restore Build,TODO from r57911

git-svn-id: svn://tug.org/texlive/trunk@57915 c570f23f-e606-0410-a88d-b1316a301751

1 files changed, 1364 insertions, 0 deletions

diff --git a/Build/source/libs/cairo/cairo-src/src/cairo-gl-composite.c b/Build/source/libs/cairo/cairo-src/src/cairo-gl-composite.c
new file mode 100644
index 00000000000..5477ef0d8ac
--- /dev/null
+++ b/Build/source/libs/cairo/cairo-src/src/cairo-gl-composite.c
@@ -0,0 +1,1364 @@
+/* cairo - a vector graphics library with display and print output
+ *
+ * Copyright © 2009 Eric Anholt
+ * Copyright © 2009 Chris Wilson
+ * Copyright © 2005,2010 Red Hat, Inc
+ * Copyright © 2011 Linaro Limited
+ * Copyright © 2011 Samsung Electronics
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it either under the terms of the GNU Lesser General Public
+ * License version 2.1 as published by the Free Software Foundation
+ * (the "LGPL") or, at your option, under the terms of the Mozilla
+ * Public License Version 1.1 (the "MPL"). If you do not alter this
+ * notice, a recipient may use your version of this file under either
+ * the MPL or the LGPL.
+ *
+ * You should have received a copy of the LGPL along with this library
+ * in the file COPYING-LGPL-2.1; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Suite 500, Boston, MA 02110-1335, USA
+ * You should have received a copy of the MPL along with this library
+ * in the file COPYING-MPL-1.1
+ *
+ * The contents of this file are subject to the Mozilla Public License
+ * Version 1.1 (the "License"); you may not use this file except in
+ * compliance with the License. You may obtain a copy of the License at
+ * http://www.mozilla.org/MPL/
+ *
+ * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY
+ * OF ANY KIND, either express or implied. See the LGPL or the MPL for
+ * the specific language governing rights and limitations.
+ *
+ * The Original Code is the cairo graphics library.
+ *
+ * The Initial Developer of the Original Code is Red Hat, Inc.
+ *
+ * Contributor(s):
+ *	Benjamin Otte <otte@gnome.org>
+ *	Carl Worth <cworth@cworth.org>
+ *	Chris Wilson <chris@chris-wilson.co.uk>
+ *	Eric Anholt <eric@anholt.net>
+ *	Alexandros Frantzis <alexandros.frantzis@linaro.org>
+ *	Henry Song <hsong@sisa.samsung.com>
+ *	Martin Robinson <mrobinson@igalia.com>
+ */
+
+#include "cairoint.h"
+
+#include "cairo-gl-private.h"
+
+#include "cairo-composite-rectangles-private.h"
+#include "cairo-clip-private.h"
+#include "cairo-error-private.h"
+#include "cairo-image-surface-private.h"
+
+/* FIXME: Copy of same routine in cairo-gl-msaa-compositor.c */
+static cairo_int_status_t
+_draw_int_rect (cairo_gl_context_t      *ctx,
+		cairo_gl_composite_t    *setup,
+		cairo_rectangle_int_t   *rect)
+{
+    cairo_box_t box;
+    cairo_point_t quad[4];
+
+    _cairo_box_from_rectangle (&box, rect);
+    quad[0].x = box.p1.x;
+    quad[0].y = box.p1.y;
+    quad[1].x = box.p1.x;
+    quad[1].y = box.p2.y;
+    quad[2].x = box.p2.x;
+    quad[2].y = box.p2.y;
+    quad[3].x = box.p2.x;
+    quad[3].y = box.p1.y;
+
+    return _cairo_gl_composite_emit_quad_as_tristrip (ctx, setup, quad);
+}
+
+static cairo_int_status_t
+_blit_texture_to_renderbuffer (cairo_gl_surface_t *surface)
+{
+    cairo_gl_context_t *ctx = NULL;
+    cairo_gl_composite_t setup;
+    cairo_surface_pattern_t pattern;
+    cairo_rectangle_int_t extents;
+    cairo_int_status_t status;
+
+    /* FIXME: This only permits blit when glesv3 is enabled.  But note that
+       glesv2 with the ANGLE extension should also be able to support this feature,
+       so once the ANGLE support code is in place this check can be relaxed. */
+    if (((cairo_gl_context_t *)surface->base.device)->gl_flavor != CAIRO_GL_FLAVOR_ES3)
+	return CAIRO_INT_STATUS_SUCCESS;
+
+    if (! surface->content_in_texture)
+	return CAIRO_INT_STATUS_SUCCESS;
+
+    memset (&setup, 0, sizeof (cairo_gl_composite_t));
+
+    status = _cairo_gl_composite_set_operator (&setup,
+					       CAIRO_OPERATOR_SOURCE,
+					       FALSE);
+
+    if (status)
+	return status;
+
+    setup.dst = surface;
+    setup.clip_region = surface->clip_region;
+
+    _cairo_pattern_init_for_surface (&pattern, &surface->base);
+    status = _cairo_gl_composite_set_source (&setup, &pattern.base,
+					     NULL, NULL, FALSE);
+    _cairo_pattern_fini (&pattern.base);
+
+    if (unlikely (status))
+	goto FAIL;
+
+    _cairo_gl_composite_set_multisample (&setup);
+
+    status = _cairo_gl_composite_begin (&setup, &ctx);
+
+    if (unlikely (status))
+	goto FAIL;
+
+    extents.x = extents.y = 0;
+    extents.width = surface->width;
+    extents.height = surface->height;
+
+    status = _draw_int_rect (ctx, &setup, &extents);
+
+    if (status == CAIRO_INT_STATUS_SUCCESS)
+	surface->content_in_texture = FALSE;
+
+FAIL:
+    _cairo_gl_composite_fini (&setup);
+
+    if (ctx) {
+	_cairo_gl_composite_flush (ctx);
+	status = _cairo_gl_context_release (ctx, status);
+    }
+
+    return status;
+}
+
+cairo_int_status_t
+_cairo_gl_composite_set_source (cairo_gl_composite_t *setup,
+				const cairo_pattern_t *pattern,
+				const cairo_rectangle_int_t *sample,
+				const cairo_rectangle_int_t *extents,
+				cairo_bool_t use_texgen)
+{
+    _cairo_gl_operand_destroy (&setup->src);
+    return _cairo_gl_operand_init (&setup->src, pattern, setup->dst,
+				   sample, extents, use_texgen);
+}
+
+void
+_cairo_gl_composite_set_source_operand (cairo_gl_composite_t *setup,
