[Fix] (DirectVulkan): suppress blended depth writes on Qualcomm and mark gl_Position invariant to fix MC 26.3 OIT cloud flicker

MobileGL/MG_Backend/DirectVulkan/Renderer/PipelineFactory.cpp

@@ -8,6 +8,7 @@
 
 #include "PipelineFactory.h"
 
+
 namespace MobileGL::MG_Backend::DirectVulkan {
     static const char* PrimitiveTopologyToString(VkPrimitiveTopology topology) {
         switch (topology) {
@@ -108,6 +109,10 @@ namespace MobileGL::MG_Backend::DirectVulkan {
                   "vkCreatePipelineCache");
     }
 
+    void PipelineFactory::SetSuppressBlendedDepthWrite(Bool enabled) {
+        s_suppressBlendedDepthWrite = enabled;
+    }
+
     PipelineFactory::~PipelineFactory() {
         DestroyAll();
         if (m_pipelineCache != VK_NULL_HANDLE) {
@@ -258,6 +263,18 @@ namespace MobileGL::MG_Backend::DirectVulkan {
         for (Uint32 i = 0; i < payload.colorAttachmentCount; ++i) {
             colorAttachments[i] = payload.colorBlendAttachments[i];
         }
+        // Suppress depth writes on blended pipelines when the active driver cannot keep
+        // vertex positions invariant across the pipelines of a multi-pass depth-equality
+        // chain (see SetSuppressBlendedDepthWrite). Blended draws that write depth are rare
+        // and the equality-dependent prepass pattern is exactly the case that breaks.
+        if (s_suppressBlendedDepthWrite && depthStencil.depthWriteEnable == VK_TRUE) {
+            for (Uint32 i = 0; i < payload.colorAttachmentCount; ++i) {
+                if (colorAttachments[i].blendEnable == VK_TRUE) {
+                    depthStencil.depthWriteEnable = VK_FALSE;
+                    break;
+                }
+            }
+        }
         VkPipelineColorBlendStateCreateInfo blend{VK_STRUCTURE_TYPE_PIPELINE_COLOR_BLEND_STATE_CREATE_INFO};
         blend.logicOpEnable = payload.logicOpEnable ? VK_TRUE : VK_FALSE;
         blend.logicOp = payload.logicOp;