/* Merge two images left-right.
 *
 * Copyright: 1990, 1991 N. Dessipris
 * Author: N. Dessipris
 * Written on: 20/09/1990
 * Updated on: 17/04/1991
 * 1/6/92: JC
 * 	- check for difference bug fixed
 *	- geometry calculations improved and simplified
 *	- small speedups
 Kirk Martinez for Sys5 29/4/93
 * 7/8/93 JC
 *	- ANSIfied
 *	- memory leaks fixed, ready for partial v2
 *	- now does IM_CODING_LABQ too
 * 8/11/93 JC
 *	- now propagates both input histories
 *	- adds magic lines for global mosaic optimisation
 *
 *
 *
 May/1994 Ahmed Abbood
 *
 *	- Modified to use partials on all IO
 *
 June/1995 Ahmed Abbood
 *
 *	- Modified to work with different types of images.
 *
 * 16/6/95 JC
 *	- tidied up a little
 *	- added to VIPS!
 * 7/9/95 JC
 *	- split into two parts: im_lrmerge() and im__lrmerge()
 *	- latter called by im_lrmosaic()
 *	- just the same as public im_lrmerge(), but adds no history
 *	- necessary for im_global_balance()
 *	- small bugs fixed
 * 10/10/95 JC
 *	- better checks that parameters are sensible
 * 11/10/95 JC
 *	- Kirk spotted what a load of rubbish Ahmed's code is
 *	- rewritten - many, many bugs fixed
 * 24/1/97 JC
 *	- now outputs bounding area of input images, rather than clipping
 *	- ignores 0 pixels in blend
 *	- small tidies
 * 7/2/97 JC
 *	- new blend, caching
 * 25/2/97 JC
 *	- old blend back, much simpler
 *	- speed this up at some point if you think of an easy way to do it
 * 29/7/97 JC
 *	- IM_CODING_LABQ blend now works, was bug in im_wrapone()
 *	- small tidies
 * 10/1/98 JC
 *	- merge LUTs now shared between all running mergers
 *	- frees memory explicitly in im__stop_merge, for much better memory
 *	  use in large mosaics, huge improvement!
 * 18/2/98 JC
 *	- im_demand_hint() call added
 * 19/2/98 JC
 *	- now works for any dx/dy by calling im_insert() for bizarre cases
 * 26/9/99 JC
 *	- ooops, blend lut was wrong! wonder how long that's been broken,
 *	  since feb97 I guess
 * 2/2/01 JC
 *	- added tunable max blend width
 * 8/3/01 JC
 *	- switched to integer arithmetic for integer blends
 * 7/11/01 JC
 *	- more sophisticated transparency handling
 *	- tiny blend speed up
 * 19/3/02 JC
 * 	- move fl cache to main state for better sharing
 * 15/8/02 JC
 *	- records Xoffset/Yoffset
 * 20/6/05
 *	- now requires all bands == 0 for transparency (used to just check
 *	  band 0)
 * 24/1/11
 * 	- gtk-doc
 * 	- match formats and bands automatically
 * 22/5/14
 * 	- wrap as a class
 * 18/6/20 kleisauke
 * 	- convert to vips8
 */

/*

	This file is part of VIPS.

	VIPS is free software; you can redistribute it and/or modify
	it under the terms of the GNU Lesser General Public License as published by
	the Free Software Foundation; either version 2 of the License, or
	(at your option) any later version.

	This program is distributed in the hope that it will be useful,
	but WITHOUT ANY WARRANTY; without even the implied warranty of
	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
	GNU Lesser General Public License for more details.

	You should have received a copy of the GNU Lesser General Public License
	along with this program; if not, write to the Free Software
	Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
	02110-1301  USA

 */

/*

	These files are distributed with VIPS - http://www.vips.ecs.soton.ac.uk

 */

#ifdef HAVE_CONFIG_H
#include <config.h>
#endif /*HAVE_CONFIG_H*/
#include <glib/gi18n-lib.h>

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>
#include <limits.h>

/* Define for debug output.
#define DEBUG
 */

#include <vips/vips.h>
#include <vips/transform.h>
#include <vips/internal.h>

#include "pmosaicing.h"

/* Blend luts. Shared between all lr and tb blends.
 */
double *vips__coef1 = NULL;
double *vips__coef2 = NULL;
int *vips__icoef1 = NULL;
int *vips__icoef2 = NULL;

/* Create a lut for the merging area. Always BLEND_SIZE entries, we
 * scale later when we index it.
 */
int
vips__make_blend_luts(void)
{
	int x;

	/* Already done?
	 */
	if (vips__coef1 && vips__coef2)
		return 0;

