The Clutter backend split is opaque enough that should allow us to just
build all possible backends inside the same shared object, and select
the wanted backend at initialization time.
This requires some work in the build system, as well as the
initialization code, to remove duplicate functions that might cause
conflicts at build and link time. We also need to defer all the checks
of the internal state of the platform-specific API to run-time type
checks.
The deprecated sections should be much more prominently separated from
the current API; we can use a new part inside the main reference index
for this.
Keeping the backing Cairo surface of a CairoTexture canvas in sync with
the actor's allocation is tedious and prone to mistakes. We can
definitely do better by simply exposing a property that does the surface
resize and invalidation automagically on ::allocate.
The current "create context/draw/destroy context" pattern presents
various problems. The first issue is that it defers memory management to
the caller of the create() or create_region() methods, which makes
bookkeeping of the cairo_t* harder for language bindings and third party
libraries. The second issue is that, while it's easier for
draw-and-forget texturs, this API is needlessly complicated for contents
that have to change programmatically - and it introduces constraints
like calling the drawing code explicitly after a surface resize (e.g.
inside an allocate() implementation).
By using a signal-based approach we can make the CairoTexture actor
behave like other actors, and like other libraries using Cairo as their
2D drawing API.
The semantics of the newly-introduced ::draw signal are the same as the
one used by GTK+:
- the signal is emitted on invalidation;
- the cairo_t* context is owned by the actor;
- it is safe to have multiple callbacks attached to the same
signal, to allow composition;
- the cairo_t* is already clipped to the invalidated area, so
that Cairo can discard geometry immediately before we upload
the texture data.
There are possible future improvements, like coalescing multiple
invalidations inside regions, and performing clipped draws during
the paint cycle; we could even perform clipped redraws if we know the
extent of the invalidated area.
This adds a public function to get the bounds of the current clipped
redraw on a stage. This should only be called while the stage is being
painted. The function diverts to a virtual function on the
ClutterStageWindow implementation. If the function isn't implemented
or it returns FALSE then the entire stage is reported. The clip bounds
are in integer pixel coordinates in the stage's coordinate space.
http://bugzilla.clutter-project.org/show_bug.cgi?id=2421
* swipe-action:
test-swipe-action: Clean up the test code
docs: Add the new actions to the API reference
gesture-action: Remove the multi-device entry points
swipe-action: Remove the required devices call
swipe-action: Clean up
gesture-action: Clean up
Add ClutterSwipeAction and ClutterGestureAction
This adds a virtual to ClutterActor so that an actor subclass can
report whether it has overlapping primitives. ClutterActor uses this
to determine whether it needs to use ClutterFlattenEffect to implement
the opacity property. The default implementation of the virtual
returns TRUE which means that most actors will end up being redirected
offscreen when the opacity != 255. ClutterTexture and ClutterRectangle
override this to return FALSE because they should never need to be
redirected. ClutterClone overrides it to divert to the source.
The values for the ClutterOffscreenRedirect enum have changed to:
AUTOMATIC_FOR_OPACITY
The actor will only be redirected if has_overlaps returns TRUE and
the opacity is < 255
ALWAYS_FOR_OPACITY
The actor will always be redirected if the opacity < 255 regardless
of the return value of has_overlaps
ALWAYS
The actor will always be redirected offscreen.
This means that the property can't be used to prevent the actor from
being redirected but only to increase the likelihood that it will be
redirected.
ClutterActor now adds and removes the flatten effect depending on
whether flattening is needed directly in clutter_actor_paint(). There
are new internal versions of add/remove_effect that don't queue a
redraw. This means that ClutterFlattenEffect is now just a no-op
subclass of ClutterOffscreen. It is only needed because
ClutterOffscreen is abstract. Removing the effect also makes it so
that the cached image will be freed as soon as an actor is repainted
without being flattened.
This adds a property which can be used to redirect the actor through
an FBO before painting so that it becomes flattened in an image. The
image can be used as a cache to avoid having to repaint the actor if
something unrelated in the scene changes. It can also be used to
implement correct opacity even if the actor has overlapping
primitives. The property is an enum that takes three values:
CLUTTER_OFFSCREEN_REDIRECT_NEVER: The default behaviour which is to
never flatten the actor.
