This updates cogl/gles in line with the integration of CoglMaterial throughout
Cogl that has been done for cogl/gl.
Note: This is still buggy, but at least it builds again and test-actors works.
Some GLES2 specific changes were made, but these haven't been tested yet.
This changes all GLES code to use the OpenGL function names instead of
the cogl_wrap_* names. For GLES2 we now define the OpenGL name to point
to the wrapper, as opposed to defining the wrapper to point to the
OpenGL name for GLES1.
I've also done a quick pass through gl/cogl.c and gles/cogl.c to make
them more easily comparable. (most of the code is now identical)
The GL blend function and alpha function are now controlled by the material
code, and even internally Cogl should now be using the material API when
it needs control of these.
The script converted calls to COGL_FIXED_MUL(x,y) to (x*y). However
this fails for cases like this:
COGL_FIXED_MUL(a + b, c)
which become
(a + b * c)
The meaning of this is of course different because multiplication has
a higher precedence than addition.
This was causing breakages in cogl_texture_quad_sw when the vertex
coordinates are not in increasing order. This was the case in
test-backface-culling when NPOTs are not available.
Boolean arguments for functions are pretty evil and usually
lead to combinatorial explosion of parameters in case multiple
settings are added.
In the case of the COGL texture constructors we have a boolean
argument for enabling the auto-mipmapping; it is conceivable that
we might want to add more settings for a COGL texture without
breaking API or ABI compatibility, so the boolean argument should
become a bitmask.
The internals have not been changed: instead of checking for
a non-zero value, we check for a bitmask being set.
This better reflects the fact that the api manages sets of vertex attributes,
and the attributes really have no implied form. It is only when you use the
attributes to draw that they become mesh like; when you specify how they should
be interpreted, e.g. as triangle lists or fans etc. This rename frees up the
term "mesh", which can later be applied to a concept slightly more fitting.
E.g. at some point it would be nice to have a higher level abstraction that
sits on top of cogl vertex buffers that adds the concept of faces. (Somthing
like Blender's mesh objects.) There have also been some discussions over
particle engines, and these can be defined in terms of emitter faces; so some
other kind of mesh abstraction might be usefull here.
To deal with all the corner cases that couldn't be scripted a number of patches
were written for the remaining 10% of the effort.
Note: again no API changes were made in Clutter, only in Cogl.
This is the result of running a number of sed and perl scripts over the code to
do 90% of the work in converting from 16.16 fixed to single precision floating
point.
Note: A pristine cogl-fixed.c has been maintained as a standalone utility API
so that applications may still take advantage of fixed point if they
desire for certain optimisations where lower precision may be acceptable.
Note: no API changes were made in Clutter, only in Cogl.
Overview of changes:
- Within clutter/* all usage of the COGL_FIXED_ macros have been changed to use
the CLUTTER_FIXED_ macros.
- Within cogl/* all usage of the COGL_FIXED_ macros have been completly stripped
and expanded into code that works with single precision floats instead.
- Uses of cogl_fixed_* have been replaced with single precision math.h
alternatives.
- Uses of COGL_ANGLE_* and cogl_angle_* have been replaced so we use a float for
angles and math.h replacements.
It looks like the changes to cogl-gles2-wrapper.h were accidentally
committed to the actual file instead of the patch in commit
de27da0e. This commit moves the changes back into the patch so
cogl-gles2-wrapper.h is reverted back to master.
The patches have been updated to apply cleanly.
The patches for the g_warnings in clutter-actor.c have been removed
because master now uses CLUTTER_UNITS_FORMAT so they aren't
necessary. The clutter-units.h patch now sets CLUTTER_UNITS_FORMAT to
'f'.
The changes from the GL version of cogl-texture.c have been mirrored
in the GLES version. This adds the cogl_texture_new_from_bitmap
function and fixes the build errors.
The GLES 2 wrapper needs to set up some state before each
draw. Previously this was acheived by wrapping glDrawArrays. Since the
multiple-texture-rectangle branch merge, glDrawElements is used
instead so we also need a wrapper for that.
