[Fix] (MG_Impl, DirectGLES): answer the texture-gather offset limit queries

glGetIntegerv(GL_MIN_PROGRAM_TEXTURE_GATHER_OFFSET) and its GL_MAX_ counterpart fell
through to the default arm of the getter and raised GL_INVALID_ENUM, leaving the
caller's variable untouched - KHR-GL40.texture_gather.api-enums read back the
uninitialised 32764 that happened to be on its stack and failed on the error alone.

Both are core state from GL 4.0 (table 23.53) and from ES 3.1 (table 20.40), so the
value is simply the host driver's, probed alongside the other limits in
FillInGLESCapabilities and carried to the getter through DynamicBackendParameters.
The probe result is widened to the -8/+7 core minimums rather than trusted blindly:
a driver that leaves the out-parameter alone (no ES 3.1, or an enum it ignores) would
otherwise hand us a range narrower than GL 4.0 requires MobileGL to advertise, and
the shaders the CTS builds assume the guaranteed range regardless.

MobileGL/MG_Backend/BackendObject.h

@@ -288,6 +288,10 @@ namespace MobileGL {
             Int MaxIntegerSamples = 1;
             Int MaxSamples = 1;
             Int MaxSampleMaskWords = 1;
+            // GL_MIN/MAX_PROGRAM_TEXTURE_GATHER_OFFSET. Defaults are the GL 4.0 core
+            // minimums, which every ES 3.1 driver also guarantees.
+            Int MinProgramTextureGatherOffset = -8;
+            Int MaxProgramTextureGatherOffset = 7;
             Int MaxTextureImageUnits = 32;
             Int MaxVertexTextureImageUnits = 32;
             Int MaxComputeTextureImageUnits = 32;

MobileGL/MG_Backend/DirectGLES/BackendObject_DirectGLES.cpp

@@ -1072,6 +1072,8 @@ namespace MobileGL::MG_Backend::DirectGLES {
         m_dynamicParameters.MaxIntegerSamples = m_GLESCapabilities.MaxIntegerSamples;
         m_dynamicParameters.MaxSamples = m_GLESCapabilities.MaxSamples;
         m_dynamicParameters.MaxSampleMaskWords = m_GLESCapabilities.MaxSampleMaskWords;
+        m_dynamicParameters.MinProgramTextureGatherOffset = m_GLESCapabilities.MinProgramTextureGatherOffset;
+        m_dynamicParameters.MaxProgramTextureGatherOffset = m_GLESCapabilities.MaxProgramTextureGatherOffset;
         // Clamp the advertised sampler limits the same way the DirectVulkan backend does: per-stage
         // GL_MAX_TEXTURE_IMAGE_UNITS must never exceed host-side fixed arrays sized off it (e.g.
         // Minecraft's 128-entry Blaze3D GlStateManager.TEXTURES[], iterated by Iris), and the combined

MobileGL/MG_Impl/GLImpl/Getter/GL_Getter.cpp

@@ -1912,6 +1912,12 @@ namespace MobileGL::MG_Impl::GLImpl {
         case GL_MAX_SAMPLE_MASK_WORDS:
             *params = dynamicParameters.MaxSampleMaskWords;
             break;
+        case GL_MIN_PROGRAM_TEXTURE_GATHER_OFFSET:
+            *params = dynamicParameters.MinProgramTextureGatherOffset;
+            break;
+        case GL_MAX_PROGRAM_TEXTURE_GATHER_OFFSET:
+            *params = dynamicParameters.MaxProgramTextureGatherOffset;
+            break;
         case GL_MAX_SHADER_STORAGE_BUFFER_BINDINGS:
             *params = static_cast<GLint>(GetIndexedBufferQueryPointCount(BufferTarget::ShaderStorage));
             break;

MobileGL/MG_Util/BackendLoaders/OpenGL/Loader.cpp

@@ -916,6 +916,10 @@ namespace MobileGL::MG_Util::BackendLoader {
         GLfloat minFragmentInterpolationOffset = -0.5f;
         GLfloat maxFragmentInterpolationOffset = 0.4375f;
         GLint fragmentInterpolationOffsetBits = 4;
+        // Core minimums of both APIs (GL 4.6 table 23.53, ES 3.1 table 20.40); the probe
+        // below only ever widens them.
+        GLint minProgramTextureGatherOffset = -8;
+        GLint maxProgramTextureGatherOffset = 7;
         glesFuncs.glGetFloatv(GL_ALIASED_LINE_WIDTH_RANGE, aliasedLineWidthRange);
         glesFuncs.glGetFloatv(GL_SMOOTH_LINE_WIDTH_RANGE, smoothLineWidthRange);
         glesFuncs.glGetFloatv(GL_SMOOTH_LINE_WIDTH_GRANULARITY, &smoothLineWidthGranularity);
@@ -944,6 +948,12 @@ namespace MobileGL::MG_Util::BackendLoader {
         // single test case. 1 is a spec-legal value (the minimum required), so cap
         // to what is actually implemented instead of forwarding the raw driver limit.
         maxSampleMaskWords = std::min(maxSampleMaskWords, 1);
+        glesFuncs.glGetIntegerv(GL_MIN_PROGRAM_TEXTURE_GATHER_OFFSET, &minProgramTextureGatherOffset);
+        glesFuncs.glGetIntegerv(GL_MAX_PROGRAM_TEXTURE_GATHER_OFFSET, &maxProgramTextureGatherOffset);
+        // A driver that leaves the probe untouched (pre-ES 3.1, or an ignored enum) must not
+        // drag the advertised range below what GL 4.0 requires of us.
+        minProgramTextureGatherOffset = std::min(minProgramTextureGatherOffset, -8);
+        maxProgramTextureGatherOffset = std::max(maxProgramTextureGatherOffset, 7);
         glesFuncs.glGetIntegerv(GL_MAX_TEXTURE_IMAGE_UNITS, &maxTextureImageUnits);
         glesFuncs.glGetIntegerv(GL_MAX_VERTEX_TEXTURE_IMAGE_UNITS, &maxVertexTextureImageUnits);
         glesFuncs.glGetIntegerv(GL_MAX_COMPUTE_TEXTURE_IMAGE_UNITS, &maxComputeTextureImageUnits);
@@ -1027,6 +1037,8 @@ namespace MobileGL::MG_Util::BackendLoader {
         caps.MaxIntegerSamples = maxIntegerSamples;
         caps.MaxSamples = maxSamples;
         caps.MaxSampleMaskWords = maxSampleMaskWords;
+        caps.MinProgramTextureGatherOffset = minProgramTextureGatherOffset;
+        caps.MaxProgramTextureGatherOffset = maxProgramTextureGatherOffset;
         caps.MaxTextureImageUnits = maxTextureImageUnits;
         caps.MaxVertexTextureImageUnits = maxVertexTextureImageUnits;
         caps.MaxComputeTextureImageUnits = maxComputeTextureImageUnits;

MobileGL/MG_Util/BackendLoaders/OpenGL/Loader.h

@@ -1102,6 +1102,8 @@ namespace MobileGL {
             Int MaxIntegerSamples = 1;
             Int MaxSamples = 1;
             Int MaxSampleMaskWords = 1;
+            Int MinProgramTextureGatherOffset = -8;
+            Int MaxProgramTextureGatherOffset = 7;
             Int MaxTextureImageUnits = 32;
             Int MaxVertexTextureImageUnits = 32;
             Int MaxComputeTextureImageUnits = 32;