CLUTTER_OFFSCREEN_REDIRECT_ALWAYS: The actor is always redirected
through an FBO.
CLUTTER_OFFSCREEN_REDIRECT_ONLY_FOR_OPACITY: The actor is only
redirected through an FBO if the paint opacity is not 255. This
value would be used if the actor wants correct opacity. It will
avoid the overhead of using an FBO whenever the actor is fully
opaque.
The property is implemented by installing a ClutterFlattenEffect.
ClutterFlattenEffect is a new internal class which subclasses
ClutterOffscreen to redirect the painting to an FBO. When
ClutterOffscreen paints, the effect sets an opacity override on the
actor so that the image will always contain the actor at full
opacity. The opacity is then applied to the resulting image before
painting it to the stage. This means the actor does not need to be
redrawn while the opacity is being animated.
The effect has a high internal priority so that it will always occur
before any other effects and it gets hidden from the application.
This adds a new public function to queue a rerun of an effect. If
nothing else queues a redraw then when the effect's actor is painted
the effect will be run without the CLUTTER_EFFECT_RUN_ACTOR_DIRTY
flag. This allows parametrised offscreen effects to report that they
need to redraw the image without having to redraw the underlying
actor. This will be used to implement the 'transparency' effect of
ClutterActor.
If multiple redraws are queued with different effects then redrawing
is started from the one that occurs last in the list of effects.
Internally the function is a wrapper around the new function
_clutter_actor_queue_redraw_full. This is intended to be the sole
point of code for queuing redraws on an actor. It has parameters for
the clip and the effect. The other two existing functions to queue a
redraw (one with a clip and one without) now wrap around this function
by passing a NULL effect.
This adds a new virtual to ClutterEffect which is intended to be a
more flexible replacement for the pre and post_paint functions. The
implementation of a run virtual would look something like this:
void
effect_run (ClutterEffect *effect,
ClutterEffectRunFlags flags)
{
/* Set up state */
/* ... */
/* Chain to the next item in the paint sequence */
clutter_actor_continue_paint (priv->actor);
/* Clean up state */
/* ... */
}
ClutterActor now just calls this virtual instead of the pre_paint and
post_paint functions. It keeps track of the next effect in the list so
that it knows what to do when clutter_actor_continue_paint is
called. clutter_actor_continue_paint is a new function added just for
implementing effects.
The default implementation of the run virtual just calls pre_paint and
post_paint so that existing effects will continue to work.
An effect is allowed to conditionally skip calling
clutter_actor_continue_paint(). This is useful to implement effects
that cache the image of an actor. The flags parameter can be used to
determine if the actor is dirty since the last paint. ClutterActor
sets this flag whenever propagated_one_redraw is TRUE which means that
a redraw for this actor or one of its children was queued.
Cogl has now been split out into a standalone project with a separate
repository at git://git.gnome.org/cogl. From now on the Clutter build
will now simply look for a cogl-1.0 pkg-config file to find a suitable
Cogl library to link against at build time.
This backend hasn't been used for years now and so because it is
untested code and almost certainly doesn't work any more it would be a
burdon to continue trying to maintain it. Considering that we are now
looking at moving OpenGL window system integration code down from
Clutter backends into Cogl that will be easier if we don't have to
consider this backend.
The OffscreenEffect class needs to expose a way for sub-classes to
track the size of FBO it creates, in case it has to do some geometry
deformations like the DeformEffect sub-classes.
Let's move the private symbol we used internally in 1.6 to fix
DeformEffect to the list of public symbols of OffscreenEffect.
http://bugzilla.clutter-project.org/show_bug.cgi?id=2570
Creating a synthetic event requires direct access to the ClutterEvent
union members; this access does not map in bindings to high-level
languages, especially run-time bindings using GObject-Introspection.
It's also midly annoying from C, as it unnecessarily exposes the guts of
ClutterEvent - something we might want to fix in the future.
http://bugzilla.clutter-project.org/show_bug.cgi?id=2575
Make sure users get the idea that clutter_init()
has a return value that needs to be checked.
These were fixed via sed magic:
sed -i -s -e "s/clutter_init (.*)/\
if (& != CLUTTER_INIT_SUCCESS)\n return 1/"\
doc/*/*/*.{c,xml} doc/*/*.xml
http://bugzilla.clutter-project.org/show_bug.cgi?id=2574
When synthesizing events coming from input devices it should be
possible to just call a setter function, to avoid a huge switch
on the type of the event.
