This is a fairly extensive second pass at exposing paint volumes for
actors.
The API has changed to allow clutter_actor_get_paint_volume to fail
since there are times - such as when an actor isn't a descendent of the
stage - when the volume can't be determined. Another example is when
something has connected to the "paint" signal of the actor and we simply
have no way of knowing what might be drawn in that handler.
The API has also be changed to return a const ClutterPaintVolume pointer
(transfer none) so we can avoid having to dynamically allocate the
volumes in the most common/performance critical code paths. Profiling was
showing the slice allocation of volumes taking about 1% of an apps time,
for some fairly basic tests. Most volumes can now simply be allocated on
the stack; for clutter_actor_get_paint_volume we return a pointer to
&priv->paint_volume and if we need a more dynamic allocation there is
now a _clutter_stage_paint_volume_stack_allocate() mechanism which lets
us allocate data which expires at the start of the next frame.
The API has been extended to make it easier to implement
get_paint_volume for containers by using
clutter_actor_get_transformed_paint_volume and
clutter_paint_volume_union. The first allows you to query the paint
volume of a child but transformed into parent actor coordinates. The
second lets you combine volumes together so you can union all the
volumes for a container's children and report that as the container's
own volume.
The representation of paint volumes has been updated to consider that
2D actors are the most common.
The effect apis, clutter-texture and clutter-group have been update
accordingly.
The blur effect will sample pixels on the edges of the offscreen buffer,
so we want to add a padding to avoid clamping the blur.
We do this by creating a larger target texture, and updating the paint
volume of the actor during paint to take that padding into account.
Following the commits:
c03544da - clutter-shader: use cogl_program_set_uniform_xyz API
a26119b5 - tests: Remove use of cogl_program_use
Remove the users of cogl_program_uniform_* and cogl_program_use() in the
shader-based effects.
Since BlurEffect and DesaturateEffect are using the shader API
implicitly and not using ClutterShaderEffect, we need to check if the
underlying GL implementation supports the GLSL shading language and warn
if not.
We might want to switch the BlurEffect from a box-blur to a
super-sampling of the texture target, in order to make it cheap(er).
If we inherit from ShaderEffect, though, we're setting in stone the
fact that we are going to use a fragment shader for blurring.
Since there is not parametrization of the blur, the code necessary
to implement effect is pretty small, and we can use the Cogl API
directly.
Sub-classes of ShaderEffect currently have to get the handle for the
Cogl shader and call cogl_shader_source(); this makes it awkward to
implement a ShaderEffect, and it exposes handles and Cogl API that we
might want to change in the future.
We should provide a ClutterShaderEffect method that allows to (safely)
set the shader source at the right time for sub-classes to use.
A simple, GLSL shader-based blur effect.
The blur shader is taken straight from the test-shader.c interactive
test case. It's a fairly clunky, inefficient and visually incorrect
implementation of a box blur, but it's all we have right now until I
figure out a way to do multi-pass shading with the current API.