	/* Allocate and fill.
	 */
	vips__coef1 = VIPS_ARRAY(NULL, BLEND_SIZE, double);
	vips__coef2 = VIPS_ARRAY(NULL, BLEND_SIZE, double);
	vips__icoef1 = VIPS_ARRAY(NULL, BLEND_SIZE, int);
	vips__icoef2 = VIPS_ARRAY(NULL, BLEND_SIZE, int);
	if (!vips__coef1 || !vips__coef2 || !vips__icoef1 || !vips__icoef2)
		return -1;

	for (x = 0; x < BLEND_SIZE; x++) {
		double a = VIPS_PI * x / (BLEND_SIZE - 1.0);

		vips__coef1[x] = (cos(a) + 1.0) / 2.0;
		vips__coef2[x] = 1.0 - vips__coef1[x];
		vips__icoef1[x] = vips__coef1[x] * BLEND_SCALE;
		vips__icoef2[x] = vips__coef2[x] * BLEND_SCALE;
	}

	return 0;
}

/* Return the position of the first non-zero pel from the left.
 */
static int
find_first(VipsRegion *ir, int *pos, int x, int y, int w)
{
	VipsPel *pr = VIPS_REGION_ADDR(ir, x, y);
	VipsImage *im = ir->im;
	int ne = w * im->Bands;
	int i;

	/* Double the number of bands in a complex.
	 */
	if (vips_band_format_iscomplex(im->BandFmt))
		ne *= 2;

/* Search for the first non-zero band element from the left edge of the image.
 */
#define lsearch(TYPE) \
	{ \
		TYPE *p = (TYPE *) pr; \
\
		for (i = 0; i < ne; i++) \
			if (p[i]) \
				break; \
	}

	switch (im->BandFmt) {
	case VIPS_FORMAT_UCHAR:
		lsearch(unsigned char);
		break;
	case VIPS_FORMAT_CHAR:
		lsearch(signed char);
		break;
	case VIPS_FORMAT_USHORT:
		lsearch(unsigned short);
		break;
	case VIPS_FORMAT_SHORT:
		lsearch(signed short);
		break;
	case VIPS_FORMAT_UINT:
		lsearch(unsigned int);
		break;
	case VIPS_FORMAT_INT:
		lsearch(signed int);
		break;
	case VIPS_FORMAT_FLOAT:
		lsearch(float);
		break;
	case VIPS_FORMAT_DOUBLE:
		lsearch(double);
		break;
	case VIPS_FORMAT_COMPLEX:
		lsearch(float);
		break;
	case VIPS_FORMAT_DPCOMPLEX:
		lsearch(double);
		break;

	default:
		g_assert_not_reached();
		return -1;
	}

	/* i is first non-zero band element, we want first non-zero pixel.
	 */
	*pos = x + i / im->Bands;

	return 0;
}

/* Return the position of the first non-zero pel from the right.
 */
static int
find_last(VipsRegion *ir, int *pos, int x, int y, int w)
{
	VipsPel *pr = VIPS_REGION_ADDR(ir, x, y);
	VipsImage *im = ir->im;
	int ne = w * im->Bands;
	int i;

	/* Double the number of bands in a complex.
	 */
	if (vips_band_format_iscomplex(im->BandFmt))
		ne *= 2;

/* Search for the first non-zero band element from the right.
 */
#define rsearch(TYPE) \
	{ \
		TYPE *p = (TYPE *) pr; \
\
		for (i = ne - 1; i >= 0; i--) \
			if (p[i]) \
				break; \
	}

	switch (im->BandFmt) {
	case VIPS_FORMAT_UCHAR:
		rsearch(unsigned char);
		break;
	case VIPS_FORMAT_CHAR:
		rsearch(signed char);
		break;
	case VIPS_FORMAT_USHORT:
		rsearch(unsigned short);
		break;
	case VIPS_FORMAT_SHORT:
		rsearch(signed short);
		break;
	case VIPS_FORMAT_UINT:
		rsearch(unsigned int);
		break;
	case VIPS_FORMAT_INT:
		rsearch(signed int);
		break;
	case VIPS_FORMAT_FLOAT:
		rsearch(float);
		break;
	case VIPS_FORMAT_DOUBLE:
		rsearch(double);
		break;
	case VIPS_FORMAT_COMPLEX:
		rsearch(float);
		break;
	case VIPS_FORMAT_DPCOMPLEX:
		rsearch(double);
		break;

	default:
		vips_error("lrmerge", "%s", _("internal error"));
		return -1;
	}

	/* i is first non-zero band element, we want first non-zero pixel.
	 */
	*pos = x + i / im->Bands;

	return 0;
}

/* Make sure we have first/last for this area.
 */
static int
make_firstlast(MergeInfo *inf, Overlapping *ovlap, VipsRect *oreg)
{
	VipsRegion *rir = inf->rir;
	VipsRegion *sir = inf->sir;
	VipsRect rr, sr;
	int y, yr, ys;
	int missing;