Clutter should also store the device pointer inside the private
data, for faster access of the pointer in allocated events.
Finally, the get_device_id() and get_device_type() accessors should
just be wrappers around clutter_event_get_device(), to reduce the
amount of code duplication.
* xi2: (41 commits)
test-devices: Actually print the axis data
device-manager/xi2: Sync the stage of source devices
event: Clean up clutter_event_copy()
device: unset the axes array pointer when resetting
device-manager/xi2: Fix device hotplugging
glx: Clean up GLX implementation
device/x11: Store min/max keycode in the XI device class
x11: Hide all private symbols
docs: More documentation fixes for InputDevice
*/event: Never manipulate the event queue directly
win32: Update DeviceManager device creation
device: Allow enabling/disabling non-master devices
backend/eglx: Add newly created stages to the translators
device: Add more doc annotations
device: Use a double for translate_axis() argument
test-devices: Clean up and show axes data
event: Fix up clutter_event_copy()
device/xi2: Translate the axis data after setting devices
device: Add more accessors for properties
docs: Update API reference
...
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.
Allow the developer to set whether the Stage should receive key focus
when mapped. The implementation is fully backend-dependent. The default
value is TRUE because that's what we've been expecting so far.
http://bugzilla.clutter-project.org/show_bug.cgi?id=2500
Keeping the Cogl 2.0 API reference in the build is getting far more
troublesome than it's worth.
It's breaking distcheck far too often, and it makes it impossible to
rebuild the build environment from tarballs - which is something that
some distributions (namely: the Debian-based ones, but not limited to
them) do in order to change build scripts using their own rules.
Other frameworks expose the same functionality as "auto-reverse",
probably to match the cassette tape player. It actually makes sense
for Clutter to follow suit.
If not configured with --enable-cogl2-reference then don't try and dist
the doc/references/cogl-2.0 manual. Although this means a tarball built
this way will not be able to build the experimental cogl-2.0 manual this
isn't considered a big problem since anyone interested in this would
hopefully be tracking git for now or we can simply be careful to
configure with --enable-cogl2-reference for our tarball releases.
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.
This add two new function that allows us to transform or project an
array of points instead of only transforming one point at a time. Recent
benchmarking has shown cogl_matrix_transform_point to be a bottleneck
sometimes, so this should allow us to reduce the overhead when
transforming lots of vertices at the same time, and also reduce the cost
of 3 component, non-projective transforms.
For now they are marked as experimental (you have to define
COGL_ENABLE_EXPERIMENTAL_API) because there is some concern that it
introduces some inconsistent naming. cogl_matrix_transform_point would
have to be renamed cogl_matrix_project_point to be consistent, but that
would be an API break.
Building the API reference for Cogl 2.0 is fairly confusing: the API
itself is experimental and for internal use only -- though we want
feedback for it.
Let's build the API reference only when Clutter is configured with a
specific configure switch, so that people that wish to give feedback on
the API and its documentation can do it.
So we can keep track of the experimental progress of Cogl 2.0 features
this adds a standalone Cogl 2.0 Reference Manual which doesn't cover
the deprecated 1.x symbols and removes the need for a "Cogl
experimental API" chapter since those sections now make up the main
table of contents.
Since EGA colors are apparently all the rage in other toolkits, Clutter
should not be left out. On top of the usual CGA/EGA palette the static
colors also include the Tango Icon palette, which at least is more
pleasant to the eye.
Static colors are accessed through an enumeration by using
clutter_color_get_static(), or using the short-hand pre-processor
macros.
http://bugzilla.clutter-project.org/show_bug.cgi?id=2066
This exposes the idea of a stack of source materials instead of just
having a single current material. This allows the writing of orthogonal
code that can change the current source material and restore it to its
previous state. It also allows the implementation of new composite
primitives that may want to validate the current source material and
possibly make override changes in a derived material.
* wip/path-constraint:
docs: Add PathConstraint
tests: Add a PathConstraint interactive test
Add ClutterPathConstraint
actor-box: Add setters for origin and size
This function handles a single windows message. The idea is that it
could be used by clutter-gtk to forward on events from a
GdkEventFilter. The function replaces the old message_translate()
function. That function didn't translate the event anymore anyway and
instead it could generate multiple events so
clutter_win32_handle_event seems like a more appropriate name. The
function returns TRUE or FALSE depending on whether the event was
completely handled instead of setting call_window_proc.
