This chapter takes you through the design of a simple FLTK-based text editor.
Determining the Goals of the Text Editor
Since this will be the first big project you'll be doing with FLTK, lets define what we want our text editor to do:
- Provide a menubar/menus for all functions.
- Edit a single text file, possibly with multiple views.
- Load from a file.
- Save to a file.
- Cut/copy/delete/paste functions.
- Search and replace functions.
- Keep track of when the file has been changed.
Designing the Main Window
Now that we've outlined the goals for our editor, we can begin with the design of our GUI. Obviously the first thing that we need is a window, which we'll place inside a class called EditorWindow:
public:
EditorWindow(int w, int h, const char* t);
~EditorWindow();
char search[256];
};
Variables
Our text editor will need some global variables to keep track of things:
int changed = 0;
char filename[256] = "";
The textbuf variable is the text editor buffer for our window class described previously. We'll cover the other variables as we build the application.
Menubars and Menus
The first goal requires us to use a menubar and menus that define each function the editor needs to perform. The Fl_Menu_Item structure is used to define the menus and items in a menubar:
{ "&File", 0, 0, 0, FL_SUBMENU },
{ 0 },
{ "&Edit", 0, 0, 0, FL_SUBMENU },
{ 0 },
{ "&Search", 0, 0, 0, FL_SUBMENU },
{
"Re&place Again",
FL_COMMAND +
't', replace2_cb },
{ 0 },
{ 0 }
};
Once we have the menus defined we can create the Fl_Menu_Bar widget and assign the menus to it with:
We'll define the callback functions later.
Editing the Text
To keep things simple our text editor will use the Fl_Text_Editor widget to edit the text:
w->editor->buffer(textbuf);
So that we can keep track of changes to the file, we also want to add a "modify" callback:
Finally, we want to use a mono-spaced font like FL_COURIER:
The Replace Dialog
We can use the FLTK convenience functions for many of the editor's dialogs, however the replace dialog needs its own custom window. To keep things simple we will have a "find" string, a "replace" string, and "replace all", "replace next", and "cancel" buttons. The strings are just Fl_Input widgets, the "replace all" and "cancel" buttons are Fl_Button widgets, and the "replace next " button is a Fl_Return_Button widget:
Figure 4-1: The search and replace dialog
Callbacks
Now that we've defined the GUI components of our editor, we need to define our callback functions.
changed_cb()
This function will be called whenever the user changes any text in the editor widget:
void changed_cb(int, int nInserted, int nDeleted,int, const char*, void* v) {
if ((nInserted || nDeleted) && !loading) changed = 1;
EditorWindow *w = (EditorWindow *)v;
set_title(w);
if (loading) w->editor->show_insert_position();
}
The set_title() function is one that we will write to set the changed status on the current file. We're doing it this way because we want to show the changed status in the window's title bar.
copy_cb()
This callback function will call Fl_Text_Editor::kf_copy() to copy the currently selected text to the clipboard:
EditorWindow* e = (EditorWindow*)v;
}
cut_cb()
This callback function will call Fl_Text_Editor::kf_cut() to cut the currently selected text to the clipboard:
EditorWindow* e = (EditorWindow*)v;
}
delete_cb()
This callback function will call Fl_Text_Buffer::remove_selection() to delete the currently selected text to the clipboard:
find_cb()
This callback function asks for a search string using the fl_input() convenience function and then calls the find2_cb() function to find the string:
EditorWindow* e = (EditorWindow*)v;
const char *val;
val =
fl_input(
"Search String:", e->search);
if (val != NULL) {
strcpy(e->search, val);
find2_cb(w, v);
}
find2_cb()
This function will find the next occurrence of the search string. If the search string is blank then we want to pop up the search dialog:
EditorWindow* e = (EditorWindow*)v;
if (e->search[0] == '\0') {
find_cb(w, v);
return;
}
int pos = e->editor->insert_position();
if (found) {
textbuf->
select(pos, pos+strlen(e->search));
e->editor->insert_position(pos+strlen(e->search));
e->editor->show_insert_position();
}
else fl_alert(
"No occurrences of \'%s\' found!", e->search);
}
If the search string cannot be found we use the fl_alert() convenience function to display a message to that effect.
new_cb()
This callback function will clear the editor widget and current filename. It also calls the check_save() function to give the user the opportunity to save the current file first as needed:
if (!check_save()) return;
filename[0] = '\0';
changed = 0;
}
open_cb()
This callback function will ask the user for a filename and then load the specified file into the input widget and current filename. It also calls the check_save() function to give the user the opportunity to save the current file first as needed:
if (!check_save()) return;
if (newfile != NULL) load_file(newfile, -1);
}
We call the load_file() function to actually load the file.
