[Fix, Test] (MG_Backend/DirectGLES, MG_Util, CI): keep an explicit LOD constant under a new avoid flag - folding the bias uniform into it kills the ANGLE llvmpipe JIT

MobileGL/Config.h

@@ -89,6 +89,13 @@ namespace MobileGL::MG_Config {
         // MOBILEGL_AVOID_SAMPLER_MIPMAP_MIN_FILTER: avoid mipmap min filters in samplers,
         // resolves certain rendering bugs on ANGLE + llvmpipe.
         Bool AvoidSamplerMipmapMinFilter = false;
+        // MOBILEGL_AVOID_EXPLICIT_LOD_BIAS: leave an already-explicit LOD argument alone when
+        // emulating GL_TEXTURE_LOD_BIAS, instead of adding the bias uniform to it. Injecting
+        // the uniform turns a compile-time-constant LOD into a runtime expression, which
+        // sends ANGLE + llvmpipe down a mip-selection path that dereferences a NULL
+        // descriptor and kills the process. Deviates from spec (Vulkan adds the bias to
+        // OpImageSampleExplicitLod), so it is an avoidance for that stack only.
+        Bool AvoidExplicitLodBias = false;
         // MOBILEGL_COHERENT_AS_FLUSH: app-compat for engines (e.g. Flywheel) that write
         // GPU-read data through persistent GL_MAP_FLUSH_EXPLICIT_BIT maps they never
         // flush. Persistent FLUSH_EXPLICIT map requests are rewritten to coherent

MobileGL/ConfigLoader.cpp

@@ -171,6 +171,7 @@ namespace MobileGL::MG_ConfigLoader {
         features.MagmaFramesInFlight = QueryEnvUint32("MOBILEGL_MAGMA_FRAMESINFLIGHT", 3, 1, 64);
         features.AvoidSamplerMipmapMinFilter =
             QueryEnvFlag("MOBILEGL_AVOID_SAMPLER_MIPMAP_MIN_FILTER");
+        features.AvoidExplicitLodBias = QueryEnvFlag("MOBILEGL_AVOID_EXPLICIT_LOD_BIAS");
         features.CoherentAsFlush = QueryEnvFlag("MOBILEGL_COHERENT_AS_FLUSH");
         features.TraceSkipAutodestroy = QueryEnvFlag("MOBILEGL_TRACE_SKIP_AUTODESTROY");
         features.DisableUboRing = QueryEnvFlag("MOBILEGL_DISABLE_UBO_RING");

MobileGL/MG_Backend/DirectGLES/Managers.cpp

@@ -55,6 +55,12 @@ namespace MobileGL::MG_Backend::DirectGLES {
         return g_GLESCapabilities.AvoidSamplerMipmapMinFilter;
     }
 
+    static Bool ShouldAvoidExplicitLodBiasOnAngleLlvmpipe() {
+        // IsAngleLlvmpipeRenderer combined with the MOBILEGL_AVOID_EXPLICIT_LOD_BIAS
+        // feature toggle, both resolved in FillInGLESCapabilities.
+        return g_GLESCapabilities.AvoidExplicitLodBias;
+    }
+
     static GLenum ResolveBackendMinFilter(const SamplerParameters& samplerParams,
                                           Bool avoidMipmapMinFilter) {
         GLenum filter = MG_Util::ConvertSamplerFilterModeToGLEnum(samplerParams.minFilter,
@@ -4466,7 +4472,7 @@ namespace MobileGL::MG_Backend::DirectGLES {
                 source = ProcessOutColorLocations(source);
                 source = ForceFlatIntegerVaryings(source, glShaderType);
                 source = BroadcastLegacyFragColor(std::move(source), glShaderType, m_fragColorBroadcastCount);
-                source = EmulateTextureLodBias(source);
+                source = EmulateTextureLodBias(source, ShouldAvoidExplicitLodBiasOnAngleLlvmpipe());
                 source = EmulateBaseInstanceInVertexShader(std::move(source), glShaderType);
                 source = PromoteDrawParameterGlobalsToUniforms(std::move(source), glShaderType);
                 source = ForceSupporterOutput(source);

MobileGL/MG_Backend/DirectGLES/Utils.cpp

@@ -957,7 +957,7 @@ namespace MobileGL::MG_Backend::DirectGLES {
             }
         } // namespace
 
