[Feat] (MG_Backend, MG_Impl): expose experimental GL 4.6 CTS limits

MobileGL/MG_Backend/BackendObject.h

@@ -300,6 +300,13 @@ namespace MobileGL {
             Float ViewportBoundsRangeMin = 0.0f;
             Float ViewportBoundsRangeMax = 0.0f;
             Int ViewportSubpixelBits = 0;
+            // GL 4.x fragment-interpolation offset limits. These defaults are the
+            // core minimums and are replaced by live GLES/Vulkan device limits.
+            Float MinFragmentInterpolationOffset = -0.5f;
+            // For four fractional bits the greatest required legal offset is
+            // 0.5 - 2^-4 = 0.4375 (GL 4.6 table 23.70).
+            Float MaxFragmentInterpolationOffset = 0.4375f;
+            Int FragmentInterpolationOffsetBits = 4;
             Bool SupportsWideLines = false;
             SizeT MaxShaderStorageBlockSize = 128 * 1024 * 1024;
             Uint32 SubgroupSize = 0;

MobileGL/MG_Backend/DirectGLES/BackendObject_DirectGLES.cpp

@@ -20,6 +20,7 @@
 #include <MG_Util/Texture/TextureFormatProcessor.h>
 #include <Config.h>
 #include <algorithm>
+#include <cmath>
 #include <format>
 
 namespace MobileGL::MG_Backend::DirectGLES {
@@ -603,7 +604,7 @@ namespace MobileGL::MG_Backend::DirectGLES {
                 .ExtraVendor = Nullopt,              // Extra vendor
                 .RendererGLInfo =
                     {
-                        .TargetGLVersion = {3, 3, 0},   // Target OpenGL Version
+                        .TargetGLVersion = {4, 6, 0},   // Experimental GL CTS target version
                         .TargetGLSLVersion = {4, 6, 0}, // Target Shading Language Version
                         // Baseline advertisement (no timer queries / anisotropy yet); reconciled
                         // once the ES capabilities exist, see UpdateAdvertisedCapabilityExtensions.
@@ -1034,6 +1035,24 @@ namespace MobileGL::MG_Backend::DirectGLES {
         m_dynamicParameters.ViewportBoundsRangeMin = m_GLESCapabilities.ViewportBoundsRangeMin;
         m_dynamicParameters.ViewportBoundsRangeMax = m_GLESCapabilities.ViewportBoundsRangeMax;
         m_dynamicParameters.ViewportSubpixelBits = m_GLESCapabilities.ViewportSubpixelBits;
+        m_dynamicParameters.MinFragmentInterpolationOffset =
+            std::isfinite(m_GLESCapabilities.MinFragmentInterpolationOffset) &&
+                    m_GLESCapabilities.MinFragmentInterpolationOffset <= -0.5f
+                ? m_GLESCapabilities.MinFragmentInterpolationOffset
+                : -0.5f;
+        m_dynamicParameters.MaxFragmentInterpolationOffset = 0.4375f;
+        m_dynamicParameters.FragmentInterpolationOffsetBits = 4;
+        if (m_GLESCapabilities.FragmentInterpolationOffsetBits >= 4 &&
+            std::isfinite(m_GLESCapabilities.MaxFragmentInterpolationOffset)) {
+            const Float requiredMaxOffset =
+                0.5f - std::ldexp(1.0f, -m_GLESCapabilities.FragmentInterpolationOffsetBits);
+            if (m_GLESCapabilities.MaxFragmentInterpolationOffset >= requiredMaxOffset) {
+                m_dynamicParameters.MaxFragmentInterpolationOffset =
+                    m_GLESCapabilities.MaxFragmentInterpolationOffset;
+                m_dynamicParameters.FragmentInterpolationOffsetBits =
+                    m_GLESCapabilities.FragmentInterpolationOffsetBits;
+            }
+        }
         m_dynamicParameters.SupportsWideLines =
             m_GLESCapabilities.AliasedLineWidthRangeMax > 1.0f || m_GLESCapabilities.SmoothLineWidthRangeMax > 1.0f;
 

MobileGL/MG_Backend/DirectVulkan/BackendObject_DirectVulkan.cpp

@@ -18,6 +18,7 @@
 #include "MG_Util/Texture/TextureFormatProcessor.h"
 