	/* We're going to build first/last ... lock it from other generate
	 * threads. In fact it's harmless if we do get two writers, but we may
	 * avoid duplicating work.
	 */
	g_mutex_lock(&ovlap->fl_lock);

	/* Do we already have first/last for this area? Bail out if we do.
	 */
	missing = 0;
	for (y = oreg->top; y < VIPS_RECT_BOTTOM(oreg); y++) {
		const int j = y - ovlap->overlap.top;
		const int first = ovlap->first[j];

		if (first < 0) {
			missing = 1;
			break;
		}
	}
	if (!missing) {
		/* No work to do!
		 */
		g_mutex_unlock(&ovlap->fl_lock);
		return 0;
	}

	/* Entire width of overlap in ref for scan-lines we want.
	 */
	rr.left = ovlap->overlap.left;
	rr.top = oreg->top;
	rr.width = ovlap->overlap.width;
	rr.height = oreg->height;
	rr.left -= ovlap->rarea.left;
	rr.top -= ovlap->rarea.top;

	/* Entire width of overlap in sec for scan-lines we want.
	 */
	sr.left = ovlap->overlap.left;
	sr.top = oreg->top;
	sr.width = ovlap->overlap.width;
	sr.height = oreg->height;
	sr.left -= ovlap->sarea.left;
	sr.top -= ovlap->sarea.top;

#ifdef DEBUG
	printf("lrmerge: making first/last for areas:\n");
	printf("ref: left = %d, top = %d, width = %d, height = %d\n",
		rr.left, rr.top, rr.width, rr.height);
	printf("sec: left = %d, top = %d, width = %d, height = %d\n",
		sr.left, sr.top, sr.width, sr.height);
#endif

	/* Make pixels.
	 */
	if (vips_region_prepare(rir, &rr) ||
		vips_region_prepare(sir, &sr)) {
		g_mutex_unlock(&ovlap->fl_lock);
		return -1;
	}

	/* Make first/last cache.
	 */
	for (y = oreg->top, yr = rr.top, ys = sr.top;
		 y < VIPS_RECT_BOTTOM(oreg); y++, yr++, ys++) {
		const int j = y - ovlap->overlap.top;
		int *first = &ovlap->first[j];
		int *last = &ovlap->last[j];

		/* Done this line already?
		 */
		if (*first < 0) {
			/* Search for start/end of overlap on this scan-line.
			 */
			if (find_first(sir, first,
					sr.left, ys, sr.width) ||
				find_last(rir, last,
					rr.left, yr, rr.width)) {
				g_mutex_unlock(&ovlap->fl_lock);
				return -1;
			}

			/* Translate to output space.
			 */
			*first += ovlap->sarea.left;
			*last += ovlap->rarea.left;

			/* Clip to maximum blend width, if necessary.
			 */
			if (ovlap->mwidth >= 0 &&
				*last - *first > ovlap->mwidth) {
				int shrinkby = (*last - *first) - ovlap->mwidth;

				*first += shrinkby / 2;
				*last -= shrinkby / 2;
			}
		}
	}

	g_mutex_unlock(&ovlap->fl_lock);

	return 0;
}

/* Test pixel == 0.
 */
#define TEST_ZERO(TYPE, T, RESULT) \
	{ \
		TYPE *tt = (T); \
		int ii; \
\
		for (ii = 0; ii < cb; ii++) \
			if (tt[i + ii]) \
				break; \
		if (ii == cb) \
			(RESULT) = 1; \
	}

