without having looked at your particular shader code, I can only imagine the horrors and countless of hours that went into writing and debugging the shader code...
Which OpenGL and GLSL versions are you targeting?
I've been thinking about possibly prototyping integrating an SVG renderer into my game engine that would rasterize the textures from .svg files on content load. Would offer some benefits of improved packing and better scaling and resolution independence. Using an GPU based solution would offer the benefit of being able to skip the whole "rasterize on CPU then upload" dance but just rasterize directly into a texture render target in some FBO and then use the texture later on. That being said CPU based solution is definitely easier and more bullet proof ;-)