+					const cairo_gl_operand_t *source)
+{
+    cairo_int_status_t status;
+
+    _cairo_gl_operand_destroy (&setup->src);
+    _cairo_gl_operand_copy (&setup->src, source);
+
+    if (source->type == CAIRO_GL_OPERAND_TEXTURE)
+	status = _cairo_gl_surface_resolve_multisampling (source->texture.surface);
+}
+
+void
+_cairo_gl_composite_set_solid_source (cairo_gl_composite_t *setup,
+				      const cairo_color_t *color)
+{
+    _cairo_gl_operand_destroy (&setup->src);
+    _cairo_gl_solid_operand_init (&setup->src, color);
+}
+
+cairo_int_status_t
+_cairo_gl_composite_set_mask (cairo_gl_composite_t *setup,
+			      const cairo_pattern_t *pattern,
+			      const cairo_rectangle_int_t *sample,
+			      const cairo_rectangle_int_t *extents,
+			      cairo_bool_t use_texgen)
+{
+    _cairo_gl_operand_destroy (&setup->mask);
+    if (pattern == NULL)
+	return CAIRO_STATUS_SUCCESS;
+
+    return _cairo_gl_operand_init (&setup->mask, pattern, setup->dst,
+				   sample, extents, use_texgen);
+}
+
+void
+_cairo_gl_composite_set_mask_operand (cairo_gl_composite_t *setup,
+				      const cairo_gl_operand_t *mask)
+{
+    cairo_int_status_t status;
+    _cairo_gl_operand_destroy (&setup->mask);
+    if (mask) {
+	_cairo_gl_operand_copy (&setup->mask, mask);
+	if (mask->type == CAIRO_GL_OPERAND_TEXTURE)
+	    status = _cairo_gl_surface_resolve_multisampling (mask->texture.surface);
+    }
+}
+
+void
+_cairo_gl_composite_set_spans (cairo_gl_composite_t *setup)
+{
+    setup->spans = TRUE;
+}
+
+void
+_cairo_gl_composite_set_multisample (cairo_gl_composite_t *setup)
+{
+    setup->multisample = TRUE;
+}
+
+void
+_cairo_gl_composite_set_clip_region (cairo_gl_composite_t *setup,
+				     cairo_region_t *clip_region)
+{
+    setup->clip_region = clip_region;
+}
+
+void
+_cairo_gl_composite_set_clip (cairo_gl_composite_t *setup,
+			      cairo_clip_t *clip)
+{
+    setup->clip = clip;
+}
+
+static void
+_cairo_gl_composite_bind_to_shader (cairo_gl_context_t   *ctx,
+				    cairo_gl_composite_t *setup)
+{
+    _cairo_gl_shader_bind_matrix4f(ctx, ctx->current_shader->mvp_location,
+				   ctx->modelviewprojection_matrix);
+    _cairo_gl_operand_bind_to_shader (ctx, &setup->src,  CAIRO_GL_TEX_SOURCE);
+    _cairo_gl_operand_bind_to_shader (ctx, &setup->mask, CAIRO_GL_TEX_MASK);
+}
+
+static void
+_cairo_gl_texture_set_filter (cairo_gl_context_t *ctx,
+			      GLuint              target,
+			      cairo_filter_t      filter)
+{
+    switch (filter) {
+    case CAIRO_FILTER_FAST:
+    case CAIRO_FILTER_NEAREST:
+	glTexParameteri (target, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
+	glTexParameteri (target, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
+	break;
+    case CAIRO_FILTER_GOOD:
+    case CAIRO_FILTER_BEST:
+    case CAIRO_FILTER_BILINEAR:
+	glTexParameteri (target, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
+	glTexParameteri (target, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
+	break;
+    default:
+    case CAIRO_FILTER_GAUSSIAN:
+	ASSERT_NOT_REACHED;
+    }
+}
+
+static void
+_cairo_gl_texture_set_extend (cairo_gl_context_t *ctx,
+			      GLuint              target,
+			      cairo_extend_t      extend)
+{
+    GLint wrap_mode;
+    assert (! _cairo_gl_device_requires_power_of_two_textures (&ctx->base) ||
+	    (extend != CAIRO_EXTEND_REPEAT && extend != CAIRO_EXTEND_REFLECT));
+
+    switch (extend) {
+    case CAIRO_EXTEND_NONE:
+	if (ctx->gl_flavor == CAIRO_GL_FLAVOR_ES3 ||
+	    ctx->gl_flavor == CAIRO_GL_FLAVOR_ES2)
+	    wrap_mode = GL_CLAMP_TO_EDGE;
+	else
+	    wrap_mode = GL_CLAMP_TO_BORDER;
+	break;
+    case CAIRO_EXTEND_PAD:
+	wrap_mode = GL_CLAMP_TO_EDGE;
+	break;
+    case CAIRO_EXTEND_REPEAT:
+	if (ctx->has_npot_repeat)
+	    wrap_mode = GL_REPEAT;
+	else
+	    wrap_mode = GL_CLAMP_TO_EDGE;
+	break;
+    case CAIRO_EXTEND_REFLECT:
+	if (ctx->has_npot_repeat)
+	    wrap_mode = GL_MIRRORED_REPEAT;
+	else
+	    wrap_mode = GL_CLAMP_TO_EDGE;
+	break;
+    default:
+	wrap_mode = 0;
+    }
+
+    if (likely (wrap_mode)) {
+	glTexParameteri (target, GL_TEXTURE_WRAP_S, wrap_mode);
+	glTexParameteri (target, GL_TEXTURE_WRAP_T, wrap_mode);
+    }
+}
+
+
+static void
+_cairo_gl_context_setup_operand (cairo_gl_context_t *ctx,
+				 cairo_gl_tex_t      tex_unit,
+				 cairo_gl_operand_t *operand,
+				 unsigned int        vertex_offset,
+				 cairo_bool_t        vertex_size_changed)
+{
+    cairo_gl_dispatch_t *dispatch = &ctx->dispatch;
+    cairo_bool_t needs_setup;
+
+    /* XXX: we need to do setup when switching from shaders
+     * to no shaders (or back) */
+    needs_setup = vertex_size_changed;
+    needs_setup |= _cairo_gl_operand_needs_setup (&ctx->operands[tex_unit],
+						 operand,
+						 vertex_offset);
+
+    if (needs_setup) {
+	_cairo_gl_composite_flush (ctx);
+	_cairo_gl_context_destroy_operand (ctx, tex_unit);
+    }
+
+    memcpy (&ctx->operands[tex_unit], operand, sizeof (cairo_gl_operand_t));
+    ctx->operands[tex_unit].vertex_offset = vertex_offset;
+
+    if (! needs_setup)
+	return;
+
+    switch (operand->type) {
+    default:
+    case CAIRO_GL_OPERAND_COUNT:
+	ASSERT_NOT_REACHED;
+    case CAIRO_GL_OPERAND_NONE:
+	break;
+	/* fall through */
+    case CAIRO_GL_OPERAND_CONSTANT:
+	break;
+    case CAIRO_GL_OPERAND_TEXTURE:
+	glActiveTexture (GL_TEXTURE0 + tex_unit);
+	glBindTexture (ctx->tex_target, operand->texture.tex);
+	_cairo_gl_texture_set_extend (ctx, ctx->tex_target,
+				      operand->texture.attributes.extend);