It was also directly calling glBindTexture. GLES 2 uses a wrapper for
this function so that it can cope with GL_ALPHA format textures. The
format of the current texture needs to be stored as well as the target
and object number for this to work.
test-cogl-material now runs on GLES 1 using the PVR GLES1 SDK (though since
only 2 texture units are supported the third rotating light map doesn't show)
Note: It currently doesn't build for GLES 2.0
Multitexturing allows blending multiple layers of texture data when texturing
some geometry. A common use is for pre-baked light maps which can give nice
lighting effects relativly cheaply. Another is for dot-3 bump mapping, and
another is applying alpha channel masks.
The dot-3 bump mapping would be really nice one day, but currently cogl doesn't
support lighting so that's not dealt with in this patch.
notable limitations:
- It can only texture rectangles a.t.m - and like cogl_texture_rectangle there
is no support for rotated texturing.
- Sliced textures are not supported. I think I've figured out how to handle
layers with different slice sizes at least for rectangular geometry, but I'm
not sure how complex it becomes once rotations are possible and texturing
arbitrary cogl_polygons.
- Except for this new API, cogl still doesn't know about more than one texture
unit, and so has no way of caching any enables related to other units. So that
things don't break it's currently necessary to disable anything to do with
additional units as soon as we are done with them which isn't ideal.
- No clutter API yet.
There's no point in clearing the index array because it is always the
same sequence of indices regardless of the vertices. Instead it is
just added to when there are more vertices than ever before.
* clutter/cogl/cogl-path.h:
* clutter/cogl/common/cogl-primitives.c:
* clutter/cogl/common/cogl-primitives.h:
* clutter/cogl/gl/cogl-primitives.c:
* clutter/cogl/gles/cogl-primitives.c: Changed the semantics of
cogl_path_move_to. Previously this always started a new path but
now it instead starts a new disjoint sub path. The path isn't
cleared until you call either cogl_path_stroke, cogl_path_fill or
cogl_path_new. There are also cogl_path_stroke_preserve and
cogl_path_fill_preserve functions.
* clutter/cogl/gl/cogl-context.c:
* clutter/cogl/gl/cogl-context.h:
* clutter/cogl/gles/cogl-context.c:
* clutter/cogl/gles/cogl-context.h: Convert the path nodes array
to a GArray.
* clutter/cogl/gl/cogl-texture.c:
* clutter/cogl/gles/cogl-texture.c: Call cogl_clip_ensure
* clutter/cogl/common/cogl-clip-stack.c:
* clutter/cogl/common/cogl-clip-stack.h: Simplified the clip
stack code quite a bit to make it more maintainable. Previously
whenever you added a new clip it would go through a separate route
to immediately intersect with the current clip and when you
removed it again it would immediately rebuild the entire clip. Now
when you add or remove a clip it doesn't do anything immediately
but just sets a dirty flag instead.
* clutter/cogl/gl/cogl.c:
* clutter/cogl/gles/cogl.c: Taken away the code to intersect
stencil clips when there is exactly one stencil bit. It won't work
with path clips and I don't know of any platform that doesn't have
eight or zero stencil bits. It needs at least three bits to
intersect a path with an existing clip. cogl_features_init now
just decides you don't have a stencil buffer at all if you have
less than three bits.
* clutter/cogl/cogl.h.in: New functions and documentation.
* tests/interactive/test-clip.c: Replaced with a different test
that lets you add and remove clips. The three different mouse
buttons add clips in different shapes. This makes it easier to
test multiple levels of clipping.
* tests/interactive/test-cogl-primitives.c: Use
cogl_path_stroke_preserve when using the same path again.
* doc/reference/cogl/cogl-sections.txt: Document the new
functions.
differences and improve maintainability.
* clutter/cogl/gl/cogl-context.h:
Adds a CoglTextureGLVertex typedef + texture_vertices and
texture_vertices_size members to CoglContext for using vertex arrays
like GLES does
* clutter/cogl/gl/cogl-context.c:
Initializes texture_vertices + texture_vertices_size members
* clutter/cogl/gl/cogl-internal.h:
Adds COGL_ENABLE_COLOR_ARRAY
* clutter/cogl/gl/cogl.c:
Add COGL_ENABLE_COLOR_ARRAY support to cogl_enable
* clutter/cogl/gles/cogl-context.h:
Change the CoglTextureGLVertex to use GLfloat for the position
and texture coord attributes and GLubyte for the color.
* clutter/cogl/gles/cogl-texture-private.h:
Adds a wrap_mode member like GL has.
