[GPU] Add workaround for occlusion queries.

src/xenia/gpu/command_processor.cc

@@ -1145,9 +1145,24 @@ bool CommandProcessor::ExecutePacketType3_EVENT_WRITE_ZPD(RingBuffer* reader,
   // Writeback initiator.
   WriteRegister(XE_GPU_REG_VGT_EVENT_INITIATOR, initiator & 0x3F);
 
-  // TODO: Flag the backend CP to write out zpass counters to
+  // Occlusion queries:
-  // REG_RB_SAMPLE_COUNT_ADDR (probably # pixels passed depth test).
+  // This command is send on query begin and end.
-  // This applies to the last draw, I believe.
+  // As a workaround report some fixed amount of passed samples.
+  auto fake_sample_count = cvars::query_occlusion_fake_sample_count;
+  if (fake_sample_count >= 0) {
+    auto* pSampleCounts =
+        memory_->TranslatePhysical<xe_gpu_depth_sample_counts*>(
+            register_file_->values[XE_GPU_REG_RB_SAMPLE_COUNT_ADDR].u32);
+    // 0xFFFFFEED is written to this two locations by D3D only on D3DISSUE_END
+    // and used to detect a finished query.
+    bool isEnd = pSampleCounts->ZPass_A == xe::byte_swap(0xFFFFFEED) &&
+                 pSampleCounts->ZPass_B == xe::byte_swap(0xFFFFFEED);
+    std::memset(pSampleCounts, 0, sizeof(xe_gpu_depth_sample_counts));
+    if (isEnd) {
+      pSampleCounts->ZPass_A = fake_sample_count;
+      pSampleCounts->Total_A = fake_sample_count;
+    }
+  }
 
   return true;
 }

src/xenia/gpu/gpu_flags.cc

@@ -27,3 +27,10 @@ DEFINE_bool(
     "may be used to bypass fetch constant type errors in certain games until "
     "the real reason why they're invalid is found.",
     "GPU");
+
+DEFINE_int32(query_occlusion_fake_sample_count, 1000,
+             "If set to -1 no sample counts are written, games may hang. Else, "
+             "the sample count of every tile will be incremented on every "
+             "EVENT_WRITE_ZPD by this number. Setting this to 0 means "
+             "everything is reported as occluded.",
+             "GPU");

src/xenia/gpu/gpu_flags.h

@@ -20,4 +20,6 @@ DECLARE_bool(vsync);
 
 DECLARE_bool(gpu_allow_invalid_fetch_constants);
 
+DECLARE_int32(query_occlusion_fake_sample_count);
+
 #endif  // XENIA_GPU_GPU_FLAGS_H_

src/xenia/gpu/xenos.h

@@ -2,7 +2,7 @@
  ******************************************************************************
  * Xenia : Xbox 360 Emulator Research Project                                 *
  ******************************************************************************
- * Copyright 2013 Ben Vanik. All rights reserved.                             *
+ * Copyright 2020 Ben Vanik. All rights reserved.                             *
  * Released under the BSD license - see LICENSE in the root for more details. *
  ******************************************************************************
  */
@@ -849,6 +849,20 @@ XEPACKEDUNION(xe_gpu_memexport_stream_t, {
   });
 });
 
+XEPACKEDSTRUCT(xe_gpu_depth_sample_counts, {
+  // This is little endian as it is swapped in D3D code.
+  // Corresponding A and B values are summed up by D3D.
+  // Occlusion there is calculated by substracting begin from end struct.
+  uint32_t Total_A;
+  uint32_t Total_B;
+  uint32_t ZFail_A;
+  uint32_t ZFail_B;
+  uint32_t ZPass_A;
+  uint32_t ZPass_B;
+  uint32_t StencilFail_A;
+  uint32_t StencilFail_B;
+});
+
 // Enum of event values used for VGT_EVENT_INITIATOR
 enum Event {
   VS_DEALLOC = 0,