+	_cairo_gl_texture_set_filter (ctx, ctx->tex_target,
+				      operand->texture.attributes.filter);
+
+	if (! operand->texture.texgen) {
+	    dispatch->VertexAttribPointer (CAIRO_GL_TEXCOORD0_ATTRIB_INDEX + tex_unit, 2,
+					   GL_FLOAT, GL_FALSE, ctx->vertex_size,
+					   ctx->vb + vertex_offset);
+	    dispatch->EnableVertexAttribArray (CAIRO_GL_TEXCOORD0_ATTRIB_INDEX + tex_unit);
+	}
+	break;
+    case CAIRO_GL_OPERAND_LINEAR_GRADIENT:
+    case CAIRO_GL_OPERAND_RADIAL_GRADIENT_A0:
+    case CAIRO_GL_OPERAND_RADIAL_GRADIENT_NONE:
+    case CAIRO_GL_OPERAND_RADIAL_GRADIENT_EXT:
+	glActiveTexture (GL_TEXTURE0 + tex_unit);
+	glBindTexture (ctx->tex_target, operand->gradient.gradient->tex);
+	_cairo_gl_texture_set_extend (ctx, ctx->tex_target, operand->gradient.extend);
+	_cairo_gl_texture_set_filter (ctx, ctx->tex_target, CAIRO_FILTER_BILINEAR);
+
+	if (! operand->gradient.texgen) {
+	    dispatch->VertexAttribPointer (CAIRO_GL_TEXCOORD0_ATTRIB_INDEX + tex_unit, 2,
+					   GL_FLOAT, GL_FALSE, ctx->vertex_size,
+					   ctx->vb + vertex_offset);
+	    dispatch->EnableVertexAttribArray (CAIRO_GL_TEXCOORD0_ATTRIB_INDEX + tex_unit);
+	}
+	break;
+    }
+}
+
+static void
+_cairo_gl_context_setup_spans (cairo_gl_context_t *ctx,
+			       cairo_bool_t        spans_enabled,
+			       unsigned int        vertex_size,
+			       unsigned int        vertex_offset)
+{
+    cairo_gl_dispatch_t *dispatch = &ctx->dispatch;
+
+    if (! spans_enabled) {
+	dispatch->DisableVertexAttribArray (CAIRO_GL_COLOR_ATTRIB_INDEX);
+	ctx->spans = FALSE;
+	return;
+    }
+
+    dispatch->VertexAttribPointer (CAIRO_GL_COLOR_ATTRIB_INDEX, 4,
+				   GL_UNSIGNED_BYTE, GL_TRUE, vertex_size,
+				   ctx->vb + vertex_offset);
+    dispatch->EnableVertexAttribArray (CAIRO_GL_COLOR_ATTRIB_INDEX);
+    ctx->spans = TRUE;
+}
+
+void
+_cairo_gl_context_destroy_operand (cairo_gl_context_t *ctx,
+				   cairo_gl_tex_t tex_unit)
+{
+    cairo_gl_dispatch_t *dispatch = &ctx->dispatch;
+
+    if  (!_cairo_gl_context_is_flushed (ctx))
+	_cairo_gl_composite_flush (ctx);
+
+    switch (ctx->operands[tex_unit].type) {
+    default:
+    case CAIRO_GL_OPERAND_COUNT:
+	ASSERT_NOT_REACHED;
+    case CAIRO_GL_OPERAND_NONE:
+	break;
+	/* fall through */
+    case CAIRO_GL_OPERAND_CONSTANT:
+	break;
+    case CAIRO_GL_OPERAND_TEXTURE:
+	dispatch->DisableVertexAttribArray (CAIRO_GL_TEXCOORD0_ATTRIB_INDEX + tex_unit);
+	break;
+    case CAIRO_GL_OPERAND_LINEAR_GRADIENT:
+    case CAIRO_GL_OPERAND_RADIAL_GRADIENT_A0:
+    case CAIRO_GL_OPERAND_RADIAL_GRADIENT_NONE:
+    case CAIRO_GL_OPERAND_RADIAL_GRADIENT_EXT:
+	dispatch->DisableVertexAttribArray (CAIRO_GL_TEXCOORD0_ATTRIB_INDEX + tex_unit);
+	break;
+    }
+
+    memset (&ctx->operands[tex_unit], 0, sizeof (cairo_gl_operand_t));
+}
+
+static void
+_cairo_gl_set_operator (cairo_gl_context_t *ctx,
+			cairo_operator_t    op,
+			cairo_bool_t        component_alpha)
+{
+    struct {
+	GLenum src;
+	GLenum dst;
+    } blend_factors[] = {
+	{ GL_ZERO, GL_ZERO }, /* Clear */
+	{ GL_ONE, GL_ZERO }, /* Source */
+	{ GL_ONE, GL_ONE_MINUS_SRC_ALPHA }, /* Over */
+	{ GL_DST_ALPHA, GL_ZERO }, /* In */
+	{ GL_ONE_MINUS_DST_ALPHA, GL_ZERO }, /* Out */
+	{ GL_DST_ALPHA, GL_ONE_MINUS_SRC_ALPHA }, /* Atop */
+
+	{ GL_ZERO, GL_ONE }, /* Dest */
+	{ GL_ONE_MINUS_DST_ALPHA, GL_ONE }, /* DestOver */
+	{ GL_ZERO, GL_SRC_ALPHA }, /* DestIn */
+	{ GL_ZERO, GL_ONE_MINUS_SRC_ALPHA }, /* DestOut */
+	{ GL_ONE_MINUS_DST_ALPHA, GL_SRC_ALPHA }, /* DestAtop */
+
+	{ GL_ONE_MINUS_DST_ALPHA, GL_ONE_MINUS_SRC_ALPHA }, /* Xor */
+	{ GL_ONE, GL_ONE }, /* Add */
+    };
+    GLenum src_factor, dst_factor;
+
+    assert (op < ARRAY_LENGTH (blend_factors));
+    /* different dst and component_alpha changes cause flushes elsewhere */
+    if (ctx->current_operator != op)
+	_cairo_gl_composite_flush (ctx);
+    ctx->current_operator = op;
+
+    src_factor = blend_factors[op].src;
+    dst_factor = blend_factors[op].dst;
+
+    /* Even when the user requests CAIRO_CONTENT_COLOR, we use GL_RGBA
+     * due to texture filtering of GL_CLAMP_TO_BORDER.  So fix those
+     * bits in that case.
+     */
+    if (ctx->current_target->base.content == CAIRO_CONTENT_COLOR) {
+	if (src_factor == GL_ONE_MINUS_DST_ALPHA)
+	    src_factor = GL_ZERO;
+	if (src_factor == GL_DST_ALPHA)
+	    src_factor = GL_ONE;
+    }
+
+    if (component_alpha) {
+	if (dst_factor == GL_ONE_MINUS_SRC_ALPHA)
+	    dst_factor = GL_ONE_MINUS_SRC_COLOR;
+	if (dst_factor == GL_SRC_ALPHA)
+	    dst_factor = GL_SRC_COLOR;
+    }
+
+    if (ctx->current_target->base.content == CAIRO_CONTENT_ALPHA) {
+	glBlendFuncSeparate (GL_ZERO, GL_ZERO, src_factor, dst_factor);
+    } else if (ctx->current_target->base.content == CAIRO_CONTENT_COLOR) {
+	glBlendFuncSeparate (src_factor, dst_factor, GL_ONE, GL_ONE);
+    } else {
+	glBlendFunc (src_factor, dst_factor);
+    }
+}
+
+static cairo_status_t
+_cairo_gl_composite_begin_component_alpha  (cairo_gl_context_t *ctx,
+					    cairo_gl_composite_t *setup)
+{
+    cairo_gl_shader_t *pre_shader = NULL;
+    cairo_status_t status;
+
+    /* For CLEAR, cairo's rendering equation (quoting Owen's description in:
+     * https://lists.cairographics.org/archives/cairo/2005-August/004992.html)
+     * is:
+     *     mask IN clip ? src OP dest : dest
+     * or more simply:
+     *     mask IN CLIP ? 0 : dest
+     *
+     * where the ternary operator A ? B : C is (A * B) + ((1 - A) * C).
