render/gles2: simplify alpha depth check

GL_ALPHA_BITS is the number of bits of the alpha channel of the
currently bound frame buffer's color buffer -- which is precisely
renderer->current_buffer->rbo . Thus, instead of binding the color
buffer and checking its properties, we can query the already bound
frame buffer.

Note that GL_IMPLEMENTATION_COLOR_READ_{FORMAT,TYPE} are also
properties of frame buffer's color buffer.

0 files changed, 0 insertions, 0 deletions