Hi all, Certain embedded GPUs do not implement coordinate transformation in hardware. Instead, section 12.5 "Coordinate Transformation" of the ES 3.2 specification is implemented in the vertex shader itself. Relevant examples include Midgard and vc4.
To handle this, a lowering pass is needed to convert gl_Position writes to screen space writes. The vc4 driver lowers this in the backend IR; however, I don't think the pass needs to be specialised to the backend. For Midgard, I have written a NIR lowering pass to implement the same, which enables the lowered instructions themselves to be optimised. At the moment, this pass lives inside the (downstream) Midgard compiler. In the future, it will be necessary for the Bifrost compiler as well, should that use NIR. That said, Bifrost will share the same Gallium driver, so the pass could still live in the driver (src/gallium/drivers/panfrost). Should this pass be moved into common code (src/compiler/nir)? If so, what would the driver agnostic way of passing viewport parameters be? Both vc4 and Midgard currently use/will use special uniforms for this purpose. Similarly, is there a driver agnostic way of representing the transformed write? The Midgard pass emits `nir_instrinic_store_output` for the final value, but I'm not sure if this is generalisable. I can send the Midgard code as an RFC if there's interest. Thanks, -Alyssa _______________________________________________ mesa-dev mailing list mesa-dev@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/mesa-dev
