This adds the following new public experimental functions to set
uniform values on a CoglPipeline:
void
cogl_pipeline_set_uniform_1f (CoglPipeline *pipeline,
int uniform_location,
float value);
void
cogl_pipeline_set_uniform_1i (CoglPipeline *pipeline,
int uniform_location,
int value);
void
cogl_pipeline_set_uniform_float (CoglPipeline *pipeline,
int uniform_location,
int n_components,
int count,
const float *value);
void
cogl_pipeline_set_uniform_int (CoglPipeline *pipeline,
int uniform_location,
int n_components,
int count,
const int *value);
void
cogl_pipeline_set_uniform_matrix (CoglPipeline *pipeline,
int uniform_location,
int dimensions,
int count,
gboolean transpose,
const float *value);
These are similar to the old functions used to set uniforms on a
CoglProgram. To get a value to pass in as the uniform_location there
is also:
int
cogl_pipeline_get_uniform_location (CoglPipeline *pipeline,
const char *uniform_name);
Conceptually the uniform locations are tied to the pipeline so that
whenever setting a value for a new pipeline the application is
expected to call this function. However in practice the uniform
locations are global to the CoglContext. The names are stored in a
linked list where the position in the list is the uniform location.
The global indices are used so that each pipeline can store a mask of
which uniforms it overrides. That way it is quicker to detect which
uniforms are different from the last pipeline that used the same
CoglProgramState so it can avoid flushing uniforms that haven't
changed. Currently the values are not actually compared which means
that it will only avoid flushing a uniform if there is a common
ancestor that sets the value (or if the same pipeline is being flushed
again - in which case the pipeline and its common ancestor are the
same thing).
The uniform values are stored in the big state of the pipeline as a
sparse linked list. A bitmask stores which values have been overridden
and only overridden values are stored in the linked list.
Reviewed-by: Robert Bragg <robert@linux.intel.com>
This adds two new experimental public functions to replace the old
internal _cogl_pipeline_set_cull_face_state function:
void
cogl_pipeline_set_cull_face_mode (CoglPipeline *pipeline,
CoglPipelineCullFaceMode cull_face_mode);
void
cogl_pipeline_set_front_face_winding (CoglPipeline *pipeline,
CoglWinding front_winding);
There are also the corresponding getters.
https://bugzilla.gnome.org/show_bug.cgi?id=663628
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>
When freeing a pipeline in _cogl_pipeline_free we weren't making sure to
free the layers_cache which was leading to a memory leak.
Thanks to Sunjin Yang for finding this.
https://bugzilla.gnome.org/show_bug.cgi?id=660986
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>
We only need a ctx pointer if we need to refer to the default_layer_x
layers to copy as templates so only call _cogl_context_get_default()
once we need to copy a template. _cogl_context_get_default() was
starting to show up in profiles and this was the main cause.
Reviewed-by: Neil Roberts <neil@linux.intel.com>
This splits out the core CoglPipelineLayer support code from
cogl-pipeline.c into cogl-pipeline-layer.c; it splits out the debugging
code for dumping a pipeline to a .dot file into cogl-pipeline-debug.c
and it splits the CoglPipelineNode support which is shared between
CoglPipeline and CoglPipelineLayer into cogl-node.c.
Note: cogl-pipeline-layer.c only contains the layer code directly
relating to CoglPipelineLayer objects; it does not contain any
_cogl_pipeline API relating to how CoglPipeline tracks and manipulates
layers.
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>
The ARBfp backend can't handle fog so it tries to check for when it's
enabled and bails out. However it was checking using the global legacy
state value on the CoglContext but this doesn't necessarily reflect
the state that will actually be used by the pipeline because Cogl may
have internally pushed a different pipeline.
This patch adds an internal _cogl_pipeline_get_fog_enabled which the
ARBfp backend now uses.
Reviewed-by: Robert Bragg <robert@linux.intel.com>
As part of an on-going effort to get cogl-pipeline.c into a more
maintainable state this splits out all the apis relating just to
layer state. This just leaves code relating to the core CoglPipeline
and CoglPipelineLayer design left in cogl-pipeline.c.
This splits out around 2k more lines from cogl-pipeline.c although we
are still left with nearly 4k lines so we still have some way to go!
Reviewed-by: Neil Roberts <neil@linux.intel.com>
Since cogl-pipeline.c has become very unwieldy this make a start at
trying to shape this code back into a manageable state. This patche
moves all the API relating to core pipeline state into
cogl-pipeline-state.c. This doesn't move code relating to layer state
out nor does it move any of the code supporting the core design
of CoglPipeline itself.
