backends: Adds a new Cogl based backend

This adds a new GPU accelerated backend for Cairo based on the Cogl 3D
graphics API.

This backend aims to support Cairo in a way that translates as naturally
as possible to using a GPU, it does not strive to compete with the
anti-aliasing quality of the image backend if it can't be done
efficiently using the GPU - raw performance isn't the only metric of
concern, so is power usage.

As an overview of how the backend works:
- fills are handled by tessellating paths into triangles
- the backend has an extra fill_rectangle drawing operation so we have
  a fast-path for drawing rectangles which are so common.
- strokes are also tessellated into triangles.
- stroke and fill tessellations are cached to avoid the cpu overhead
  of tessellation and cost of upload given that its common for apps to
  re-draw the same path multiple times. The tessellations can survive
  translations and rotations increasing the probability that they can be
  re-used.
- sources and masks are handled using multi-texturing.
- clipping is handled with a scissor and the stencil buffer which
  we're careful to only update when they really change.
- linear gradients are rendered to a 1d texture using a triangle
  strip + interpolating color attributes. All cairo extend modes
  are handled by corresponding texture sampler wrap modes without
  needing programmable fragment processing.
- antialiasing should be handled using Cogl's multisampling API

XXX: This is a work in progress!!
TODO:
- handle at least basic radial gradients (No need to handle full
  pdf semantics, since css, svg and canvas only allow radial gradients
  defined as one circle + a point that must lie within the first
  circle.) - currently we fall back to pixman for radial gradients.
- support glyph rendering with a decent glyph cache design. The
  current plan is a per scaled-font growable cache texture + a
  scratch cache for one-shot/short-lived glyphs.
- decide how to handle npot textures when lacking hardware support.
  Current plan is to add a transparent border to npot textures and use
  CLAMP_TO_EDGE for the default EXTEND_NONE semantics. For anything else
  we can allocate a shadow npot texture and scale the original to fit
  that so we can map extend modes to texture sampler modes.

1 files changed, 89 insertions, 0 deletions

diff --git a/src/cairo-cogl-gradient-private.h b/src/cairo-cogl-gradient-private.h
new file mode 100644
index 000000000..9589b0785
--- /dev/null
+++ b/src/cairo-cogl-gradient-private.h
@@ -0,0 +1,89 @@
+/* cairo - a vector graphics library with display and print output
+ *
+ * Copyright © 2011 Intel Corporation.
+ *
+ * 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.og/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.
+ *
+ * Contributor(s):
+ *      Robert Bragg <robert@linux.intel.com>
+ */
+
+#ifndef CAIRO_COGL_GRADIENT_PRIVATE_H
+#define CAIRO_COGL_GRADIENT_PRIVATE_H
+
+#include "cairoint.h"
+#include "cairo-pattern-private.h"
+
+#include <cogl/cogl2-experimental.h>
+
+#define CAIRO_COGL_LINEAR_GRADIENT_CACHE_SIZE (1024 * 1024)
+
+typedef enum _cairo_cogl_gradient_compatability {
+    CAIRO_COGL_GRADIENT_CAN_EXTEND_PAD	    = 1<<0,
+    CAIRO_COGL_GRADIENT_CAN_EXTEND_REPEAT   = 1<<1,
+    CAIRO_COGL_GRADIENT_CAN_EXTEND_REFLECT  = 1<<2,
+    CAIRO_COGL_GRADIENT_CAN_EXTEND_NONE	    = 1<<3
+} cairo_cogl_gradient_compatability_t;
+#define CAIRO_COGL_GRADIENT_CAN_EXTEND_ALL (CAIRO_COGL_GRADIENT_CAN_EXTEND_PAD |\
+					    CAIRO_COGL_GRADIENT_CAN_EXTEND_REPEAT|\
+					    CAIRO_COGL_GRADIENT_CAN_EXTEND_REFLECT|\
+					    CAIRO_COGL_GRADIENT_CAN_EXTEND_NONE)
+
+typedef struct _cairo_cogl_linear_texture_entry {
+    cairo_cogl_gradient_compatability_t compatability;
+    CoglTexture	*texture;
+    float translate_x;
+    float scale_x;
+} cairo_cogl_linear_texture_entry_t;
+
+typedef struct _cairo_cogl_linear_gradient {
+    cairo_cache_entry_t		 cache_entry;
+    cairo_reference_count_t	 ref_count;
+    GList			*textures;
+    int				 n_stops;
+    const cairo_gradient_stop_t	*stops;
+    cairo_gradient_stop_t	 stops_embedded[1];
+} cairo_cogl_linear_gradient_t;
+
+cairo_int_status_t
+_cairo_cogl_get_linear_gradient (cairo_cogl_device_t *context,
+				 cairo_extend_t extend_mode,
+				 int n_stops,
+				 const cairo_gradient_stop_t *stops,
+				 cairo_cogl_linear_gradient_t **gradient_out);
+
+cairo_cogl_linear_texture_entry_t *
+_cairo_cogl_linear_gradient_texture_for_extend (cairo_cogl_linear_gradient_t *gradient,
+						cairo_extend_t extend_mode);
+
+cairo_cogl_linear_gradient_t *
+_cairo_cogl_linear_gradient_reference (cairo_cogl_linear_gradient_t *gradient);
+
+void
+_cairo_cogl_linear_gradient_destroy (cairo_cogl_linear_gradient_t *gradient);
+
+cairo_bool_t
+_cairo_cogl_linear_gradient_equal (const void *key_a, const void *key_b);
+
+#endif /* CAIRO_COGL_GRADIENT_PRIVATE_H */