[Feat] (GL): advertise ARB_cull_distance where the backend has cull distances

MobileGL/MG_Backend/BackendObject.h

@@ -316,6 +316,10 @@ namespace MobileGL {
         struct AdvertisedFeatureSupport {
             // ES 3.2 or GL_EXT_tessellation_shader; VkPhysicalDeviceFeatures::tessellationShader.
             Bool TessellationShader = false;
+            // At least one cull distance: GL_EXT_clip_cull_distance with a non-zero
+            // GL_MAX_CULL_DISTANCES; VkPhysicalDeviceFeatures::shaderCullDistance with a non-zero
+            // maxCullDistances.
+            Bool CullDistance = false;
         };
 
         // Coarse GPU vendor identity for gating device-specific quirks. Detected from the

MobileGL/MG_Backend/DirectGLES/BackendObject_DirectGLES.cpp

@@ -842,7 +842,8 @@ namespace MobileGL::MG_Backend::DirectGLES {
                 capabilities.SupportsDrawIndirect,
                 capabilities.SupportsDrawIndirect && capabilities.SupportsBaseInstance,
                 capabilities.SupportsTextureView, capabilities.SupportsTextureCubeMapArray,
-                AdvertisedFeatureSupport{.TessellationShader = capabilities.SupportsTessellationShader});
+                AdvertisedFeatureSupport{.TessellationShader = capabilities.SupportsTessellationShader,
+                                         .CullDistance = capabilities.MaxCullDistances > 0});
             // Exactly what InitCapabilities forwards into the dynamic parameters: the base
             // extension and _primitive when the driver has them, _attachment not yet.
             auto& extensions = MutableRendererInfo().RendererGLInfo.Extensions;
@@ -1523,6 +1524,11 @@ namespace MobileGL::MG_Backend::DirectGLES {
         if (features.TessellationShader) {
             extensions.push_back(E_GL_ARB_tessellation_shader);
         }
+        // gl_CullDistance goes through GL_EXT_clip_cull_distance, whose cull half the loader only
+        // reports where the driver answers a non-zero GL_MAX_CULL_DISTANCES.
+        if (features.CullDistance) {
+            extensions.push_back(E_GL_ARB_cull_distance);
+        }
         // Minecraft 26.3 checks this prerequisite before it even considers
         // GL_ARB_multi_draw_indirect. ES 3.1 supplies both single-draw entry points; the loader
         // folds the version and pointer checks into SupportsDrawIndirect.

MobileGL/MG_Backend/DirectVulkan/BackendObject_DirectVulkan.cpp

@@ -925,6 +925,10 @@ namespace MobileGL::MG_Backend::DirectVulkan {
         if (features.TessellationShader) {
             extensions.push_back(E_GL_ARB_tessellation_shader);
         }
+        // Follows the shaderCullDistance device feature, the same gate GL_MAX_CULL_DISTANCES uses.
+        if (features.CullDistance) {
+            extensions.push_back(E_GL_ARB_cull_distance);
+        }
         // Vulkan's drawIndirectFirstInstance feature is optional. Direct base-instance calls work
         // without it, but ARB_base_instance also promises non-zero firstInstance in GPU indirect
         // commands; the renderer supplies true only when that word is legal and gl_InstanceID can
@@ -1106,7 +1110,9 @@ namespace MobileGL::MG_Backend::DirectVulkan {
             pVulkanRenderer && pVulkanRenderer->IsSamplerAnisotropySupported(),
             pVulkanRenderer && pVulkanRenderer->IsNonZeroIndirectBaseInstanceSupported(),
             m_vulkanCaps.SupportsImageCubeArray,
-            AdvertisedFeatureSupport{.TessellationShader = m_vulkanCaps.SupportsTessellationShader});
+            AdvertisedFeatureSupport{.TessellationShader = m_vulkanCaps.SupportsTessellationShader,
+                                     .CullDistance = m_vulkanCaps.SupportsShaderCullDistance &&
+                                                     m_vulkanCaps.MaxCullDistances > 0});
         // GL_EXT_fragment_shading_rate rides on VK_KHR_fragment_shading_rate's pipeline rate, and
         // its _primitive companion on the primitive rate; both only when the renderer enabled them.
         // _attachment is not advertised: no framebuffer carries a rate attachment to this backend.

MobileGL/MG_Test/BackendLoader/BackendLoaderTest.cpp

@@ -1281,6 +1281,27 @@ TEST(CoreSurfaceAdvertisement, BatchIsUnconditionalAndTessellationFollowsTheDevi
                          MobileGL::E_GL_ARB_tessellation_shader));
 }
 
+// ARB_cull_distance follows the backend's cull-distance capability, never the context version.
+TEST(CoreSurfaceAdvertisement, CullDistanceFollowsTheDevice) {
+    const auto contains = [](const MobileGL::Vector<MobileGL::GLExtension>& extensions,
+                             MobileGL::GLExtension wanted) {
+        return std::find(extensions.begin(), extensions.end(), wanted) != extensions.end();
+    };
+    EXPECT_FALSE(contains(MobileGL::MG_Backend::DirectGLES::BuildAdvertisedExtensions(false, false, false, false,
+                                                                                       false, false),
+                          MobileGL::E_GL_ARB_cull_distance));
+    EXPECT_FALSE(contains(MobileGL::MG_Backend::DirectVulkan::BuildAdvertisedExtensions(false, false, false, false,
+                                                                                         false),
+                          MobileGL::E_GL_ARB_cull_distance));
+    const MobileGL::MG_Backend::AdvertisedFeatureSupport cull{.CullDistance = true};
+    EXPECT_TRUE(contains(MobileGL::MG_Backend::DirectGLES::BuildAdvertisedExtensions(false, false, false, false,
+                                                                                      false, false, cull),
+                         MobileGL::E_GL_ARB_cull_distance));
+    EXPECT_TRUE(contains(MobileGL::MG_Backend::DirectVulkan::BuildAdvertisedExtensions(false, false, false, false,
+                                                                                        false, cull),
+                         MobileGL::E_GL_ARB_cull_distance));
+}
+
 // ES 3.2 has tessellation in core; ES 3.1 only through GL_EXT_tessellation_shader. Either way the
 // patch-size entry point has to have resolved.
 TEST(TessellationCapabilities, FollowTheVersionOrTheExtension) {