We are currently using a pipeline as a key into our arbfp program cache
but because we weren't making a copy of the pipelines used as keys there
were times when doing a lookup in the cache would end up trying to
compare a lookup key with an entry key that would point to invalid
memory.
Note: the current approach isn't ideal from the pov that that key
pipeline may reference some arbitrarily large user textures will now be
kept alive indefinitely. The plan to improve on this is that we will
have a mechanism to create a special "key pipeline" which will derive
from the default Cogl pipeline (to avoid affecting the lifetime of
other pipelines) and only copy state from the original pipeline that
affects the arbfp program and will reference small dummy textures
instead of potentially large user textures.
In the arbfp backend there is a seqential approach to finding a suitable
arbfp program to use for a given pipeline; first we see if there's
already a program associated with the pipeline, 2nd we try and find a
program associated with the "arbfp-authority" 3rd we try and lookup a
program in a cache and finally we resort to starting code-generation for
a new program. This patch slightly reworks the code of these steps to
hopefully make them a bit clearer.
_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.
Since c6493885c3 when building the EGL backend for eglx there was
no fallback in the init_events implementation so the X11 backend init
function would never get called. This was stopping it from receiving
any X events so a lot of things broke. It now just chains up.
When clutter_score_append_at_marker is called instead of
clutter_score_append the complete_id field of ClutterScoreEntry was
being left uninitialised. When the entry is eventually freed it would
sometimes try to disconnect an invalid signal id. This was causing
conformance test failures for me on GLES2.
We were trying to declare and initializing an arbfp program cache for
GLES but since the prototypes for the _hash and _equal functions were
only available for GL this broke the GLES builds. By #ifdefing the code
to conditionally declare/initialize for GL only this should hopefully
fix GLES builds.
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 adds a cache (A GHashTable) of ARBfp programs and before ever
starting to code-generate a new program we will always first try and
find an existing program in the cache. This uses _cogl_pipeline_hash and
_cogl_pipeline_equal to hash and compare the keys for the cache.
There is a new COGL_DEBUG=disable-program-caches option that can disable
the cache for debugging purposes.
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.
A non-static function named cogl_object_get_type was inadvertently added
during the addition of the CoglObject base type, but there is no public
prototype in the headers and it's only referenced inside cogl-object.c
to implement cogl_handle_get_type() for compatibility. This removes the
function since we don't want to commit to CoglObject always simply being
a boxed type. In the future we may want to register hierarchical
GTypeInstance based types.
To allow us to have gobject properties that accept a CoglMatrix value we
need to register a GType. This adds a cogl_gtype_matrix_get_type function
that will register a static boxed type called "CoglMatrix".
This adds a new section to the reference manual for GType integration
functions.
As a pre-requisite for being able to register a boxed GType for
CoglMatrix (enabling us to define gobject properties that accept a
CoglMatrix) this adds cogl_matrix_copy and _free functions.
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.
This moves _cogl_pipeline_get_parent and _cogl_pipeline_get_authority
into cogl-pipeline-private.h so they can be inlined since they have been
seen to get quite high in profiles. Given that they both contain such
small amounts of code the function call overhead is significant.
This adds a debug option called disable-software-clipping which causes
the journal to always log the clip stack state rather than trying to
manually clip rectangles.
Before flushing the journal there is now a separate iteration that
will try to determine if the matrix of the clip stack and the matrix
of the rectangle in each entry are on the same plane. If they are it
can completely avoid the clip stack and instead manually modify the
vertex and texture coordinates to implement the clip. The has the
advantage that it won't break up batching if a single clipped
rectangle is used in a scene.
The software clip is only used if there is no user program and no
texture matrices. There is a threshold to the size of the batch where
it is assumed that it is worth the cost to break up a batch and
program the GPU to do the clipping. Currently this is set to 8
although this figure is plucked out of thin air.
To check whether the two matrices are on the same plane it tries to
determine if one of the matrices is just a simple translation of the
other. In the process of this it also works out what the translation
would be. These values can be used to translate the clip rectangle
into the coordinate space of the rectangle to be logged. Then we can
do the clip directly in the rectangle's coordinate space.