-        String EmulateTextureLodBias(const String& glslCode) {
+        String EmulateTextureLodBias(const String& glslCode, Bool avoidExplicitLodBias) {
 #ifdef TRACY_ENABLE
             ZoneScopedC(TRACY_ZONECOLOR_BACKEND);
 #endif
@@ -1018,6 +1018,11 @@ namespace MobileGL::MG_Backend::DirectGLES {
                 if (samplerIt == samplerNames.end()) continue;
 
                 const String& biasName = samplerIt->second;
+                if (form->explicitLodArg >= 0 && avoidExplicitLodBias) {
+                    // The lookup already names its level; leaving it alone keeps a constant
+                    // LOD constant. Costs the bias on explicit-LOD lookups only.
+                    continue;
+                }
                 if (form->explicitLodArg >= 0) {
                     // Explicit LOD: the bias adds to it, as Vulkan does for
                     // OpImageSampleExplicitLod and as the CTS reference expects.

MobileGL/MG_Backend/DirectGLES/Utils.h

@@ -183,7 +183,12 @@ namespace MobileGL::MG_Backend::DirectGLES {
         // the bound texture's (or sampler object's) value into it; a shader whose samplers
         // all have a zero bias is therefore unaffected. Returns the source unchanged when
         // there is nothing to rewrite.
-        String EmulateTextureLodBias(const String& glslCode);
+        //
+        // avoidExplicitLodBias leaves lookups that already carry an explicit LOD untouched,
+        // so their constant level stays constant; only the implicit-LOD forms take the bias.
+        // Off by default and only ever set on ANGLE + llvmpipe, where injecting the uniform
+        // into a constant LOD crashes the driver (MOBILEGL_AVOID_EXPLICIT_LOD_BIAS).
+        String EmulateTextureLodBias(const String& glslCode, Bool avoidExplicitLodBias = false);
     } // namespace PrgramImpl
 
     namespace Utils {

MobileGL/MG_Util/BackendLoaders/OpenGL/Loader.cpp

@@ -1343,6 +1343,8 @@ namespace MobileGL::MG_Util::BackendLoader {
             caps.IsAngleRenderer && caps.GLESRendererString.find("llvmpipe") != String::npos;
         caps.AvoidSamplerMipmapMinFilter =
             caps.IsAngleLlvmpipeRenderer && MG_Config::Features.AvoidSamplerMipmapMinFilter;
+        caps.AvoidExplicitLodBias =
+            caps.IsAngleLlvmpipeRenderer && MG_Config::Features.AvoidExplicitLodBias;
         MGLOG_I("    GL_EXT_disjoint_timer_query supported: %s",
                 caps.SupportsDisjointTimerQuery ? "true" : "false");
         MGLOG_I("    GL_KHR_parallel_shader_compile supported: %s",
@@ -1351,6 +1353,7 @@ namespace MobileGL::MG_Util::BackendLoader {
         MGLOG_I("    ANGLE llvmpipe renderer: %s", caps.IsAngleLlvmpipeRenderer ? "true" : "false");
         MGLOG_I("    Avoid sampler mipmap min filter: %s",
                 caps.AvoidSamplerMipmapMinFilter ? "true" : "false");
+        MGLOG_I("    Avoid explicit LOD bias: %s", caps.AvoidExplicitLodBias ? "true" : "false");
 
         return true;
     }

MobileGL/MG_Util/BackendLoaders/OpenGL/Loader.h

@@ -1156,6 +1156,9 @@ namespace MobileGL {
             // MOBILEGL_AVOID_SAMPLER_MIPMAP_MIN_FILTER feature toggle:
             // sampler min filters should drop their mipmap component.
             Bool AvoidSamplerMipmapMinFilter = false;
+            // IsAngleLlvmpipeRenderer combined with the MOBILEGL_AVOID_EXPLICIT_LOD_BIAS
+            // feature toggle: LOD-bias emulation should not touch explicit-LOD lookups.
+            Bool AvoidExplicitLodBias = false;
             // True when indirect draws leak the command's baseInstance word ("reserved,
             // must be zero" in unextended ES) into gl_InstanceID. Conforming ES drivers
             // keep gl_InstanceID zero-based; ANGLE's Vulkan backend hands the command