 #include <Config.h>
+#include <cmath>
 #include <cstdlib>
 #include <cstring>
 
@@ -505,7 +506,7 @@ namespace MobileGL::MG_Backend::DirectVulkan {
             .ExtraVendor = Nullopt,
             .RendererGLInfo =
                 {
-                    .TargetGLVersion = {3, 3, 0},
+                    .TargetGLVersion = {4, 6, 0}, // Experimental GL CTS target version
                     .TargetGLSLVersion = {4, 6, 0},
                     // Baseline advertisement (no shader subgroup, no timer queries); a
                     // live backend reconciles its copy in UpdateAdvertisedExtensions.
@@ -796,6 +797,23 @@ namespace MobileGL::MG_Backend::DirectVulkan {
         m_dynamicParameters.ViewportBoundsRangeMin = m_vulkanCaps.ViewportBoundsRangeMin;
         m_dynamicParameters.ViewportBoundsRangeMax = m_vulkanCaps.ViewportBoundsRangeMax;
         m_dynamicParameters.ViewportSubpixelBits = m_vulkanCaps.ViewportSubpixelBits;
+        m_dynamicParameters.MinFragmentInterpolationOffset =
+            std::isfinite(m_vulkanCaps.MinFragmentInterpolationOffset) &&
+                    m_vulkanCaps.MinFragmentInterpolationOffset <= -0.5f
+                ? m_vulkanCaps.MinFragmentInterpolationOffset
+                : -0.5f;
+        m_dynamicParameters.MaxFragmentInterpolationOffset = 0.4375f;
+        m_dynamicParameters.FragmentInterpolationOffsetBits = 4;
+        if (m_vulkanCaps.FragmentInterpolationOffsetBits >= 4 &&
+            std::isfinite(m_vulkanCaps.MaxFragmentInterpolationOffset)) {
+            const Float requiredMaxOffset =
+                0.5f - std::ldexp(1.0f, -m_vulkanCaps.FragmentInterpolationOffsetBits);
+            if (m_vulkanCaps.MaxFragmentInterpolationOffset >= requiredMaxOffset) {
+                m_dynamicParameters.MaxFragmentInterpolationOffset = m_vulkanCaps.MaxFragmentInterpolationOffset;
+                m_dynamicParameters.FragmentInterpolationOffsetBits =
+                    m_vulkanCaps.FragmentInterpolationOffsetBits;
+            }
+        }
         m_dynamicParameters.SupportsWideLines = m_vulkanCaps.SupportsWideLines;
         m_dynamicParameters.MaxShaderStorageBlockSize =
             std::min(m_vulkanCaps.MaxShaderStorageBlockSize, kMaxAdvertisedShaderStorageBlockSize);

MobileGL/MG_Impl/GLImpl/Getter/GL_Getter.cpp

@@ -465,6 +465,14 @@ namespace MobileGL::MG_Impl::GLImpl {
         case GL_STENCIL_TEST:
             *params = MG_State::pGLContext->IsCapabilityEnabled(CapabilityInput::StencilTest) ? GL_TRUE : GL_FALSE;
             return;
+        case GL_MIN_FRAGMENT_INTERPOLATION_OFFSET:
+        case GL_MAX_FRAGMENT_INTERPOLATION_OFFSET:
+        case GL_FRAGMENT_INTERPOLATION_OFFSET_BITS: {
+            GLfloat value = 0.0f;
+            GetFloatv(pname, &value);
+            *params = value != 0.0f ? GL_TRUE : GL_FALSE;
+            return;
+        }
         default:
             break;
         }
@@ -520,6 +528,19 @@ namespace MobileGL::MG_Impl::GLImpl {
             params[1] = dynamicParameters.ViewportBoundsRangeMax;
             return;
         }
+        case GL_MIN_FRAGMENT_INTERPOLATION_OFFSET:
+        case GL_MAX_FRAGMENT_INTERPOLATION_OFFSET:
+        case GL_FRAGMENT_INTERPOLATION_OFFSET_BITS: {
+            const auto& dynamicParameters = MG_Backend::pActiveBackendObject->GetDynamicParameters();
+            if (pname == GL_MIN_FRAGMENT_INTERPOLATION_OFFSET) {
+                params[0] = dynamicParameters.MinFragmentInterpolationOffset;
+            } else if (pname == GL_MAX_FRAGMENT_INTERPOLATION_OFFSET) {
+                params[0] = dynamicParameters.MaxFragmentInterpolationOffset;
+            } else {
+                params[0] = static_cast<GLfloat>(dynamicParameters.FragmentInterpolationOffsetBits);
+            }
+            return;
+        }
         case GL_DEPTH_CLEAR_VALUE:
             params[0] = MG_State::pGLContext->GetClearDepth();
             return;
@@ -1957,6 +1978,15 @@ namespace MobileGL::MG_Impl::GLImpl {
         case GL_SUBPIXEL_BITS:
             *params = std::max(dynamicParameters.ViewportSubpixelBits, kFrontendSubpixelBits);
             break;
+        case GL_MIN_FRAGMENT_INTERPOLATION_OFFSET:
+            *params = static_cast<GLint>(std::lround(dynamicParameters.MinFragmentInterpolationOffset));
+            break;
+        case GL_MAX_FRAGMENT_INTERPOLATION_OFFSET:
+            *params = static_cast<GLint>(std::lround(dynamicParameters.MaxFragmentInterpolationOffset));
+            break;
+        case GL_FRAGMENT_INTERPOLATION_OFFSET_BITS:
+            *params = dynamicParameters.FragmentInterpolationOffsetBits;
+            break;
         case GL_UNIFORM_BUFFER_OFFSET_ALIGNMENT:
             *params = static_cast<Int>(dynamicParameters.UniformBufferOffsetAlignment);
             break;