/* Blend two integer images.
 */
#define iblend(TYPE, B, IN1, IN2, OUT) \
	{ \
		TYPE *tr = (TYPE *) (IN1); \
		TYPE *ts = (TYPE *) (IN2); \
		TYPE *tq = (TYPE *) (OUT); \
		const int cb = (B); \
		const int left = VIPS_CLIP(0, first - oreg->left, oreg->width); \
		const int right = VIPS_CLIP(left, last - oreg->left, oreg->width); \
		int ref_zero; \
		int sec_zero; \
		int x, b; \
		int i; \
\
		/* Left of the blend area. \
		 */ \
		for (i = 0, x = 0; x < left; x++) { \
			ref_zero = 0; \
			TEST_ZERO(TYPE, tr, ref_zero); \
			if (!ref_zero) \
				for (b = 0; b < cb; b++, i++) \
					tq[i] = tr[i]; \
			else \
				for (b = 0; b < cb; b++, i++) \
					tq[i] = ts[i]; \
		} \
\
		/* In blend area. \
		 */ \
		for (x = left; x < right; x++) { \
			ref_zero = 0; \
			sec_zero = 0; \
			TEST_ZERO(TYPE, tr, ref_zero); \
			TEST_ZERO(TYPE, ts, sec_zero); \
\
			if (!ref_zero && !sec_zero) { \
				int inx = ((x + oreg->left - first) << BLEND_SHIFT) / bwidth; \
				int c1 = vips__icoef1[inx]; \
				int c2 = vips__icoef2[inx]; \
\
				for (b = 0; b < cb; b++, i++) \
					tq[i] = c1 * tr[i] / BLEND_SCALE + \
						c2 * ts[i] / BLEND_SCALE; \
			} \
			else if (!ref_zero) \
				for (b = 0; b < cb; b++, i++) \
					tq[i] = tr[i]; \
			else \
				for (b = 0; b < cb; b++, i++) \
					tq[i] = ts[i]; \
		} \
\
		/* Right of blend. \
		 */ \
		for (x = right; x < oreg->width; x++) { \
			sec_zero = 0; \
			TEST_ZERO(TYPE, ts, sec_zero); \
			if (!sec_zero) \
				for (b = 0; b < cb; b++, i++) \
					tq[i] = ts[i]; \
			else \
				for (b = 0; b < cb; b++, i++) \
					tq[i] = tr[i]; \
		} \
	}

/* Blend two float images.
 */
#define fblend(TYPE, B, IN1, IN2, OUT) \
	{ \
		TYPE *tr = (TYPE *) (IN1); \
		TYPE *ts = (TYPE *) (IN2); \
		TYPE *tq = (TYPE *) (OUT); \
		const int cb = (B); \
		const int left = VIPS_CLIP(0, first - oreg->left, oreg->width); \
		const int right = VIPS_CLIP(left, last - oreg->left, oreg->width); \
		int ref_zero; \
		int sec_zero; \
		int x, b; \
		int i; \
\
		/* Left of the blend area. \
		 */ \
		for (i = 0, x = 0; x < left; x++) { \
			ref_zero = 0; \
			TEST_ZERO(TYPE, tr, ref_zero); \
			if (!ref_zero) \
				for (b = 0; b < cb; b++, i++) \
					tq[i] = tr[i]; \
			else \
				for (b = 0; b < cb; b++, i++) \
					tq[i] = ts[i]; \
		} \
\
		/* In blend area. \
		 */ \
		for (x = left; x < right; x++) { \
			ref_zero = 0; \
			sec_zero = 0; \
			TEST_ZERO(TYPE, tr, ref_zero); \
			TEST_ZERO(TYPE, ts, sec_zero); \
\
			if (!ref_zero && !sec_zero) { \
				int inx = ((x + oreg->left - first) << BLEND_SHIFT) / bwidth; \
				double c1 = vips__coef1[inx]; \
				double c2 = vips__coef2[inx]; \
\
				for (b = 0; b < cb; b++, i++) \
					tq[i] = c1 * tr[i] + c2 * ts[i]; \
			} \
			else if (!ref_zero) \
				for (b = 0; b < cb; b++, i++) \
					tq[i] = tr[i]; \
			else \
				for (b = 0; b < cb; b++, i++) \
					tq[i] = ts[i]; \
		} \
\
		/* Right of blend. \
		 */ \
		for (x = right; x < oreg->width; x++) { \
			sec_zero = 0; \
			TEST_ZERO(TYPE, ts, sec_zero); \
			if (!sec_zero) \
				for (b = 0; b < cb; b++, i++) \
					tq[i] = ts[i]; \
			else \
				for (b = 0; b < cb; b++, i++) \
					tq[i] = tr[i]; \
		} \
	}

/* Left-right blend function for non-labpack images.
 */
static int
lr_blend(VipsRegion *out_region, MergeInfo *inf, Overlapping *ovlap,
	VipsRect *oreg)
{
	VipsRegion *rir = inf->rir;
	VipsRegion *sir = inf->sir;
	VipsImage *im = out_region->im;

	VipsRect prr, psr;
	int y, yr, ys;

	/* Make sure we have a complete first/last set for this area.
	 */
	if (make_firstlast(inf, ovlap, oreg))
		return -1;

	/* Part of rr which we will output.
	 */
	prr = *oreg;
	prr.left -= ovlap->rarea.left;
	prr.top -= ovlap->rarea.top;

	/* Part of sr which we will output.
	 */
	psr = *oreg;
	psr.left -= ovlap->sarea.left;
	psr.top -= ovlap->sarea.top;