The interpolate() method does what it says on the tin: it interpolates
between two colors using the given factor.
ClutterColor uses it to register a progress function for Intervals.
The internal copy of JSON-GLib was meant to go away right after the 1.0
release, given that JSON-GLib was still young and relatively unknown.
Nowadays, many projects started depending on this little library, and
distributions ship it and keep it up to date.
Keeping a copy of JSON-GLib means keeping it up to date; unfortunately,
this would also imply updating the code not just for the API but for the
internal implementations.
Starting with the 1.2 release, Clutter preferably dependend on the
system copy; with the 1.4 release we stopped falling back automatically.
The 1.6 cycle finally removes the internal copy and requires a copy of
JSON-GLib installed on the target system in order to compile Clutter.
This adds a "Cogl deprecated API" chapter to the Cogl reference manual
so we can group all the documentation for deprecated symbols together
instead of having them clutter up the documentation of symbols we would
rather developers used.
The CoglTexture3D API is only available when defining
COGL_ENABLE_EXPERIMENTAL_API so it should be listed in the experimental
section of the API reference.
The keysyms defines in clutter-keysyms.h are generated from the X11 key
symbols headers by doing the equivalent of a pass of sed from XK_* to
CLUTTER_*. This might lead to namespace collisions, down the road.
Instead, we should use the CLUTTER_KEY_* namespace.
This commit includes the script, taken from GDK, that parses the X11
key symbols and generates two headers:
- clutter-keysyms.h: the default included header, with CLUTTER_KEY_*
- clutter-keysyms-compat.h: the compatibility header, with CLUTTER_*
The compat.h header file is included if CLUTTER_DISABLE_DEPRECATED is
not defined - essentially deprecating all the old key symbols.
This does not change any ABI and, assuming that an application or
library is not compiling with CLUTTER_DISABLE_DEPRECATED, the source
compatibility is still guaranteed.
When animating an actor through clutter_actor_animate() and friends we
might want forcibly detach the animation instance from the actor in
order to start a new one - for instance, in response to user
interaction.
Currently, there is no way to do that except in a very convoluted way,
by emitting the ::completed signal and adding a special case in the
signal handlers; this is due to the fact that clutter_actor_animate()
adds more logic than the one added by clutter_animation_set_object(),
so calling set_object(NULL) or unreferencing the animation instance
itself won't be enough.
The right way to approach this is to add a new method to Clutter.Actor
that detaches any eventual Animation currently referencing it.
http://bugzilla.clutter-project.org/show_bug.cgi?id=2051
Intel CE3100 and CE4100 have several planes (framebuffers) and a
hardware blender to blend the planes togeteher to produce the final
image.
clutter_cex100_set_plane() lets you configure which framebuffer clutter
will use for its rendering.
*** This is an API change ***
The create_target() virtual function should return a CoglHandle to a
texture; clutter_offscreen_effect_get_target(), instead, returns a
CoglMaterial to be painted in the implementation of the paint_target()
virtual function.
Instead of equating textures with materials, and confusing the user of
the API, we should mark the difference more prominently.
First of all, we should return a CoglMaterial* (now that we have that
as a public type) in get_target(); having handles all over the place
does not make it easier to distinguish the semantics of the virtual
functions.
Then we should rename create_target() to create_texture(), to make it
clear that what should be returned is a texture that is used as the
backing for the offscreen framebuffer.
It can be useful to be able to forcibly break the grab set up by the
ClickAction. The newly added release() method provides a mechanism to
release the grab and unset the :held state of the ClickAction.
This removes all references to SDL in the build instructions as the
backend is no longer available. The OpenGL version required is only
1.2 not 1.4. The Windows build instructions were out of date and have
been replaced with a link to the wiki instead.
Instead of exposing an API that provides an OpenGL state machine style
where you first have to bind the program to the context using
cogl_program_use() followed by updating uniforms using
cogl_program_uniform_xyz we now have uniform setter methods that take an
explicit CoglHandle for the program.
