From 50bb35b4b44b025633bb513ca9d9da4a509561dd Mon Sep 17 00:00:00 2001
From: Triang3l <triang3l@yandex.ru>
Date: Wed, 9 Jun 2021 20:46:24 +0300
Subject: [PATCH] [GPU] Polygon offset scale factor in xenos.h

---
 src/xenia/gpu/d3d12/d3d12_command_processor.cc |  7 ++++---
 src/xenia/gpu/d3d12/pipeline_cache.cc          |  5 +++--
 src/xenia/gpu/draw_util.h                      |  2 +-
 src/xenia/gpu/xenos.h                          | 10 ++++++++++
 4 files changed, 18 insertions(+), 6 deletions(-)

diff --git a/src/xenia/gpu/d3d12/d3d12_command_processor.cc b/src/xenia/gpu/d3d12/d3d12_command_processor.cc
index 74646a459..7259efc68 100644
--- a/src/xenia/gpu/d3d12/d3d12_command_processor.cc
+++ b/src/xenia/gpu/d3d12/d3d12_command_processor.cc
@@ -3241,9 +3241,10 @@ void D3D12CommandProcessor::UpdateSystemConstantValues(
         poly_offset_back_offset = poly_offset_front_offset;
       }
     }
-    // "slope computed in subpixels ([...] 1/16)" - R5xx Acceleration.
-    poly_offset_front_scale *= (1.0f / 16.0f) * resolution_scale;
-    poly_offset_back_scale *= (1.0f / 16.0f) * resolution_scale;
+    float poly_offset_scale_factor =
+        xenos::kPolygonOffsetScaleSubpixelUnit * resolution_scale;
+    poly_offset_front_scale *= poly_offset_scale_factor;
+    poly_offset_back_scale *= poly_offset_scale_factor;
     dirty |= system_constants_.edram_poly_offset_front_scale !=
              poly_offset_front_scale;
     system_constants_.edram_poly_offset_front_scale = poly_offset_front_scale;
diff --git a/src/xenia/gpu/d3d12/pipeline_cache.cc b/src/xenia/gpu/d3d12/pipeline_cache.cc
index b28369d54..556c7cacf 100644
--- a/src/xenia/gpu/d3d12/pipeline_cache.cc
+++ b/src/xenia/gpu/d3d12/pipeline_cache.cc
@@ -36,6 +36,7 @@
 #include "xenia/gpu/d3d12/d3d12_render_target_cache.h"
 #include "xenia/gpu/draw_util.h"
 #include "xenia/gpu/gpu_flags.h"
+#include "xenia/gpu/xenos.h"
 #include "xenia/ui/d3d12/d3d12_util.h"
 
 DEFINE_bool(d3d12_dxbc_disasm, false,
@@ -1456,7 +1457,7 @@ bool PipelineCache::GetCurrentStateDescription(
     }
   }
   if (!edram_rov_used) {
-    float poly_offset_host_scale = draw_util::GetD3D10PolygonOffsetScale(
+    float poly_offset_host_scale = draw_util::GetD3D10PolygonOffsetFactor(
         regs.Get<reg::RB_DEPTH_INFO>().depth_format, true);
     // Using ceil here just in case a game wants the offset but passes a value
     // that is too small - it's better to apply more offset than to make depth
@@ -1467,7 +1468,7 @@ bool PipelineCache::GetCurrentStateDescription(
         (poly_offset < 0.0f ? -1 : 1);
     // "slope computed in subpixels ([...] 1/16)" - R5xx Acceleration.
     description_out.depth_bias_slope_scaled =
-        poly_offset_scale * (1.0f / 16.0f);
+        poly_offset_scale * xenos::kPolygonOffsetScaleSubpixelUnit;
   }
   if (tessellated && cvars::d3d12_tessellation_wireframe) {
     description_out.fill_mode_wireframe = 1;
diff --git a/src/xenia/gpu/draw_util.h b/src/xenia/gpu/draw_util.h
index 75d3d4053..d23d0d25a 100644
--- a/src/xenia/gpu/draw_util.h
+++ b/src/xenia/gpu/draw_util.h
@@ -106,7 +106,7 @@ inline reg::RB_DEPTHCONTROL GetDepthControlForCurrentEdramMode(
   return regs.Get<reg::RB_DEPTHCONTROL>();
 }
 
-constexpr float GetD3D10PolygonOffsetScale(
+constexpr float GetD3D10PolygonOffsetFactor(
     xenos::DepthRenderTargetFormat depth_format, bool float24_as_0_to_0_5) {
   if (depth_format == xenos::DepthRenderTargetFormat::kD24S8) {
     return float(1 << 24);
diff --git a/src/xenia/gpu/xenos.h b/src/xenia/gpu/xenos.h
index 97d668513..98fd8741b 100644
--- a/src/xenia/gpu/xenos.h
+++ b/src/xenia/gpu/xenos.h
@@ -347,6 +347,16 @@ constexpr float UNorm24To32(uint32_t n24) {
   return float(n24 + (n24 >> 23)) * (1.0f / float(1 << 24));
 }
 
+// Scale for conversion of slope scales from PA_SU_POLY_OFFSET_FRONT/BACK_SCALE
+// units to those used when the slope is computed from the difference between
+// adjacent pixels, for conversion from the guest to common host APIs or to
+// calculation using max(|ddx(z)|, |ddy(z)|).
+// "slope computed in subpixels (1/12 or 1/16)" - R5xx Acceleration.
+// But the correct scale for conversion of the slope scale from subpixels to
+// pixels is likely 1/16 according to:
+// https://github.com/mesa3d/mesa/blob/54ad9b444c8e73da498211870e785239ad3ff1aa/src/gallium/drivers/radeonsi/si_state.c#L946
+constexpr float kPolygonOffsetScaleSubpixelUnit = 1.0f / 16.0f;
+
 constexpr uint32_t kColorRenderTargetFormatBits = 4;
 constexpr uint32_t kDepthRenderTargetFormatBits = 1;
 constexpr uint32_t kRenderTargetFormatBits =