+     *
+     * The model we use in _cairo_gl_set_operator() is Render's:
+     *     src IN mask IN clip OP dest
+     * which would boil down to:
+     *     0 (bounded by the extents of the drawing).
+     *
+     * However, we can do a Render operation using an opaque source
+     * and DEST_OUT to produce:
+     *    1 IN mask IN clip DEST_OUT dest
+     * which is
+     *    mask IN clip ? 0 : dest
+     */
+    if (setup->op == CAIRO_OPERATOR_CLEAR) {
+	_cairo_gl_solid_operand_init (&setup->src, CAIRO_COLOR_WHITE);
+	setup->op = CAIRO_OPERATOR_DEST_OUT;
+    }
+
+    /*
+     * implements component-alpha %CAIRO_OPERATOR_OVER using two passes of
+     * the simpler operations %CAIRO_OPERATOR_DEST_OUT and %CAIRO_OPERATOR_ADD.
+     *
+     * From http://anholt.livejournal.com/32058.html:
+     *
+     * The trouble is that component-alpha rendering requires two different sources
+     * for blending: one for the source value to the blender, which is the
+     * per-channel multiplication of source and mask, and one for the source alpha
+     * for multiplying with the destination channels, which is the multiplication
+     * of the source channels by the mask alpha. So the equation for Over is:
+     *
+     * dst.A = src.A * mask.A + (1 - (src.A * mask.A)) * dst.A
+     * dst.R = src.R * mask.R + (1 - (src.A * mask.R)) * dst.R
+     * dst.G = src.G * mask.G + (1 - (src.A * mask.G)) * dst.G
+     * dst.B = src.B * mask.B + (1 - (src.A * mask.B)) * dst.B
+     *
+     * But we can do some simpler operations, right? How about PictOpOutReverse,
+     * which has a source factor of 0 and dest factor of (1 - source alpha). We
+     * can get the source alpha value (srca.X = src.A * mask.X) out of the texture
+     * blenders pretty easily. So we can do a component-alpha OutReverse, which
+     * gets us:
+     *
+     * dst.A = 0 + (1 - (src.A * mask.A)) * dst.A
+     * dst.R = 0 + (1 - (src.A * mask.R)) * dst.R
+     * dst.G = 0 + (1 - (src.A * mask.G)) * dst.G
+     * dst.B = 0 + (1 - (src.A * mask.B)) * dst.B
+     *
+     * OK. And if an op doesn't use the source alpha value for the destination
+     * factor, then we can do the channel multiplication in the texture blenders
+     * to get the source value, and ignore the source alpha that we wouldn't use.
+     * We've supported this in the Radeon driver for a long time. An example would
+     * be PictOpAdd, which does:
+     *
+     * dst.A = src.A * mask.A + dst.A
+     * dst.R = src.R * mask.R + dst.R
+     * dst.G = src.G * mask.G + dst.G
+     * dst.B = src.B * mask.B + dst.B
+     *
+     * Hey, this looks good! If we do a PictOpOutReverse and then a PictOpAdd right
+     * after it, we get:
+     *
+     * dst.A = src.A * mask.A + ((1 - (src.A * mask.A)) * dst.A)
+     * dst.R = src.R * mask.R + ((1 - (src.A * mask.R)) * dst.R)
+     * dst.G = src.G * mask.G + ((1 - (src.A * mask.G)) * dst.G)
+     * dst.B = src.B * mask.B + ((1 - (src.A * mask.B)) * dst.B)
+     *
+     * This two-pass trickery could be avoided using a new GL extension that
+     * lets two values come out of the shader and into the blend unit.
+     */
+    if (setup->op == CAIRO_OPERATOR_OVER) {
+	setup->op = CAIRO_OPERATOR_ADD;
+	status = _cairo_gl_get_shader_by_type (ctx,
+					       &setup->src,
+					       &setup->mask,
+					       setup->spans,
+					       CAIRO_GL_SHADER_IN_CA_SOURCE_ALPHA,
+					       &pre_shader);
+	if (unlikely (status))
+	    return status;
+    }
+
+    if (ctx->pre_shader != pre_shader)
+	_cairo_gl_composite_flush (ctx);
+    ctx->pre_shader = pre_shader;
+
+    return CAIRO_STATUS_SUCCESS;
+}
+
+static void
+_scissor_to_doubles (cairo_gl_surface_t	*surface,
+		     double x1, double y1,
+		     double x2, double y2)
+{
+    double height;
+
+    height = y2 - y1;
+    if (_cairo_gl_surface_is_texture (surface) == FALSE)
+	y1 = surface->height - (y1 + height);
+    glScissor (x1, y1, x2 - x1, height);
+    glEnable (GL_SCISSOR_TEST);
+}
+
+void
+_cairo_gl_scissor_to_rectangle (cairo_gl_surface_t *surface,
+		       const cairo_rectangle_int_t *r)
+{
+    _scissor_to_doubles (surface, r->x, r->y, r->x+r->width, r->y+r->height);
+}
+
+static void
+_scissor_to_box (cairo_gl_surface_t	*surface,
+		 const cairo_box_t	*box)
+{
+    double x1, y1, x2, y2;
+    _cairo_box_to_doubles (box, &x1, &y1, &x2, &y2);
+    _scissor_to_doubles (surface, x1, y1, x2, y2);
+}
+
+static cairo_bool_t
+_cairo_gl_composite_setup_vbo (cairo_gl_context_t *ctx,
+			       unsigned int size_per_vertex)
+{
+    cairo_bool_t vertex_size_changed = ctx->vertex_size != size_per_vertex;
+    if (vertex_size_changed) {
+	ctx->vertex_size = size_per_vertex;
+	_cairo_gl_composite_flush (ctx);
+    }
+
+    if (_cairo_gl_context_is_flushed (ctx)) {
+	ctx->dispatch.VertexAttribPointer (CAIRO_GL_VERTEX_ATTRIB_INDEX, 2,
+					   GL_FLOAT, GL_FALSE, size_per_vertex,
+					   ctx->vb);
+	ctx->dispatch.EnableVertexAttribArray (CAIRO_GL_VERTEX_ATTRIB_INDEX);
+    }
+
+    return vertex_size_changed;
+}
+
+static void
+_disable_stencil_buffer (void)
+{
+    glDisable (GL_STENCIL_TEST);
+    glDepthMask (GL_FALSE);
+}
+
+static cairo_int_status_t
+_cairo_gl_composite_setup_painted_clipping (cairo_gl_composite_t *setup,
+					    cairo_gl_context_t *ctx,
+					    int vertex_size)
+{
+    cairo_int_status_t status = CAIRO_INT_STATUS_SUCCESS;
+
+    cairo_gl_surface_t *dst = setup->dst;
+    cairo_clip_t *clip = setup->clip;
+
+    if (clip->num_boxes == 1 && clip->path == NULL) {
+	_scissor_to_box (dst, &clip->boxes[0]);
+	goto disable_stencil_buffer_and_return;
+    }
+
+    if (! _cairo_gl_ensure_stencil (ctx, setup->dst)) {
+	status = CAIRO_INT_STATUS_UNSUPPORTED;
+	goto disable_stencil_buffer_and_return;
+    }
+
+    /* We only want to clear the part of the stencil buffer
+     * that we are about to use. It also does not hurt to
+     * scissor around the painted clip. */
+    _cairo_gl_scissor_to_rectangle (dst, _cairo_clip_get_extents (clip));
+
+    /* The clip is not rectangular, so use the stencil buffer. */
+    glDepthMask (GL_TRUE);
+    glEnable (GL_STENCIL_TEST);
+
+    /* Texture surfaces have private depth/stencil buffers, so we can
+     * rely on any previous clip being cached there. */
+    if (_cairo_gl_surface_is_texture (setup->dst)) {
+	cairo_clip_t *old_clip = setup->dst->clip_on_stencil_buffer;
+	if (_cairo_clip_equal (old_clip, setup->clip))
+	    goto activate_stencil_buffer_and_return;
+
+	if (old_clip) {
+	    _cairo_clip_destroy (setup->dst->clip_on_stencil_buffer);
+	}
+
+	setup->dst->clip_on_stencil_buffer = _cairo_clip_copy (setup->clip);
+    }
+
+    glClearStencil (0);
+    glClear (GL_STENCIL_BUFFER_BIT);
+
+    glStencilOp (GL_REPLACE, GL_REPLACE, GL_REPLACE);
+    glStencilFunc (GL_EQUAL, 1, 0xffffffff);
+    glColorMask (0, 0, 0, 0);
+
+    status = _cairo_gl_msaa_compositor_draw_clip (ctx, setup, clip);
+
+    if (unlikely (status)) {
+	glColorMask (1, 1, 1, 1);
+	goto disable_stencil_buffer_and_return;
+    }
+
+    /* We want to only render to the stencil buffer, so draw everything now.
