This patch moves the call to _cogl_destroy_texture_units() from
_cogl_context_free() to later on. When destroying a GL texture the
texture units are checked. This would end up accessing invalid memory
so we need to try to destroy the texture units only after everything
that might be referencing a texture has been destroyed.
Reviewed-by: Robert Bragg <robert@linux.intel.com>
Since we've had several developers from admirable projects say they
would like to use Cogl but would really prefer not to pull in
gobject,gmodule and glib as extra dependencies we are investigating if
we can get to the point where glib is only an optional dependency.
Actually we feel like we only make minimal use of glib anyway, so it may
well be quite straightforward to achieve this.
This adds a --disable-glib configure option that can be used to disable
features that depend on glib.
Actually --disable-glib doesn't strictly disable glib at this point
because it's more helpful if cogl continues to build as we make
incremental progress towards this.
The first use of glib that this patch tackles is the use of
g_return_val_if_fail and g_return_if_fail which have been replaced with
equivalent _COGL_RETURN_VAL_IF_FAIL and _COGL_RETURN_IF_FAIL macros.
Reviewed-by: Neil Roberts <neil@linux.intel.com>
This factors out the CoglOnscreen code from cogl-framebuffer.c so we now
have cogl-onscreen.c, cogl-onscreen.h and cogl-onscreen-private.h.
Notably some of the functions pulled out are currently namespaced as
cogl_framebuffer but we know we are planning on renaming them to be in
the cogl_onscreen namespace; such as cogl_framebuffer_swap_buffers().
Reviewed-by: Neil Roberts <neil@linux.intel.com>
Currently features are represented as bits in a 32bit mask so we
obviously can't have more than 32 features with that approach. The new
approach is to use the COGL_FLAGS_ macros which lets us handle bitmasks
without a size limit and we change the public api to accept individual
feature enums instead of a mask. This way there is no limit on the
number of features we can add to Cogl.
Instead of using cogl_features_available() there is a new
cogl_has_feature() function and for checking multiple features there is
cogl_has_features() which takes a zero terminated vararg list of
features.
In addition to being able to check for individual features this also
adds a way to query all the features currently available via
cogl_foreach_feature() which will call a callback for each feature.
Since the new functions take an explicit context pointer there is also
no longer any ambiguity over when users can first start to query
features.
Reviewed-by: Neil Roberts <neil@linux.intel.com>
Cogl provides a consistent public interface regardless of whether the
underlying GL driver supports VBOs so it doesn't make much sense to have
this feature as part of the public api. We can't break the api by
removing the enum but at least we no longer ever set the feature flag.
We now have a replacement private feature flag COGL_PRIVATE_FEATURE_VBOS
which cogl now checks for internally.
Reviewed-by: Neil Roberts <neil@linux.intel.com>
Cogl provides a consistent public interface regardless of whether the
underlying GL driver supports PBOs so it doesn't make much sense to have
this feature as part of the public api. We can't break the api by
removing the enum but at least we no longer ever set the feature flag.
We now have a replacement private feature flag COGL_PRIVATE_FEATURE_PBOS
which cogl now checks for internally.
Reviewed-by: Neil Roberts <neil@linux.intel.com>
This optimizes the layer and pipeline _compare_differences functions so
neither of them use the GArray api since building up the list of
ancestors by appending to a shared GArray was showing quite high on
profiles due to how frequently pipeline comparisons are made. Instead
we now build up a transient, singly linked list by allocating GList
nodes via alloca to build up the parallel lists of ancestors.
This tweaked approach actually ends up being a bit more concise than
before, we avoid the overhead of the GArray api and now avoid making any
function calls while comparing (assuming the _get_parent() calls always
inline), we avoiding needing to get the default cogl context.
Reviewed-by: Neil Roberts <neil@linux.intel.com>
As part of the on going, incremental effort to purge the non type safe
CoglHandle type from the Cogl API this patch tackles most of the
CoglHandle uses relating to textures.
We'd postponed making this change for quite a while because we wanted to
have a clearer understanding of how we wanted to evolve the texture APIs
towards Cogl 2.0 before exposing type safety here which would be
difficult to change later since it would imply breaking APIs.
