Merge pull request #117 from EvgeniiG/master

Fix the flipped Y axis (due to a D3D convention) for the procedural sky

Assets/ScriptableRenderLoop/HDRenderPipeline/Sky/ProceduralSky/ProceduralSkyRenderer.cs

             {
                 cmd.SetGlobalTexture("_CameraDepthTexture", builtinParams.depthBuffer);
                 properties.SetFloat("_DisableSkyOcclusionTest", 0.0f);
+                properties.SetFloat("_FlipY", 0.0f);
+                properties.SetFloat("_FlipY", 1.0f);
             }
 
             cmd.DrawMesh(builtinParams.skyMesh, Matrix4x4.identity, m_ProceduralSkyMaterial, 0, 0, properties);

Assets/ScriptableRenderLoop/HDRenderPipeline/Sky/ProceduralSky/Resources/SkyProcedural.shader

 
             float _DisableSkyOcclusionTest;
 
+            float _FlipY;
+
             #define IS_RENDERING_SKY
             #include "AtmosphericScattering.hlsl"
 
                 }
 
                 // Since we only need the world space position, so we don't pass the view-projection matrix.
-                UpdatePositionInput(depthRaw, _InvViewProjMatrix, k_identity4x4, posInput);
+                UpdatePositionInput(depthRaw, _InvViewProjMatrix, k_identity4x4, posInput, _FlipY != 0);
 
                 float4 c1, c2, c3;
                 VolundTransferScatter(posInput.positionWS, c1, c2, c3);

Assets/ScriptableRenderLoop/ShaderLibrary/Common.hlsl

 // From deferred or compute shader
 // depth must be the depth from the raw depth buffer. This allow to handle all kind of depth automatically with the inverse view projection matrix.
 // For information. In Unity Depth is always in range 0..1 (even on OpenGL) but can be reversed.
-void UpdatePositionInput(float depth, float4x4 invViewProjectionMatrix, float4x4 ViewProjectionMatrix, inout PositionInputs posInput)
+// It may be necessary to flip the Y axis as the origin of the screen-space coordinate system
+// of Direct3D is at the top left corner of the screen, with the Y axis pointing downwards.
+void UpdatePositionInput(float depth, float4x4 invViewProjectionMatrix, float4x4 ViewProjectionMatrix,
+                         inout PositionInputs posInput, bool flipY = false)
-    // TODO: Do we need to flip Y axis here on OGL ?
-    posInput.positionCS = float4(posInput.positionSS.xy * 2.0 - 1.0, depth, 1.0);
-    float4 hpositionWS = mul(invViewProjectionMatrix, posInput.positionCS);
+    float2 screenSpacePos;
+    screenSpacePos.x = posInput.positionSS.x;
+    screenSpacePos.y = flipY ? 1.0 - posInput.positionSS.y : posInput.positionSS.y;
+
+    posInput.positionCS = float4(screenSpacePos * 2.0 - 1.0, depth, 1.0);
+    float4 hpositionWS  = mul(invViewProjectionMatrix, posInput.positionCS);
     posInput.positionWS = hpositionWS.xyz / hpositionWS.w;
 
     // The compiler should optimize this (less expensive than reconstruct depth VS from depth buffer)