* clutter/cogl/gl/cogl-texture.c
* clutter/cogl/gles/cogl-texture.c:
Improves the comparability of the files, such that the remaining
differences, better reflect the fundamental differences needed
between GL and GLES. Notably GL no longer uses glBegin/glEnd for
submitting vertices, it uses vertex arrays like GLES and this gives
a small but measurable fps improvement for test-text.
* clutter/cogl/cogl-shader.h: Add a function for setting an
integer uniform, similar to cogl_program_uniform_1f().
* clutter/cogl/gl/cogl-program.c: Implement the GL version
of cogl_program_uniform_1i().
* clutter/cogl/gles/cogl-program.c: Implement the GLES version
of cogl_program_uniform_1i().
Bug 1049 - Clutter doesn't support most GLSL uniforms (patch
by Chris Lord and Neil Roberts)
* README: Update release notes.
* clutter/Makefile.am:
* clutter/clutter-shader-types.[ch]: Add GValue types for
shader values.
* clutter/clutter-actor.[ch]: Update the shader API to use
the newly added GValue support for GLSL shader uniform
setters.
* clutter/clutter-shader.[ch]: Add float and integer convenience
API for single value GLSL uniform setters.
* clutter/cogl/cogl-shader.h: Add new uniform setters.
* clutter/cogl/gl/cogl-context.c:
* clutter/cogl/gl/cogl-context.h:
* clutter/cogl/gl/cogl-defines.h.in:
* clutter/cogl/gl/cogl-program.c:
* clutter/cogl/gl/cogl.c: Update the GL implementation of COGL
to handle the GLSL uniform setters.
* clutter/cogl/gles/cogl-gles2-wrapper.c:
* clutter/cogl/gles/cogl-gles2-wrapper.h:
* clutter/cogl/gles/cogl-internal.h:
* clutter/cogl/gles/cogl-program.c: Update the GLES 2.0 implementation
of COGL to handle the GLSL uniform setters.
* doc/reference/clutter/clutter-sections.txt:
* doc/reference/cogl/cogl-sections.txt: Update the documentation.
* tests/interactive/test-fbo.c:
* tests/interactive/test-shader.c: Update the shader tests.
* clutter/cogl/gles/cogl-gles2-wrapper.c:
Initialise the 'tex' sampler uniform to 0. The GLSL spec
specifically says that you must initialize sampler uniforms. This
fixes texturing for GLES 2 when using the PowerVR simulator via
software Mesa.
* clutter/cogl/common/cogl-mesh.c:
Make sure we use the appropriate cogl_wrap_gl* funcs as appropriate
* clutter/cogl/gles/cogl-gles2-wrapper.c
* clutter/cogl/gles/cogl-gles2-wrapper.h:
In our glColorPointer wrapper we needed to mark our color attribute
as normalized.
* tests/conform/Makefile.am:
When creating unit test symlinks we use the -l gtester option to
list tests, but when using the PVR SDK the test binary also spews
out some extra info that caused lots of random symlinks to be
created. We now grep for lines starting with a '/'
* tests/conform/test-mesh-contiguous.c
* tests/conform/test-mesh-mutability.c:
Use cogl_set_source_color instead of directly calling glColor4ub
* clutter/cogl/cogl-color.h:
* clutter/cogl/cogl-path.h:
* clutter/cogl/cogl-types.h:
* clutter/cogl/common/cogl-color.c: Deprecated cogl_color()
in favour of cogl_set_source_color() and friends; store the
CoglColor components as unsigned bytes instead of fixed point
normalized values; add functions for allocating, copying and
freeing CoglColor, for use of language bindings.
* clutter/cogl/cogl.h.in:
* clutter/cogl/cogl-deprecated.h: Added cogl-deprecated.h,
an header file containing the deprecation symbols similar
to clutter-deprecated.h.
* clutter/cogl/gl/Makefile.am:
* clutter/cogl/gl/cogl-texture.c:
* clutter/cogl/gl/cogl.c:
* clutter/cogl/gles/Makefile.am:
* clutter/cogl/gles/cogl-texture.c:
* clutter/cogl/gles/cogl.c: Update the GL and GLES implementations
of COGL after the CoglColor changes.
* clutter/clutter-actor.c:
* clutter/clutter-clone-texture.c:
* clutter/clutter-entry.c:
* clutter/clutter-label.c:
* clutter/clutter-rectangle.c:
* clutter/clutter-texture.c: Do not use CoglColor whenever it
is possible, and use cogl_set_source_color4ub() instead.