The basic idea that we are steering towards now is that CoglTexture
can be considered to be the most primitive interface we have for any
object representing a texture. The texture interface would provide
roughly these methods:
cogl_texture_get_width
cogl_texture_get_height
cogl_texture_can_repeat
cogl_texture_can_mipmap
cogl_texture_generate_mipmap;
cogl_texture_get_format
cogl_texture_set_region
cogl_texture_get_region
Besides the texture interface we will then start to expose types
corresponding to specific texture types: CoglTexture2D,
CoglTexture3D, CoglTexture2DSliced, CoglSubTexture, CoglAtlasTexture and
CoglTexturePixmapX11.
We will then also expose an interface for the high-level texture types
we have (such as CoglTexture2DSlice, CoglSubTexture and
CoglAtlasTexture) called CoglMetaTexture. CoglMetaTexture is an
additional interface that lets you iterate a virtual region of a meta
texture and get mappings of primitive textures to sub-regions of that
virtual region. Internally we already have this kind of abstraction for
dealing with sliced texture, sub-textures and atlas textures in a
consistent way, so this will just make that abstraction public. The aim
here is to clarify that there is a difference between primitive textures
(CoglTexture2D/3D) and some of the other high-level textures, and also
enable developers to implement primitives that can support meta textures
since they can only be used with the cogl_rectangle API currently.
The thing that's not so clean-cut with this are the texture constructors
we have currently; such as cogl_texture_new_from_file which no longer
make sense when CoglTexture is considered to be an interface. These
will basically just become convenient factory functions and it's just a
bit unusual that they are within the cogl_texture namespace. It's worth
noting here that all the texture type APIs will also have their own type
specific constructors so these functions will only be used for the
convenience of being able to create a texture without really wanting to
know the details of what type of texture you need. Longer term for 2.0
we may come up with replacement names for these factory functions or the
other thing we are considering is designing some asynchronous factory
functions instead since it's so often detrimental to application
performance to be blocked waiting for a texture to be uploaded to the
GPU.
Reviewed-by: Neil Roberts <neil@linux.intel.com>
This adds an internal function to set the backface culling state on a
pipeline. This includes properties to set the culling mode (front,
back or both) and also to set which face is considered the front
(COGL_WINDING_CLOCKWISE or COGL_WINDING_COUNTER_CLOCKWISE). The actual
front face flushed to GL depends on whether we are rendering to an
offscreen buffer or not. This means that when changing between on- and
off- screen framebuffers it now checks whether the last flushed
pipeline has backface culling enabled and forces a reflush of the cull
face state if so.
The backface culling is now set on a pipeline as part of the legacy
state. This is important because some code in Cogl assumes it can
flush a temporary pipeline to revert to a known state, but previously
this wouldn't disable backface culling so things such as flushing the
clip stack could get confused.
Reviewed-by: Robert Bragg <robert@linux.intel.com>
When changing between two framebuffers that have different color masks
it now forces the pipeline to flush the mask by setting
current_pipeline_changes_since_flush. For this to work there needs to
be a common bit of code that gets called when the framebuffers are
changed that has access to both the old framebuffer and the new
framebuffer. _cogl_set_framebuffers_real can't be used for this
because when it is called from cogl_pop_framebuffer the stack entries
have already changed so it can't know the old framebuffer. This patch
adds a new function called notify_buffers_changed which should get
called whenever the buffers are changed and it explicitly gets passed
pointers to the old and new buffers. cogl_pop_framebuffer now calls
this instead of trying to use _cogl_set_framebuffers_real to force a
flush.
This patch also fixes the ctx->window_buffer pointer. Previously this
was implemented by searching in the framebuffer stack for an onscreen
framebuffer whenever the current buffers are changed. However it does
this after the stack has already changed so it won't usually find the
right buffer.
Reviewed-by: Robert Bragg <robert@linux.intel.com>
This function was not used in the opengl pipeline, probably because of
the more precise get_max_activable_texture_units().
Remove it then.
https://bugzilla.gnome.org/show_bug.cgi?id=657347
Reviewed-by: Robert Bragg <robert@linux.intel.com>
This adds CoglPipeline and CoglFramebuffer support for setting a color
mask which is a bit mask defining which color channels should be written
to the current framebuffer.
The final color mask is the intersection of the framebuffer color mask
and the pipeline color mask. The framebuffer mask affects all rendering
to the framebuffer while the pipeline masks can be used to affect
individual primitives.