	/* Make pixels.
	 */
	if (vips_region_prepare(rir, &prr) ||
		vips_region_prepare(sir, &psr))
		return -1;

	/* Loop down overlap area.
	 */
	for (y = oreg->top, yr = prr.top, ys = psr.top;
		 y < VIPS_RECT_BOTTOM(oreg); y++, yr++, ys++) {
		VipsPel *pr = VIPS_REGION_ADDR(rir, prr.left, yr);
		VipsPel *ps = VIPS_REGION_ADDR(sir, psr.left, ys);
		VipsPel *q = VIPS_REGION_ADDR(out_region, oreg->left, y);

		const int j = y - ovlap->overlap.top;
		const int first = ovlap->first[j];
		const int last = ovlap->last[j];
		const int bwidth = last - first;

		switch (im->BandFmt) {
		case VIPS_FORMAT_UCHAR:
			iblend(unsigned char, im->Bands, pr, ps, q);
			break;
		case VIPS_FORMAT_CHAR:
			iblend(signed char, im->Bands, pr, ps, q);
			break;
		case VIPS_FORMAT_USHORT:
			iblend(unsigned short, im->Bands, pr, ps, q);
			break;
		case VIPS_FORMAT_SHORT:
			iblend(signed short, im->Bands, pr, ps, q);
			break;
		case VIPS_FORMAT_UINT:
			iblend(unsigned int, im->Bands, pr, ps, q);
			break;
		case VIPS_FORMAT_INT:
			iblend(signed int, im->Bands, pr, ps, q);
			break;
		case VIPS_FORMAT_FLOAT:
			fblend(float, im->Bands, pr, ps, q);
			break;
		case VIPS_FORMAT_DOUBLE:
			fblend(double, im->Bands, pr, ps, q);
			break;
		case VIPS_FORMAT_COMPLEX:
			fblend(float, im->Bands * 2, pr, ps, q);
			break;
		case VIPS_FORMAT_DPCOMPLEX:
			fblend(double, im->Bands * 2, pr, ps, q);
			break;

		default:
			g_assert_not_reached();
			return -1;
		}
	}

	return 0;
}

/* Left-right blend function for VIPS_CODING_LABQ images.
 */
static int
lr_blend_labpack(VipsRegion *out_region, MergeInfo *inf, Overlapping *ovlap,
	VipsRect *oreg)
{
	VipsRegion *rir = inf->rir;
	VipsRegion *sir = inf->sir;
	VipsRect prr, psr;
	int y, yr, ys;

	/* Make sure we have a complete first/last set for this area. This
	 * will just look at the top 8 bits of L, not all 10, but should be OK.
	 */
	if (make_firstlast(inf, ovlap, oreg))
		return -1;

	/* Part of rr which we will output.
	 */
	prr = *oreg;
	prr.left -= ovlap->rarea.left;
	prr.top -= ovlap->rarea.top;

	/* Part of sr which we will output.
	 */
	psr = *oreg;
	psr.left -= ovlap->sarea.left;
	psr.top -= ovlap->sarea.top;

	/* Make pixels.
	 */
	if (vips_region_prepare(rir, &prr) ||
		vips_region_prepare(sir, &psr))
		return -1;

	/* Loop down overlap area.
	 */
	for (y = oreg->top, yr = prr.top, ys = psr.top;
		 y < VIPS_RECT_BOTTOM(oreg); y++, yr++, ys++) {
		VipsPel *pr = VIPS_REGION_ADDR(rir, prr.left, yr);
		VipsPel *ps = VIPS_REGION_ADDR(sir, psr.left, ys);
		VipsPel *q = VIPS_REGION_ADDR(out_region, oreg->left, y);

		const int j = y - ovlap->overlap.top;
		const int first = ovlap->first[j];
		const int last = ovlap->last[j];
		const int bwidth = last - first;

		float *fq = inf->merge;
		float *r = inf->from1;
		float *s = inf->from2;

		/* Unpack two bits we want.
		 */
		vips__LabQ2Lab_vec(r, pr, oreg->width);
		vips__LabQ2Lab_vec(s, ps, oreg->width);

		/* Blend as floats.
		 */
		fblend(float, 3, r, s, fq);

		/* Re-pack to output buffer.
		 */
		vips__Lab2LabQ_vec(q, inf->merge, oreg->width);
	}

	return 0;
}

static void
ovlap_free(VipsImage *image, Overlapping *ovlap)
{
	g_mutex_clear(&ovlap->fl_lock);
}

