--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/mupdf-source/source/fitz/transition.c	Mon Sep 15 11:43:07 2025 +0200
@@ -0,0 +1,225 @@
+// Copyright (C) 2004-2021 Artifex Software, Inc.
+//
+// This file is part of MuPDF.
+//
+// MuPDF is free software: you can redistribute it and/or modify it under the
+// terms of the GNU Affero General Public License as published by the Free
+// Software Foundation, either version 3 of the License, or (at your option)
+// any later version.
+//
+// MuPDF 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 Affero General Public License for more
+// details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with MuPDF. If not, see <https://www.gnu.org/licenses/agpl-3.0.en.html>
+//
+// Alternative licensing terms are available from the licensor.
+// For commercial licensing, see <https://www.artifex.com/> or contact
+// Artifex Software, Inc., 39 Mesa Street, Suite 108A, San Francisco,
+// CA 94129, USA, for further information.
+
+#include "mupdf/fitz.h"
+
+#include <string.h>
+
+/*
+	FIXME: Currently transitions only work with alpha. Our app only
+	uses alpha.
+*/
+
+static int
+fade(fz_pixmap *tpix, const fz_pixmap *opix, const fz_pixmap *npix, int time)
+{
+	unsigned char *t, *o, *n;
+	int size;
+	int h;
+	int tstride, ostride, nstride;
+
+	if (!tpix || !opix || !npix || tpix->w != opix->w || opix->w != npix->w || tpix->h != opix->h || opix->h != npix->h || tpix->n != opix->n || opix->n != npix->n)
+		return 0;
+	h = tpix->h;
+	size = tpix->w * tpix->n;
+	ostride = opix->stride - size;
+	nstride = npix->stride - size;
+	tstride = tpix->stride - size;
+	t = tpix->samples;
+	o = opix->samples;
+	n = npix->samples;
+	while (h--)
+	{
+		int ww = size;
+		while (ww-- > 0)
+		{
+			int op = *o++;
+			int np = *n++;
+			*t++ = ((op<<8) + ((np-op) * time) + 0x80)>>8;
+		}
+		o += ostride;
+		n += nstride;
+		t += tstride;
+	}
+	return 1;
+}
+
+static int
+blind_horiz(fz_pixmap *tpix, fz_pixmap *opix, fz_pixmap *npix, int time)
+{
+	unsigned char *t, *o, *n;
+	int blind_height, size, position, y;
+	int tstride, ostride, nstride;
+
+	if (!tpix || !opix || !npix || tpix->w != opix->w || opix->w != npix->w || tpix->h != opix->h || opix->h != npix->h || tpix->n != opix->n || opix->n != npix->n)
+		return 0;
+	size = tpix->w * tpix->n;
+	blind_height = (tpix->h+7) / 8;
+	position = blind_height * time / 256;
+	ostride = opix->stride;
+	nstride = npix->stride;
+	tstride = tpix->stride;
+	t = tpix->samples;
+	o = opix->samples;
+	n = npix->samples;
+	for (y = 0; y < tpix->h; y++)
+	{
+		memcpy(t, ((y % blind_height) <= position ? n : o), size);
+		t += tstride;
+		o += ostride;
+		n += nstride;
+	}
+	return 1;
+}
+
+static int
+blind_vertical(fz_pixmap *tpix, fz_pixmap *opix, fz_pixmap *npix, int time)
+{
+	unsigned char *t, *o, *n;
+	int blind_width, size, position, y;
+	int tstride, ostride, nstride;
+
+	if (!tpix || !opix || !npix || tpix->w != opix->w || opix->w != npix->w || tpix->h != opix->h || opix->h != npix->h || tpix->n != opix->n || opix->n != npix->n)