Reviewed-by: Neil Roberts <neil@linux.intel.com>
The _cogl_context_check_gl_version function is meant to be called once
Cogl has a GL context so that it can check whether the context found
is supported by Cogl. However, only the stub winsys was calling this
and it was doing it before Cogl had a chance to retrieve the function
pointer for glString so it would just crash. This patch combines the
two functions into one so that _cogl_context_update_features returns a
gboolean and a GError. Then it can just check the context itself.
https://bugzilla.gnome.org/show_bug.cgi?id=654440
Reviewed-by: Robert Bragg <robert@linux.intel.com>
This adds a getter and setter for requesting dithering to be enabled.
Dithering is a hardware dependent technique to increase the visible
color resolution beyond what the underlying hardware supports by playing
tricks with the colors placed into the framebuffer to give the illusion
of other colors. (For example this can be compared to half-toning used
by some news papers to show varying levels of grey even though their may
only be black and white are available).
The results of enabling dithering are platform dependent and may have no
effect.
Signed-off-by: Neil Roberts <neil@linux.intel.com>
The pipeline cache is now handled in CoglPipelineCache instead of
directly in the ARBfp fragend. The flags needed to hash a pipeline
should be exactly the same for the ARBfp and GLSL fragends so it's
convenient to share the code. The hash table now stores the actual
pipeline as the value instead of the private data so that the two
fragends can attach their data to it. That way it's possible to use
the same pipeline key with ancestors that are using different
fragends.
The hash table is created with g_hash_table_new_full to set a
destructor for the key and value and there is a destructor for
CoglPipelineCache that gets called when the CoglContext is
destroyed. That way we no longer leak the pipelines and shader state
when the context is desroyed.
This renames cogl_context_egl_get_egl_context to
cogl_egl_context_get_egl_context to be consistent with other platform
specific APIs.
Signed-off-by: Neil Roberts <neil@linux.intel.com>
For cogl 2.0 we don't want to have a default context. In the meantime
we can simply assume that calling cogl_context_new() implicitly
sets that context as the default context before returning.
Signed-off-by: Neil Roberts <neil@linux.intel.com>
The GL or GLES library is now dynamically loaded by the CoglRenderer
so that it can choose between GL, GLES1 and GLES2 at runtime. The
library is loaded by the renderer because it needs to be done before
calling eglInitialize. There is a new environment variable called
COGL_DRIVER to choose between gl, gles1 or gles2.
The #ifdefs for HAVE_COGL_GL, HAVE_COGL_GLES and HAVE_COGL_GLES2 have
been changed so that they don't assume the ifdefs are mutually
exclusive. They haven't been removed entirely so that it's possible to
compile the GLES backends without the the enums from the GL headers.
When using GLX the winsys additionally dynamically loads libGL because
that also contains the GLX API. It can't be linked in directly because
that would probably conflict with the GLES API if the EGL is
selected. When compiling with EGL support the library links directly
to libEGL because it doesn't contain any GL API so it shouldn't have
any conflicts.
When building for WGL or OSX Cogl still directly links against the GL
API so there is a #define in config.h so that Cogl won't try to dlopen
the library.
Cogl-pango previously had a #ifdef to detect when the GL backend is
used so that it can sneakily pass GL_QUADS to
cogl_vertex_buffer_draw. This is now changed so that it queries the
CoglContext for the backend. However to get this to work Cogl now
needs to export the _cogl_context_get_default symbol and cogl-pango
needs some extra -I flags to so that it can include
cogl-context-private.h
The texture driver functions are now accessed through a vtable pointed
to by a struct in the CoglContext so that eventually it will be
possible to compile both the GL and GLES texture drivers into a single
binary and then select between them at runtime.
cogl-ext-functions.h now contains definitions for all of the core GL
and GLES functions that we would normally link to directly. All of the
code has changed to access them through the cogl context pointer. The
GE macro now takes an extra parameter to specify the context because
the macro itself needs to make GL calls but various points in the Cogl
source use different names for the context variable.
Instead of storing all of the feature function pointers in the driver
specific data of the CoglContext they are now all stored directly in
CoglContext. There is a single header containing the description of
the functions which gets included by cogl-context.h. There is a single
function in cogl-feature-private.c to check for all of these
functions.
The name of the function pointer variables have been changed from
ctx->drv.pf_glWhatever to just ctx->glWhatever.
The feature flags that get set when an extension is available are now
separated from the table of extensions. This is necessary because
different extensions can mean different things on GLES and GL. For
example, having access to glMapBuffer implies read and write support
on GL but only write support on GLES. The flags are instead set in the
driver specific init function by checking whether the function
pointers were successfully resolved.