/* Build basic per-call state and do some geometry calculations. Shared with
 * tbmerge, so not static.
 */
Overlapping *
vips__build_mergestate(const char *domain,
	VipsImage *ref, VipsImage *sec, VipsImage *out,
	int dx, int dy, int mwidth)
{
	VipsImage **t = (VipsImage **)
		vips_object_local_array(VIPS_OBJECT(out), 4);

	VipsImage **array;
	Overlapping *ovlap;
	int x;

	/* TODO(kleisauke): Copied from vips_insert, perhaps we
	 * need a separate function for this?
	 * (just like im__insert_base)
	 */
	if (vips_image_pio_input(ref) ||
		vips_image_pio_input(sec) ||
		vips_check_bands_1orn(domain, ref, sec) ||
		vips_check_coding_known(domain, ref) ||
		vips_check_coding_same(domain, ref, sec))
		return NULL;

	/* Cast our input images up to a common format and bands.
	 */
	if (vips__formatalike(ref, sec, &t[0], &t[1]) ||
		vips__bandalike(domain, t[0], t[1], &t[2], &t[3]))
		return NULL;

	if (!(array = vips_allocate_input_array(out, t[2], t[3], NULL)))
		return NULL;

	if (vips_image_pipeline_array(out, VIPS_DEMAND_STYLE_SMALLTILE, array))
		return NULL;

	if (mwidth < -1) {
		vips_error(domain, "%s", _("mwidth must be -1 or >= 0"));
		return NULL;
	}

	if (!(ovlap = VIPS_NEW(out, Overlapping)))
		return NULL;

	ovlap->ref = array[0];
	ovlap->sec = array[1];
	ovlap->out = out;
	ovlap->dx = dx;
	ovlap->dy = dy;
	ovlap->mwidth = mwidth;

	/* Area occupied by ref image. Place at (0,0) to start with.
	 */
	ovlap->rarea.left = 0;
	ovlap->rarea.top = 0;
	ovlap->rarea.width = ovlap->ref->Xsize;
	ovlap->rarea.height = ovlap->ref->Ysize;

	/* Area occupied by sec image.
	 */
	ovlap->sarea.left = -dx;
	ovlap->sarea.top = -dy;
	ovlap->sarea.width = ovlap->sec->Xsize;
	ovlap->sarea.height = ovlap->sec->Ysize;

	/* Compute overlap.
	 */
	vips_rect_intersectrect(&ovlap->rarea, &ovlap->sarea, &ovlap->overlap);
	if (vips_rect_isempty(&ovlap->overlap)) {
		vips_error(domain, "%s", _("no overlap"));
		return NULL;
	}

	/* Find position and size of output image.
	 */
	vips_rect_unionrect(&ovlap->rarea, &ovlap->sarea, &ovlap->oarea);

	/* Now: translate everything, so that the output image, not the left
	 * image, is at (0,0).
	 */
	ovlap->rarea.left -= ovlap->oarea.left;
	ovlap->rarea.top -= ovlap->oarea.top;
	ovlap->sarea.left -= ovlap->oarea.left;
	ovlap->sarea.top -= ovlap->oarea.top;
	ovlap->overlap.left -= ovlap->oarea.left;
	ovlap->overlap.top -= ovlap->oarea.top;
	ovlap->oarea.left = 0;
	ovlap->oarea.top = 0;

	/* Make sure blend luts are built.
	 */
	vips__make_blend_luts();

	/* Size of first/last cache. Could be either of these ... just pick
	 * the larger.
	 */
	ovlap->flsize = VIPS_MAX(ovlap->overlap.width, ovlap->overlap.height);

	/* Build first/last cache.
	 */
	ovlap->first = VIPS_ARRAY(out, ovlap->flsize, int);
	ovlap->last = VIPS_ARRAY(out, ovlap->flsize, int);
	if (!ovlap->first || !ovlap->last)
		return NULL;
	for (x = 0; x < ovlap->flsize; x++)
		ovlap->first[x] = -1;

	g_mutex_init(&ovlap->fl_lock);

	g_signal_connect(out, "close", G_CALLBACK(ovlap_free), ovlap);

	return ovlap;
}

/* Build per-call state.
 */
static Overlapping *
build_lrstate(VipsImage *ref, VipsImage *sec, VipsImage *out,
	int dx, int dy, int mwidth)
{
	Overlapping *ovlap;

	if (!(ovlap = vips__build_mergestate("lrmerge",
			  ref, sec, out, dx, dy, mwidth)))
		return NULL;

	/* Select blender.
	 */
	switch (ovlap->ref->Coding) {
	case VIPS_CODING_LABQ:
		ovlap->blend = lr_blend_labpack;
		break;

	case VIPS_CODING_NONE:
		ovlap->blend = lr_blend;
		break;

	default:
		vips_error("lrmerge", "%s", _("unknown coding type"));
		return NULL;
	}