* clutter/pango/cogl-pango-render.c: Ditto as above.
* doc/reference/clutter/subclassing-ClutterActor.xml:
* doc/reference/cogl/cogl-sections.txt: Update the documentation.
* tests/interactive/test-cogl-offscreen.c:
* tests/interactive/test-cogl-primitives.c:
* tests/interactive/test-cogl-tex-convert.c:
* tests/interactive/test-cogl-tex-foreign.c:
* tests/interactive/test-cogl-tex-getset.c:
* tests/interactive/test-cogl-tex-polygon.c:
* tests/interactive/test-cogl-tex-tile.c:
* tests/interactive/test-paint-wrapper.c: Drop the usage of
CoglColor whenever it is possible.
coordinates
* clutter/cogl/gl/cogl-texture.c: Instead of sorting the vertex
and texture coordinates passed to cogl_texture_rectangle, just
swap both sets whenever the texture coordinates are backward.
* clutter/cogl/gl/Makefile.am (libclutterinclude_HEADERS):
* clutter/cogl/common/Makefile.am
(libclutter_cogl_common_la_SOURCES): Move cogl-mesh.h into the
headers for libclutter so that it will get installed.
* clutter/cogl/cogl-mesh.h
* clutter/cogl/cogl-types.h
* clutter/cogl/cogl.h.in
* clutter/cogl/common/Makefile.am
* clutter/cogl/common/cogl-mesh-private.h
* clutter/cogl/common/cogl-mesh.c
* clutter/cogl/gl/cogl-context.c
* clutter/cogl/gl/cogl-context.h
* clutter/cogl/gl/cogl-defines.h.in
* clutter/cogl/gl/cogl.c
* clutter/cogl/gles/cogl-context.c
* clutter/cogl/gles/cogl-context.h
* doc/reference/cogl/cogl-docs.sgml
* doc/reference/cogl/cogl-sections.txt:
The Mesh API provides a means for submitting an extensible number of
per vertex attributes to OpenGL in a way that doesn't require format
conversions and so that the data can be mapped into the GPU (in vertex
buffer objects) for - hopefully - fast re-use.
There are a number of things we can potentially use this API for, but
right now this just provides a foundation to build on. Please read
the extensive list of TODO items in cogl-mesh.c for examples.
Please refer to the cogl-mesh section in the reference manual for
documentation of the API.
* tests/conform/Makefile.am
* tests/conform/test-conform-main.c
* tests/conform/test-mesh-contiguous.c
* tests/conform/test-mesh-interleved.c
* tests/conform/test-mesh-mutability.c:
Privides basic coverage testing for the mesh API.
* clutter/cogl/common/cogl-fixed.c (cogl_fixed_sin)
(cogl_angle_sin, cogl_angle_tan, cogl_fixed_sqrt): Replaced uses
of 1 + ~x with just -x which is equivalent and easier to
understand.
Bug 1231 - Build fails in gles flavour in revision 3442
* clutter/cogl/gles/cogl-context.h: Fix remaining use of
ClutterFixed over CoglFixed. (Michael Boccara)
Bug 1219 - Clean up cogl.h
* clutter/cogl/cogl.h.in:
* clutter/cogl/cogl-offscreen.h:
* clutter/cogl/cogl-path.h:
* clutter/cogl/cogl-shader.h:
* clutter/cogl/cogl-texture.h:
* clutter/cogl/cogl-types.h: Split up the massive cogl.h file
into sub-header for each section of the API.
* clutter/cogl/gl/*:
* clutter/cogl/gles/*: Update the GL and GLES implementations
of COGL to cope with the new header structure.
* doc/reference/cogl/Makefile.am: Fix symbol retrieval.
Bug 1211 - Drop ClutterFeatureFlags usage from COGL
* clutter/cogl/cogl.h.in:
* clutter/cogl/gl/cogl.c:
* clutter/cogl/gles/cogl.c: Do not use ClutterFeatureFlags
when CoglFeatureFlags will do. This removes the last usage
of Clutter API inside COGL.