Previously in cogl-clip-state.c when it detected that the current
modelview matrix is screen-aligned it would convert the clip entry to
a window clip. Instead of doing this cogl-clip-stack.c now contains
the detection and keeps the entry as a rectangle clip but marks that
it is entirely described by its scissor rect. When flusing the clip
stack it doesn't do anything extra for entries that have this mark
(because the clip will already been setup by the scissor). This is
needed so that we can still track the original rectangle coordinates
and modelview matrix to help detect when it would be faster to modify
the rectangle when adding it to the journal rather than having to
break up the batch to set the clip state.
When logging a quad we now only store the 2 vertices representing the
top left and bottom right of the quad. The color is only stored once
per entry. Once we come to upload the data we expand the 2 vertices
into four and copy the color to each vertex. We do this by mapping the
buffer and directly expanding into it. We have to copy the data before
we can render it anyway so it doesn't make much sense to expand the
vertices before uploading and this way should save some space in the
size of the journal. It also makes it slightly easier if we later want
to do pre-processing on the journal entries before uploading such as
doing software clipping.
The modelview matrix is now always copied to the journal entry whereas
before it would only be copied if we aren't doing software
transform. The journal entry struct always has the space for the
modelview matrix so hopefully it's only a small cost to copy the
matrix.
The transform for the four entries is now done using
cogl_matrix_transform_points which may be slightly faster than
transforming them each individually with a call to
cogl_matrix_transfom.
This reverts commit 4cfe90bde2.
GLSL 1.00 on GLES doesn't support unsized arrays so the whole idea
can't work.
Conflicts:
clutter/cogl/cogl/cogl-pipeline-glsl.c
The check for whether we can reuse a program we've already generated
was only being done if the pipeline already had a
glsl_program_state. When there is no glsl_program_state it then looks
for the nearest ancestor it can share the program with. It then
wasn't checking whether that ancestor already had a GL program so it
would start generating the source again. It wouldn't however compile
that source again because _cogl_pipeline_backend_glsl_end does check
whether there is already a program. This patch moves the check until
after it has found the glsl_program_state, whether or not it was found
from an ancestor or as its own state.
Under GLES2 we were defining the cogl_tex_coord_in varying as an array
with a size determined by the number of texture coordinate arrays
enabled whenever the program is used. This meant that we may have to
regenerate the shader with a different size if the shader is used with
more texture coord arrays later. However in OpenGL the equivalent
builtin varying gl_TexCoord is simply defined as:
varying vec4 gl_TexCoord[]; /* <-- no size */
GLSL is documented that if you declare an array with no size then you
can only access it with a constant index and the size of the array
will be determined by the highest index used. If you want to access it
with a non-constant expression you need to redeclare the array
yourself with a size.
We can replicate the same behaviour in our Cogl shaders by instead
declaring the cogl_tex_coord_in with no size. That way we don't have
to pass around the number of tex coord attributes enabled when we
flush a material. It also means that CoglShader can go back to
directly uploading the source string to GL when cogl_shader_source is
called so that we don't have to keep a copy of it around.
If the user wants to access cogl_tex_coord_in with a non-constant
index then they can simply redeclare the array themself. Hopefully
developers will expect to have to do this if they are accustomed to
the gl_TexCoord array.
When compiling for GLES2, the codegen is affected by state other than
the layers. That means when we find an authority for the codegen state
we can't directly look at authority->n_layers to determine the number
of layers because it isn't necessarily the layer state authority. This
patch changes it to use cogl_pipeline_get_n_layers instead. Once we
have two authorities that differ in codegen state we then compare all
of the layers to decide if they would affect codegen. However it was
ignoring the fact that the authorities might also differ by the other
codegen state. This path also adds an extra check for whether
_cogl_pipeline_compare_differences contains any codegen bits other
than COGL_PIPELINE_STATE_LAYERS.
