filter2d can render into a destination FBO
add RendererTexture, usefull to debug/display a Texture
FBO add makeP2 to create texture with size power of 2
experiment rendering "distance field" into texture for quicker reuse in raymarching
fbo: allow to keep texture/framebuffer after dispose
glf_rendererr: add makeExtrudeZinTex to speedup rendering of static object created by extrusion on Z axis