_cogl_feature_check has been changed to assume the feature is
supported if any of the listed extensions are available instead of
requiring all of them. This makes it more convenient to specify
alternate names for the extension. Nothing else had previously listed
more than one name for an extension so this shouldn't cause any
problems.
This adds a _cogl_init function for Cogl that we expect to be the first
thing called before anything else is done with Cogl. It's not a public
API so it's expected that all entry points for Cogl that might be the
first function used should call _cogl_init().
We currently call _cogl_init() in these functions:
cogl_renderer_new
cogl_display_new
cogl_context_new
cogl_android_set_native_window
_cogl_init() can be called multiple times, and only the first call has
any affect.
For example _cogl_init() gives us a place check and parse the COGL_DEBUG
environment variable.
Since we don't have any need to parse command line arguments (we can
always get user configuration options from the environment) our init
function doesn't require argc/argv pointers.
By saying up front that we aren't interested in command line arguments
that means we can avoid the mess that is GOption based library
initialization which is extremely fragile due to its lack of dependency
tracking between modules.
Signed-off-by: Neil Roberts <neil@linux.intel.com>
This adds a --enable-profile option which enables uprof based profiling.
It was also necessary to fixup a CLUTTER_ENABLE_PROFILING #ifdef in
cogl-context.c to renamed COGL_ENABLE_PROFILING instead. By default Cogl
doesn't output uprof reports directly, instead it assumes a higher level
toolkit will output a report. If you want a report from Cogl you can
export COGL_PROFILE_OUTPUT_REPORT=1 before running your app.
The latest version of uprof can be fetched from:
git://github.com/rib/UProf.git
This adds an internal texture_2d constructor that can wrap an EGLImage
as a CoglTexture2D. The plan is to utilize this for texture-from-pixmap
support with EGL as well as creating textures from wayland buffers.
Instead of the stub winsys being a special case set of #ifdef'd code
used when COGL_HAS_FULL_WINSYS wasn't defined, the stub winsys now
implements a CoglWinsysVtable like all other winsys backends (it's just
that everything is a NOP). This way we can get rid of the
COGL_HAS_FULL_WINSYS define and also the stub winsys can be runtime
selected whereas before it was incompatible with all other winsys
backends.
Some of the virtual functions in CoglWinsysVtable only need to be
implemented for specific backends or when a specific feature is
advertised. This splits the vtable struct into two commented sections
marking which are optional and which are required. Wherever an
optional function is used there is now a g_return_if_fail to ensure
there is an implementation.
This adds cogl_atlas_texture_* functions to register a callback that
will get invoked whenever any of the CoglAtlas's the textures use get
reorganized. The callback is global and is not tied to any particular
atlas texture.
So that we can dynamically select what winsys backend to use at runtime
we need to have some indirection to how code accesses the winsys instead
of simply calling _cogl_winsys* functions that would collide if we
wanted to compile more than one backend into Cogl.
As was recently done for the GLX window system code, this commit moves
the EGL window system code down from the Clutter backend code into a
Cogl winsys.
Note: currently the cogl/configure.ac is hard coded to only build the GLX
winsys so currently this is only available when building Cogl as part
of Clutter.
Previously the mask of available winsys features was stored in a
CoglBitmask. That isn't the ideal type to use for this because it is
intended for a growable array of bits so it can allocate extra memory
if there are more than 31 flags set. For the winsys feature flags the
highest used bit is known at compile time so it makes sense to
allocate a fixed array instead. This is conceptually similar to the
CoglDebugFlags which are stored in an array of integers with macros to
test a bit in the array. This moves the macros used for CoglDebugFlags
to cogl-flags.h and makes them more generic so they can be shared with
CoglContext.
This migrates all the GLX window system code down from the Clutter
backend code into a Cogl winsys. Moving OpenGL window system binding
code down from Clutter into Cogl is the biggest blocker to having Cogl
become a standalone 3D graphics library, so this is an important step in
that direction.
As part of the process of splitting Cogl out as a standalone graphics
API we need to introduce some API concepts that will allow us to
initialize a new CoglContext when Clutter isn't there to handle that for
us...
The new objects roughly in the order that they are (optionally) involved
in constructing a context are: CoglRenderer, CoglOnscreenTemplate,
CoglSwapChain and CoglDisplay.
