Add a GSK_GPU_IMAGE_STRAIGHT_ALPHA and use it for images that have
straight alpha.
Make sure those images get passed through a premultiplying pass with
the new straight alpha shader.
Also remove the old Postprocess flags from the Vulkan image that were a
leftover from copying that code from the old Vulkan renderer.
There's multiple uses I want it for:
1. Generating the box-shadow area for blurring
2. Generating masks for rounded-rect masking
3. Optimizing the common use case of rounded-clip + color
Only the last one is implemented in this commit.
The code generated by glslc -O is optimized worse by Mesa than
code generated unoptimized.
So generate unoptimized code until somebody figures out what's going
wrong here.
... and use it for glyphs.
The name is a slight variation of the "coloring" name from the GL
renderer.
The functionality is exactly what the "glyph" shader from the Vulkan
renderer does.
Pretty much a copy of the Vulkan border shader.
A notable change is that the input arguments are changed, because GL
gets confused if you put a mat4 at the end.
This heaves over an inital chunk of code from the Vulkan renderer to
execute shaders.
The only shader that exists for now is a shader that draws a single
texture.
We use that to replace the blit op we were doing before.