When determining if a layer would require a different shader to be
generated it needs to check a certain set of state changes and it
needs to check whether the texture target is different. However it was
checking whether texture texture was different only if the other state
was also different which doesn't make any sense. It also only checked
the texture difference if that was the only state change which meant
that effectively the code was impossible to reach. Now it does the
texture target check indepent of the other state changes.
The fixed pipeline backend wasn't correctly flushing the combine
constant because it was using the wrong flag to determine if the
combine constant has changed since the last flushed material.
When enabling a unit that was disabled from a previous flush pipeline
it was forgetting to rebind the right texture unit so it wouldn't
work. This was causing the redhand to disappear when using the fixed
function backend in test-cogl-multitexture if anything else is added
to the scene.
For shader generation backends we don't need to worry about changes to
the texture object and changing the user matrix. The missing user
matrix flag was causing test-cogl-multitexture to regenerate the
shader every frame.
Having ctx here produces a warning on GLES. However it's needed for Big
GL as we have at the top of the file:
#ifdef HAVE_COGL_GL
#define glClientActiveTexture ctx->drv.pf_glClientActiveTexture
#endif
This reverts commit 27a3a2056a.
That what happens when you test things only with 2 configure options
instead of 3. The 2 tested compile, the third one breaks. Another good
catch for the eglx bot!
With glib 2.28, we'll be able to have one GSource per device manager
with child sources for earch device. Make a note to update the code
in a few months.
An array is used to translate the button to its mask. Clutter defines
the masks for button 1 to 5 but we report BTN_LEFT..BTN_TASK ie
0x110..0x117. We need to pad the array for the translation not to access
random data for buttons between 0x115 and 0x117.
Discarding the event without any warning when the device has no
associated stage makes it hard to find the bug for people implementing
new event backends. We should really warn for that abnormal condition in
_clutter_input_device_update().
We know support EV_REL events comming from evdev devices. This addition
is pretty straigthforward, it adds a x,y per GSource listening to a
evdev device, updates from EL_REL (relative) events and craft new
ClutterMotionEvents. As for buttons, BTN_LEFT..BTN_TASK are translated
to ClutterButtonEvents with 1..8 as button number.
Even with udev, the read fails before udev has a chance to signal the
change. Hence (and to handle errors gracefully anyway), let's remove the
device from the device manager in case of a read() error.
The device manager now fully owns the GSources corresponding to the
devices it manages. This will allow not only to remove the source when
udev signals a device removal but also handle read() errors gracefully
by removing the faulty device from the manager.
Just connect to the GUdevClient "uevent" signal and deals with
"add"/"remove" commands. This drives the installation/removal of
GSource to listen to the device.
Let's use the sysfs path of the device to make sure we only load evdev
device, not legacy mousedev ones for instance. We rely on the sysfs
API/ABI guarantees and look for devices finishing by /input%d/event%d.
This backend is a event backend that can be enabled for EGL (for now).
It uses udev (gudev) to query input devices on a linux system, listens to
keyboard events from input devices and xkbcommon to translate raw key
codes into key keysyms.
This commit only supports key events, more to follow.
Looking at what the X11 backend does: the unicode value is being
translated to the unicode codepoint of the symbol if possible. Let's do
the same then.
Before that, key events for say KEY_Right (0xff53) had the unicode_value
set to the keysym, which meant "This key event is actually printable and
is Unicode codepoint is 0xff53", which lead to interesting results.
The wayland client code has support for translating raw linux input
device key codes coming from the wayland compositor into key symbols
thanks to libxkbcommon.
A backend directly listening to linux input devices (called evdev, just
like the Xorg one) could use exactly the same code for the translation,
so abstract it a bit in a separate file.
In 6246c2bd6 I moved the code to add the boilerplate to a shader to a
separate function and also made it so that the common boilerplate is
added as a separate string to glShaderSource. However I didn't notice
that the #define for the vertex and fragment shaders already includes
the common part so it was being added twice. Mesa seems to accept this
but it was causing problems on the IMG driver because COGL_VERSION was
defined twice.