This change alone factors out 2k lines of code from cogl-pipeline.c
which is obviously a good start. The next step will be to factor
out the layer state and then probably look at breaking all of this
state code down into state-groups.
Reviewed-by: Neil Roberts <neil@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>
Previously the fragends had a separate private data pointer which was
used by the GLSL and ARBfp fragends to store a tiny struct containing
a single pointer to the ref-counted shader state. The space for the
private data pointer is reserved in all of the pipelines for all of
the potential backends. The vertends and progends however did this
differently by directly storing the pointer to the ref counted data
using cogl_object_set_user_data. This patch unifies the different
methods so that they all use cogl_object_set_user_data and the
fragends don't bother with the separate tiny allocation for the
private data. The private data pointer array has been removed from
CoglPipeline and the corresponding fragend virtual to free the private
data has also been removed because this can instead be done with the
destroy notify from the object user data.
The variable names used have been unified so that all of the vertends
and fragends name their data struct CoglPipelineShaderState and use a
variable called shader_state to refer to it. The progend uses
CoglPipelineProgramState and a variable called program_state.
This should also fix two potential bugs. the ARBfp fragend was
apprently leaking a reference to the private state when it creates the
private data because it was adding a reference before stroring the
pointer to the newly allocated data but the ref count is already set
to 1 on creation. The other potential bug is that the free function
for CoglPipeline was only calling the free_priv virtual for the
currently used fragend of the pipeline. The design of the fragends is
meant to allow a pipeline to have multiple fragend priv datas because
a child pipeline could be attaching its fragend data to the ancestor
and its allowed to pick a different fragend.
That list is tracking the layers for get_layers_list() and needs to be
freed later on. However _copy() did not initialize it and we ended up
trying to free some garbage pointer.
_cogl_pipeline_get_layers() allocates a list on the pipeline to be able
to get the pointer valid as long as possible and store that list in the
pipeline object.
You need to free that list when freeing the pipeline.
Signed-off-by: Robert Bragg <robert@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
When a copy is made of a weak pipeline it tries to promote the weak
parent by taking a reference on that weak pipeline's parent. However
promote_weak_ancestors was instead always taking a reference on the
first parent, regardless of whether it was weak. The corresponding
revert_weak_ancestors function which is supposed to undo the effect of
promote_weak_ancestors only unref'd the parent if was weak. This meant
that any non-weak pipeline copy would end up leaking a reference on
its parent.
This patch changes both functions to have a similar loop. It loops
through all of the parents of the pipeline until it finds one that is
not weak and refs or unrefs the *parent* of that pipeline instead of
the pipeline itself.
Signed-off-by: Robert Bragg <robert@linux.intel.com>
Instead of having a separate GList for the children we can use the
linked list code from FreeBSD and store the list node directly in the
struct. That way we can avoid having a separate slice allocation for
the list node. It also means that we effectively have a pointer to the
list node given a pointer to the pipeline node. That means we can
unparent a pipeline without having to walk the entire list of
children. With this change there is no need to have the optimisation
to fast track a pipeline that only has one child which simplifies the
code somewhat.
With this patch we are removing a pointer and a gboolean from the
CoglPipeline struct and adding two pointers. On 32-bit architectures
this should end up exactly the same size because a gboolean is the
same size as a pointer. On 64-bit architectures I think it should end
up 4 bytes smaller because it also ends up removing two cases where a
pointer follows a gboolean which presumably would mean the compiler
would have to insert 4 bytes of padding to keep the pointer aligned to
8 bytes.
https://bugzilla.gnome.org/show_bug.cgi?id=652514
When setting a NULL texture on a CoglPipeline we would also reset the
texture target to a dummy value of 0. Reseting the target also had the
effect of making fragends discard any associated program. In cases where
the NULL texture was only transient until a replacement texture could be
set we were re-running lots of redundant codegen and shader
compilations.
Signed-off-by: Neil Roberts <neil@linux.intel.com>
There is a documented rule that layer changes should only be notified to
the fragend once; either as a pipeline change or as a layer change. When
the number of layers associated with a material changes then that should
get notified against the pipeline. All other layer changes get notified
against the layer.
There was a mistake in the _cogl_pipeline_add/remove_layer_difference
functions, in that we weren't using the 'inc/dec_n_layers' boolean to
determine if the fragend should be notified of the change.
It was also noticed that the logic of _cogl_pipeline_prune_to_n_layers
would also break this rule, by failing to notify some changes at all.
