From 2ab6711f43d77d987850a782f5ef88cb9996e399 Mon Sep 17 00:00:00 2001
From: Jules Blok <jules.blok@gmail.com>
Date: Tue, 27 Dec 2016 14:26:11 +0100
Subject: [PATCH] VideoBackends: Use the full depth range when inverted depth
 range is unsupported.

---
 Source/Core/VideoBackends/D3D/Render.cpp      | 15 ++++++++-------
 Source/Core/VideoBackends/D3D12/Render.cpp    | 15 ++++++++-------
 Source/Core/VideoBackends/Vulkan/Renderer.cpp | 13 ++++++++-----
 3 files changed, 24 insertions(+), 19 deletions(-)

diff --git a/Source/Core/VideoBackends/D3D/Render.cpp b/Source/Core/VideoBackends/D3D/Render.cpp
index 1877fde9d7..35fd561e5e 100644
--- a/Source/Core/VideoBackends/D3D/Render.cpp
+++ b/Source/Core/VideoBackends/D3D/Render.cpp
@@ -573,10 +573,13 @@ void Renderer::SetViewport()
     Y += Ht;
     Ht = -Ht;
   }
+
+  // If an inverted depth range is used, which D3D doesn't support,
+  // we need to calculate the depth range in the vertex shader.
   if (xfmem.viewport.zRange < 0.0f)
   {
-    min_depth = 1.0f - min_depth;
-    max_depth = 1.0f - max_depth;
+    min_depth = 0.0f;
+    max_depth = GX_MAX_DEPTH;
   }
 
   // In D3D, the viewport rectangle must fit within the render target.
@@ -585,11 +588,9 @@ void Renderer::SetViewport()
   Wd = (X + Wd <= GetTargetWidth()) ? Wd : (GetTargetWidth() - X);
   Ht = (Y + Ht <= GetTargetHeight()) ? Ht : (GetTargetHeight() - Y);
 
-  // We do depth clipping and depth range in the vertex shader instead of relying
-  // on the graphics API. However we still need to ensure depth values don't exceed
-  // the maximum value supported by the console GPU. We also need to account for the
-  // fact that the entire depth buffer is inverted on D3D, so we set GX_MAX_DEPTH as
-  // an inverted near value.
+  // We use an inverted depth range here to apply the Reverse Z trick.
+  // This trick makes sure we match the precision provided by the 1:0
+  // clipping depth range on the hardware.
   D3D11_VIEWPORT vp = CD3D11_VIEWPORT(X, Y, Wd, Ht, 1.0f - max_depth, 1.0f - min_depth);
   D3D::context->RSSetViewports(1, &vp);
 }
diff --git a/Source/Core/VideoBackends/D3D12/Render.cpp b/Source/Core/VideoBackends/D3D12/Render.cpp
index ce22583c68..2b8e204ee2 100644
--- a/Source/Core/VideoBackends/D3D12/Render.cpp
+++ b/Source/Core/VideoBackends/D3D12/Render.cpp
@@ -478,10 +478,13 @@ void Renderer::SetViewport()
     y += height;
     height = -height;
   }
+
+  // If an inverted depth range is used, which D3D doesn't support,
+  // we need to calculate the depth range in the vertex shader.
   if (xfmem.viewport.zRange < 0.0f)
   {
-    min_depth = 1.0f - min_depth;
-    max_depth = 1.0f - max_depth;
+    min_depth = 0.0f;
+    max_depth = GX_MAX_DEPTH;
   }
 
   // In D3D, the viewport rectangle must fit within the render target.
@@ -490,11 +493,9 @@ void Renderer::SetViewport()
   width = (x + width <= GetTargetWidth()) ? width : (GetTargetWidth() - x);
   height = (y + height <= GetTargetHeight()) ? height : (GetTargetHeight() - y);
 
-  // We do depth clipping and depth range in the vertex shader instead of relying
-  // on the graphics API. However we still need to ensure depth values don't exceed
-  // the maximum value supported by the console GPU. We also need to account for the
-  // fact that the entire depth buffer is inverted on D3D, so we set GX_MAX_DEPTH as
-  // an inverted near value.
+  // We use an inverted depth range here to apply the Reverse Z trick.
+  // This trick makes sure we match the precision provided by the 1:0
+  // clipping depth range on the hardware.
   D3D12_VIEWPORT vp = {x, y, width, height, 1.0f - max_depth, 1.0f - min_depth};
   D3D::current_command_list->RSSetViewports(1, &vp);
 }
diff --git a/Source/Core/VideoBackends/Vulkan/Renderer.cpp b/Source/Core/VideoBackends/Vulkan/Renderer.cpp
index a375d89012..43d3f5e280 100644
--- a/Source/Core/VideoBackends/Vulkan/Renderer.cpp
+++ b/Source/Core/VideoBackends/Vulkan/Renderer.cpp
@@ -1649,15 +1649,18 @@ void Renderer::SetViewport()
     y += height;
     height = -height;
   }
+
+  // If an inverted depth range is used, which D3D doesn't support,
+  // we need to calculate the depth range in the vertex shader.
   if (xfmem.viewport.zRange < 0.0f)
   {
-    min_depth = 1.0f - min_depth;
-    max_depth = 1.0f - max_depth;
+    min_depth = 0.0f;
+    max_depth = GX_MAX_DEPTH;
   }
 
-  // If we do depth clipping and depth range in the vertex shader we only need to ensure
-  // depth values don't exceed the maximum value supported by the console GPU. If not,
-  // we simply clamp the near/far values themselves to the maximum value as done above.
+  // We use an inverted depth range here to apply the Reverse Z trick.
+  // This trick makes sure we match the precision provided by the 1:0
+  // clipping depth range on the hardware.
   VkViewport viewport = {x, y, width, height, 1.0f - max_depth, 1.0f - min_depth};
   StateTracker::GetInstance()->SetViewport(viewport);
 }