[Mesa-dev] [PATCH 3/3] st/mesa: round lod_bias to a multiple of 1/256

[Marek Olšák]

From: Marek Olšák <marek.olsak at amd.com>

This reduces the number of sampler states 3.6x in Batman Arkham: Origins.
(from ~7200 to ~2000)
---
 src/mesa/state_tracker/st_atom_sampler.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/src/mesa/state_tracker/st_atom_sampler.c b/src/mesa/state_tracker/st_atom_sampler.c
index 4568630..daf98c3 100644
--- a/src/mesa/state_tracker/st_atom_sampler.c
+++ b/src/mesa/state_tracker/st_atom_sampler.c
@@ -152,20 +152,26 @@ convert_sampler(struct st_context *st,
    sampler->wrap_r = gl_wrap_xlate(msamp->WrapR);
 
    sampler->min_img_filter = gl_filter_to_img_filter(msamp->MinFilter);
    sampler->min_mip_filter = gl_filter_to_mip_filter(msamp->MinFilter);
    sampler->mag_img_filter = gl_filter_to_img_filter(msamp->MagFilter);
 
    if (texobj->Target != GL_TEXTURE_RECTANGLE_ARB)
       sampler->normalized_coords = 1;
 
    sampler->lod_bias = ctx->Texture.Unit[texUnit].LodBias + msamp->LodBias;
+   /* Reduce the number of states by allowing only the values that AMD GCN
+    * can represent. Apps use lod_bias for smooth transitions to bigger mipmap
+    * levels.
+    */
+   sampler->lod_bias = CLAMP(sampler->lod_bias, -16, 16);
+   sampler->lod_bias = floorf(sampler->lod_bias * 256) / 256;
 
    sampler->min_lod = MAX2(msamp->MinLod, 0.0f);
    sampler->max_lod = msamp->MaxLod;
    if (sampler->max_lod < sampler->min_lod) {
       /* The GL spec doesn't seem to specify what to do in this case.
        * Swap the values.
        */
       float tmp = sampler->max_lod;
       sampler->max_lod = sampler->min_lod;
       sampler->min_lod = tmp;
-- 
2.7.4