paste_cb()
This callback function will call Fl_Text_Editor::kf_paste() to paste the clipboard at the current position:
EditorWindow* e = (EditorWindow*)v;
}
quit_cb()
The quit callback will first see if the current file has been modified, and if so give the user a chance to save it. It then exits from the program:
if (changed && !check_save())
return;
exit(0);
}
replace_cb()
The replace callback just shows the replace dialog:
EditorWindow* e = (EditorWindow*)v;
e->replace_dlg->show();
}
replace2_cb()
This callback will replace the next occurrence of the replacement string. If nothing has been entered for the replacement string, then the replace dialog is displayed instead:
EditorWindow* e = (EditorWindow*)v;
const char *find = e->replace_find->value();
const char *replace = e->replace_with->value();
if (find[0] == '\0') {
e->replace_dlg->show();
return;
}
e->replace_dlg->hide();
int pos = e->editor->insert_position();
if (found) {
textbuf->
select(pos, pos+strlen(find));
textbuf->
insert(pos, replace);
textbuf->
select(pos, pos+strlen(replace));
e->editor->insert_position(pos+strlen(replace));
e->editor->show_insert_position();
}
else fl_alert(
"No occurrences of \'%s\' found!", find);
}
replall_cb()
This callback will replace all occurrences of the search string in the file:
EditorWindow* e = (EditorWindow*)v;
const char *find = e->replace_find->value();
const char *replace = e->replace_with->value();
find = e->replace_find->value();
if (find[0] == '\0') {
e->replace_dlg->show();
return;
}
e->replace_dlg->hide();
e->editor->insert_position(0);
int times = 0;
for (int found = 1; found;) {
int pos = e->editor->insert_position();
if (found) {
textbuf->
select(pos, pos+strlen(find));
textbuf->
insert(pos, replace);
e->editor->insert_position(pos+strlen(replace));
e->editor->show_insert_position();
times++;
}
}
if (times)
fl_message(
"Replaced %d occurrences.", times);
else fl_alert(
"No occurrences of \'%s\' found!", find);
}
replcan_cb()
This callback just hides the replace dialog:
EditorWindow* e = (EditorWindow*)v;
e->replace_dlg->hide();
}
save_cb()
This callback saves the current file. If the current filename is blank it calls the "save as" callback:
void save_cb(void) {
if (filename[0] == '\0') {
saveas_cb();
return;
}
else save_file(filename);
}
The save_file() function saves the current file to the specified filename.
saveas_cb()
This callback asks the user for a filename and saves the current file:
void saveas_cb(void) {
char *newfile;
if (newfile != NULL) save_file(newfile);
}
The save_file() function saves the current file to the specified filename.
Other Functions
Now that we've defined the callback functions, we need our support functions to make it all work:
check_save()
This function checks to see if the current file needs to be saved. If so, it asks the user if they want to save it:
int check_save(void) {
if (!changed) return 1;
int r =
fl_choice(
"The current file has not been saved.\n"
"Would you like to save it now?",
"Cancel", "Save", "Discard");
if (r == 1) {
save_cb();
return !changed;
}
return (r == 2) ? 1 : 0;
}
load_file()
This function loads the specified file into the textbuf variable:
int loading = 0;
void load_file(char *newfile, int ipos) {
loading = 1;
int insert = (ipos != -1);
changed = insert;
if (!insert) strcpy(filename, "");
int r;
if (!insert) r = textbuf->
loadfile(newfile);
if (r)
fl_alert(
"Error reading from file \'%s\':\n%s.", newfile, strerror(errno));
else
if (!insert) strcpy(filename, newfile);
loading = 0;
}
When loading the file we use the Fl_Text_Buffer::loadfile() method to "replace" the text in the buffer, or the Fl_Text_Buffer::insertfile() method to insert text in the buffer from the named file.
save_file()
This function saves the current buffer to the specified file:
void save_file(char *newfile) {
fl_alert(
"Error writing to file \'%s\':\n%s.", newfile, strerror(errno));
else
strcpy(filename, newfile);
changed = 0;
}
set_title()
This function checks the changed variable and updates the window label accordingly:
if (filename[0] == '\0') strcpy(title, "Untitled");
else {
char *slash;
slash = strrchr(filename, '/');
#ifdef WIN32
if (slash == NULL) slash = strrchr(filename, '\\');
#endif
if (slash != NULL) strcpy(title, slash + 1);
else strcpy(title, filename);
}
if (changed) strcat(title, " (modified)");
}
The main() Function
Once we've created all of the support functions, the only thing left is to tie them all together with the main() function. The main() function creates a new text buffer, creates a new view (window) for the text, shows the window, loads the file on the command-line (if any), and then enters the FLTK event loop:
int main(int argc, char **argv) {
if (argc > 1) load_file(argv[1], -1);
}
Compiling the Editor
The complete source for our text editor can be found in the test/editor.cxx source file. Both the Makefile and Visual C++ workspace include the necessary rules to build the editor. You can also compile it using a standard compiler with:
CC -o editor editor.cxx -lfltk -lXext -lX11 -lm
or by using the fltk-config script with:
fltk-config --compile editor.cxx
As noted in Compiling Programs with Standard Compilers, you may need to include compiler and linker options to tell them where to find the FLTK library. Also, the CC command may also be called gcc or c++ on your system.