MobileGL/MG_Test/BackendLoader/BackendLoaderTest.cpp

@@ -34,6 +34,11 @@ namespace {
         GLint maxFragmentImageUniforms = 4;
         GLint maxComputeImageUniforms = 5;
         bool maxGeometryImageUniformsQueried = false;
+        GLfloat minFragmentInterpolationOffset = -0.75f;
+        GLfloat maxFragmentInterpolationOffset = 0.625f;
+        GLint fragmentInterpolationOffsetBits = 6;
+        bool fragmentInterpolationLimitsQueried = false;
+        bool fragmentInterpolationQueryRaisesError = false;
         // Emulates ANGLE-on-Vulkan: the draw reads the indirect command's
         // baseInstance word and exposes it through gl_InstanceID.
         bool drawLeaksBaseInstanceWord = false;
@@ -108,6 +113,14 @@ namespace {
             case GL_MAX_COMPUTE_IMAGE_UNIFORMS:
                 *data = g_fake.maxComputeImageUniforms;
                 break;
+            case GL_FRAGMENT_INTERPOLATION_OFFSET_BITS:
+                g_fake.fragmentInterpolationLimitsQueried = true;
+                if (g_fake.fragmentInterpolationQueryRaisesError) {
+                    g_fake.pendingError = GL_INVALID_ENUM;
+                } else {
+                    *data = g_fake.fragmentInterpolationOffsetBits;
+                }
+                break;
             // FillInGLESCapabilities reads the context version before running the
             // baseInstance probe, which requires ES >= 3.1.
             case GL_MAJOR_VERSION:
@@ -155,6 +168,22 @@ namespace {
                 g_fake.maxTextureMaxAnisotropyQueried = true;
                 data[0] = g_fake.maxTextureMaxAnisotropy;
                 break;
+            case GL_MIN_FRAGMENT_INTERPOLATION_OFFSET:
+                g_fake.fragmentInterpolationLimitsQueried = true;
+                if (g_fake.fragmentInterpolationQueryRaisesError) {
+                    g_fake.pendingError = GL_INVALID_ENUM;
+                } else {
+                    data[0] = g_fake.minFragmentInterpolationOffset;
+                }
+                break;
+            case GL_MAX_FRAGMENT_INTERPOLATION_OFFSET:
+                g_fake.fragmentInterpolationLimitsQueried = true;
+                if (g_fake.fragmentInterpolationQueryRaisesError) {
+                    g_fake.pendingError = GL_INVALID_ENUM;
+                } else {
+                    data[0] = g_fake.maxFragmentInterpolationOffset;
+                }
+                break;
             // Two-component range queries.
             case GL_ALIASED_LINE_WIDTH_RANGE:
             case GL_SMOOTH_LINE_WIDTH_RANGE:
@@ -462,6 +491,52 @@ TEST(ImageUniformCapabilities, QueriesRealPerStageLimitsAndConservativelyGatesGe
     EXPECT_TRUE(g_fake.maxGeometryImageUniformsQueried);
 }
 
