copy_clip_rectangles()`

Since 1.4

### cairo_copy_clip_rectangle_list ()

    cairo_rectangle_list_t * cairo_copy_clip_rectangle_list (cairo_t *cr);

Gets the current clip region as a list of rectangles in user coordinates. Never returns `NULL`.

The status in the list may be `CAIRO_STATUS_CLIP_NOT_REPRESENTABLE` to indicate that the clip region cannot be represented as a list of user-space rectangles. The status may have other values to indicate other errors.

`cr` : | a cairo context
Returns : | the current clip region as a list of rectangles in user coordinates, which should be destroyed using `cairo_rectangle_list_destroy()`.

Since 1.4

### cairo_fill ()

    void                cairo_fill                          (cairo_t *cr);

A drawing operator that fills the current path according to the current fill rule, (each sub-path is implicitly closed before being filled). After `cairo_fill()`, the current path will be cleared from the cairo context. See `cairo_set_fill_rule()` and `cairo_fill_preserve()`.

`cr` : | a cairo context

### cairo_fill_preserve ()

    void                cairo_fill_preserve                 (cairo_t *cr);

A drawing operator that fills the current path according to the current fill rule, (each sub-path is implicitly closed before being filled). Unlike `cairo_fill()`, `cairo_fill_preserve()` preserves the path within the cairo context.

See `cairo_set_fill_rule()` and `cairo_fill()`.

`cr` : | a cairo context

### cairo_fill_extents ()

    void                cairo_fill_extents                  (cairo_t *cr,
                                                             double *x1,
                                                             double *y1,
                                                             double *x2,
                                                             double *y2);

Computes a bounding box in user coordinates covering the area that would be affected, (the "inked" area), by a `cairo_fill()` operation given the current path and fill parameters. If the current path is empty, returns an empty rectangle ((0,0), (0,0)). Surface dimensions and clipping are not taken into account.

Contrast with `cairo_path_extents()`, which is similar, but returns non-zero extents for some paths with no inked area, (such as a simple line segment).

Note that `cairo_fill_extents()` must necessarily do more work to compute the precise inked areas in light of the fill rule, so `cairo_path_extents()` may be more desirable for sake of performance if the non-inked path extents are desired.

See `cairo_fill()`, `cairo_set_fill_rule()` and `cairo_fill_preserve()`.

`cr` : | a cairo context
`x1` : | left of the resulting extents
`y1` : | top of the resulting extents
`x2` : | right of the resulting extents
`y2` : | bottom of the resulting extents

### cairo_in_fill ()

    cairo_bool_t        cairo_in_fill                       (cairo_t *cr,
                                                             double x,
                                                             double y);

Tests whether the given point is inside the area that would be affected by a `cairo_fill()` operation given the current path and filling parameters. Surface dimensions and clipping are not taken into account.

See `cairo_fill()`, `cairo_set_fill_rule()` and `cairo_fill_preserve()`.

`cr` : | a cairo context
`x` : | X coordinate of the point to test
`y` : | Y coordinate of the point to test
Returns : | A non-zero value if the point is inside, or zero if outside.

### cairo_mask ()

    void                cairo_mask                          (cairo_t *cr,
                                                             cairo_pattern_t *pattern);

A drawing operator that paints the current source using the alpha channel of `pattern` as a mask. (Opaque areas of `pattern` are painted with the source, transparent areas are not painted.)

`cr` : | a cairo context
`pattern` : | a cairo_pattern_t

### cairo_mask_surface ()

    void                cairo_mask_surface                  (cairo_t *cr,
                                                             cairo_surface_t *surface,
                                                             double surface_x,
                                                             double surface_y);

A drawing operator that paints the current source using the alpha channel of `surface` as a mask. (Opaque areas of `surface` are painted with the source, transparent areas are not painted.)

`cr` : | a cairo context
`surface` : | a cairo_surface_t
`surface_x` : | X coordinate at which to place the origin of `surface`
`surface_y` : | Y coordinate at which to place the origin of `surface`

### cairo_paint ()

    void                cairo_paint                         (cairo_t *cr);

A drawing operator that paints the current source everywhere within the current clip region.

`cr` : | a cairo context

### cairo_paint_with_alpha ()

    void                cairo_paint_with_alpha              (cairo_t *cr,
                                                             double alpha);

A drawing operator that paints the current source everywhere within the current clip region using a mask of constant alpha value `alpha`. The effect is similar to `cairo_paint()`, but the drawing is faded out using the alpha value.

`cr` : | a cairo context
`alpha` : | alpha value, between 0 (transparent) and 1 (opaque)

### cairo_stroke ()

    void                cairo_stroke                        (cairo_t *cr);

A drawing operator that strokes the current path according to the current line width, line join, line cap, and dash settings. After `cairo_stroke()`, the current path will be cleared from the cairo context. See `cairo_set_line_width()`, `cairo_set_line_join()`, `cairo_set_line_cap()`, `cairo_set_dash()`, and `cairo_stroke_preserve()`.

Note: Degenerate segments and sub-paths are treated specially and provide a useful result. These can result in two different situations:

1. Zero-length "on" segments set in `cairo_set_dash()`. If the cap style is `CAIRO_LINE_CAP_ROUND` or `CAIRO_LINE_CAP_SQUARE` then these segments will be drawn as circular dots or squares respectively. In the case of `CAIRO_LINE_CAP_SQUARE`, the orientation of the squares is determined by the direction of the underlying path.