Congratulations, you've just built your own text editor!
The Final Product
The final editor window should look like the image in Figure 4-2.
Figure 4-2: The completed editor window
Advanced Features
Now that we've implemented the basic functionality, it is time to show off some of the advanced features of the Fl_Text_Editor widget.
Syntax Highlighting
The Fl_Text_Editor widget supports highlighting of text with different fonts, colors, and sizes. The implementation is based on the excellent NEdit text editor core, from http://www.nedit.org/, which uses a parallel "style" buffer which tracks the font, color, and size of the text that is drawn.
Styles are defined using the Fl_Text_Display::Style_Table_Entry structure defined in <FL/Fl_Text_Display.H>:
struct Style_Table_Entry {
int size;
unsigned attr;
};
The color member sets the color for the text, the font member sets the FLTK font index to use, and the size member sets the pixel size of the text. The attr member is currently not used.
For our text editor we'll define 7 styles for plain code, comments, keywords, and preprocessor directives:
You'll notice that the comments show a letter next to each style - each style in the style buffer is referenced using a character starting with the letter 'A'.
You call the highlight_data() method to associate the style data and buffer with the text editor widget:
w->editor->highlight_data(stylebuf, styletable,
sizeof(styletable) / sizeof(styletable[0]),
'A', style_unfinished_cb, 0);
Finally, you need to add a callback to the main text buffer so that changes to the text buffer are mirrored in the style buffer:
The style_update() function, like the change_cb() function described earlier, is called whenever text is added or removed from the text buffer. It mirrors the changes in the style buffer and then updates the style data as necessary:
void
style_update(int pos,
int nInserted,
int nDeleted,
int nRestyled,
const char *deletedText,
void *cbArg) {
int start,
end;
char last,
*style,
*text;
if (nInserted == 0 && nDeleted == 0) {
return;
}
if (nInserted > 0) {
style = new char[nInserted + 1];
memset(style, 'A', nInserted);
style[nInserted] = '\0';
stylebuf->
replace(pos, pos + nDeleted, style);
delete[] style;
} else {
stylebuf->
remove(pos, pos + nDeleted);
}
stylebuf->
select(pos, pos + nInserted - nDeleted);
end = textbuf->
line_end(pos + nInserted - nDeleted);
last = style[end - start - 1];
style_parse(text, style, end - start);
stylebuf->
replace(start, end, style);
if (last != style[end - start - 1]) {
free(text);
free(style);
style_parse(text, style, end - start);
stylebuf->
replace(start, end, style);
}
free(text);
free(style);
}
The style_parse() function scans a copy of the text in the buffer and generates the necessary style characters for display. It assumes that parsing begins at the start of a line:
void
style_parse(const char *text,
char *style,
int length) {
char current;
int col;
int last;
char buf[255],
*bufptr;
const char *temp;
for (current = *style, col = 0, last = 0; length > 0; length --, text ++) {
if (current == 'A') {
if (col == 0 && *text == '#') {
current = 'E';
} else if (strncmp(text, "//", 2) == 0) {
current = 'B';
} else if (strncmp(text, "/*", 2) == 0) {
current = 'C';
} else if (strncmp(text, "\\\"", 2) == 0) {
*style++ = current;
*style++ = current;
text ++;
length --;
col += 2;
continue;
} else if (*text == '\"') {
current = 'D';
} else if (!last && islower(*text)) {
for (temp = text, bufptr = buf;
islower(*temp) && bufptr < (buf + sizeof(buf) - 1);
*bufptr++ = *temp++);
if (!islower(*temp)) {
*bufptr = '\0';
bufptr = buf;
if (bsearch(&bufptr, code_types,
sizeof(code_types) / sizeof(code_types[0]),
sizeof(code_types[0]), compare_keywords)) {
while (text < temp) {
*style++ = 'F';
text ++;
length --;
col ++;
}
text --;
length ++;
last = 1;
continue;
} else if (bsearch(&bufptr, code_keywords,
sizeof(code_keywords) / sizeof(code_keywords[0]),
sizeof(code_keywords[0]), compare_keywords)) {
while (text < temp) {
*style++ = 'G';
text ++;
length --;
col ++;
}
text --;
length ++;
last = 1;
continue;
}
}
}
} else if (current == 'C' && strncmp(text, "*/", 2) == 0) {
*style++ = current;
*style++ = current;
text ++;
length --;
current = 'A';
col += 2;
continue;
} else if (current == 'D') {
if (strncmp(text, "\\\"", 2) == 0) {
*style++ = current;
*style++ = current;
text ++;
length --;
col += 2;
continue;
} else if (*text == '\"') {
*style++ = current;
col ++;
current = 'A';
continue;
}
}
if (current == 'A' && (*text == '{' || *text == '}')) *style++ = 'G';
else *style++ = current;
col ++;
last = isalnum(*text) || *text == '.';
if (*text == '\n') {
col = 0;
if (current == 'B' || current == 'E') current = 'A';
}
}
}