Added "refract" pass to default renderpaths. This has the rendered scene so far (opaque + sky) available in the environment texture unit.

Renamed the "prealpha" pass to "postopaque" (will break custom techniques and renderpaths referring to prealpha.)
If a scene pass has nothing to render, skip it completely during View processing, including rendertarget allocations. This makes the refract pass free when there is no refractive geometry.

Bin/CoreData/RenderPaths/Deferred.xml

@@ -14,7 +14,10 @@
         <texture unit="normal" name="normal" />
         <texture unit="depth" name="depth" />
     </command>
-    <command type="scenepass" pass="prealpha" />
+    <command type="scenepass" pass="postopaque" />
+    <command type="scenepass" pass="refract">
+        <texture unit="environment" name="viewport" />
+    </command>
     <command type="scenepass" pass="alpha" usescissor="true" vertexlights="true" sort="backtofront" metadata="alpha" />
     <command type="scenepass" pass="postalpha" sort="backtofront" />
 </renderpath>

Bin/CoreData/RenderPaths/Forward.xml

@@ -2,7 +2,10 @@
     <command type="clear" color="fog" depth="1.0" stencil="0" />
     <command type="scenepass" pass="base" vertexlights="true" metadata="base" />
     <command type="forwardlights" pass="light" />
-    <command type="scenepass" pass="prealpha" />
+    <command type="scenepass" pass="postopaque" />
+    <command type="scenepass" pass="refract">
+        <texture unit="environment" name="viewport" />
+    </command>
     <command type="scenepass" pass="alpha" usescissor="true" vertexlights="true" sort="backtofront" metadata="alpha" />
     <command type="scenepass" pass="postalpha" sort="backtofront" />
 </renderpath>

Bin/CoreData/RenderPaths/ForwardDepth.xml

@@ -5,7 +5,10 @@
     <command type="clear" color="fog" depth="1.0" stencil="0" />
     <command type="scenepass" pass="base" vertexlights="true" metadata="base" />
     <command type="forwardlights" pass="light" />
-    <command type="scenepass" pass="prealpha" />
+    <command type="scenepass" pass="postopaque" />
+    <command type="scenepass" pass="refract">
+        <texture unit="environment" name="viewport" />
+    </command>
     <command type="scenepass" pass="alpha" usescissor="true" vertexlights="true" sort="backtofront" metadata="alpha" />
     <command type="scenepass" pass="postalpha" sort="backtofront" />
 </renderpath>

Bin/CoreData/RenderPaths/Prepass.xml

@@ -15,7 +15,10 @@
     <command type="scenepass" pass="material" vertexlights="true">
         <texture unit="light" name="light" />
     </command>
-    <command type="scenepass" pass="prealpha"/>
+    <command type="scenepass" pass="postopaque" />
+    <command type="scenepass" pass="refract">
+        <texture unit="environment" name="viewport" />
+    </command>
     <command type="scenepass" pass="alpha" usescissor="true" vertexlights="true" sort="backtofront" metadata="alpha" />
     <command type="scenepass" pass="postalpha" sort="backtofront" />
 </renderpath>

Bin/CoreData/Techniques/DiffSkybox.xml

@@ -1,3 +1,3 @@
 <technique>
-    <pass name="prealpha" vs="Skybox" ps="Skybox" depthwrite="false" />
+    <pass name="postopaque" vs="Skybox" ps="Skybox" depthwrite="false" />
 </technique>

Docs/Reference.dox

@@ -894,7 +894,7 @@ A technique definition looks like this:
 
 \code
 <technique>
-    <pass name="base|litbase|light|alpha|litalpha|prealpha|postalpha|prepass|material|deferred|depth|shadow" vs="VertexShaderName" ps="PixelShaderName"
+    <pass name="base|litbase|light|alpha|litalpha|postopaque|refract|postalpha|prepass|material|deferred|depth|shadow" vs="VertexShaderName" ps="PixelShaderName"
         lighting="unlit|pervertex|perpixel" alphatest="true|false" blend="replace|add|multiply|alpha|addalpha|premulalpha|invdestalpha"
         depthtest="always|equal|less|lessequal|greater|greaterequal" depthwrite="true|false" alphamask="true|false" />
     <pass ... />
@@ -909,7 +909,8 @@ The purposes of the different passes are:
 - light: Renders one per-pixel light's contribution additively for an opaque object.
 - alpha: Renders ambient light, per-vertex lights and fog for a transparent object.
 - litalpha: Renders one per-pixel light's contribution additively for a transparent object
-- prealpha: Custom rendering pass after opaque geometry. Can be used for example to render the skybox.
+- postopaque: Custom rendering pass after opaque geometry. Can be used to render the skybox.
+- refract: Custom rendering pass after postopaque pass. Can sample the viewport texture from the environment texture unit to render refractive objects.
 - postalpha: Custom rendering pass after transparent geometry.
 - prepass: %Light pre-pass only - renders normals, specular power and depth to the G-buffer.
 - material: %Light pre-pass only - renders opaque geometry final color by combining ambient light, per-vertex lights and per-pixel light accumulation.
@@ -927,6 +928,8 @@ The optional "litbase" pass reduces draw call count by combining ambient lightin
 
 "Alphamask" is not an actual rendering state, but a hint which tells that the pixel shader will use discard based on alpha. Because this may interfere with the early-Z culling, materials without the alpha masking hint will be drawn first.
 
