This is another example for a 2-texture shader.
So far, only separable blend modes are implemented.
The implementation is not optimized, with an
if-else cascade in the shader.
We were looking at uninitialized memory here, instead
of the type of the source clip, as we should.
This showed up as mispositioned clip in the first frame
of a crossfade stack transition, and also as overdraw in
sliding stack transitions.
We already move the descriptor set layout out of it,
so we can just as well keep the pipeline layouts in
the render object as well, and get rid of this extra
object. Update all callers.
Instead of doing multiple copy commands with a tiny buffer
for each glyph, we can just batch them all together. This
also avoids the issue of creating multiple barriers for the
same image.
By tracking the last transition we can build the appropriate barriers.
Also use the most appropriate initial layout/access at creation :
for linear image : predefined (we prepare the content ourself through memcpy)
for everything else : undefined (we don't care about the content, will most likely be erase)
Move the glyph caching api to something that can support using
multiple textures. We now split the text render ops into multiple
ops for different textures, and make each op render just a substring
of the text node's glyph string.
This is just a proof of concept - we use a single 1024x1024 surface,
and just give up when we run out of space. The cache is populated
incrementally, and items are never removed.
This commit takes several steps towards rendering text
like we want to.
The creation of the cairo surface and texture is moved
to the backend (in GskVulkanRenderer). We add a mask
shader that is used in the next text pipeline to use
the texture as a mask, like cairo_mask_surface does.
There is a separate color text pipeline that uses the
already existing blend shaders to use the texture as
a source, like cairo_paint does.
The text node api is simplified to have just a single
offset, which determines the left end of the text baseline,
like all our other text drawing APIs.
This fixes the proper dependencies getting set up for generating
the shaders and only the necessary things getting rebuilt on
resources changing in gsk.
Currently, this information is not used since cairo_show_glyphs
deals with color glyphs for us. But when we get to uploading
glyphs to a texture atlas, we will need it to do the right thing.
We don't look at individual glyphs here, but just whether the
font has the has-color flag set. In practice, all glyphs in
such a font will be color glyphs, and we can avoid loading all
the glyphs this way.
