From ef8a60e011707f8eda3880315b76f067023eee71 Mon Sep 17 00:00:00 2001
From: Triang3l <triang3l@yandex.ru>
Date: Thu, 14 Apr 2022 21:19:12 +0300
Subject: [PATCH] [GPU] Round tessellation patch vertex count up (by @deaklajos
 #2007)

Also move the clamping of the guest index count to the index buffer size to the place before it's read in calculations
---
 src/xenia/gpu/primitive_processor.cc | 47 +++++++++++++++++++---------
 1 file changed, 32 insertions(+), 15 deletions(-)

diff --git a/src/xenia/gpu/primitive_processor.cc b/src/xenia/gpu/primitive_processor.cc
index fcb57634e..0e0a53c3f 100644
--- a/src/xenia/gpu/primitive_processor.cc
+++ b/src/xenia/gpu/primitive_processor.cc
@@ -222,7 +222,8 @@ bool PrimitiveProcessor::Process(ProcessingResult& result_out) {
   // Parse the primitive type and the tessellation state (VGT_OUTPUT_PATH_CNTL
   // is only used in the explicit major mode) - there are cases in games when
   // this register is left over after usage of tessellation in draws that don't
-  // need it.
+  // need it. Also perform needed vertex count adjustments based on the
+  // primitive type.
   xenos::PrimitiveType guest_primitive_type = vgt_draw_initiator.prim_type;
   xenos::PrimitiveType host_primitive_type = guest_primitive_type;
   bool tessellation_enabled =
@@ -233,6 +234,7 @@ bool PrimitiveProcessor::Process(ProcessingResult& result_out) {
   xenos::TessellationMode tessellation_mode =
       regs.Get<reg::VGT_HOS_CNTL>().tess_mode;
   Shader::HostVertexShaderType host_vertex_shader_type;
+  uint32_t guest_draw_vertex_count = vgt_draw_initiator.num_indices;
   if (tessellation_enabled) {
     // Currently only supporting tessellation in known cases for safety, and not
     // yet converting patch strips / fans to patch lists until games using them
@@ -289,12 +291,29 @@ bool PrimitiveProcessor::Process(ProcessingResult& result_out) {
         // - 4D5307ED - water - adaptive.
         host_vertex_shader_type =
             Shader::HostVertexShaderType::kTriangleDomainPatchIndexed;
+        // See the comment about the rounding for kQuadPatch.
+        guest_draw_vertex_count =
+            xe::round_up(guest_draw_vertex_count, uint32_t(3), false);
         break;
       case xenos::PrimitiveType::kQuadPatch:
-        // - 4D5307F1 - continuous.
+        // - 4D5307F1 - ground - continuous.
         // - 4D5307F2 - garden ground - adaptive.
         host_vertex_shader_type =
             Shader::HostVertexShaderType::kQuadDomainPatchIndexed;
+        // While it's known that num_indices represents the control point count
+        // (4D5307E6, for example, for water triangle patches, performs N
+        // invocations of the memexporting shader calculating the edge
+        // tessellation factors for one patch, and then draws the water with
+        // num_indices = 3 * N), 4D5307F1 ground is drawn with num_indices = 1
+        // rather than 4. Unlike Direct3D 11 tessellation, where the patch count
+        // is `floor(vertex count / control points per patch)`, on the Xenos,
+        // the count appears to be `ceil` of that value (like a
+        // `for (i = 0; i < num_indices; i += 4)` loop is used to emit the
+        // patches). It's unlikely, however, that this adjustment should also be
+        // done for regular primitive types with tessellation enabled, as
+        // they're handled as usual primitive topologies, just post-tessellated.
+        guest_draw_vertex_count =
+            xe::align(guest_draw_vertex_count, uint32_t(4));
         break;
       default:
         // TODO(Triang3l): Support line patches.
@@ -346,7 +365,17 @@ bool PrimitiveProcessor::Process(ProcessingResult& result_out) {
   }
 
   // Process the indices.
-  uint32_t guest_draw_vertex_count = vgt_draw_initiator.num_indices;
+  auto vgt_dma_size = regs.Get<reg::VGT_DMA_SIZE>();
+  if (vgt_draw_initiator.source_select == xenos::SourceSelect::kDMA &&
+      guest_draw_vertex_count > vgt_dma_size.num_words) {
+    XELOGW(
+        "Primitive processor: {} vertices attempted to be drawn with an index "
+        "buffer only containing {}. Should be fetching zero indices instead of "
+        "overflowing ones, but this is a rare situation, so not handled yet. "
+        "Report the game to Xenia developers!",
+        guest_draw_vertex_count, vgt_dma_size.num_words);
+    guest_draw_vertex_count = vgt_dma_size.num_words;
+  }
   uint32_t line_loop_closing_index = 0;
   uint32_t guest_index_base;
   CachedResult cacheable;
@@ -420,9 +449,6 @@ bool PrimitiveProcessor::Process(ProcessingResult& result_out) {
           uint32_t(vgt_draw_initiator.source_select));
       return false;
     }
-
-    auto vgt_dma_size = regs.Get<reg::VGT_DMA_SIZE>();
-
     xenos::IndexFormat guest_index_format = vgt_draw_initiator.index_size;
     cacheable.host_index_format = guest_index_format;
     // Normalize the endian and the reset index.
@@ -490,15 +516,6 @@ bool PrimitiveProcessor::Process(ProcessingResult& result_out) {
     }
 
     // Get the index buffer memory range.
-    if (guest_draw_vertex_count > vgt_dma_size.num_words) {
-      XELOGW(
-          "Primitive processor: {} vertices attempted to be drawn with an "
-          "index buffer only containing {}. Should be fetching zero indices "
-          "instead of overflowing ones, but this is a rare situation, so not "
-          "handled yet. Report the game to Xenia developers!",
-          guest_draw_vertex_count, vgt_dma_size.num_words);
-      guest_draw_vertex_count = vgt_dma_size.num_words;
-    }
     uint32_t index_size_log2 =
         guest_index_format == xenos::IndexFormat::kInt16 ? 1 : 2;
     // The base should already be aligned, but aligning here too for safety.