+TEST(FragmentInterpolationCapabilities, QueriesOnlyWhenSupportedAndPreservesDriverLimits) {
+    const auto funcs = MakeFakeGLESFunctions();
+
+    ResetFakeDriver();
+    g_fake.maxVertexSsboBlocks = 0;
+    MobileGL::MG_External::GLESCapabilities unsupportedCaps;
+    ASSERT_TRUE(MobileGL::MG_Util::BackendLoader::FillInGLESCapabilities(unsupportedCaps, funcs));
+    EXPECT_FALSE(unsupportedCaps.SupportsShaderMultisampleInterpolation);
+    EXPECT_FALSE(g_fake.fragmentInterpolationLimitsQueried);
+    EXPECT_FLOAT_EQ(unsupportedCaps.MinFragmentInterpolationOffset, -0.5f);
+    EXPECT_FLOAT_EQ(unsupportedCaps.MaxFragmentInterpolationOffset, 0.4375f);
+    EXPECT_EQ(unsupportedCaps.FragmentInterpolationOffsetBits, 4);
+
+    ResetFakeDriver();
+    g_fake.maxVertexSsboBlocks = 0;
+    g_fake.extensions.emplace_back("GL_OES_shader_multisample_interpolation");
+    // A stale error from an earlier capability probe must not make the optional
+    // interpolation query look like it failed.
+    g_fake.pendingError = GL_INVALID_OPERATION;
+    MobileGL::MG_External::GLESCapabilities supportedCaps;
+    ASSERT_TRUE(MobileGL::MG_Util::BackendLoader::FillInGLESCapabilities(supportedCaps, funcs));
+    EXPECT_TRUE(supportedCaps.SupportsShaderMultisampleInterpolation);
+    EXPECT_TRUE(g_fake.fragmentInterpolationLimitsQueried);
+    EXPECT_FLOAT_EQ(supportedCaps.MinFragmentInterpolationOffset, g_fake.minFragmentInterpolationOffset);
+    EXPECT_FLOAT_EQ(supportedCaps.MaxFragmentInterpolationOffset, g_fake.maxFragmentInterpolationOffset);
+    EXPECT_EQ(supportedCaps.FragmentInterpolationOffsetBits, g_fake.fragmentInterpolationOffsetBits);
+    EXPECT_EQ(funcs.glGetError(), GL_NO_ERROR);
+}
+
+TEST(FragmentInterpolationCapabilities, QueryErrorIsDrainedAndFallsBackToCoreMinimums) {
+    ResetFakeDriver();
+    g_fake.maxVertexSsboBlocks = 0;
+    g_fake.extensions.emplace_back("GL_OES_shader_multisample_interpolation");
+    g_fake.fragmentInterpolationQueryRaisesError = true;
+    const auto funcs = MakeFakeGLESFunctions();
+
+    MobileGL::MG_External::GLESCapabilities caps;
+    ASSERT_TRUE(MobileGL::MG_Util::BackendLoader::FillInGLESCapabilities(caps, funcs));
+
+    EXPECT_TRUE(g_fake.fragmentInterpolationLimitsQueried);
+    EXPECT_FLOAT_EQ(caps.MinFragmentInterpolationOffset, -0.5f);
+    EXPECT_FLOAT_EQ(caps.MaxFragmentInterpolationOffset, 0.4375f);
+    EXPECT_EQ(caps.FragmentInterpolationOffsetBits, 4);
+    EXPECT_EQ(funcs.glGetError(), GL_NO_ERROR);
+}
+
 // The extension string is what apps gate on (LWJGL builds GLCapabilities from it), so advertising
 // it on a driver that cannot filter anisotropically would leave them silently on trilinear.
 TEST(TextureAnisotropyCapabilities, ExtensionIsAdvertisedOnlyWhenTheHostDriverSupportsIt) {

MobileGL/MG_Test/SanityTest.cpp

@@ -197,13 +197,13 @@ TEST(DirectGLESSanity, AdvertisesDepthTextureForGlmarkShadowScenes) {
     EXPECT_NE(std::find(extensions.begin(), extensions.end(), MobileGL::E_GL_ARB_depth_texture), extensions.end());
 }
 
-TEST(DirectGLESSanity, AdvertisesVoxyRequiredRenderingExtensionsWithoutRaisingGLVersion) {
+TEST(DirectGLESSanity, AdvertisesVoxyRequiredRenderingExtensionsAtExperimentalCTSVersion) {
     MobileGL::MG_Backend::DirectGLES::BackendObject_DirectGLES backend;
     const auto& rendererInfo = backend.GetRendererInfo().RendererGLInfo;
     const auto& extensions = rendererInfo.Extensions;
 
-    EXPECT_EQ(rendererInfo.TargetGLVersion.Major, 3);
+    EXPECT_EQ(rendererInfo.TargetGLVersion.Major, 4);
-    EXPECT_EQ(rendererInfo.TargetGLVersion.Minor, 3);
+    EXPECT_EQ(rendererInfo.TargetGLVersion.Minor, 6);
     EXPECT_EQ(rendererInfo.TargetGLVersion.Patch, 0);
 
     EXPECT_NE(std::find(extensions.begin(), extensions.end(), MobileGL::E_GL_ARB_compute_shader),
@@ -397,13 +397,13 @@ TEST(DirectVulkanSanity, RenderPassExtentUsesSwapchainSizeOnlyForDefaultFramebuf
               MobileGL::IntVec2(512, 512));
 }
 
-TEST(DirectVulkanSanity, AdvertisesVoxyRequiredRenderingExtensionsWithoutRaisingGLVersion) {
+TEST(DirectVulkanSanity, AdvertisesVoxyRequiredRenderingExtensionsAtExperimentalCTSVersion) {
     MobileGL::MG_Backend::DirectVulkan::BackendObject_DirectVulkan backend;
     const auto& rendererInfo = backend.GetRendererInfo().RendererGLInfo;
     const auto& extensions = rendererInfo.Extensions;
 