+The refract pass requires pingponging the scene rendertarget to a texture, but this will not be performed if there is no refractive geometry to render, so there is no unnecessary cost to it.
+
 
 \page Shaders Shaders
 

Source/Engine/Graphics/GraphicsDefs.cpp

@@ -76,7 +76,8 @@ StringHash PASS_SHADOW("shadow");
 StringHash PASS_DEFERRED("deferred");
 StringHash PASS_PREPASS("prepass");
 StringHash PASS_MATERIAL("material");
-StringHash PASS_PREALPHA("prealpha");
+StringHash PASS_POSTOPAQUE("postopaque");
+StringHash PASS_REFRACT("refract");
 StringHash PASS_POSTALPHA("postalpha");
 
 Vector3 DOT_SCALE(1 / 3.0f, 1 / 3.0f, 1 / 3.0f);

Source/Engine/Graphics/GraphicsDefs.h

@@ -244,7 +244,8 @@ extern StringHash PASS_SHADOW;
 extern StringHash PASS_DEFERRED;
 extern StringHash PASS_PREPASS;
 extern StringHash PASS_MATERIAL;
-extern StringHash PASS_PREALPHA;
+extern StringHash PASS_POSTOPAQUE;
+extern StringHash PASS_REFRACT;
 extern StringHash PASS_POSTALPHA;
 
 // Scale calculation from bounding box diagonal.

Source/Engine/Graphics/View.cpp

@@ -1078,11 +1078,13 @@ void View::UpdateGeometries()
         for (unsigned i = 0; i < renderPath_->commands_.Size(); ++i)
         {
             const RenderPathCommand& command = renderPath_->commands_[i];
-            if (!command.enabled_)
+            if (!IsNecessary(command))
                 continue;
             
             if (command.type_ == CMD_SCENEPASS)
             {
+                BatchQueue* passQueue = &batchQueues_[command.pass_];
+                
                 item.workFunction_ = command.sortMode_ == SORT_FRONTTOBACK ? SortBatchQueueFrontToBackWork :
                     SortBatchQueueBackToFrontWork;
                 item.start_ = &batchQueues_[command.pass_];
@@ -1248,7 +1250,7 @@ void View::ExecuteRenderPathCommands()
         unsigned lastCommandIndex = 0;
         for (unsigned i = 0; i < renderPath_->commands_.Size(); ++i)
         {
-            if (!renderPath_->commands_[i].enabled_)
+            if (!IsNecessary(renderPath_->commands_[i]))
                 continue;
             lastCommandIndex = i;
         }
@@ -1256,7 +1258,7 @@ void View::ExecuteRenderPathCommands()
         for (unsigned i = 0; i < renderPath_->commands_.Size(); ++i)
         {
             RenderPathCommand& command = renderPath_->commands_[i];
-            if (!command.enabled_)
+            if (!IsNecessary(command))
                 continue;
             
             // If command writes and reads the target at same time, pingpong automatically
@@ -1573,6 +1575,11 @@ void View::RenderQuad(RenderPathCommand& command)
     DrawFullscreenQuad(false);
 }
 
+bool View::IsNecessary(const RenderPathCommand& command)
+{
+    return command.enabled_ && (command.type_ != CMD_SCENEPASS || !batchQueues_[command.pass_].IsEmpty());
+}
+
 bool View::CheckViewportRead(const RenderPathCommand& command)
 {
     for (unsigned i = 0; i < MAX_TEXTURE_UNITS; ++i)
@@ -1614,7 +1621,7 @@ void View::AllocateScreenBuffers()
     for (unsigned i = 0; i < renderPath_->commands_.Size(); ++i)
     {
         const RenderPathCommand& command = renderPath_->commands_[i];
-        if (!command.enabled_)
+        if (!IsNecessary(command))
             continue;
         if (CheckViewportRead(command))
         {

Source/Engine/Graphics/View.h

@@ -161,6 +161,8 @@ private:
     void SetTextures(RenderPathCommand& command);
     /// Perform a quad rendering command.
     void RenderQuad(RenderPathCommand& command);
+    /// Check if a command is enabled and has content to render. To be called only after render update has completed for the frame.
+    bool IsNecessary(const RenderPathCommand& command);
     /// Check if a command reads the rendered scene.
     bool CheckViewportRead(const RenderPathCommand& command);
     /// Allocate needed screen buffers.