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, 16 insertions, 0 deletions

diff --git a/src/Makefile.win32.features b/src/Makefile.win32.features
index 4b90d6490..2274f4ad6 100644
--- a/src/Makefile.win32.features
+++ b/src/Makefile.win32.features
@@ -325,6 +325,22 @@ ifeq ($(CAIRO_HAS_GLESV2_SURFACE),1)
 enabled_cairo_pkgconf += cairo-glesv2.pc
 endif
 
+unsupported_cairo_headers += $(cairo_cogl_headers)
+all_cairo_headers += $(cairo_cogl_headers)
+all_cairo_private += $(cairo_cogl_private)
+all_cairo_cxx_sources += $(cairo_cogl_cxx_sources)
+all_cairo_sources += $(cairo_cogl_sources)
+ifeq ($(CAIRO_HAS_COGL_SURFACE),1)
+enabled_cairo_headers += $(cairo_cogl_headers)
+enabled_cairo_private += $(cairo_cogl_private)
+enabled_cairo_cxx_sources += $(cairo_cogl_cxx_sources)
+enabled_cairo_sources += $(cairo_cogl_sources)
+endif
+all_cairo_pkgconf += cairo-cogl.pc
+ifeq ($(CAIRO_HAS_COGL_SURFACE),1)
+enabled_cairo_pkgconf += cairo-cogl.pc
+endif
+
 unsupported_cairo_headers += $(cairo_directfb_headers)
 all_cairo_headers += $(cairo_directfb_headers)
 all_cairo_private += $(cairo_directfb_private)