Don't calculate an extra layout in clutter_text_get_preferred_height for
single-line strings, when it's unnecessary. There's no need to set the
width of a layout when in single-line mode, as wrapping will not happen.
Previously when the shader effect is used with a new actor it would
end up throwing away the old program. I don't think this is neccessary
and it means if you use an effect to temporarily bind to an actor then
it will recompile the shader whenever it is applied.
http://bugzilla.clutter-project.org/show_bug.cgi?id=2454
When a new actor is set for ClutterOffscreenEffect it would throw away
the old material. I don't think there is anything specifically tied to
the actor in the material so throwing away just loses Cogl's cached
state about the material. This ends up relinking the shader every time
a new actor is set in ClutterShaderEffect.
http://bugzilla.clutter-project.org/show_bug.cgi?id=2454
Do not use the compiler to zero the first field of the GValue member,
since it's apparently non-portable. As we're allocating memory anyway we
can let the slice allocator do the zero-ing for us.
Mentioned in: http://bugzilla.clutter-project.org/show_bug.cgi?id=2455
Before commit 49898d43 CoglPipeline would compare whether a pipeline
layer's texture is equal by fetching the underlying GL handle. I
changed that so that it would only compare the CoglHandles because
that commit removes the GL handle texture overrides and sliced
textures instead log the underlying primitive texture. However I
forgot that the primitives don't always use
_cogl_texture_foreach_sub_texture_in_region when the quad fits within
the single texture so it won't use a texture override. This meant that
atlas textures and sub textures get logged with the atlas handle so
the comparison still needs to be done using the GL handles. It might
be nice to add a CoglTexture virtual to get the underlying primitive
texture instead to avoid having the pipeline poke around with GL
handles.
If we have to make override changes to the user's source material to
handle cogl_polygon then we need to make sure we unref the override
material at the end.
Previously we used the layers->backend_priv[] members to determine when
to notify backends about layer changes, but it entirely up to the
backends if they want to associate private state with layers, even
though they may still be interested in layer change notifications (they
may associate layer related state with the owner pipeline).
We now make the observation that in
_cogl_pipeline_backend_layer_change_notify we should be able to assume
there can only be one backend currently associated with the layer
because we wouldn't allow changes to a layer with multiple dependants.
This means we can determine the backend to notify by looking at the
owner pipeline instead.
Previously whenever the size of the FBO changes it would create a new
material and attach the texture to it. This is not good for Cogl
because it throws away any cached state for the material. In
test-rotate the size of the FBO changes constantly so it effectively
uses a new material every paint. For shader effects this also ends up
relinking the shader every paint because the linked programs are part
of the material state.
The features_cached member of CoglContext is intended to mark when
we've calculated the features so that we know if they are ready in
cogl_get_features. However we always intialize the features while
creating the context so features_cached will never be FALSE so it's
not useful. We also had the odd behaviour that the COGL_DEBUG feature
overrides were only applied in the first call to
cogl_get_features. However there are other functions that use the
feature flags such as cogl_features_available that don't use this
function so in some cases the feature flags will be interpreted before
the overrides are applied. This patch makes it always initialize the
features and apply the overrides immediately while creating the
context. This fixes a problem with COGL_DEBUG=disable-arbfp where the
first material flushed is done before any call to cogl_get_features so
it may still use ARBfp.
Now that the GLSL backend can generate code it can effectively handle
any pipeline unless there is an ARBfp program. However with current
open source GL drivers the ARBfp compiler is more stable so it makes
sense to prefer ARBfp when possible. The GLSL backend is also lower
than the fixed function backend on the assumption that any driver that
supports GLSL will also support ARBfp so it's quicker to try the fixed
function backend next.
This adds COGL_DEBUG=disable-fixed to disable the fixed function
pipeline backend. This is needed to test the GLSL shader generation
because otherwise the fixed function backend would always override it.