Signed-off-by: Neil Roberts <neil@linux.intel.com>
Instead of simply extending the cogl_pipeline_ namespace to add api for
controlling the depth testing state we now break the api out. This adds
a CoglDepthState type that can be stack allocated. The members of the
structure are private but we have the following API to setup the state:
cogl_depth_state_init
cogl_depth_state_set_test_enabled
cogl_depth_state_get_test_enabled
cogl_depth_state_set_test_function
cogl_depth_state_get_test_function
cogl_depth_state_set_writing_enabled
cogl_depth_state_get_writing_enabled
cogl_depth_state_set_range
cogl_depth_state_get_range
This removes the following experimental API which is now superseded:
cogl_material_set_depth_test_enabled
cogl_material_get_depth_test_enabled
cogl_material_set_depth_test_function
cogl_material_get_depth_test_function
cogl_material_set_depth_writing_enabled
cogl_material_get_depth_writing_enabled
cogl_material_set_depth_range
cogl_material_get_depth_range
Once a CoglDepthState structure is setup it can be set on a pipeline
using cogl_pipeline_set_depth_state().
When comparing the wrap modes of two pipeline layers it now considers
COGL_WRAP_MODE_AUTOMATIC to be equivalent to CLAMP_TO_EDGE. By the
time the pipeline is in the journal, the upper primitive code is
expected to have overridden this wrap mode with something else if it
wants any other behaviour. This is important for getting text to batch
together with textures because the text explicitly sets the wrap mode
to CLAMP_TO_EDGE on its pipeline.
In _cogl_pipeline_prune_empty_layer_difference if the layer's parent
has no owner then it just takes ownership of it. However this could
theoretically end up taking ownership of the root layer because
according to the comment above in the same function that should never
have an owner. This patch just adds an extra check to ensure that the
unowned layer has a parent.
http://bugzilla.clutter-project.org/show_bug.cgi?id=2588
In _cogl_pipeline_prune_empty_layer_difference if we are reverting to
the immediate parent of an empty/redundant layer then it is not enough
to simply add a reference to the pipeline's ->layer_differences list
without also updating parent_layer->owner to point back to its new
owner.
This oversight was leading us to break the invariable that all layers
referenced in layer_differences have an owner and was also causing us to
break another invariable whereby after calling
_cogl_pipeline_layer_pre_change_notify the returned layer must always be
owned by the given 'required_owner'.
http://bugzilla.clutter-project.org/show_bug.cgi?id=2588
In cogl_pipeline_set_layer_combine_constant it was comparing whether
the new color is the same as the old color using a memcmp on the
constant_color parameter. However the combine constant is stored in
the layer data as an array of four floats but the passed in color is a
CoglColor (which is currently an array of four guint8s). This was
causing valgrind errors and presumably also the check for setting the
same color twice would always fail.
This patch makes it do the conversion to a float array upfront before
the comparison.
When copying COMBINE state in
_cogl_pipeline_layer_init_multi_property_sparse_state we would read some
state from the destination layer (invalid data potentially), then
redundantly set the value back on the destination. This was picked up by
valgrind, and the code is now more careful about how it references the
src layer vs the destination layer.
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.
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.
When determining whether to hash the combine constant Cogl checks the
arguments to the combine funcs to determine whether the combine
constant is used. However is was using the GLenums GL_CONSTANT_COLOR
and GL_CONSTANT_ALPHA but these are not valid values for the
CoglPipelineCombineSource enum so presumably the constant would never
get hashed. This patch makes it use Cogl's enum of
COGL_PIPELINE_COMBINE_SOURCE_CONSTANT instead.
http://bugzilla.clutter-project.org/show_bug.cgi?id=2516
There are several places where we need to compare the texture state of a
pipeline and sometimes we need to take into consideration if the
underlying texture has changed but other times we may only care to know
if the texture target has changed.
For example the fragends typically generate programs that they want to
share with all pipelines with equivalent fragment processing state, and
in this case when comparing pipelines we only care about the texture
targets since changes to the underlying texture won't affect the
programs generated.
Prior to this we had tried to handle this by passing around some special
flags to various functions that evaluate pipeline state to say when we
do/don't care about the texture data, but this wasn't working in all
cases and was more awkward to manage than the new approach.
Now we simply have two state bits:
COGL_PIPELINE_LAYER_STATE_TEXTURE_TARGET and
COGL_PIPELINE_LAYER_STATE_TEXTURE_DATA and CoglPipelineLayer has an
additional target member. Since all the appropriate code takes masks of
these state bits to determine what to evaluate we don't need any extra
magic flags.
When notifying that a pipeline property is going to change, then at
times a pipeline will take over being the authority of the corresponding
state group. Some state groups can contain multiple properties and so to
maintain the integrity of all of the properties we have to initialize
all the property values in the new authority. For state groups with only
one property we don't have to initialize anything during the
pre_change_notify() because we can assume the value will be initialized
as part of the change being notified.
