add passlist for imgui

assets/example.passlist

@@ -0,0 +1,58 @@
+passlist "Forward Passlist"
+{
+    attachment "DepthBuffer"
+    {
+        format "PreferredDepthStencil"
+    }
+
+    pass "DepthPrepass"
+    {
+        impl "Depth"
+        {
+            MatPass "DepthPass"
+        }
+
+        depthstenciloutput "DepthBuffer"
+    }
+
+    attachment "ForwardOutput"
+    {
+        format "RGBA16F"
+    }
+
+    pass "ForwardPass"
+    {
+        impl "Forward"
+        output "Output" "ForwardOutput"
+        depthstencilinput "DepthBuffer"
+        depthstenciloutput "DepthBuffer"
+        flag "LightShadowing"
+    }
+
+    attachment "Gamma"
+    {
+        format "RGBA8"
+    }
+
+    pass "Gamma correction"
+    {
+        impl "PostProcess"
+        {
+            Shader "PostProcess.GammaCorrection"
+        }
+
+        input "Input" "ForwardOutput"
+        output "Output" "Gamma"
+    }
+
+    attachmentproxy "ImguiOutput" "Gamma"
+
+    pass "Imgui"
+    {
+        impl "Imgui"
+        input "Input" "Gamma"
+        output "Output" "ImguiOutput"
+    }
+
+    output "ImguiOutput"
+}