VideoBackends: Account for pixel quads in bounding box calculation

The GC/Wii GPU rasterizes in 2x2 pixel groups, so bounding box values
will be rounded to the extents of these groups, rather than the exact
pixel. To account for this, we'll round the top/left down to even and
the bottom/right up to odd. I have verified that the values resulting
from this change exactly match a real Wii.

Source/Core/VideoBackends/D3D/D3DRender.cpp

@@ -266,7 +266,16 @@ void Renderer::UnbindTexture(const AbstractTexture* texture)
 
 u16 Renderer::BBoxRead(int index)
 {
-  return static_cast<u16>(BBox::Get(index));
+  u16 value = static_cast<u16>(BBox::Get(index));
+
+  // The GC/Wii GPU rasterizes in 2x2 pixel groups, so bounding box values will be rounded to the
+  // extents of these groups, rather than the exact pixel.
+  if (index == 0 || index == 2)
+    value &= ~1;
+  else
+    value |= 1;
+
+  return value;
 }
 
 void Renderer::BBoxWrite(int index, u16 value)

Source/Core/VideoBackends/D3D12/D3D12Renderer.cpp

@@ -108,7 +108,16 @@ std::unique_ptr<AbstractPipeline> Renderer::CreatePipeline(const AbstractPipelin
 
 u16 Renderer::BBoxRead(int index)
 {
-  return static_cast<u16>(m_bounding_box->Get(index));
+  u16 value = static_cast<u16>(m_bounding_box->Get(index));
+
+  // The GC/Wii GPU rasterizes in 2x2 pixel groups, so bounding box values will be rounded to the
+  // extents of these groups, rather than the exact pixel.
+  if (index == 0 || index == 2)
+    value &= ~1;
+  else
+    value |= 1;
+
+  return value;
 }
 
 void Renderer::BBoxWrite(int index, u16 value)

Source/Core/VideoBackends/OGL/OGLRender.cpp

@@ -867,6 +867,13 @@ u16 Renderer::BBoxRead(int index)
     value = EFB_HEIGHT - value;
   }
 
+  // The GC/Wii GPU rasterizes in 2x2 pixel groups, so bounding box values will be rounded to the
+  // extents of these groups, rather than the exact pixel.
+  if (index == 0 || index == 3)
+    value &= ~1;
+  else
+    value |= 1;
+
   return static_cast<u16>(value);
 }
 

Source/Core/VideoBackends/Software/SWRenderer.cpp

@@ -128,7 +128,16 @@ u32 SWRenderer::AccessEFB(EFBAccessType type, u32 x, u32 y, u32 InputData)
 
 u16 SWRenderer::BBoxRead(int index)
 {
-  return BoundingBox::GetCoordinate(static_cast<BoundingBox::Coordinate>(index));
+  u16 value = BoundingBox::GetCoordinate(static_cast<BoundingBox::Coordinate>(index));
+
+  // The GC/Wii GPU rasterizes in 2x2 pixel groups, so bounding box values will be rounded to the
+  // extents of these groups, rather than the exact pixel.
+  if (index == 0 || index == 2)
+    value &= ~1;
+  else
+    value |= 1;
+
+  return value;
 }
 
 void SWRenderer::BBoxWrite(int index, u16 value)

Source/Core/VideoBackends/Vulkan/VKRenderer.cpp

@@ -133,7 +133,16 @@ void Renderer::SetPipeline(const AbstractPipeline* pipeline)
 
 u16 Renderer::BBoxRead(int index)
 {
-  return static_cast<u16>(m_bounding_box->Get(index));
+  u16 value = static_cast<u16>(m_bounding_box->Get(index));
+
+  // The GC/Wii GPU rasterizes in 2x2 pixel groups, so bounding box values will be rounded to the
+  // extents of these groups, rather than the exact pixel.
+  if (index == 0 || index == 2)
+    value &= ~1;
+  else
+    value |= 1;
+
+  return value;
 }
 
 void Renderer::BBoxWrite(int index, u16 value)