This patch optimizes how we handle this initialization of state groups
in a couple of ways; firstly we no longer do anything to initialize
state-groups with only one property, secondly we no longer use
_cogl_pipeline_copy_differences - (we have a new
_cogl_pipeline_init_multi_property_sparse_state() func) so we can avoid
lots calls to handle_automatic_blend_enable() which is sometimes seen
high in sysprof profiles.
Once the GLES2 wrapper is removed then we won't have the GLenums
needed for setting up the layer combine state. This adds Cogl enums
instead which have the same values as the corresponding GLenums. The
enums are:
CoglPipelineCombineFunc
CoglPipelineCombineSource
and
CoglPipelineCombineOp
This returns the layer matrix given a pipeline and a layer index. The
API is kept as internal because it directly returns a pointer into the
layer private data to avoid a copy into an out-param. We might also
want to add a public function which does the copy.
The GLSL vertend is mostly only useful for GLES2. The fixed function
vertend is kept at higher priority than the GLSL vertend so it is
unlikely to be used in any other circumstances.
The vertends are intended to flush state that would be represented in
a vertex program. Code to handle the layer matrix, lighting and
point size has now been moved from the common cogl-pipeline-opengl
backend to the fixed vertend.
'progend' is short for 'program backend'. The progend is intended to
operate on combined state from a fragment backend and a vertex
backend. The progend has an 'end' function which is run whenever the
pipeline is flushed and the two pipeline change notification
functions. All of the progends are run whenever the pipeline is
flushed instead of selecting a single one because it is possible that
multiple progends may be in use for example if the vertends and
fragends are different. The GLSL progend will take the shaders
generated by the fragend and vertend and link them into a single
program. The fragend code has been changed to only generate the shader
and not the program. The idea is that pipelines can share fragment
shader objects even if their vertex state is different. The authority
for the progend needs to be the combined authority on the vertend and
fragend state.
The pipeline function _cogl_pipeline_find_codegen_authority has been
renamed to _cogl_pipeline_find_equivalent_parent and it now takes a
set of flags for the pipeline and layer state that affects the
authority. This is needed so that we can reuse the same code in the
vertend and progends.
The current Cogl pipeline backends are entirely concerned with the
fragment processing state. We also want to eventually have separate
backends to generate shaders for the vertex processing state so we
need to rename the fragment backends. 'Fragend' is a somewhat weird
name but we wanted to avoid ending up with illegible symbols like
CoglPipelineFragmentBackendGlslPrivate.
_cogl_pipeline_needs_blending_enabled tries to determine whether each
layer is using the default combine state. However it was using
argument 0 for both checks so the if-statement would never be true.
There are a set of "EvalFlags" that get passed to _cogl_pipeline_hash
that can tweak the semantics of what state is evaluated for hashing but
these flags weren't getting passed via the HashState state structure
so it would be undefined if you would get the correct semantics.
According to 9cc9033347 the windows headers #define near as nothing,
and presumable the same is true for 'far' too. Apparently this define is
to improve compatibility with code written for Windows 3.1, so it's good
that people will be able to incorporate such code into their Clutter
applications.
The constant 'True' is defined by Xlib which isn't used for all clutter
builds so this replaces occurrences of True with TRUE which is defined
by glib. This should hopefully fix the win32 builds.
This allows us to get a hash for a set of state groups for a given
pipeline. This can be used for example to get a hash of the fragment
processing state of a pipeline so we can implement a cache for compiled
arbfp/glsl programs.
_cogl_pipeline_equal now accepts a mask of pipeline differences and layer
differences to constrain what state will be compared. In addition a set
of flags are passed that can tweak the comparison semantics for some
state groups. For example when comparing layer textures we sometimes
only need to compare the texture target and can ignore the data itself.
In updating the code this patch also changes it so all required pipeline
authorities are resolved in one step up-front instead of resolving the
authority for each state group in turn and repeatedly having to traverse
the pipeline's ancestry. This adds two new functions
_cogl_pipeline_resolve_authorities and
_cogl_pipeline_layer_resolve_authorities to handle resolving a set of
authorities.
This removes the unused array of per-packend priv data pointers
associated with every CoglPipelineLayer. This reduces the size of all
layer allocations and avoids having to zero an array for each
_cogl_pipeline_layer_copy.
In _cogl_pipeline_needs_blending_enabled after first checking whether
the property most recently changed requires blending we would then
resort to checking all other properties too in case some other state
also requires blending. We now avoid checking all other properties in
the case that blending was previously disabled and checking the property
recently changed doesn't require blending.
Note: the plan is to improve this further by explicitly keeping track
of the properties that currently cause blending to be enabled so that we
never have to resort to checking all other properties we can constrain
the checks to those masked properties.