-    EXPECT_EQ(rendererInfo.TargetGLVersion.Major, 3);
+    EXPECT_EQ(rendererInfo.TargetGLVersion.Major, 4);
-    EXPECT_EQ(rendererInfo.TargetGLVersion.Minor, 3);
+    EXPECT_EQ(rendererInfo.TargetGLVersion.Minor, 6);
     EXPECT_EQ(rendererInfo.TargetGLVersion.Patch, 0);
 
     EXPECT_NE(std::find(extensions.begin(), extensions.end(), MobileGL::E_GL_ARB_compute_shader),
@@ -516,6 +516,50 @@ TEST(DirectGLESSanity, PreservesHostPerStageImageUniformLimits) {
     EXPECT_EQ(params.MaxComputeImageUniforms, 5);
 }
 
+TEST(FragmentInterpolationCapabilities, PlumbsGLESAndBothVulkanPropertyPaths) {
+    using namespace MobileGL;
+
+    MG_External::GLESCapabilities glesCaps;
+    glesCaps.MinFragmentInterpolationOffset = -0.75f;
+    glesCaps.MaxFragmentInterpolationOffset = 0.625f;
+    glesCaps.FragmentInterpolationOffsetBits = 6;
+    MG_Backend::DirectGLES::BackendObject_DirectGLES glesBackend;
+    glesBackend.ApplyGLESCapabilitiesForTesting(glesCaps);
+    EXPECT_FLOAT_EQ(glesBackend.GetDynamicParameters().MinFragmentInterpolationOffset, -0.75f);
+    EXPECT_FLOAT_EQ(glesBackend.GetDynamicParameters().MaxFragmentInterpolationOffset, 0.625f);
+    EXPECT_EQ(glesBackend.GetDynamicParameters().FragmentInterpolationOffsetBits, 6);
+
+    VkPhysicalDeviceProperties properties{};
+    // A common Vulkan limit pair: max is one representable 4-bit step below 0.5.
+    properties.limits.minInterpolationOffset = -0.5f;
+    properties.limits.maxInterpolationOffset = 0.4375f;
+    properties.limits.subPixelInterpolationOffsetBits = 4;
+    MG_External::VulkanCapabilities vkCaps;
+    MG_Util::BackendLoader::FillInVulkanCapabilities(vkCaps, properties);
+    EXPECT_FLOAT_EQ(vkCaps.MinFragmentInterpolationOffset, -0.5f);
+    EXPECT_FLOAT_EQ(vkCaps.MaxFragmentInterpolationOffset, 0.4375f);
+    EXPECT_EQ(vkCaps.FragmentInterpolationOffsetBits, 4);
+
+    vkCaps.MinFragmentInterpolationOffset = -0.875f;
+    vkCaps.MaxFragmentInterpolationOffset = 0.75f;
+    vkCaps.FragmentInterpolationOffsetBits = 7;
+    MG_Backend::DirectVulkan::BackendObject_DirectVulkan vkBackend;
+    vkBackend.ApplyVulkanCapabilitiesForTesting(vkCaps);
+    EXPECT_FLOAT_EQ(vkBackend.GetDynamicParameters().MinFragmentInterpolationOffset, -0.875f);
+    EXPECT_FLOAT_EQ(vkBackend.GetDynamicParameters().MaxFragmentInterpolationOffset, 0.75f);
+    EXPECT_EQ(vkBackend.GetDynamicParameters().FragmentInterpolationOffsetBits, 7);
+
+    // Invalid/zero host data cannot under-advertise the OpenGL 4 minimums.
+    MG_External::VulkanCapabilities invalidCaps;
+    invalidCaps.MinFragmentInterpolationOffset = 0.0f;
+    invalidCaps.MaxFragmentInterpolationOffset = 0.0f;
+    invalidCaps.FragmentInterpolationOffsetBits = 0;
+    vkBackend.ApplyVulkanCapabilitiesForTesting(invalidCaps);
+    EXPECT_LE(vkBackend.GetDynamicParameters().MinFragmentInterpolationOffset, -0.5f);
+    EXPECT_FLOAT_EQ(vkBackend.GetDynamicParameters().MaxFragmentInterpolationOffset, 0.4375f);
+    EXPECT_EQ(vkBackend.GetDynamicParameters().FragmentInterpolationOffsetBits, 4);
+}
+
 TEST(DirectVulkanSanity, AdvertisesSubgroupOnlyWhenVulkanReportsUsableSupport) {
     using namespace MobileGL;
 
