[Feat] (DirectVulkan): run the tessellation stages

The backend already turned a tessellation control/evaluation shader into the
right VkShaderStage, but nothing downstream knew what to do with it: GL_PATCHES
had no topology, so it fell through to the triangle-list default, and the
pipeline carried no tessellation state at all. A GL_PATCHES draw therefore ran
the vertex and fragment stages over raw triangles.

Map GL_PATCHES to VK_PRIMITIVE_TOPOLOGY_PATCH_LIST, carry GL_PATCH_VERTICES into
the pipeline as patchControlPoints (part of the key, since two patch sizes are
two pipelines), attach VkPipelineTessellationStateCreateInfo for a patch topology
only, and enable the tessellationShader device feature.

POST reports the feature, because without it a program with a tessellation stage
cannot build a pipeline at all and GL_PATCHES draws render nothing.

MobileGL/MG_Backend/DirectVulkan/Renderer/PipelineFactory.cpp

@@ -205,6 +205,7 @@ namespace MobileGL::MG_Backend::DirectVulkan {
         XXHASH_VERIFY(XXH64_update(m_hashState, &payload.topology, sizeof(payload.topology)));
         XXHASH_VERIFY(
             XXH64_update(m_hashState, &payload.primitiveRestartEnable, sizeof(payload.primitiveRestartEnable)));
+        XXHASH_VERIFY(XXH64_update(m_hashState, &payload.patchControlPoints, sizeof(payload.patchControlPoints)));
         XXHASH_VERIFY(XXH64_update(m_hashState, &payload.polygonMode, sizeof(payload.polygonMode)));
         XXHASH_VERIFY(XXH64_update(m_hashState, &payload.cullMode, sizeof(payload.cullMode)));
         XXHASH_VERIFY(XXH64_update(m_hashState, &payload.frontFace, sizeof(payload.frontFace)));
@@ -380,6 +381,11 @@ namespace MobileGL::MG_Backend::DirectVulkan {
         ia.topology = payload.topology;
         ia.primitiveRestartEnable = payload.primitiveRestartEnable ? VK_TRUE : VK_FALSE;
 
+        // Only a patch topology has a tessellation stage to configure; leaving the pointer null
+        // otherwise is what the spec expects.
+        VkPipelineTessellationStateCreateInfo tessellation{VK_STRUCTURE_TYPE_PIPELINE_TESSELLATION_STATE_CREATE_INFO};
+        tessellation.patchControlPoints = payload.patchControlPoints;
+
         VkPipelineViewportStateCreateInfo vpci{VK_STRUCTURE_TYPE_PIPELINE_VIEWPORT_STATE_CREATE_INFO};
         vpci.viewportCount = 1;
         vpci.scissorCount = 1;
@@ -444,6 +450,8 @@ namespace MobileGL::MG_Backend::DirectVulkan {
         gpi.pStages = payload.stages->data();
         gpi.pVertexInputState = payload.vertexInputState;
         gpi.pInputAssemblyState = &ia;
+        gpi.pTessellationState =
+            payload.topology == VK_PRIMITIVE_TOPOLOGY_PATCH_LIST ? &tessellation : nullptr;
         gpi.pViewportState = &vpci;
         gpi.pRasterizationState = &raster;
         gpi.pMultisampleState = &ms;

MobileGL/MG_Backend/DirectVulkan/Renderer/PipelineFactory.h

@@ -30,6 +30,8 @@ namespace MobileGL::MG_Backend::DirectVulkan {
             Uint32 subpass = 0;
             VkPrimitiveTopology topology = VK_PRIMITIVE_TOPOLOGY_TRIANGLE_LIST;
             Bool primitiveRestartEnable = false;
+            // GL_PATCH_VERTICES; only read for a PATCH_LIST topology.
+            Uint32 patchControlPoints = 3;
             VkPolygonMode polygonMode = VK_POLYGON_MODE_FILL;
             VkCullModeFlags cullMode = VK_CULL_MODE_BACK_BIT;
             VkFrontFace frontFace = VK_FRONT_FACE_CLOCKWISE;

MobileGL/MG_Backend/DirectVulkan/Renderer/VulkanRenderer.cpp

@@ -4209,6 +4209,7 @@ void main() {
             .subpass = 0,
             .topology = vkTopology,
             .primitiveRestartEnable = primitiveRestartEnabled,
+            .patchControlPoints = static_cast<Uint32>(MG_State::pGLContext->GetPatchVertices()),
             .polygonMode = effectivePolygonMode,
             .cullMode = cullFaceEnabled
                 ? MG_Util::ConvertCullFaceModeToVkEnum(MG_State::pGLContext->GetCullFaceMode(), invertClockwise)
@@ -9794,6 +9795,7 @@ void main() {
                                                 ? VK_FALSE
                                                 : supportedDeviceFeatures.robustBufferAccess;
         deviceFeatures.geometryShader = supportedDeviceFeatures.geometryShader;
+        deviceFeatures.tessellationShader = supportedDeviceFeatures.tessellationShader;
         deviceFeatures.independentBlend = supportedDeviceFeatures.independentBlend;
         m_independentBlendFeatureEnabled = deviceFeatures.independentBlend == VK_TRUE;
         deviceFeatures.fillModeNonSolid = supportedDeviceFeatures.fillModeNonSolid;

MobileGL/MG_Util/Converters/MGToVk/RenderStateEnumConverter.cpp

@@ -38,6 +38,10 @@ namespace MobileGL {
                 return VK_PRIMITIVE_TOPOLOGY_TRIANGLE_LIST_WITH_ADJACENCY;
             case GL_TRIANGLE_STRIP_ADJACENCY:
                 return VK_PRIMITIVE_TOPOLOGY_TRIANGLE_STRIP_WITH_ADJACENCY;
+            case GL_PATCHES:
+                // The tessellator decides what a patch becomes; its vertex count is pipeline
+                // state (patchControlPoints), not part of the topology.
+                return VK_PRIMITIVE_TOPOLOGY_PATCH_LIST;
             default:
                 MGLOG_W("Unrecognized primitive topology");
                 return VK_PRIMITIVE_TOPOLOGY_TRIANGLE_LIST;

MobileGL/MG_Util/SelfTest/DriverPost.cpp

@@ -1431,6 +1431,18 @@ namespace MobileGL::MG_Util::SelfTest {
                          "hard-fails at draw");
         }
 
+        // Core 1.0 features the backend turns GL stages into pipeline stages with.
+        VkPhysicalDeviceFeatures coreFeatures{};
+        vkGetPhysicalDeviceFeatures(physicalDevice, &coreFeatures);
+        if (coreFeatures.tessellationShader == VK_TRUE) {
+            builder.Pass("tessellationShader",
+                         "supported (GL_PATCHES draws run the tessellation control/evaluation stages)");
+        } else {
+            builder.Warn("tessellationShader",
+                         "unsupported; a program with a tessellation control/evaluation shader cannot build a "
+                         "pipeline, so GL_PATCHES draws render nothing");
+        }
+
         Bool vertexAttributeInstanceRateDivisor = false;
         if (vkGetPhysicalDeviceFeatures2Fn != nullptr &&
             HasVkExtension(deviceExtensions, VK_EXT_VERTEX_ATTRIBUTE_DIVISOR_EXTENSION_NAME)) {