Conceptually a CoglRenderer represents a means for rendering. Cogl
supports rendering via OpenGL or OpenGL ES 1/2.0 and those APIs are
accessed through a number of different windowing APIs such as GLX, EGL,
SDL or WGL and more. Potentially in the future Cogl could render using
D3D or even by using libdrm and directly banging the hardware. All these
choices are wrapped up in the configuration of a CoglRenderer.
Conceptually a CoglDisplay represents a display pipeline for a renderer.
Although Cogl doesn't aim to provide a detailed abstraction of display
hardware, on some platforms we can give control over multiple display
planes (On TV platforms for instance video content may be on one plane
and 3D would be on another so a CoglDisplay lets you select the plane
up-front.)
Another aspect of CoglDisplay is that it lets us negotiate a display
pipeline that best supports the type of CoglOnscreen framebuffers we are
planning to create. For instance if you want transparent CoglOnscreen
framebuffers then we have to be sure the display pipeline wont discard
the alpha component of your framebuffers. Or if you want to use
double/tripple buffering that requires support from the display
pipeline.
CoglOnscreenTemplate and CoglSwapChain are how we describe our default
CoglOnscreen framebuffer configuration which can affect the
configuration of the display pipeline.
The default/simple way we expect most CoglContexts to be constructed
will be via something like:
if (!cogl_context_new (NULL, &error))
g_error ("Failed to construct a CoglContext: %s", error->message);
Where that NULL is for an optional "display" parameter and NULL says to
Cogl "please just try to do something sensible".
If you want some more control though you can manually construct a
CoglDisplay something like:
display = cogl_display_new (NULL, NULL);
cogl_gdl_display_set_plane (display, plane);
if (!cogl_display_setup (display, &error))
g_error ("Failed to setup a CoglDisplay: %s", error->message);
And in a similar fashion to cogl_context_new() you can optionally pass
a NULL "renderer" and/or a NULL "onscreen template" so Cogl will try to
just do something sensible.
If you need to change the CoglOnscreen defaults you can provide a
template something like:
chain = cogl_swap_chain_new ();
cogl_swap_chain_set_has_alpha (chain, TRUE);
cogl_swap_chain_set_length (chain, 3);
onscreen_template = cogl_onscreen_template_new (chain);
cogl_onscreen_template_set_pixel_format (onscreen_template,
COGL_PIXEL_FORMAT_RGB565);
display = cogl_display_new (NULL, onscreen_template);
if (!cogl_display_setup (display, &error))
g_error ("Failed to setup a CoglDisplay: %s", error->message);
This moves the functionality of _cogl_create_context_driver from
driver/{gl,gles}/cogl-context-driver-{gl,gles}.c into
driver/{gl,gles}/cogl-{gl,gles}.c as a static function called
initialize_context_driver.
cogl-context-driver-{gl,gles}.[ch] have now been removed.
This adds a new experimental function (you need to define
COGL_ENABLE_EXPERIMENTAL_API to access it) which takes us towards being
able to have a standalone Cogl API. This is really a minor aesthetic
change for now since all the GL context creation code still lives in
Clutter but it's a step forward none the less.
Since our current designs introduce a CoglDisplay object as something
that would be passed to the context constructor this provides a stub
cogl-display.h with CoglDisplay typedef.
_cogl_context_get_default() which Clutter uses to access the Cogl
context has been modified to use cogl_context_new() to initialize
the default context.
There is one rather nasty hack used in this patch which is that the
implementation of cogl_context_new() has to forcibly make the allocated
context become the default context because currently all the code in
Cogl assumes it can access the context using _COGL_GET_CONTEXT including
code used to initialize the context.
Instead of directly banging GL to migrate textures the atlas now uses
the CoglFramebuffer API. It will use one of four approaches; it can
set up two FBOs and use _cogl_blit_framebuffer to copy between them;
it can use a single target fbo and then render the source texture to
the FBO using a Cogl draw call; it can use a single FBO and call
glCopyTexSubImage2D; or it can fallback to reading all of the texture
data back to system memory and uploading it again with a sub texture
update.
Previously GL calls were used directly because Cogl wasn't able to
create a framebuffer without a stencil and depth buffer. However there
is now an internal version of cogl_offscreen_new_to_texture which
takes a set of flags to disable the two buffers.
The code for blitting has now been moved into a separate file called
cogl-blit.c because it has become quite long and it may be useful
outside of the atlas at some point.