We don't want to use gl_PointCoord to implement point sprites on big
GL because in that case we already use glTexEnv(GL_COORD_REPLACE) to
replace the texture coords with the point sprite coords. Although GL
also supports the gl_PointCoord variable, it requires GLSL 1.2 which
would mean we would have to declare the GLSL version and check for
it. We continue to use gl_PointCoord for GLES2 because it has no
glTexEnv function.
The GLES2 wrapper no longer needs to generate any fragment shader
state because the GLSL pipeline backend will always give the wrapper a
custom fragment shader. This simplifies a lot of the state comparison
done by the wrapper. The fog generation is also removed even though
it's actually part of the vertex shader because only the fixed
function pipeline backend actually calls the fog functions so it would
be disabled when using any of the other backends anyway. We can fix
this when the two shader backends also start generating vertex
shaders.
GLES2 has no glAlphaFunc function so we need to simulate the behaviour
in the fragment shader. The alpha test function is simulated with an
if-statement and a discard statement. The reference value is stored as
a uniform.
Previously the flag to mark the differences for the alpha test
function and reference value were conflated into one. However this is
awkward when generating shader code to simulate the alpha testing for
GLES 2 because in that case changing the function would need a
different program but changing the reference value just requires
updating a uniform. This patch makes the function and reference have
their own state flags.
The GLSL shader generation supports layer combine constants so there's
no need to disable it for GLES2. It looks like there was also code for
it in the GLES2 wrapper so I'm not sure why it was disabled in the
first place.
The GLSL pipeline backend can now generate code to represent the
pipeline state in a similar way to the ARBfp backend. Most of the code
for this is taken from the GLES 2 wrapper.
_cogl_shader_compile_real had some code to create a set of strings to
combine the boilerplate code with a shader before calling
glShaderSource. This has now been moved to its own internal function
so that it could be used from the GLSL pipeline backend as well.
need_texture_combine_separate is moved to cogl-pipeline.c and renamed
to _cogl_pipeline_need_texture_combine_separate. The function is
needed by both the ARBfp and GLSL codegen backends so it makes sense to
share it.
The code for finding the arbfp authority for a pipeline should be the
same as finding the GLSL authority. So that the code can be shared the
function has been moved to cogl-pipeline.c and renamed to
_cogl_pipeline_find_codegen_authority.
Only one of the material backends can be generating code at the same
time so it seems to make sense to share the same source buffer between
arbfp and glsl. The new name is fragment_source_buffer in case we
later want to create a new buffer for the vertex shader. That probably
couldn't share the same buffer because it will likely need to be
generated at the same time.
Use the internal child list for the default map/unmap vfuncs. This removes
the requirement for non-container composite actors to implement their own
map/unmap functions.
Unrealizing an actor is a recursive process that needs to traverse the
children of an actor to ensure they are also unrealized. This maintains
the invariant that if any given actor is marked as unrealized then you
know that all its children have also been unrealized.
The previous implementation would use the container interface's
foreach_with_internals vfunc to explicitly traverse the children of
container actors but this didn't consider composite actors that aren't
containers.
Since clutter-actor now maintains an explicit list of children we can
also handle composite actors that aren't containers using
_clutter_actor_traverse.
This makes it possible to choose the traversal order; either depth first
or breadth first and when visiting actors in a depth first order there
is now a callback called before children are traversed and one called
after. Some tasks such as unrealizing actors need to explicitly control
the traversal order to maintain the invariable that all children of an
actor are unrealized before we actually mark the parent as unrealized.
The callbacks are now passed the relative depth in the graph of the
actor being visited and instead of only being able to return a boolean
to bail out of further traversal it can now do one of: continue,
skip_children or break. To implement something like unrealize it's
desirable to skip children that you find have already been unrealized.
ClutterX11TexturePixmap watches for configure events to tell when it
needs to name a new pixmap for the window. However, ConfigureEvents
occur on moves in addition to resizes, and doing round trips and
naming new pixmaps every time a window is moved is a real performance
killer.
Add clutter_x11_texture_pixmap_sync_window_internal() that takes the
size/position of the window as arguments rather than always calling
XGetWindowAttributes. This allows us to bypass all work other than
notifying the window-x/window-y properties when we get a ConfigurEvent
for a move.