Bug 1210 - Add CoglColor API
* clutter/cogl/cogl-color.h:
* clutter/cogl/cogl.h.in:
* clutter/cogl/common/Makefile.am:
* clutter/cogl/common/cogl-color.c:
* clutter/cogl/gl/Makefile.am:
* clutter/cogl/gl/cogl.c:
* clutter/cogl/gles/Makefile.am:
* clutter/cogl/gles/cogl-texture.c:
* clutter/cogl/gles/cogl.c: Add a new color-type, to be used by
COGL. CoglColor is optimized to allow the minimum amount of
conversions possible for both GL and GLES implementations.
* clutter/clutter-actor.c:
* clutter/clutter-clone-texture.c:
* clutter/clutter-entry.c:
* clutter/clutter-main.c:
* clutter/clutter-rectangle.c:
* clutter/clutter-stage.c:
* clutter/clutter-texture.c: Use CoglColor when needed.
* clutter/pango/pangoclutter-render.c: Use CoglColor when needed.
* doc/reference/cogl/cogl-docs.sgml:
* doc/reference/cogl/cogl-sections.txt: Update the documentation.
* tests/test-cogl-offscreen.c:
* tests/test-cogl-primitives.c:
* tests/test-cogl-tex-convert.c:
* tests/test-cogl-tex-foreign.c:
* tests/test-cogl-tex-getset.c:
* tests/test-cogl-tex-polygon.c:
* tests/test-cogl-tex-tile.c:
* tests/test-paint-wrapper.c: Update the tests.
* README: Update release notes.
Bug 1209 - Move fixed point API in COGL
* clutter/cogl/cogl-fixed.h:
* clutter/cogl/cogl.h.in:
* clutter/cogl/common/Makefile.am:
* clutter/cogl/common/cogl-fixed.c: Add fixed point API, modelled
after the ClutterFixed. The CoglFixed API supercedes the ClutterFixed
one and avoids the dependency of COGL on Clutter's own API.
* clutter/cogl/common/cogl-clip-stack.c:
* clutter/cogl/common/cogl-primitives.c:
* clutter/cogl/common/cogl-primitives.h: Update internal usage of
ClutterFixed to CoglFixed.
* clutter/cogl/gl/Makefile.am:
* clutter/cogl/gl/cogl-primitives.c:
* clutter/cogl/gl/cogl-texture.c:
* clutter/cogl/gl/cogl.c: Ditto, in the GL implementation of the
COGL API.
* clutter/cogl/gles/Makefile.am:
* clutter/cogl/gles/cogl-fbo.c:
* clutter/cogl/gles/cogl-gles2-wrapper.c:
* clutter/cogl/gles/cogl-primitives.c:
* clutter/cogl/gles/cogl-texture.c:
* clutter/cogl/gles/cogl.c: Ditto, in the GLES implementation of
the COGL API.
* clutter/pango/pangoclutter-glyph-cache.c:
* clutter/pango/pangoclutter-glyph-cache.h: Ditto, in the Pango
renderer glyphs cache.
* clutter/clutter-fixed.c:
* clutter/clutter-fixed.h: ClutterFixed and related API becomes
a simple transition API for bindings and public Clutter API.
* clutter/clutter-actor.c:
* clutter/clutter-alpha.c:
* clutter/clutter-backend.c:
* clutter/clutter-behaviour-depth.c:
* clutter/clutter-behaviour-ellipse.c:
* clutter/clutter-behaviour-path.c:
* clutter/clutter-behaviour-rotate.c:
* clutter/clutter-behaviour-scale.c:
* clutter/clutter-clone-texture.c:
* clutter/clutter-color.c:
* clutter/clutter-entry.c:
* clutter/clutter-stage.c:
* clutter/clutter-texture.c:
* clutter/clutter-timeline.c:
* clutter/clutter-units.h: Move from the internal usage of
ClutterFixed to CoglFixed.
* doc/reference/clutter/clutter-sections.txt:
* doc/reference/cogl/cogl-docs.sgml:
* doc/reference/cogl/cogl-sections.txt: Update the documentation.
* tests/test-cogl-tex-tile.c:
* tests/test-project.c: Fix tests after the API change
* README: Add release notes.
* clutter/cogl/gles/cogl-fbo.c: Copy the code from gl/cogl-fbo but
use the API calls directly instead of loading an extension because
it is part of the core in GLES 2.
* clutter/cogl/gles/cogl.c (_cogl_features_init): Report
COGL_FEATURE_OFFSCREEN.
