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.

3 files changed, 5 insertions, 0 deletions

diff --git a/build/Makefile.win32.features b/build/Makefile.win32.features
index 650b224c..8cb155dc 100644
--- a/build/Makefile.win32.features
+++ b/build/Makefile.win32.features
@@ -19,6 +19,7 @@ CAIRO_HAS_GALLIUM_SURFACE=0
 CAIRO_HAS_PNG_FUNCTIONS=1
 CAIRO_HAS_GL_SURFACE=0
 CAIRO_HAS_GLESV2_SURFACE=0
+CAIRO_HAS_COGL_SURFACE=0
 CAIRO_HAS_DIRECTFB_SURFACE=0
 CAIRO_HAS_VG_SURFACE=0
 CAIRO_HAS_EGL_FUNCTIONS=0
diff --git a/build/Makefile.win32.features-h b/build/Makefile.win32.features-h
index 84d65f4f..13904cfa 100644
--- a/build/Makefile.win32.features-h
+++ b/build/Makefile.win32.features-h
@@ -62,6 +62,9 @@ endif
 ifeq ($(CAIRO_HAS_GLESV2_SURFACE),1)
 	@echo "#define CAIRO_HAS_GLESV2_SURFACE 1" >> $(top_srcdir)/src/cairo-features.h
 endif
+ifeq ($(CAIRO_HAS_COGL_SURFACE),1)
+	@echo "#define CAIRO_HAS_COGL_SURFACE 1" >> $(top_srcdir)/src/cairo-features.h
+endif
 ifeq ($(CAIRO_HAS_DIRECTFB_SURFACE),1)
 	@echo "#define CAIRO_HAS_DIRECTFB_SURFACE 1" >> $(top_srcdir)/src/cairo-features.h
 endif
diff --git a/build/configure.ac.features b/build/configure.ac.features
index faa762ca..e4a2aafc 100644
--- a/build/configure.ac.features
+++ b/build/configure.ac.features
@@ -388,6 +388,7 @@ AC_DEFUN([CAIRO_REPORT],
 	echo "  DirectFB:      $use_directfb"
 	echo "  OpenVG:        $use_vg"
 	echo "  DRM:           $use_drm"
+	echo "  Cogl:          $use_cogl"
 	echo ""
 	echo "The following font backends:"
 	echo "  User:          yes (always builtin)"