+       Flushing also unbinds the VBO, which we want to rebind for regular
+       drawing. */
+    _cairo_gl_composite_flush (ctx);
+    _cairo_gl_composite_setup_vbo (ctx, vertex_size);
+
+activate_stencil_buffer_and_return:
+    glColorMask (1, 1, 1, 1);
+    glStencilOp (GL_KEEP, GL_KEEP, GL_KEEP);
+    glStencilFunc (GL_EQUAL, 1, 0xffffffff);
+    return CAIRO_INT_STATUS_SUCCESS;
+
+disable_stencil_buffer_and_return:
+    _disable_stencil_buffer ();
+    return status;
+}
+
+static cairo_int_status_t
+_cairo_gl_composite_setup_clipping (cairo_gl_composite_t *setup,
+				    cairo_gl_context_t *ctx,
+				    int vertex_size)
+{
+    cairo_bool_t clip_changing = TRUE;
+    cairo_bool_t clip_region_changing = TRUE;
+
+    if (! ctx->clip && ! setup->clip && ! setup->clip_region && ! ctx->clip_region)
+	goto disable_all_clipping;
+
+    clip_changing = ! _cairo_clip_equal (ctx->clip, setup->clip);
+    clip_region_changing = ! cairo_region_equal (ctx->clip_region, setup->clip_region);
+    if (! _cairo_gl_context_is_flushed (ctx) &&
+	(clip_region_changing || clip_changing))
+	_cairo_gl_composite_flush (ctx);
+
+    assert (!setup->clip_region || !setup->clip);
+
+    /* setup->clip is only used by the msaa compositor and setup->clip_region
+     * only by the other compositors, so it's safe to wait to clean up obsolete
+     * clips. */
+    if (clip_region_changing) {
+	cairo_region_destroy (ctx->clip_region);
+	ctx->clip_region = cairo_region_reference (setup->clip_region);
+    }
+    if (clip_changing) {
+	_cairo_clip_destroy (ctx->clip);
+	ctx->clip = _cairo_clip_copy (setup->clip);
+    }
+
+    /* For clip regions, we scissor right before drawing. */
+    if (setup->clip_region)
+	goto disable_all_clipping;
+
+    if (setup->clip)
+	return _cairo_gl_composite_setup_painted_clipping (setup, ctx,
+							   vertex_size);
+disable_all_clipping:
+    _disable_stencil_buffer ();
+    glDisable (GL_SCISSOR_TEST);
+    return CAIRO_INT_STATUS_SUCCESS;
+}
+
+cairo_status_t
+_cairo_gl_set_operands_and_operator (cairo_gl_composite_t *setup,
+				     cairo_gl_context_t *ctx)
+{
+    unsigned int dst_size, src_size, mask_size, vertex_size;
+    cairo_status_t status;
+    cairo_gl_shader_t *shader;
+    cairo_bool_t component_alpha;
+    cairo_bool_t vertex_size_changed;
+
+    component_alpha =
+	setup->mask.type == CAIRO_GL_OPERAND_TEXTURE &&
+	setup->mask.texture.attributes.has_component_alpha;
+
+    /* Do various magic for component alpha */
+    if (component_alpha) {
+	status = _cairo_gl_composite_begin_component_alpha (ctx, setup);
+	if (unlikely (status))
+	    return status;
+     } else {
+	if (ctx->pre_shader) {
+	    _cairo_gl_composite_flush (ctx);
+	    ctx->pre_shader = NULL;
+	}
+    }
+
+    status = _cairo_gl_get_shader_by_type (ctx,
+					   &setup->src,
+					   &setup->mask,
+					   setup->spans,
+					   component_alpha ?
+					   CAIRO_GL_SHADER_IN_CA_SOURCE :
+					   CAIRO_GL_SHADER_IN_NORMAL,
+					   &shader);
+    if (unlikely (status)) {
+	ctx->pre_shader = NULL;
+	return status;
+    }
+    if (ctx->current_shader != shader)
+	_cairo_gl_composite_flush (ctx);
+
+    status = CAIRO_STATUS_SUCCESS;
+
+    dst_size = 2 * sizeof (GLfloat);
+    src_size = _cairo_gl_operand_get_vertex_size (&setup->src);
+    mask_size = _cairo_gl_operand_get_vertex_size (&setup->mask);
+    vertex_size = dst_size + src_size + mask_size;
+
+    if (setup->spans)
+	vertex_size += sizeof (GLfloat);
+
+    vertex_size_changed = _cairo_gl_composite_setup_vbo (ctx, vertex_size);
+
+    _cairo_gl_context_setup_operand (ctx, CAIRO_GL_TEX_SOURCE, &setup->src, dst_size, vertex_size_changed);
+    _cairo_gl_context_setup_operand (ctx, CAIRO_GL_TEX_MASK, &setup->mask, dst_size + src_size, vertex_size_changed);
+
+    _cairo_gl_context_setup_spans (ctx, setup->spans, vertex_size,
+				   dst_size + src_size + mask_size);
+
+    _cairo_gl_set_operator (ctx, setup->op, component_alpha);
+
+    if (_cairo_gl_context_is_flushed (ctx)) {
+	if (ctx->pre_shader) {
+	    _cairo_gl_set_shader (ctx, ctx->pre_shader);
+	    _cairo_gl_composite_bind_to_shader (ctx, setup);
+	}
+	_cairo_gl_set_shader (ctx, shader);
+	_cairo_gl_composite_bind_to_shader (ctx, setup);
+    }
+
+    return status;
+}
+
+cairo_status_t
+_cairo_gl_composite_begin (cairo_gl_composite_t *setup,
+			   cairo_gl_context_t **ctx_out)
+{
+    cairo_gl_context_t *ctx;
+    cairo_status_t status;
+
+    assert (setup->dst);
+
+    status = _cairo_gl_context_acquire (setup->dst->base.device, &ctx);
+    if (unlikely (status))
+	return status;
+
+    _cairo_gl_context_set_destination (ctx, setup->dst, setup->multisample);
+    glEnable (GL_BLEND);
+
+    status = _cairo_gl_set_operands_and_operator (setup, ctx);
+    if (unlikely (status))
+	goto FAIL;
+
+    status = _cairo_gl_composite_setup_clipping (setup, ctx, ctx->vertex_size);
+    if (unlikely (status))
+	goto FAIL;
+
+    *ctx_out = ctx;
