Vulkan: Apply a half-pixel offset where necessary.

src/xenia/gpu/vulkan/vulkan_command_processor.cc

@@ -957,13 +957,15 @@ bool VulkanCommandProcessor::IssueCopy() {
   const uint8_t* vertex_addr = memory_->TranslatePhysical(fetch->address << 2);
   trace_writer_.WriteMemoryRead(fetch->address << 2, fetch->size * 4);
 
+  // Most vertices have a negative half pixel offset applied, which we reverse.
+  auto& vtx_cntl = *(reg::PA_SU_VTX_CNTL*)&regs[XE_GPU_REG_PA_SU_VTX_CNTL].u32;
+  float vtx_offset = vtx_cntl.pix_center == 0 ? 0.5f : 0.f;
+
   float dest_points[6];
   for (int i = 0; i < 6; i++) {
-    // TODO(DrChat): I believe there is a register dictating whether this
-    // half-pixel offset needs to be applied.
     dest_points[i] =
         GpuSwap(xe::load<float>(vertex_addr + i * 4), Endian(fetch->endian)) +
-        0.5f;
+        vtx_offset;
   }
 
   // Note: The xenos only supports rectangle copies (luckily)