* clutter/cogl/gles/cogl-fbo.h (CoglFbo): Add gl_stencil_handle.
* clutter/cogl/gles/cogl-context.h (CoglContext): Add
viewport_store
* tests/test-fbo.c (make_shader): Conditionally use the GLES 2
names of the shader variables
* clutter/cogl/gl/cogl-texture.c (cogl_texture_polygon)
(_cogl_texture_quad_sw, _cogl_texture_quad_hw):
* clutter/cogl/gles/cogl-texture.c (cogl_texture_polygon)
(_cogl_texture_quad_sw, _cogl_texture_quad_hw): Enable backface
culling in GL if it is requested.
* clutter/cogl/gles/cogl-texture.c (_cogl_texture_quad_sw)
(_cogl_texture_quad_hw):
* clutter/cogl/gl/cogl-texture.c (_cogl_texture_quad_sw)
(_cogl_texture_quad_hw): Reorder the
vertices so that they are counter-clockwise.
* clutter/cogl/gles/cogl-context.h (CoglContext):
* clutter/cogl/gl/cogl-context.h (CoglContext): Added a flag to
store whether backface culling is currently enabled.
* clutter/cogl/gles/cogl.c (cogl_enable_backface_culling):
* clutter/cogl/gl/cogl.c (cogl_enable_backface_culling): New
function
* doc/reference/cogl/cogl-sections.txt: Add
cogl_enable_backface_culling
* clutter/cogl/gl/cogl-texture.c (_cogl_texture_upload_subregion_to_gl)
(_cogl_texture_upload_to_gl):
* clutter/cogl/gles/cogl-texture.c (_cogl_texture_upload_to_gl)
(_cogl_texture_upload_subregion_to_gl):
When uploading data to a sliced texture, fill the waste pixels
with copies of the edge of the real texture data. Otherwise the
value of the waste pixels are undefined so it will show artifacts
when the texture is scaled with GL_LINEAR and the pixels are
blended in.
* clutter/cogl/gl/cogl-texture.c (cogl_texture_set_region):
* clutter/cogl/gles/cogl-texture.c (cogl_texture_set_region):
Don't attempt to upload any data if the width or height of the
subregion is zero. Thanks to Gwenole Beauchesne.
* clutter/cogl/gles/cogl.c (cogl_get_viewport): Use glGetIntegerv
instead of glGetFixedv to read the viewport because the latter
converts incorrectly on some hardware.
* clutter/cogl/gl/cogl.c:
* clutter/cogl/gles/cogl.c:
* clutter/cogl/cogl.h.in: Add cogl_clip_stack_save,
cogl_clip_stack_restore, cogl_viewport and cogl_frustum.
* clutter/cogl/gl/cogl-fbo.h:
* clutter/cogl/gl/cogl-fbo.c: Try to attach a stencil buffer when
creating an FBO.
* clutter/cogl/common/cogl-clip-stack.c: Add functions to save and
restore the whole state of the stack.
* clutter/clutter-texture.c (clutter_texture_paint): When
rendering the FBO source, setup a temporary asymmetric perspective
projection matrix to render it as it would appear on screen.
* clutter/clutter-private.h:
* clutter/clutter-actor.c
(_clutter_actor_apply_modelview_transform_recursive): No longer
static and exported in clutter-private.h
* clutter/cogl/gles/cogl-gles2-wrapper.c: All of the settings and
uniforms are now proxied into COGL variables instead of setting
the GL uniforms directly. Just before glDrawArrays is executed a
shader is generated using the given settings to avoid using 'if'
statements. The shaders are cached.
* clutter/cogl/gles/cogl-fixed-vertex-shader.glsl:
* clutter/cogl/gles/cogl-fixed-fragment-shader.glsl: The shaders
are now split into parts using comments instead of 'if' statements
so that the simplest shader can be generated on the fly.
* clutter/cogl/gles/stringify.sh: Now splits up the shader sources
into separate C strings where deliminated by special comments.
* clutter/cogl/gles/cogl-program.h:
* clutter/cogl/gles/cogl-program.c: A custom shader can no longer
be directly linked with the fixed-functionality replacement
because the replacement changes depending on the settings. Instead
the bound shader is linked with the appropriate replacement shader
just before glDrawArrays is executed. The custom uniform variables
must also be proxied through COGL variables because their location
can change when relinked.