+
+FAIL:
+    if (unlikely (status))
+	status = _cairo_gl_context_release (ctx, status);
+
+    return status;
+}
+
+static inline void
+_cairo_gl_composite_draw_tristrip (cairo_gl_context_t *ctx)
+{
+    cairo_array_t* indices = &ctx->tristrip_indices;
+    const unsigned short *indices_array = _cairo_array_index_const (indices, 0);
+
+    if (ctx->pre_shader) {
+	cairo_gl_shader_t *prev_shader = ctx->current_shader;
+
+	_cairo_gl_set_shader (ctx, ctx->pre_shader);
+	_cairo_gl_set_operator (ctx, CAIRO_OPERATOR_DEST_OUT, TRUE);
+	glDrawElements (GL_TRIANGLE_STRIP, _cairo_array_num_elements (indices), GL_UNSIGNED_SHORT, indices_array);
+
+	_cairo_gl_set_shader (ctx, prev_shader);
+	_cairo_gl_set_operator (ctx, CAIRO_OPERATOR_ADD, TRUE);
+    }
+
+    glDrawElements (GL_TRIANGLE_STRIP, _cairo_array_num_elements (indices), GL_UNSIGNED_SHORT, indices_array);
+    _cairo_array_truncate (indices, 0);
+}
+
+static inline void
+_cairo_gl_composite_draw_triangles (cairo_gl_context_t *ctx,
+				    unsigned int count)
+{
+    if (! ctx->pre_shader) {
+	glDrawArrays (GL_TRIANGLES, 0, count);
+    } else {
+	cairo_gl_shader_t *prev_shader = ctx->current_shader;
+
+	_cairo_gl_set_shader (ctx, ctx->pre_shader);
+	_cairo_gl_set_operator (ctx, CAIRO_OPERATOR_DEST_OUT, TRUE);
+	glDrawArrays (GL_TRIANGLES, 0, count);
+
+	_cairo_gl_set_shader (ctx, prev_shader);
+	_cairo_gl_set_operator (ctx, CAIRO_OPERATOR_ADD, TRUE);
+	glDrawArrays (GL_TRIANGLES, 0, count);
+    }
+}
+
+static void
+_cairo_gl_composite_draw_triangles_with_clip_region (cairo_gl_context_t *ctx,
+						     unsigned int count)
+{
+    int i, num_rectangles;
+
+    if (!ctx->clip_region) {
+	_cairo_gl_composite_draw_triangles (ctx, count);
+	return;
+    }
+
+    num_rectangles = cairo_region_num_rectangles (ctx->clip_region);
+    for (i = 0; i < num_rectangles; i++) {
+	cairo_rectangle_int_t rect;
+
+	cairo_region_get_rectangle (ctx->clip_region, i, &rect);
+
+	_cairo_gl_scissor_to_rectangle (ctx->current_target, &rect);
+	_cairo_gl_composite_draw_triangles (ctx, count);
+    }
+}
+
+static void
+_cairo_gl_composite_unmap_vertex_buffer (cairo_gl_context_t *ctx)
+{
+    ctx->vb_offset = 0;
+}
+
+void
+_cairo_gl_composite_flush (cairo_gl_context_t *ctx)
+{
+    unsigned int count;
+    int i;
+
+    if (_cairo_gl_context_is_flushed (ctx))
+	return;
+
+    count = ctx->vb_offset / ctx->vertex_size;
+    _cairo_gl_composite_unmap_vertex_buffer (ctx);
+
+    if (ctx->primitive_type == CAIRO_GL_PRIMITIVE_TYPE_TRISTRIPS) {
+	_cairo_gl_composite_draw_tristrip (ctx);
+    } else {
+	assert (ctx->primitive_type == CAIRO_GL_PRIMITIVE_TYPE_TRIANGLES);
+	_cairo_gl_composite_draw_triangles_with_clip_region (ctx, count);
+    }
+
+    for (i = 0; i < ARRAY_LENGTH (ctx->glyph_cache); i++)
+	_cairo_gl_glyph_cache_unlock (&ctx->glyph_cache[i]);
+}
+
+static void
+_cairo_gl_composite_prepare_buffer (cairo_gl_context_t *ctx,
+				    unsigned int n_vertices,
+				    cairo_gl_primitive_type_t primitive_type)
+{
+    if (ctx->primitive_type != primitive_type) {
+	_cairo_gl_composite_flush (ctx);
+	ctx->primitive_type = primitive_type;
+    }
+
+    assert(ctx->vbo_size > 0);
+    if (ctx->vb_offset + n_vertices * ctx->vertex_size > ctx->vbo_size)
+	_cairo_gl_composite_flush (ctx);
+}
+
+static inline void
+_cairo_gl_composite_emit_vertex (cairo_gl_context_t *ctx,
+				 GLfloat x, GLfloat y)
+{
+    GLfloat *vb = (GLfloat *) (void *) &ctx->vb[ctx->vb_offset];
+
+    *vb++ = x;
+    *vb++ = y;
+
+    _cairo_gl_operand_emit (&ctx->operands[CAIRO_GL_TEX_SOURCE], &vb, x, y);
+    _cairo_gl_operand_emit (&ctx->operands[CAIRO_GL_TEX_MASK  ], &vb, x, y);
+
+    ctx->vb_offset += ctx->vertex_size;
+}
+
+static inline void
+_cairo_gl_composite_emit_alpha_vertex (cairo_gl_context_t *ctx,
+				       GLfloat x, GLfloat y, uint8_t alpha)
+{
+    GLfloat *vb = (GLfloat *) (void *) &ctx->vb[ctx->vb_offset];
+    union fi {
+	float f;
+	GLbyte bytes[4];
+    } fi;
+
+    *vb++ = x;
+    *vb++ = y;
+
+    _cairo_gl_operand_emit (&ctx->operands[CAIRO_GL_TEX_SOURCE], &vb, x, y);
+    _cairo_gl_operand_emit (&ctx->operands[CAIRO_GL_TEX_MASK  ], &vb, x, y);
+
+    fi.bytes[0] = 0;
+    fi.bytes[1] = 0;
+    fi.bytes[2] = 0;
+    fi.bytes[3] = alpha;
+    *vb++ = fi.f;
+
+    ctx->vb_offset += ctx->vertex_size;
+}
+
+static void
+_cairo_gl_composite_emit_point (cairo_gl_context_t	*ctx,
+				const cairo_point_t	*point)
+{
+    _cairo_gl_composite_emit_vertex (ctx,
+				     _cairo_fixed_to_double (point->x),
+				     _cairo_fixed_to_double (point->y));
+}
+
+static void
+_cairo_gl_composite_emit_rect (cairo_gl_context_t *ctx,
+			       GLfloat x1, GLfloat y1,
+			       GLfloat x2, GLfloat y2)
+{
+    _cairo_gl_composite_prepare_buffer (ctx, 6,
+					CAIRO_GL_PRIMITIVE_TYPE_TRIANGLES);
+
+    _cairo_gl_composite_emit_vertex (ctx, x1, y1);
+    _cairo_gl_composite_emit_vertex (ctx, x2, y1);
+    _cairo_gl_composite_emit_vertex (ctx, x1, y2);
