Renderer|FX: Check 5 depth points for partial occlusion of a light

Could be improved further with resolution independence, and/or
taking into account the radius of the light source.

doomsday/client/data/renderer.pack/shaders/lensflares.vsh

@@ -1,5 +1,6 @@
 uniform highp mat4 uMvpMatrix;
 uniform highp vec2 uViewUnit;
+uniform highp vec2 uPixelAsUv;
 uniform sampler2D uDepthBuf;
 
 attribute highp vec4 aVertex;
@@ -11,40 +12,44 @@ attribute highp vec2 aUV3;
 varying highp vec4 vColor;
 varying highp vec2 vUV;
 
+bool isOccluded(highp vec2 uv) {
+    float depth = texture2D(uDepthBuf, uv).r;
+    return (depth < (gl_Position.z/gl_Position.w + 1.0) / 2.0);
+}
+
+float occlusionLevel() {
+    highp vec2 depthUv = gl_Position.xy / gl_Position.w / 2.0 + vec2(0.5, 0.5);
+    float occ = 0.0;
+    if(!isOccluded(depthUv)) occ += 0.2;
+    if(!isOccluded(depthUv + vec2(uPixelAsUv.x * 4.0, uPixelAsUv.y))) occ += 0.2;
+    if(!isOccluded(depthUv - vec2(uPixelAsUv.x * 4.0, uPixelAsUv.y))) occ += 0.2;
+    if(!isOccluded(depthUv + vec2(uPixelAsUv.x, uPixelAsUv.y * 4.0))) occ += 0.2;
+    if(!isOccluded(depthUv - vec2(uPixelAsUv.x, uPixelAsUv.y * 4.0))) occ += 0.2;
+    return occ;
+}
+
 void main(void) {
     vUV = aUV;
     vColor = aColor;
 
     gl_Position = uMvpMatrix * aVertex;
 
-    // Is this occluded in the depth buffer?
-    highp vec2 depthUv = gl_Position.xy / gl_Position.w / 2.0 + vec2(0.5, 0.5);
-    float depth = texture2D(uDepthBuf, depthUv).r;
-/*    if(depth < (gl_Position.z/gl_Position.w + 1.0)/2.0) {
-        // Occluded!
+    // Is the origin occluded in the depth buffer?
+    float ocl = occlusionLevel();    
+    if(ocl <= 0.0) {
+        // Occluded! Make it invisibile and leave the quad zero-sized.
         vUV = aUV;
         vColor = vec4(0.0, 0.0, 0.0, 0.0);
-        return;        
-    }    */
+        return;
+    }
+    else {
+        vColor.a *= ocl;
+    }
 
     // Position on the axis that passes through the center of the view.
     highp float axisPos = aUV3.s;
     gl_Position.xy *= axisPos;
 
+    // Position the quad corners.
     gl_Position.xy += aUV2 * uViewUnit * vec2(gl_Position.w);
-
-    /*
-    // Testing
-    vColor = vec4(1.0, 1.0, 1.0, 1.0);
-    vUV = (aUV2 + 1.0) / 2.0;
-    gl_Position.xy = aUV2;
-    gl_Position.z = 0.0;
-    gl_Position.w = 1.0;
-    */
-
-    if(depth < (gl_Position.z/gl_Position.w + 1.0)/2.0) {
-        // Occluded!
-        vColor = vec4(1.0, 0.0, 0.0, 1.0);
-    }    
-
 }

doomsday/client/src/render/fx/lensflares.cpp

@@ -227,6 +227,7 @@ DENG2_PIMPL(LensFlares)
     Drawable drawable;
     GLUniform uMvpMatrix;
     GLUniform uViewUnit;
+    GLUniform uPixelAsUv;
     GLUniform uAtlas;
     GLUniform uDepthBuf;
 
@@ -236,6 +237,7 @@ DENG2_PIMPL(LensFlares)
         , buffer(0)
         , uMvpMatrix("uMvpMatrix", GLUniform::Mat4)
         , uViewUnit ("uViewUnit",  GLUniform::Vec2)
+        , uPixelAsUv("uPixelAsUv", GLUniform::Vec2)
         , uAtlas    ("uTex",       GLUniform::Sampler2D)
         , uDepthBuf ("uDepthBuf",  GLUniform::Sampler2D)
     {}
@@ -255,7 +257,7 @@ DENG2_PIMPL(LensFlares)
         buffer = new VBuf;
         drawable.addBuffer(buffer);
         self.shaders().build(drawable.program(), "fx.lensflares")
-                << uMvpMatrix << uViewUnit
+                << uMvpMatrix << uViewUnit << uPixelAsUv
                 << uAtlas << uDepthBuf;
 
         uAtlas = res->atlas;
@@ -485,9 +487,12 @@ void LensFlares::draw()
     Rectanglef const rect = viewRect();
     float const    aspect = rect.height() / rect.width();
 
+    Canvas &canvas = ClientWindow::main().canvas();
+
     d->uViewUnit  = Vector2f(aspect, 1.f);
+    d->uPixelAsUv = Vector2f(1.f / canvas.width(), 1.f / canvas.height());
     d->uMvpMatrix = GL_GetProjectionMatrix() * Rend_GetModelViewMatrix(console());
-    d->uDepthBuf  = ClientWindow::main().canvas().depthBufferTexture();
+    d->uDepthBuf  = canvas.depthBufferTexture();
 
     GLState::push()
             .setCull(gl::None)

doomsday/libgui/include/de/gui/gltarget.h

@@ -177,9 +177,9 @@ class LIBGUI_PUBLIC GLTarget : public Asset
 
     /**
      * Sets the subregion inside the render target where scissor and viewport
-     * will be constrained to. Scissor and viewport can still be defined as if
-     * the entire window was in use; the target window only applies an offset
-     * and scaling to both.
+     * will be scaled into. Scissor and viewport can still be defined as if the
+     * entire window was in use; this only applies an offset and scaling to
+     * both.
      *
      * @param rect   Target window rectangle. Set a null rectangle to
      *               use the entire window (like normally).