Rework texture streaming and tracking.

This is a big one:
- Reworks the discard signal almost entirely.  Now has a normalized 0..1 discard signal: distance x size x channel exponent, floored by staleness and background app state.  Shaped by VRAM pressure.
- Textures can now scale down to the smallest GPU mip (1×1), independent of the codec's encoded mip
  count.
- Terrain texture LOD now works.  Useful for 2K textures and PBR on terrain.  Based upon camera distance to nearest terrain patch.
- New texture quality setting.  Low/Medium/High/Ultra
  - Caps texture resolution on Low to 1024, and otherwise shifts the discard signal around.  Makes distance based texture LOD work a lot more predictably.
- We now track last bind state for textures, and discard accordingly.  We progressively discard based upon last bind time.
- Avatar textures get a residency boost to stay loaded in VRAM longer under pressure.

1 files changed, 14 insertions, 0 deletions

diff --git a/indra/llrender/llrender.cpp b/indra/llrender/llrender.cpp
index 1a3a499b20..696a0d145f 100644
--- a/indra/llrender/llrender.cpp
+++ b/indra/llrender/llrender.cpp
@@ -197,6 +197,9 @@ void LLTexUnit::bindFast(LLTexture* texture)
     glActiveTexture(GL_TEXTURE0 + mIndex);
     gGL.mCurrTextureUnitIndex = mIndex;
     mCurrTexture = gl_tex->getTexName();
+    // bindFast bypasses updateBindStats(); stamp directly so the staleness
+    // signal sees per-frame use of batched textures.
+    gl_tex->stampBound();
     if (!mCurrTexture)
     {
         LL_PROFILE_ZONE_NAMED("MISSING TEXTURE");
@@ -249,11 +252,17 @@ bool LLTexUnit::bind(LLTexture* texture, bool for_rendering, bool forceBind)
                         setTextureFilteringOption(gl_tex->mFilterOption);
                     }
                 }
+                else
+                {
+                    // Already current - still being used, keep it fresh.
+                    gl_tex->stampBound();
+                }
             }
             else
             {
                 //if deleted, will re-generate it immediately
                 texture->forceImmediateUpdate() ;
+                gl_tex->stampBound();
 
                 gl_tex->forceUpdateBindStats() ;
                 return texture->bindDefaultImage(mIndex);
@@ -325,6 +334,11 @@ bool LLTexUnit::bind(LLImageGL* texture, bool for_rendering, bool forceBind, S32
             stop_glerror();
         }
     }
+    else
+    {
+        // Already current - still being used, keep it fresh.
+        texture->stampBound();
+    }
 
     stop_glerror();