+
+    _cairo_gl_composite_emit_vertex (ctx, x2, y1);
+    _cairo_gl_composite_emit_vertex (ctx, x2, y2);
+    _cairo_gl_composite_emit_vertex (ctx, x1, y2);
+}
+
+cairo_gl_emit_rect_t
+_cairo_gl_context_choose_emit_rect (cairo_gl_context_t *ctx)
+{
+    return _cairo_gl_composite_emit_rect;
+}
+
+void
+_cairo_gl_context_emit_rect (cairo_gl_context_t *ctx,
+			     GLfloat x1, GLfloat y1,
+			     GLfloat x2, GLfloat y2)
+{
+    _cairo_gl_composite_emit_rect (ctx, x1, y1, x2, y2);
+}
+
+static void
+_cairo_gl_composite_emit_span (cairo_gl_context_t *ctx,
+			       GLfloat x1, GLfloat y1,
+			       GLfloat x2, GLfloat y2,
+			       uint8_t alpha)
+{
+    _cairo_gl_composite_prepare_buffer (ctx, 6,
+					CAIRO_GL_PRIMITIVE_TYPE_TRIANGLES);
+
+    _cairo_gl_composite_emit_alpha_vertex (ctx, x1, y1, alpha);
+    _cairo_gl_composite_emit_alpha_vertex (ctx, x2, y1, alpha);
+    _cairo_gl_composite_emit_alpha_vertex (ctx, x1, y2, alpha);
+
+    _cairo_gl_composite_emit_alpha_vertex (ctx, x2, y1, alpha);
+    _cairo_gl_composite_emit_alpha_vertex (ctx, x2, y2, alpha);
+    _cairo_gl_composite_emit_alpha_vertex (ctx, x1, y2, alpha);
+}
+
+static void
+_cairo_gl_composite_emit_solid_span (cairo_gl_context_t *ctx,
+				     GLfloat x1, GLfloat y1,
+				     GLfloat x2, GLfloat y2,
+				     uint8_t alpha)
+{
+    GLfloat *v;
+    union fi {
+	float f;
+	GLbyte bytes[4];
+    } fi;
+
+    _cairo_gl_composite_prepare_buffer (ctx, 6,
+					CAIRO_GL_PRIMITIVE_TYPE_TRIANGLES);
+    v = (GLfloat *) (void *) &ctx->vb[ctx->vb_offset];
+
+    v[15] = v[ 6] = v[0] = x1;
+    v[10] = v[ 4] = v[1] = y1;
+    v[12] = v[ 9] = v[3] = x2;
+    v[16] = v[13] = v[7] = y2;
+
+    fi.bytes[0] = 0;
+    fi.bytes[1] = 0;
+    fi.bytes[2] = 0;
+    fi.bytes[3] = alpha;
+    v[17] =v[14] = v[11] = v[8] = v[5] = v[2] = fi.f;
+
+    ctx->vb_offset += 6*3 * sizeof(GLfloat);
+}
+
+cairo_gl_emit_span_t
+_cairo_gl_context_choose_emit_span (cairo_gl_context_t *ctx)
+{
+    if (ctx->operands[CAIRO_GL_TEX_MASK].type != CAIRO_GL_OPERAND_NONE) {
+	    switch (ctx->operands[CAIRO_GL_TEX_MASK].type) {
+	    default:
+	    case CAIRO_GL_OPERAND_COUNT:
+		    ASSERT_NOT_REACHED;
+	    case CAIRO_GL_OPERAND_NONE:
+	    case CAIRO_GL_OPERAND_CONSTANT:
+		    break;
+
+	    case CAIRO_GL_OPERAND_LINEAR_GRADIENT:
+	    case CAIRO_GL_OPERAND_RADIAL_GRADIENT_A0:
+	    case CAIRO_GL_OPERAND_RADIAL_GRADIENT_NONE:
+	    case CAIRO_GL_OPERAND_RADIAL_GRADIENT_EXT:
+		    if (!ctx->operands[CAIRO_GL_TEX_MASK].gradient.texgen)
+			    return _cairo_gl_composite_emit_span;
+		    break;
+
+	    case CAIRO_GL_OPERAND_TEXTURE:
+		    if (!ctx->operands[CAIRO_GL_TEX_MASK].texture.texgen)
+			    return _cairo_gl_composite_emit_span;
+		    break;
+	    }
+    }
+
+    switch (ctx->operands[CAIRO_GL_TEX_SOURCE].type) {
+    default:
+    case CAIRO_GL_OPERAND_COUNT:
+	ASSERT_NOT_REACHED;
+    case CAIRO_GL_OPERAND_NONE:
+    case CAIRO_GL_OPERAND_CONSTANT:
+	break;
+
+    case CAIRO_GL_OPERAND_LINEAR_GRADIENT:
+    case CAIRO_GL_OPERAND_RADIAL_GRADIENT_A0:
+    case CAIRO_GL_OPERAND_RADIAL_GRADIENT_NONE:
+    case CAIRO_GL_OPERAND_RADIAL_GRADIENT_EXT:
+	if (!ctx->operands[CAIRO_GL_TEX_SOURCE].gradient.texgen)
+		return _cairo_gl_composite_emit_span;
+	break;
+
+    case CAIRO_GL_OPERAND_TEXTURE:
+	if (!ctx->operands[CAIRO_GL_TEX_SOURCE].texture.texgen)
+		return _cairo_gl_composite_emit_span;
+    }
+
+    return _cairo_gl_composite_emit_solid_span;
+}
+
+static inline void
+_cairo_gl_composite_emit_glyph_vertex (cairo_gl_context_t *ctx,
+				       GLfloat x, GLfloat y,
+				       GLfloat glyph_x, GLfloat glyph_y)
+{
+    GLfloat *vb = (GLfloat *) (void *) &ctx->vb[ctx->vb_offset];
+
+    *vb++ = x;
+    *vb++ = y;
+
+    _cairo_gl_operand_emit (&ctx->operands[CAIRO_GL_TEX_SOURCE], &vb, x, y);
+
+    *vb++ = glyph_x;
+    *vb++ = glyph_y;
+
+    ctx->vb_offset += ctx->vertex_size;
+}
+
+static void
+_cairo_gl_composite_emit_glyph (cairo_gl_context_t *ctx,
+				GLfloat x1, GLfloat y1,
+				GLfloat x2, GLfloat y2,
+				GLfloat glyph_x1, GLfloat glyph_y1,
+				GLfloat glyph_x2, GLfloat glyph_y2)
+{
+    _cairo_gl_composite_prepare_buffer (ctx, 6,
+					CAIRO_GL_PRIMITIVE_TYPE_TRIANGLES);
+
+    _cairo_gl_composite_emit_glyph_vertex (ctx, x1, y1, glyph_x1, glyph_y1);
+    _cairo_gl_composite_emit_glyph_vertex (ctx, x2, y1, glyph_x2, glyph_y1);
+    _cairo_gl_composite_emit_glyph_vertex (ctx, x1, y2, glyph_x1, glyph_y2);
+
+    _cairo_gl_composite_emit_glyph_vertex (ctx, x2, y1, glyph_x2, glyph_y1);
+    _cairo_gl_composite_emit_glyph_vertex (ctx, x2, y2, glyph_x2, glyph_y2);
+    _cairo_gl_composite_emit_glyph_vertex (ctx, x1, y2, glyph_x1, glyph_y2);
+}
+
+static void
+_cairo_gl_composite_emit_solid_glyph (cairo_gl_context_t *ctx,
+				      GLfloat x1, GLfloat y1,
+				      GLfloat x2, GLfloat y2,
+				      GLfloat glyph_x1, GLfloat glyph_y1,
+				      GLfloat glyph_x2, GLfloat glyph_y2)
+{
