This port the Blurring of blf fonts to the final drawing shader.
We add a bit of extra padding to each glyph so that jittering the texture
coord does not sample the neighbor glyphs.
I've made a separate version of the geom shader that works with full
3D modelviewmat.
This commit also includes some fixup inside blf_batching_start().
This means smaller imm buffer usage.
This does not reduce the number of drawcalls.
This uses geometry shader which is slow for the GPU but given we are really
CPU bound on this case, it should not matter.
A perfect implementation would:
- Set the glyph coord in a bufferTexture and just send the glyph ID to the
GPU to read the bufferTexture.
- Use GWN_draw_primitive and draw 2*strllen triangle and just retrieve the
glyph ID and color based on gl_VertexID / 6.
- Stream fixed size buffer that the Driver can discard quickly but this is
the same as improving IMM directly.