	/* Find the parts of output which come just from ref and just from sec.
	 */
	ovlap->rpart = ovlap->rarea;
	ovlap->spart = ovlap->sarea;
	ovlap->rpart.width -= ovlap->overlap.width;
	ovlap->spart.left += ovlap->overlap.width;
	ovlap->spart.width -= ovlap->overlap.width;

	/* Is there too much overlap? ie. right edge of ref image is greater
	 * than right edge of sec image, or left > left.
	 */
	if (VIPS_RECT_RIGHT(&ovlap->rarea) >
			VIPS_RECT_RIGHT(&ovlap->sarea) ||
		ovlap->rarea.left > ovlap->sarea.left) {
		vips_error("lrmerge", "%s", _("too much overlap"));
		return NULL;
	}

	/* Max number of pixels we may have to blend over.
	 */
	ovlap->blsize = ovlap->overlap.width;

	return ovlap;
}

/* The area being demanded can be filled using only pels from either the ref
 * or the sec images. Attach output to the appropriate part of the input image.
 * area is the position that ir->im occupies in the output image.
 *
 * Shared with tbmerge, so not static.
 */
int
vips__attach_input(VipsRegion *out_region, VipsRegion *ir, VipsRect *area)
{
	VipsRect r = out_region->valid;

	/* Translate to source coordinate space.
	 */
	r.left -= area->left;
	r.top -= area->top;

	/* Demand input.
	 */
	if (vips_region_prepare(ir, &r))
		return -1;

	/* Attach or to ir.
	 */
	if (vips_region_region(out_region, ir, &out_region->valid, r.left, r.top))
		return -1;

	return 0;
}

/* The area being demanded requires pixels from the ref and sec images. As
 * above, but just do a sub-area of the output, and make sure we copy rather
 * than just pointer-fiddling. reg is the sub-area of out_region->valid we
 * should do.
 *
 * Shared with tbmerge, so not static.
 */
int
vips__copy_input(VipsRegion *out_region, VipsRegion *ir,
	VipsRect *area, VipsRect *reg)
{
	VipsRect r = *reg;

	/* Translate to source coordinate space.
	 */
	r.left -= area->left;
	r.top -= area->top;

	/* Paint this area of ir into out_region.
	 */
	if (vips_region_prepare_to(ir, out_region, &r, reg->left, reg->top))
		return -1;

	return 0;
}

/* Generate function for merge. This is shared between lrmerge and
 * tbmerge.
 */
int
vips__merge_gen(VipsRegion *out_region,
	void *seq, void *a, void *b, gboolean *stop)
{
	MergeInfo *inf = (MergeInfo *) seq;
	Overlapping *ovlap = (Overlapping *) a;
	VipsRect *r = &out_region->valid;
	VipsRect rreg, sreg, oreg;

	/* Find intersection with overlap, ref and sec parts.
	 */
	vips_rect_intersectrect(r, &ovlap->rpart, &rreg);
	vips_rect_intersectrect(r, &ovlap->spart, &sreg);

	/* Do easy cases first: can we satisfy this demand with pixels just
	 * from ref, or just from sec.
	 */
	if (vips_rect_equalsrect(r, &rreg)) {
		if (vips__attach_input(out_region, inf->rir, &ovlap->rarea))
			return -1;
	}
	else if (vips_rect_equalsrect(r, &sreg)) {
		if (vips__attach_input(out_region, inf->sir, &ovlap->sarea))
			return -1;
	}
	else {
		/* Difficult case - do in three stages: black out whole area,
		 * copy in parts of ref and sec we touch, write blend area.
		 * This could be sped up somewhat ... we will usually black
		 * out far too much, and write to the blend area three times.
		 * Upgrade in the future!
		 */

		/* Need intersections with whole of left & right, and overlap
		 * too.
		 */
		vips_rect_intersectrect(r, &ovlap->rarea, &rreg);
		vips_rect_intersectrect(r, &ovlap->sarea, &sreg);
		vips_rect_intersectrect(r, &ovlap->overlap, &oreg);

		vips_region_black(out_region);
		if (!vips_rect_isempty(&rreg))
			if (vips__copy_input(out_region,
					inf->rir, &ovlap->rarea, &rreg))
				return -1;
		if (!vips_rect_isempty(&sreg))
			if (vips__copy_input(out_region,
					inf->sir, &ovlap->sarea, &sreg))
				return -1;

		/* Nasty: inf->rir and inf->sir now point to the same bit of
		 * memory (part of out_region), and we've written twice. We
		 * need to make sure we get fresh pixels for the blend, so
		 * we must invalidate them both. Should maybe add a call to
		 * the API for this.
		 */
		inf->rir->valid.width = inf->sir->valid.width = 0;