+    GLfloat *v;
+
+    _cairo_gl_composite_prepare_buffer (ctx, 6,
+					CAIRO_GL_PRIMITIVE_TYPE_TRIANGLES);
+
+    v = (GLfloat *) (void *) &ctx->vb[ctx->vb_offset];
+
+    v[20] = v[ 8] = v[0] = x1;
+    v[13] = v[ 5] = v[1] = y1;
+    v[22] = v[10] = v[2] = glyph_x1;
+    v[15] = v[ 7] = v[3] = glyph_y1;
+
+    v[16] = v[12] = v[4] = x2;
+    v[18] = v[14] = v[6] = glyph_x2;
+
+    v[21] = v[17] = v[ 9] = y2;
+    v[23] = v[19] = v[11] = glyph_y2;
+
+    ctx->vb_offset += 4 * 6 * sizeof (GLfloat);
+}
+
+cairo_gl_emit_glyph_t
+_cairo_gl_context_choose_emit_glyph (cairo_gl_context_t *ctx)
+{
+    switch (ctx->operands[CAIRO_GL_TEX_SOURCE].type) {
+    default:
+    case CAIRO_GL_OPERAND_COUNT:
+	ASSERT_NOT_REACHED;
+    case CAIRO_GL_OPERAND_NONE:
+    case CAIRO_GL_OPERAND_CONSTANT:
+	return _cairo_gl_composite_emit_solid_glyph;
+
+    case CAIRO_GL_OPERAND_LINEAR_GRADIENT:
+    case CAIRO_GL_OPERAND_RADIAL_GRADIENT_A0:
+    case CAIRO_GL_OPERAND_RADIAL_GRADIENT_NONE:
+    case CAIRO_GL_OPERAND_RADIAL_GRADIENT_EXT:
+    case CAIRO_GL_OPERAND_TEXTURE:
+	return _cairo_gl_composite_emit_glyph;
+    }
+}
+
+void
+_cairo_gl_composite_fini (cairo_gl_composite_t *setup)
+{
+    _cairo_gl_operand_destroy (&setup->src);
+    _cairo_gl_operand_destroy (&setup->mask);
+}
+
+cairo_status_t
+_cairo_gl_composite_set_operator (cairo_gl_composite_t *setup,
+				  cairo_operator_t op,
+				  cairo_bool_t assume_component_alpha)
+{
+    if (assume_component_alpha) {
+	if (op != CAIRO_OPERATOR_CLEAR &&
+	    op != CAIRO_OPERATOR_OVER &&
+	    op != CAIRO_OPERATOR_ADD)
+	    return UNSUPPORTED ("unsupported component alpha operator");
+    } else {
+	if (! _cairo_gl_operator_is_supported (op))
+	    return UNSUPPORTED ("unsupported operator");
+    }
+
+    setup->op = op;
+    return CAIRO_STATUS_SUCCESS;
+}
+
+cairo_status_t
+_cairo_gl_composite_init (cairo_gl_composite_t *setup,
+			  cairo_operator_t op,
+			  cairo_gl_surface_t *dst,
+			  cairo_bool_t assume_component_alpha)
+{
+    cairo_status_t status;
+
+    status = _blit_texture_to_renderbuffer (dst);
+
+    memset (setup, 0, sizeof (cairo_gl_composite_t));
+
+    status = _cairo_gl_composite_set_operator (setup, op,
+					       assume_component_alpha);
+    if (status)
+	return status;
+
+    setup->dst = dst;
+    setup->clip_region = dst->clip_region;
+
+    return CAIRO_STATUS_SUCCESS;
+}
+
+static cairo_int_status_t
+_cairo_gl_composite_append_vertex_indices (cairo_gl_context_t	*ctx,
+					   int			 number_of_new_indices)
+{
+    cairo_int_status_t status = CAIRO_INT_STATUS_SUCCESS;
+    cairo_array_t *indices = &ctx->tristrip_indices;
+    int number_of_indices = _cairo_array_num_elements (indices);
+    unsigned short current_vertex_index = 0;
+    int i;
+
+    assert (number_of_new_indices > 0);
+
+    /* If any preexisting triangle triangle strip indices exist on this
+       context, we insert a set of degenerate triangles from the last
+       preexisting vertex to our first one. */
+    if (number_of_indices > 0) {
+	const unsigned short *indices_array = _cairo_array_index_const (indices, 0);
+	current_vertex_index = indices_array[number_of_indices - 1];
+
+	status = _cairo_array_append (indices, &current_vertex_index);
+	if (unlikely (status))
+	    return status;
+
+	current_vertex_index++;
+	status =_cairo_array_append (indices, &current_vertex_index);
+	if (unlikely (status))
+	    return status;
+    }
+
+    for (i = 0; i < number_of_new_indices; i++) {
+	status = _cairo_array_append (indices, &current_vertex_index);
+	current_vertex_index++;
+	if (unlikely (status))
+	    return status;
+    }
+
+    return CAIRO_STATUS_SUCCESS;
+}
+
+cairo_int_status_t
+_cairo_gl_composite_emit_quad_as_tristrip (cairo_gl_context_t	*ctx,
+					   cairo_gl_composite_t	*setup,
+					   const cairo_point_t	quad[4])
+{
+    _cairo_gl_composite_prepare_buffer (ctx, 4,
+					CAIRO_GL_PRIMITIVE_TYPE_TRISTRIPS);
+
+    _cairo_gl_composite_emit_point (ctx, &quad[0]);
+    _cairo_gl_composite_emit_point (ctx, &quad[1]);
+
+    /* Cairo stores quad vertices in counter-clockwise order, but we need to
+       emit them from top to bottom in the triangle strip, so we need to reverse
+       the order of the last two vertices. */
+    _cairo_gl_composite_emit_point (ctx, &quad[3]);
+    _cairo_gl_composite_emit_point (ctx, &quad[2]);
+
+    return _cairo_gl_composite_append_vertex_indices (ctx, 4);
+}
+
+cairo_int_status_t
+_cairo_gl_composite_emit_triangle_as_tristrip (cairo_gl_context_t	*ctx,
+					       cairo_gl_composite_t	*setup,
+					       const cairo_point_t	 triangle[3])
+{
+    _cairo_gl_composite_prepare_buffer (ctx, 3,
+					CAIRO_GL_PRIMITIVE_TYPE_TRISTRIPS);
+
+    _cairo_gl_composite_emit_point (ctx, &triangle[0]);
+    _cairo_gl_composite_emit_point (ctx, &triangle[1]);
+    _cairo_gl_composite_emit_point (ctx, &triangle[2]);
+    return _cairo_gl_composite_append_vertex_indices (ctx, 3);
+}