read
abstract fun readPixelsToBuffer(x: Int, y: Int, width: Int, height: Int, format: Int, type: Int, offset: Int)
glReadPixels variant that writes into the buffer currently bound to GL_PIXEL_PACK_BUFFER at byte offset from its start. Non-blocking on the CPU side - the GPU continues to fill the PBO asynchronously. Pair with fenceSync / isSyncSignalled to know when the data is ready, then getBufferSubData to drain it. Requires GLES3+ / WebGL2 / GL3+; falls back to a synchronous CPU-target readPixels is the responsibility of the caller when those features aren't available.