@@ -638,6 +682,48 @@ TEST(GetterSanity, ClampsMaxVertexAttribsToCurrentValueStorageCapacity) {
     MG_State::pGLContext.reset();
 }
 
+TEST(GetterSanity, ReportsFragmentInterpolationLimitsForFloatAndIntegerQueries) {
+    using namespace MobileGL;
+
+    auto previousContext = Move(MG_State::pGLContext);
+    auto previousBackend = Move(MG_Backend::pActiveBackendObject);
+    MG_State::pGLContext = MakeUnique<MG_State::GLState::GLContext>();
+
+    MG_Backend::DynamicBackendParameters params;
+    params.MinFragmentInterpolationOffset = -0.75f;
+    params.MaxFragmentInterpolationOffset = 0.4375f;
+    params.FragmentInterpolationOffsetBits = 6;
+    MG_Backend::pActiveBackendObject = MakeUnique<DynamicParameterBackend>(params);
+
+    GLfloat floatValue = 0.0f;
+    MG_Impl::GLImpl::GetFloatv(GL_MIN_FRAGMENT_INTERPOLATION_OFFSET, &floatValue);
+    EXPECT_FLOAT_EQ(floatValue, -0.75f);
+    MG_Impl::GLImpl::GetFloatv(GL_MAX_FRAGMENT_INTERPOLATION_OFFSET, &floatValue);
+    EXPECT_FLOAT_EQ(floatValue, 0.4375f);
+    MG_Impl::GLImpl::GetFloatv(GL_FRAGMENT_INTERPOLATION_OFFSET_BITS, &floatValue);
+    EXPECT_FLOAT_EQ(floatValue, 6.0f);
+
+    GLint intValue = 0;
+    MG_Impl::GLImpl::GetIntegerv(GL_MIN_FRAGMENT_INTERPOLATION_OFFSET, &intValue);
+    EXPECT_EQ(intValue, -1);
+    MG_Impl::GLImpl::GetIntegerv(GL_MAX_FRAGMENT_INTERPOLATION_OFFSET, &intValue);
+    EXPECT_EQ(intValue, 0);
+    MG_Impl::GLImpl::GetIntegerv(GL_FRAGMENT_INTERPOLATION_OFFSET_BITS, &intValue);
+    EXPECT_EQ(intValue, 6);
+
+    GLboolean boolValue = GL_FALSE;
+    MG_Impl::GLImpl::GetBooleanv(GL_MIN_FRAGMENT_INTERPOLATION_OFFSET, &boolValue);
+    EXPECT_EQ(boolValue, GL_TRUE);
+    MG_Impl::GLImpl::GetBooleanv(GL_MAX_FRAGMENT_INTERPOLATION_OFFSET, &boolValue);
+    EXPECT_EQ(boolValue, GL_TRUE);
+    MG_Impl::GLImpl::GetBooleanv(GL_FRAGMENT_INTERPOLATION_OFFSET_BITS, &boolValue);
+    EXPECT_EQ(boolValue, GL_TRUE);
+    EXPECT_EQ(MG_Impl::GLImpl::GetError(), GL_NO_ERROR);
+
+    MG_Backend::pActiveBackendObject = Move(previousBackend);
+    MG_State::pGLContext = Move(previousContext);
+}
+
 TEST(GetterSanity, PerStageImageUniformQueriesMatchShaderCompilerLimits) {
     using namespace MobileGL;
 

MobileGL/MG_Util/BackendLoaders/OpenGL/Loader.cpp

@@ -9,6 +9,7 @@
 #include "Loader.h"
 #include "MG_Util/Types.h"
 #include <Config.h>
+#include <cmath>
 #if defined(_WIN32)
 #ifndef WIN32_LEAN_AND_MEAN
 #define WIN32_LEAN_AND_MEAN 1
@@ -838,8 +839,14 @@ namespace MobileGL::MG_Util::BackendLoader {
                 if (std::strcmp(extension, "GL_NV_shader_noperspective_interpolation") == 0) {
                     caps.SupportsNoperspectiveInterpolation = true;
                 }
+                if (std::strcmp(extension, "GL_OES_shader_multisample_interpolation") == 0) {
+                    caps.SupportsShaderMultisampleInterpolation = true;
+                }
             }
         }
+        caps.SupportsShaderMultisampleInterpolation =
+            caps.SupportsShaderMultisampleInterpolation || caps.GLESVersion.Major > 3 ||
+            (caps.GLESVersion.Major == 3 && caps.GLESVersion.Minor >= 2);
 