		/* Now blat in the blended area.
		 */
		if (!vips_rect_isempty(&oreg))
			if (ovlap->blend(out_region, inf, ovlap, &oreg))
				return -1;
	}

	return 0;
}

/* Stop function. Shared with tbmerge. Free explicitly to reduce mem
 * requirements quickly for large mosaics.
 */
int
vips__stop_merge(void *seq, void *a, void *b)
{
	MergeInfo *inf = (MergeInfo *) seq;

	VIPS_UNREF(inf->rir);
	VIPS_UNREF(inf->sir);
	VIPS_FREE(inf->from1);
	VIPS_FREE(inf->from2);
	VIPS_FREE(inf->merge);
	g_free(inf);

	return 0;
}

/* Start function. Shared with tbmerge.
 */
void *
vips__start_merge(VipsImage *out, void *a, void *b)
{
	Overlapping *ovlap = (Overlapping *) a;
	MergeInfo *inf;

	if (!(inf = VIPS_NEW(NULL, MergeInfo)))
		return NULL;

	inf->rir = NULL;
	inf->sir = NULL;
	inf->from1 = NULL;
	inf->from2 = NULL;
	inf->merge = NULL;

	/* If this is going to be a VIPS_CODING_LABQ, we need VIPS_CODING_LABQ
	 * blend buffers.
	 */
	if (out->Coding == VIPS_CODING_LABQ) {
		inf->from1 = VIPS_ARRAY(NULL, ovlap->blsize * 3, float);
		inf->from2 = VIPS_ARRAY(NULL, ovlap->blsize * 3, float);
		inf->merge = VIPS_ARRAY(NULL, ovlap->blsize * 3, float);
		if (!inf->from1 || !inf->from2 || !inf->merge) {
			vips__stop_merge(inf, NULL, NULL);
			return NULL;
		}
	}

	inf->rir = vips_region_new(ovlap->ref);
	inf->sir = vips_region_new(ovlap->sec);

	if (!inf->rir || !inf->sir) {
		vips__stop_merge(inf, NULL, NULL);
		return NULL;
	}

	return inf;
}

int
vips__lrmerge(VipsImage *ref, VipsImage *sec, VipsImage *out,
	int dx, int dy, int mwidth)
{
	Overlapping *ovlap;

#ifdef DEBUG
	printf("lrmerge %s %s %s %d %d %d\n",
		ref->filename, sec->filename, out->filename,
		dx, dy, mwidth);
	printf("ref is %d x %d pixels\n", ref->Xsize, ref->Ysize);
	printf("sec is %d x %d pixels\n", sec->Xsize, sec->Ysize);
#endif

	if (dx > 0 || dx < 1 - ref->Xsize) {
		VipsImage *x;

#ifdef DEBUG
		printf("lrmerge: no overlap, using insert\n");
#endif

		/* No overlap, use insert instead.
		 */
		if (vips_insert(ref, sec, &x, -dx, -dy,
				"expand", TRUE,
				NULL))
			return -1;
		if (vips_image_write(x, out)) {
			g_object_unref(x);
			return -1;
		}
		g_object_unref(x);

		out->Xoffset = -dx;
		out->Yoffset = -dy;

		return 0;
	}

	if (!(ovlap = build_lrstate(ref, sec, out, dx, dy, mwidth)))
		return -1;

	if (vips_image_pipelinev(out,
			VIPS_DEMAND_STYLE_THINSTRIP, ovlap->ref, ovlap->sec, NULL))
		return -1;

	out->Xsize = ovlap->oarea.width;
	out->Ysize = ovlap->oarea.height;
	out->Xoffset = -dx;
	out->Yoffset = -dy;

	if (vips_image_generate(out,
			vips__start_merge, vips__merge_gen, vips__stop_merge,
			ovlap, NULL))
		return -1;

	return 0;
}

const char *
vips__get_mosaic_name(VipsImage *image)
{
	const char *name;

	if (vips_image_get_typeof(image, "mosaic-name")) {
		if (vips_image_get_string(image, "mosaic-name", &name))
			return NULL;
	}
	else
		name = image->filename;

	return name;
}

void
vips__add_mosaic_name(VipsImage *image)
{
	static int global_serial = 0;

	/* TODO(kleisauke): Could we call vips_image_temp_name instead?
	 */
	int serial = g_atomic_int_add(&global_serial, 1);

	char name[256];

	/* We must override any inherited name, so don't test for doesn't
	 * exist before setting.
	 */
	g_snprintf(name, 256, "mosaic-temp-%d", serial);
	vips_image_set_string(image, "mosaic-name", name);
}
