gallium,mesa/st: Add PIPE_CONTEXT_NO_LOD_BIAS flag

While desktop GL supports sampler LOD bias, GLES does not. To support the GL use
case, all Gallium drivers are expected to handle sampler LOD bias. However, this
may require shader code to implement (lowering tex to txb, txl to fadd+txl) and
cost resources to push the LOD bias constants into the shader. The issue is
compounded with something like Dolphin's GLES renderer, which does this LOD bias
emulation itself -- meaning that LOD bias is lowered twice when using Dolphin
with GLES! As such, this commit adds a context flag for frontends to communicate
that they will never use sampler LOD bias, allowing the driver to omit the
lowering as a GLES fast path (or, for Dolphin, for performance parity between
GLES and GL).

This will be used on Asahi. It could also be used to optimize a path on
Mali-T720 supported in Panfrost, though I don't intend to write that patch.

Originally https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/25034

Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/25052>

diff --git a/src/gallium/include/pipe/p_defines.h b/src/gallium/include/pipe/p_defines.h
index 3b9a6a9..3a62986 100644 (file)
--- a/src/gallium/include/pipe/p_defines.h
+++ b/src/gallium/include/pipe/p_defines.h
@@ -394,6 +394,15 @@ enum pipe_flush_flags
 #define PIPE_CONTEXT_PROTECTED         (1 << 7)
 
 /**
+ * Create a context that does not use sampler LOD bias. If this is set, the
+ * frontend MUST set pipe_sampler_state::lod_bias to 0.0f for all samplers used
+ * with the context. Drivers MAY ignore lod_bias for such contexts.
+ *
+ * This may allow driver fast paths for GLES, which lacks sampler LOD bias.
+ */
+#define PIPE_CONTEXT_NO_LOD_BIAS (1 << 8)
+
+/**
  * Flags for pipe_context::memory_barrier.
  */
 #define PIPE_BARRIER_MAPPED_BUFFER     (1 << 0)

diff --git a/src/mesa/state_tracker/st_manager.c b/src/mesa/state_tracker/st_manager.c
index 5176cca..34938b4 100644 (file)
--- a/src/mesa/state_tracker/st_manager.c
+++ b/src/mesa/state_tracker/st_manager.c
@@ -978,8 +978,15 @@ st_api_create_context(struct pipe_frontend_screen *fscreen,
    if (attribs->flags & ST_CONTEXT_FLAG_NO_ERROR)
       no_error = true;
 
+   /* OpenGL ES 2.0+ does not support sampler state LOD bias. If we are creating
+    * a GLES context, communicate that to the the driver to allow optimization.
+    */
+   bool is_gles = attribs->profile == API_OPENGLES2;
+   unsigned lod_bias_flag = is_gles ? PIPE_CONTEXT_NO_LOD_BIAS : 0;
+
    pipe = fscreen->screen->context_create(fscreen->screen, NULL,
                                           PIPE_CONTEXT_PREFER_THREADED |
+                                          lod_bias_flag |
                                           attribs->context_flags);
    if (!pipe) {
       *error = ST_CONTEXT_ERROR_NO_MEMORY;