This implements a variation of frustum culling whereby we convert screen
space clip rectangles into eye space mini-frustums so that we don't have
to repeatedly transform actor paint-volumes all the way into screen
coordinates to perform culling, we just have to apply the modelview
transform and then determine each points distance from the planes that
make up the clip frustum.
By avoiding the projective transform, perspective divide and viewport
scale for each point culled this makes culling much cheaper.
OpenGL < 4.0 only supports integer based viewports and internally we
have a mixture of code using floats and integers for viewports. This
patch switches all viewports throughout clutter and cogl to be
represented using floats considering that in the future we may want to
take advantage of floating point viewports with modern hardware/drivers.
When transforming a paint-volume or transforming allocation vertices we
are transforming more than one point at a time so we can batch those
together with cogl_matrix_transform_points instead of
cogl_matrix_transform_point. Also in both of these cases we don't need
to do a projective transform so using cogl_matrix_transform_points also
lets us reduce the per-vertex computation.
The paint volume structure is cached in the Actor it references, and
this causes a reference cycle.
The paint volume is going to be used when painting, so the actor must
still be valid - otherwise Clutter will bail out far before than
accessing the actor pointer in ClutterPaintVolume.
Otherwise, we could have used dispose() to check for a valid actor and
remove a reference if the actor field is !NULL; it feels less clean,
though, since we're effectively managing an extra reference on
ourselves.
http://bugzilla.clutter-project.org/show_bug.cgi?id=2431
For Clone actors we will need a way to report the volume of the source
actor as the volume of the clone actor. To make this work though we need
to be able to replace the reference to the source actor with a reference
to the clone actor instead. This adds a private
_clutter_paint_volume_set_reference_actor function to do that.
This adds a way to initialize a paint volume from another source paint
volume. This lets us for instance pass the contents of one paint volume
back through the out param of a get_paint_volume implementation.
This splits out all the clutter_paint_volume code from clutter-actor.c
into clutter-paint-volume.c. Since clutter-actor.c and
clutter-paint-volume.c both needed the functionality of
_fully_transform_vertices, this function has now been moved to
clutter-utils.c as _clutter_util_fully_transform_vertices.
