Pre-compiled shaders in GLUP

[BrunoLevy]

Use SPIR-V pre-compiled shaders in GLUP

• try fullscreen effects first
• then implement a new GLUP context (that can cohabit with the existing ones) and a flag to enable it
• remove the old GLUP context

... and later

• Vulcan version (SPIR-V is a smooth transition towards that direction)

... and also, if possible

• Make GLUP a standalone library (usable in Polyscope for instance)

This may not work with WebGL that probably does not have pre-compiled shaders (but we might keep the WebGL context in the end, and only compile it in Emscripten mode)

SPIR-V documentation
Works mostly like GLSL shaders (pass a pre-compiled binary instead of an ASCII shader source). There are interesting differences that will make things easier for GLUP:

• a single SPIR-V binary can contain multiple stages / multiple entry points
• some constants can be specified (like templates): can be used to implement GLUP state toggles

and also some differences that will make it more difficult:

• location needs to be explicit (for all interface blocks)
• unfortunately it will not be possible to use the same source for OpenGL and Vulkan (because resource binding is too different)