         // Detect optional raster/color-mask entry points by whether they loaded. glColorMaski is GLES
         // 3.2 core (no extension string), so pointer presence is the reliable signal for all of these.
@@ -900,6 +907,9 @@ namespace MobileGL::MG_Util::BackendLoader {
         GLint maxColorAttachments = 8;
         GLint maxClipDistances = 8;
         GLint maxViewports = 16;
+        GLfloat minFragmentInterpolationOffset = -0.5f;
+        GLfloat maxFragmentInterpolationOffset = 0.4375f;
+        GLint fragmentInterpolationOffsetBits = 4;
         glesFuncs.glGetFloatv(GL_ALIASED_LINE_WIDTH_RANGE, aliasedLineWidthRange);
         glesFuncs.glGetFloatv(GL_SMOOTH_LINE_WIDTH_RANGE, smoothLineWidthRange);
         glesFuncs.glGetFloatv(GL_SMOOTH_LINE_WIDTH_GRANULARITY, &smoothLineWidthGranularity);
@@ -950,6 +960,29 @@ namespace MobileGL::MG_Util::BackendLoader {
         glesFuncs.glGetIntegerv(GL_MAX_VIEWPORTS, &maxViewports);
         glesFuncs.glGetIntegerv(GL_MAX_VIEWPORT_DIMS, maxViewportDims);
         glesFuncs.glGetIntegerv(GL_VIEWPORT_SUBPIXEL_BITS, &viewportSubpixelBits);
+        if (caps.SupportsShaderMultisampleInterpolation && glesFuncs.glGetFloatv) {
+            const auto drainErrors = [&glesFuncs]() {
+                Bool hadError = false;
+                if (glesFuncs.glGetError) {
+                    while (glesFuncs.glGetError() != GL_NO_ERROR) hadError = true;
+                }
+                return hadError;
+            };
+
+            // Isolate these optional queries from errors raised by preceding capability
+            // probes, then consume any query error so initialization never leaks it into
+            // the application's first glGetError call.
+            drainErrors();
+            glesFuncs.glGetFloatv(GL_MIN_FRAGMENT_INTERPOLATION_OFFSET, &minFragmentInterpolationOffset);
+            glesFuncs.glGetFloatv(GL_MAX_FRAGMENT_INTERPOLATION_OFFSET, &maxFragmentInterpolationOffset);
+            glesFuncs.glGetIntegerv(GL_FRAGMENT_INTERPOLATION_OFFSET_BITS, &fragmentInterpolationOffsetBits);
+            if (drainErrors()) {
+                MGLOG_W("Fragment interpolation limit query failed; using OpenGL minimums");
+                minFragmentInterpolationOffset = -0.5f;
+                maxFragmentInterpolationOffset = 0.4375f;
+                fragmentInterpolationOffsetBits = 4;
+            }
+        }
         // Only legal to query once the extension has been seen in the loop above, hence not batched
         // with the unconditional probes: on a driver without it this raises GL_INVALID_ENUM.
         if (caps.SupportsTextureFilterAnisotropy) {
@@ -1007,6 +1040,19 @@ namespace MobileGL::MG_Util::BackendLoader {
         caps.ViewportBoundsRangeMin = viewportBoundsRange[0];
         caps.ViewportBoundsRangeMax = viewportBoundsRange[1];
         caps.ViewportSubpixelBits = viewportSubpixelBits;
+        caps.MinFragmentInterpolationOffset =
+            std::isfinite(minFragmentInterpolationOffset) && minFragmentInterpolationOffset <= -0.5f
+                ? minFragmentInterpolationOffset
+                : -0.5f;
+        caps.MaxFragmentInterpolationOffset = 0.4375f;
+        caps.FragmentInterpolationOffsetBits = 4;
+        if (fragmentInterpolationOffsetBits >= 4 && std::isfinite(maxFragmentInterpolationOffset)) {
+            const Float requiredMaxOffset = 0.5f - std::ldexp(1.0f, -fragmentInterpolationOffsetBits);
+            if (maxFragmentInterpolationOffset >= requiredMaxOffset) {
+                caps.MaxFragmentInterpolationOffset = maxFragmentInterpolationOffset;
+                caps.FragmentInterpolationOffsetBits = fragmentInterpolationOffsetBits;
+            }
+        }
         MGLOG_I("    GL_ALIASED_LINE_WIDTH_RANGE: [%.3f, %.3f]", caps.AliasedLineWidthRangeMin,
                 caps.AliasedLineWidthRangeMax);
         MGLOG_I("    GL_SMOOTH_LINE_WIDTH_RANGE: [%.3f, %.3f]", caps.SmoothLineWidthRangeMin,