The 4 different methods have a fixed order of preference which is:
* Texture render between two FBOs
* glBlitFramebuffer
* glCopyTexSubImage2D
* glGetTexImage + glTexSubImage2D
Once a method is succesfully used it is tried first for all subsequent
blits. The default default can be overridden by setting the
environment variable COGL_ATLAS_DEFAULT_BLIT_MODE to one of the
following values:
* texture-render
* framebuffer
* copy-tex-sub-image
* get-tex-data
The CoglDebugFlags are now stored in an array of unsigned ints rather
than a single variable. The flags are accessed using macros instead of
directly peeking at the cogl_debug_flags variable. The index values
are stored in the enum rather than the actual mask values so that the
enum doesn't need to be more than 32 bits wide. The hope is that the
code to determine the index into the array can be optimized out by the
compiler so it should have exactly the same performance as the old
code.
This is part of a broader cleanup of some of the experimental Cogl API.
One of the reasons for this particular rename is to reduce the verbosity
of using the API. Another reason is that CoglVertexArray is going to be
renamed CoglAttributeBuffer and we want to help emphasize the
relationship between CoglAttributes and CoglAttributeBuffers.
Instead of having a single journal per context, we now have a
CoglJournal object for each CoglFramebuffer. This means we now don't
have to flush the journal when switching/pushing/popping between
different framebuffers so for example a Clutter scene that involves some
ClutterEffect actors that transiently redirect to an FBO can still be
batched.
This also allows us to track state in the journal that relates to the
current frame of its associated framebuffer which we'll need for our
optimization for using the CPU to handle reading a single pixel back
from a framebuffer when we know the whole scene is currently comprised
of simple rectangles in a journal.
In the journal code and when generating the stroke path the vertices
are generated on the fly and stored in a CoglBuffer using
cogl_buffer_map. However cogl_buffer_map is allowed to fail but it
wasn't checking for a NULL return value. In particular on GLES it will
always fail because glMapBuffer is only provided by an extension. This
adds a new pair of internal functions called
_cogl_buffer_{un,}map_for_fill_or_fallback which wrap
cogl_buffer_map. If the map fails then it will instead return a
pointer into a GByteArray attached to the context. When the buffer is
unmapped the array is copied into the buffer using
cogl_buffer_set_data.
On GLES2 there's no builtin mechanism to replace texture coordinates
with point sprite coordinates so calling glEnable(GL_POINT_SPRITE)
isn't valid. Instead the point sprite coords are implemented by using
a special builtin varying variable in GLSL.
Previously Cogl would only ever use one atlas for textures and if it
reached the maximum texture size then all other new textures would get
their own GL texture. This patch makes it so that we create as many
atlases as needed. This should avoid breaking up some batches and it
will be particularly good if we switch to always using multi-texturing
with a default shader that selects between multiple atlases using a
vertex attribute.
Whenever a new atlas is created it is stored in a GSList on the
context. A weak weference is taken on the atlas using
cogl_object_set_user_data so that it can be removed from the list when
the atlas is destroyed. The atlas textures themselves take a reference
to the atlas and this is the only thing that keeps the atlas
alive. This means that once the atlas becomes empty it will
automatically be destroyed.
All of the COGL_NOTEs pertaining to atlases are now prefixed with the
atlas pointer to make it clearer which atlas is changing.
The GLES2 wrapper is no longer needed because the shader generation is
done within the GLSL fragend and vertend and any functions that are
different for GLES2 are now guarded by #ifdefs.
Once the GLES2 wrapper is removed we won't be able to upload the
matrices with the fixed function API any more. The fixed function API
gives a global state for setting the matrix but if a custom shader
uniform is used for the matrices then the state is per
program. _cogl_matrix_stack_flush_to_gl is called in a few places and
it is assumed the current pipeline doesn't need to be flushed before
it is called. To allow these semantics to continue to work, on GLES2
the matrix flush now just stores a reference to the matrix stack in
the CoglContext. A pre_paint virtual is added to the progend which is
called whenever a pipeline is flushed, even if the same pipeline was
flushed already. This gives the GLSL progend a chance to upload the
matrices to the uniforms. The combined modelview/projection matrix is
only calculated if it is used. The generated programs end up never
using the modelview or projection matrix so it usually only has to
upload the combined matrix. When a matrix stack is flushed a reference
is taked to it by the pipeline progend and the age is stored so that
if the same state is used with the same program again then we don't
need to reupload the uniform.