This deprecates cogl_program_use and all the cogl_program_uniform
variants and provides the following replacements:
cogl_program_set_uniform_1i
cogl_program_set_uniform_1f
cogl_program_set_uniform_int
cogl_program_set_uniform_float
cogl_program_set_uniform_matrix
A TableLayout is a layout manager that allocates its children in rows
and columns. Each child is assigned to a cell (or more if a cell span
is set).
The supported child properties are:
• x-expand and y-expand: if this cell with try to allocate the
available extra space for the table.
• x-fill and y-fill: if the child will get all the space available in
the cell.
• x-align and y-align: if the child does not fill the cell, then
where the child will be aligned inside the cell.
• row-span and col-span: number of cells the child will allocate for
itself.
Also, the TableLayout has row-spacing and col-spacing for specifying
the space in pixels between rows and between columns.
We also include a simple test of the layout manager, and the
documentation updates.
The TableLayout was implemented starting from MxTable and
ClutterBoxLayout.
http://bugzilla.clutter-project.org/show_bug.cgi?id=2038
Signed-off-by: Emmanuele Bassi <ebassi@linux.intel.com>
Layout managers are using the same code to allocate a child while taking
into consideration:
• horizontal and vertical alignment
• horizontal and vertical fill
• the preferred minimum and natural size, depending
on the :request-mode property
• the text direction for the horizontal alignment
• an offset given by the fixed position properties
Given the amount of code involved, and the amount of details that can go
horribly wrong while copy and pasting such code in various classes - let
alone various projects - Clutter should provide an allocate() variant
that does the right thing in the right way. This way, we have a single
point of failure.
Some apps or some use cases don't need to clear the stage on immediate
rendering GPUs. A media player playing a fullscreen video or a
tile-based game, for instance.
These apps are redrawing the whole screen, so we can avoid clearing the
color buffer when preparing to paint the stage, since there is no
blending with the stage color being performed.
We can add an private set of hints to ClutterStage, and expose accessors
for each potential hint; the first hint is the 'no-clear' one.
http://bugzilla.clutter-project.org/show_bug.cgi?id=2058
This adds a publicly exposed experimental API for a 3D texture
backend. There is a feature flag which can be checked for whether 3D
textures are supported. Although we require OpenGL 1.2 which has 3D
textures in core, GLES only provides them through an extension so the
feature can be used to detect that.
The textures can be created with one of two new API functions :-
cogl_texture_3d_new_with_size
and
cogl_texture_3d_new_from_data
There is also internally a new_from_bitmap function. new_from_data is
implemented in terms of this function.
The two constructors are effectively the only way to upload data to a
3D texture. It does not work to call glTexImage2D with the
GL_TEXTURE_3D target so the virtual for cogl_texture_set_region does
nothing. It would be possible to make cogl_texture_get_data do
something sensible like returning all of the images as a single long
image but this is not currently implemented and instead the virtual
just always fails. We may want to add API specific to the 3D texture
backend to get and set a sub region of the texture.
All of those three functions can throw a GError. This will happen if
the GPU does not support 3D textures or it does not support NPOTs and
an NPOT size is requested. It will also fail if the FBO extension is
not supported and the COGL_TEXTURE_NO_AUTO_MIPMAP flag is not
given. This could be avoided by copying the code for the
GL_GENERATE_MIPMAP TexParameter fallback, but in the interests of
keeping the code simple this is not yet done.
This adds a couple of functions to cogl-texture-driver for uploading
3D data and querying the 3D proxy
texture. prep_gl_for_pixels_upload_full now also takes sets the
GL_UNPACK_IMAGE_HEIGHT parameter so that 3D textures can have padding
between the images. Whenever 3D texture is uploading, both the height
of the images and the height of all of the data is specified (either
explicitly or implicilty from the CoglBitmap) so that the image height
can be deduced by dividing by the depth.
There are many places in the texture backend that need to do
conversion using the CoglBitmap code. Currently none of these
functions can throw an error but they do return a value to indicate
failure. In future it would make sense if new texture functions could
throw an error and in that case they would want to use a CoglBitmap
error if the failure was due to the conversion. This moves the
internal CoglBitmap error from the quartz backend to be public in
cogl-bitmap.h so that it can be used in this way.