2. A sub-path created by `cairo_move_to()` followed by either a `cairo_close_path()` or one or more calls to `cairo_line_to()` to the same coordinate as the `cairo_move_to()`. If the cap style is `CAIRO_LINE_CAP_ROUND` then these sub-paths will be drawn as circular dots. Note that in the case of `CAIRO_LINE_CAP_SQUARE` a degenerate sub-path will not be drawn at all, (since the correct orientation is indeterminate).

In no case will a cap style of `CAIRO_LINE_CAP_BUTT` cause anything to be drawn in the case of either degenerate segments or sub-paths.

`cr` : | a cairo context

### cairo_stroke_preserve ()

    void                cairo_stroke_preserve               (cairo_t *cr);

A drawing operator that strokes the current path according to the current line width, line join, line cap, and dash settings. Unlike `cairo_stroke()`, `cairo_stroke_preserve()` preserves the path within the cairo context.

See `cairo_set_line_width()`, `cairo_set_line_join()`, `cairo_set_line_cap()`, `cairo_set_dash()`, and `cairo_stroke_preserve()`.

`cr` : | a cairo context

### cairo_stroke_extents ()

    void                cairo_stroke_extents                (cairo_t *cr,
                                                             double *x1,
                                                             double *y1,
                                                             double *x2,
                                                             double *y2);

Computes a bounding box in user coordinates covering the area that would be affected, (the "inked" area), by a `cairo_stroke()` operation given the current path and stroke parameters. If the current path is empty, returns an empty rectangle ((0,0), (0,0)). Surface dimensions and clipping are not taken into account.

Note that if the line width is set to exactly zero, then `cairo_stroke_extents()` will return an empty rectangle. Contrast with `cairo_path_extents()` which can be used to compute the non-empty bounds as the line width approaches zero.

Note that `cairo_stroke_extents()` must necessarily do more work to compute the precise inked areas in light of the stroke parameters, so `cairo_path_extents()` may be more desirable for sake of performance if non-inked path extents are desired.

See `cairo_stroke()`, `cairo_set_line_width()`, `cairo_set_line_join()`, `cairo_set_line_cap()`, `cairo_set_dash()`, and `cairo_stroke_preserve()`.

`cr` : | a cairo context
`x1` : | left of the resulting extents
`y1` : | top of the resulting extents
`x2` : | right of the resulting extents
`y2` : | bottom of the resulting extents

### cairo_in_stroke ()

    cairo_bool_t        cairo_in_stroke                     (cairo_t *cr,
                                                             double x,
                                                             double y);

Tests whether the given point is inside the area that would be affected by a `cairo_stroke()` operation given the current path and stroking parameters. Surface dimensions and clipping are not taken into account.

See `cairo_stroke()`, `cairo_set_line_width()`, `cairo_set_line_join()`, `cairo_set_line_cap()`, `cairo_set_dash()`, and `cairo_stroke_preserve()`.

`cr` : | a cairo context
`x` : | X coordinate of the point to test
`y` : | Y coordinate of the point to test
Returns : | A non-zero value if the point is inside, or zero if outside.

### cairo_copy_page ()

    void                cairo_copy_page                     (cairo_t *cr);

Emits the current page for backends that support multiple pages, but doesn't clear it, so, the contents of the current page will be retained for the next page too. Use `cairo_show_page()` if you want to get an empty page after the emission.

This is a convenience function that simply calls `cairo_surface_copy_page()` on `cr`'s target.

`cr` : | a cairo context

### cairo_show_page ()

    void                cairo_show_page                     (cairo_t *cr);

Emits and clears the current page for backends that support multiple pages. Use `cairo_copy_page()` if you don't want to clear the page.

This is a convenience function that simply calls `cairo_surface_show_page()` on `cr`'s target.

`cr` : | a cairo context

### cairo_get_reference_count ()

    unsigned int        cairo_get_reference_count           (cairo_t *cr);

Returns the current reference count of `cr`.

`cr` : | a cairo_t
Returns : | the current reference count of `cr`. If the object is a nil object, 0 will be returned.

Since 1.4

### cairo_set_user_data ()

    cairo_status_t      cairo_set_user_data                 (cairo_t *cr,
                                                             const cairo_user_data_key_t *key,
                                                             void *user_data,
                                                             cairo_destroy_func_t destroy);

Attach user data to `cr`. To remove user data from a surface, call this function with the key that was used to set it and `NULL` for `data`.

`cr` : | a cairo_t
`key` : | the address of a cairo_user_data_key_t to attach the user data to
`user_data` : | the user data to attach to the cairo_t
`destroy` : | a cairo_destroy_func_t which will be called when the cairo_t is destroyed or when new user data is attached using the same key.
Returns : | `CAIRO_STATUS_SUCCESS` or `CAIRO_STATUS_NO_MEMORY` if a slot could not be allocated for the user data.

Since 1.4

### cairo_get_user_data ()

    void *              cairo_get_user_data                 (cairo_t *cr,
                                                             const cairo_user_data_key_t *key);

Return user data previously attached to `cr` using the specified key. If no user data has been attached with the given key this function returns `NULL`.

`cr` : | a cairo_t
`key` : | the address of the cairo_user_data_key_t the user data was attached to
Returns : | the user data previously attached or `NULL`.

Since 1.4

## See Also

cairo_surface_t