The last received width/height is saved to allow us to also omit
XGetWindowAttributes on MapNotify events.
The public clutter_x11_texture_pixmap_sync_window() becomes a bit less
efficient since we no longer combine the roundtrips for
XGetWindowAttributes() and XCompositeNameWindowPixmap(), but it appears
to have no callers in current publicly available code.
Several FIXME's are added for areas where there are still weird things
going on in the code or improvements could be made.
http://bugzilla.clutter-project.org/show_bug.cgi?id=2356
* cogl_texture_get_data() is converted to use
_cogl_texture_foreach_sub_texture_in_region() to iterate
through the underlying textures.
* When we need to read only a portion of the underlying
texture, we set up a FBO and use _cogl_read_pixels()
to read the portion we need. This is enormously more
efficient for reading a small portion of a large atlas
texture.
* The CoglAtlasTexture, CoglSubTexture, and CoglTexture2dSliced
implementation of get_texture() are removed.
http://bugzilla.clutter-project.org/show_bug.cgi?id=2414
Previously in cogl_read_pixels we assume the format of the framebuffer
is always premultiplied because that is the most likely format with
the default Cogl blend mode. However when the framebuffer is bound to
a texture we should be able to make a better guess at the format
because we know the texture keeps track of the premult status. This
patch adds an internal format member to CoglFramebuffer. For onscreen
framebuffers we still assume it is RGBA_8888_PRE but for offscreen to
textures we copy the texture format. cogl_read_pixels uses this to
determine whether the data returned by glReadPixels will be
premultiplied.
http://bugzilla.clutter-project.org/show_bug.cgi?id=2414
When converting the data in cogl_read_pixels it was using bmp_format
instead of the format passed in to the function. bmp_format is the
same as the passed in format except that it always has the premult bit
set. Therefore the conversion would not handle premultiply correctly.
http://bugzilla.clutter-project.org/show_bug.cgi?id=2414
This is the same as _cogl_read_pixels except that it takes a rowstride
parameter for the destination buffer. Under OpenGL setting the
rowstride this will end up calling GL_ROW_LENGTH so that the buffer
region can be directly written to. Under GLES GL_ROW_LENGTH is not
supported so it will use an intermediate buffer as it does if the
format is not GL_RGBA.
cogl_read_pixels now just calls the full version of the function with
the rowstride set to width*bpp.
http://bugzilla.clutter-project.org/show_bug.cgi?id=2414
This function is the same as cogl_offscreen_new_to_texture but it
takes a level parameter and a set of flags so that FBOs can be used to
render to higher mipmap levels and to disable the depth and stencil
buffers. cogl_offscreen_new_to_texture now just calls the new function
with the level set to zero. This function could be useful in a few
places in Cogl where we want to use FBOs as an implementation detail
such as when copying between textures.
http://bugzilla.clutter-project.org/show_bug.cgi?id=2414
In clutter_stage_real_queue_redraw we were checking to see if the
backend will ignore any subsequent redraw_clip so we can avoid the cost
of projecting the paint-volume of an actor into stage coordinates, but
we weren't ensuring that a full redraw would be queued instead we just
bailed out immediately. This makes sure to call
_clutter_stage_window_add_redraw_clip (stage_window, NULL) in this case
to make sure the backend will do an un-clipped redraw.
This tweaks the semantics of the has_redraw_clips vfunc so we can assume
that at the start of a new frame there is an implied, initial,
redraw_clip that clips everything (i.e. nothing would be redrawn) so in
that case we would expect the has_redraw_clips vfunc to return True at
the start of a new frame for backends that support clipping.
Previously there was an ambiguity when this function returned False
since it could either mean a full screen redraw had been queued or it
could mean that the clip state wasn't yet initialized for that frame.
This would result in _clutter_stage_has_full_redraw_queued() returning
True at the start of a new frame even before any actors have been
updated, which in turn meant we would incorrectly ignore queue_redraw
requests for actors, believing them to be redundant.
