* opengl: remove unnecessery glflush calls
glflushing forces the driver to break batching and issue commands
prematurely and prevents optimisations like command reordering and
merging.
many glFunctions already internally glflushes and eglsync creation still
has a glflush at end render. so lets reduce the overhead of these calls.
* opengl: reduce glUseProgram calls
apitrace shows cases where the same program gets called multiple times,
add a helper function that keeps track of current program and only call
it once on same program. reduces slight overhead.
* opengl: use more efficient vertex array object
use a more modern vertex array object approach with the shaders, makes
it a onetime setup on shader creation instead of once per drawcall, also
should make the driver not have to revalidate the vertex format on each
call.
ensure framebuffer textures are detached and deleted, avoid leaving framebuffers bound when not needed
* render: avoid calling glDeleteProgram on no program
its safe to do so but it adds a bunch of unnecessery lines in apitrace
when tracing. if guard it and return early.
* opengl: ensure texture and buffers are unbound
ensure bound buffers are unbound after use, also detach textures from
framebuffer before deleting it otherwise it will become dangling and
essentially leak.