MobileGL/MG_Util/BackendLoaders/OpenGL/Loader.h

@@ -1055,6 +1055,9 @@ namespace MobileGL {
             // SPIRV-Cross's `#extension ... : require` would fail to compile and MobileGL falls back
             // to stripping the NoPerspective decoration (smooth interpolation) via StripNoPerspectivePass.
             Bool SupportsNoperspectiveInterpolation = false;
+            // GLES 3.2 core or GL_OES_shader_multisample_interpolation exposes
+            // interpolateAtOffset and the three fragment-offset limit queries.
+            Bool SupportsShaderMultisampleInterpolation = false;
             // GL_RENDERER contains "ANGLE".
             Bool IsAngleRenderer = false;
             // GL_RENDERER contains both "ANGLE" and "llvmpipe".
@@ -1120,6 +1123,9 @@ namespace MobileGL {
             Float ViewportBoundsRangeMin = 0.0f;
             Float ViewportBoundsRangeMax = 0.0f;
             Int ViewportSubpixelBits = 0;
+            Float MinFragmentInterpolationOffset = -0.5f;
+            Float MaxFragmentInterpolationOffset = 0.4375f;
+            Int FragmentInterpolationOffsetBits = 4;
         };
     } // namespace MG_External
 

MobileGL/MG_Util/BackendLoaders/Vulkan/Loader.cpp

@@ -9,6 +9,7 @@
 #include "Loader.h"
 
 #include <Config.h>
+#include <cmath>
 
 namespace MobileGL::MG_Util::BackendLoader {
     namespace {
@@ -40,6 +41,25 @@ namespace MobileGL::MG_Util::BackendLoader {
             return MaxSampleCountFromFlags(commonFlags);
         }
 
+        void FillFragmentInterpolationLimits(MG_External::VulkanCapabilities& caps,
+                                             const VkPhysicalDeviceLimits& limits) {
+            caps.MinFragmentInterpolationOffset =
+                std::isfinite(limits.minInterpolationOffset) && limits.minInterpolationOffset <= -0.5f
+                    ? limits.minInterpolationOffset
+                    : -0.5f;
+
+            caps.MaxFragmentInterpolationOffset = 0.4375f;
+            caps.FragmentInterpolationOffsetBits = 4;
+            const Int bits = static_cast<Int>(limits.subPixelInterpolationOffsetBits);
+            if (bits >= 4 && std::isfinite(limits.maxInterpolationOffset)) {
+                const Float requiredMaxOffset = 0.5f - std::ldexp(1.0f, -bits);
+                if (limits.maxInterpolationOffset >= requiredMaxOffset) {
+                    caps.MaxFragmentInterpolationOffset = limits.maxInterpolationOffset;
+                    caps.FragmentInterpolationOffsetBits = bits;
+                }
+            }
+        }
+
         VulkanDynamicFunctions LoadVulkanDynamicFunctions(VkInstance instance) {
             VulkanDynamicFunctions loaded{};
             if (instance == VK_NULL_HANDLE) {
@@ -171,6 +191,7 @@ namespace MobileGL::MG_Util::BackendLoader {
         caps.ViewportBoundsRangeMin = p.limits.viewportBoundsRange[0];
         caps.ViewportBoundsRangeMax = p.limits.viewportBoundsRange[1];
         caps.ViewportSubpixelBits = static_cast<Int>(p.limits.viewportSubPixelBits);
+        FillFragmentInterpolationLimits(caps, p.limits);
 
         VkPhysicalDeviceFeatures supportedFeatures{};
         vkGetPhysicalDeviceFeatures(physicalDevice, &supportedFeatures);
@@ -261,6 +282,7 @@ namespace MobileGL::MG_Util::BackendLoader {
         caps.ViewportBoundsRangeMin = properties.limits.viewportBoundsRange[0];
         caps.ViewportBoundsRangeMax = properties.limits.viewportBoundsRange[1];
         caps.ViewportSubpixelBits = static_cast<Int>(properties.limits.viewportSubPixelBits);
+        FillFragmentInterpolationLimits(caps, properties.limits);
         caps.SupportsWideLines = false;
         // This helper only receives properties, not VkPhysicalDeviceFeatures. Leave optional
         // stage writes disabled rather than inferring them from descriptor limits alone.

MobileGL/MG_Util/BackendLoaders/Vulkan/Loader.h

@@ -68,6 +68,9 @@ namespace MobileGL {
             Float ViewportBoundsRangeMin = 0.0f;
             Float ViewportBoundsRangeMax = 0.0f;
             Int ViewportSubpixelBits = 0;
+            Float MinFragmentInterpolationOffset = -0.5f;
+            Float MaxFragmentInterpolationOffset = 0.4375f;
+            Int FragmentInterpolationOffsetBits = 4;
             Bool SupportsWideLines = false;
             // Storage-image descriptors are limited per stage by
             // maxPerStageDescriptorStorageImages, but writes/atomics outside compute additionally