This adds a new API call to enable point sprite coordinate generation
for a material layer:
void
cogl_material_set_layer_point_sprite_coords_enabled (CoglHandle material,
int layer_index,
gboolean enable);
There is also a corresponding get function.
Enabling point sprite coords simply sets the GL_COORD_REPLACE of the
GL_POINT_SPRITE glTexEnv when flusing the material. There is no
separate application control for glEnable(GL_POINT_SPRITE). Instead it
is left permanently enabled under the assumption that it has no affect
unless GL_COORD_REPLACE is enabled for a texture unit.
http://bugzilla.openedhand.com/show_bug.cgi?id=2047
* cally-merge:
cally: Add introspection generation
cally: Improving cally doc
cally: Cleaning CallyText
cally: Refactoring "window:create" and "window:destroy" emission code
cally: Use proper backend information on CallyActor
cally: Check HAVE_CONFIG_H on cally-util.c
docs: Fix Cally documentation
cally: Clean up the headers
Add binaries of the Cally examples to the ignore file
docs: Add Cally API reference
Avoid to load cally module on a11y examples
Add accessibility tests
Initialize accessibility support on clutter_init
Rename some methods and includes to avoid -Wshadow warnings
Cally initialization code
Add Cally
Make Cally follow the single-include header file policy of Clutter and
Cogl; this means making cally.h the single include header, and requires
a new cally-main.h file for the functions defined by cally.h.
Also:
• clean up the licensing notice and remove the FSF address;
• document the object structures (instance and class);
• G_GNUC_CONST-ify the get_type() functions;
• reduce the padding for CallyActor sub-classes;
• reduce the amount of headers included.
The documentation for cogl_vertex_buffer_indices_get_for_quads was
using ugly ASCII art to draw the diagrams. These have now been
replaced with PNG figures.
CoglMaterialWrapMode was missing from the cogl-sections.txt file so it
wasn't getting displayed. There were also no documented return values
from the getters.
This adds two new API calls- cogl_path_set_fill_rule and
cogl_path_get_fill_rule. This allows modifying the fill rule of the
current path. In addition to the previous default fill rule of
'even-odd' it now supports the 'non-zero' rule. The fill rule is a
property of the path (not the Cogl context) so creating a new path or
preserving a path with cogl_path_get_handle affects the fill rule.
This adds a separate variable name "CLUTTER_SONAME_INFIX" to define the
infix for the clutter library that gets linked. Currently the WINSYS
corresponds to the directory we enter when building to compile the
window system and input support, but it is desirable to be able to
define multiple flavours that use the same WINSYS but should result in
different library names.
For example we are planning to combine the eglx and eglnative window
systems into one "egl" winsys but we will need to preserve the current
library names for the eglx and eglnative flavours.
cogl_ortho is one of those APIs whos style was, for better or worse,
copied from OpenGL and for some inexplicable reason the near and far
arguments are inconsistent with the left, right, top, bottom arguments
because they don't take z coordinates they take a "distance" which
should be negative for a plane behind the viewer.
This updates the documentation to explain this.
* wip/deform-effect:
docs: Add DeformEffect and PageTurnEffect to the API reference
effect: Add PageTurnEffect
effect: Add DeformEffect
offscreen-effect: Traslate the modelview with the offsets
docs: Fix Effect subclassing section
It is often useful to determine if one actor is an ancestor of
another. Add a method to do that.
http://bugzilla.openedhand.com/show_bug.cgi?id=2162
Signed-off-by: Emmanuele Bassi <ebassi@linux.intel.com>
By default, ShaderEffect creates a fragment shader; in order to be able
to deprecate ClutterShader we need a way for ShaderEffect sub-classes to
create a vertex shader if needed - By using a write-only, constructor
only property.
ClutterShader has, internally, a ClutterShaderType enumeration that can
be used exactly for this. We just need to expose it and create a GObject
property for ClutterShaderEffect.
We only had getters for the red, green, blue and alpha channels of a
color. This meant that, if you wanted to change, say, the alpha
component of a color, one would need to query the red, green and blue
channels and use set_from_4ub() or set_from_4f().
Instead of this, just provide some setters for CoglColor, using the same
naming scheme than the existing getters.
For some operations on pre-multiplied colors (say, replace the alpha
value), you need to unpremultiply the color.
This patch provides the counterpart to cogl_color_premultiply().