+		return 0;
+	size = tpix->w * tpix->n;
+	blind_width = (tpix->w+7) / 8;
+	position = blind_width * time / 256;
+	blind_width *= tpix->n;
+	position *= tpix->n;
+	ostride = opix->stride - size;
+	nstride = npix->stride - size;
+	tstride = tpix->stride - size;
+	t = tpix->samples;
+	o = opix->samples;
+	n = npix->samples;
+	for (y = 0; y < tpix->h; y++)
+	{
+		int w, x;
+		x = 0;
+		while ((w = size - x) > 0)
+		{
+			int p;
+			if (w > blind_width)
+				w = blind_width;
+			p = position;
+			if (p > w)
+				p = w;
+			memcpy(t, n, p);
+			memcpy(t+position, o+position, w - p);
+			x += blind_width;
+			t += w;
+			o += w;
+			n += w;
+		}
+		o += ostride;
+		n += nstride;
+		t += tstride;
+	}
+	return 1;
+}
+
+static int
+wipe_tb(fz_pixmap *tpix, fz_pixmap *opix, fz_pixmap *npix, int time)
+{
+	unsigned char *t, *o, *n;
+	int size, position, y;
+	int tstride, ostride, nstride;
+
+	if (!tpix || !opix || !npix || tpix->w != opix->w || opix->w != npix->w || tpix->h != opix->h || opix->h != npix->h || tpix->n != opix->n || opix->n != npix->n)
+		return 0;
+	size = tpix->w * tpix->n;
+	position = tpix->h * time / 256;
+	ostride = opix->stride;
+	nstride = npix->stride;
+	tstride = tpix->stride;
+	t = tpix->samples;
+	o = opix->samples;
+	n = npix->samples;
+	for (y = 0; y < position; y++)
+	{
+		memcpy(t, n, size);
+		t += tstride;
+		o += ostride;
+		n += nstride;
+	}
+	for (; y < tpix->h; y++)
+	{
+		memcpy(t, o, size);
+		t += tstride;
+		o += ostride;
+		n += nstride;
+	}
+	return 1;
+}
+
+static int
+wipe_lr(fz_pixmap *tpix, fz_pixmap *opix, fz_pixmap *npix, int time)
+{
+	unsigned char *t, *o, *n;
+	int size, position, y;
+	int tstride, ostride, nstride;
+
+	if (!tpix || !opix || !npix || tpix->w != opix->w || opix->w != npix->w || tpix->h != opix->h || opix->h != npix->h || tpix->n != opix->n || opix->n != npix->n)
+		return 0;
+	size = tpix->w * tpix->n;
+	position = tpix->w * time / 256;
+	position *= tpix->n;
+	ostride = opix->stride;
+	nstride = npix->stride;
+	tstride = tpix->stride;
+	t = tpix->samples;
+	o = opix->samples + position;
+	n = npix->samples;
+	for (y = 0; y < tpix->h; y++)
+	{
+		memcpy(t, n, position);
+		memcpy(t+position, o, size-position);
+		t += tstride;
+		o += ostride;
+		n += nstride;
+	}
+	return 1;
+}
+
+int fz_generate_transition(fz_context *ctx, fz_pixmap *tpix, fz_pixmap *opix, fz_pixmap *npix, int time, fz_transition *trans)
+{
+	switch (trans->type)
+	{
+	default:
+	case FZ_TRANSITION_FADE:
+		return fade(tpix, opix, npix, time);
+	case FZ_TRANSITION_BLINDS:
+		if (trans->vertical)
+			return blind_vertical(tpix, opix, npix, time);
+		else
+			return blind_horiz(tpix, opix, npix, time);
+	case FZ_TRANSITION_WIPE:
+		switch (((trans->direction + 45 + 360) % 360) / 90)
+		{
+		default:
+		case 0: return wipe_lr(tpix, opix, npix, time);
+		case 1: return wipe_tb(tpix, npix, opix, 256-time);
+		case 2: return wipe_lr(tpix, npix, opix, 256-time);
+		case 3: return wipe_tb(tpix, opix, npix, time);
+		}
+	}
+}