Fix image dilation (closing #108)

- Using pixel(=texel) coordinates and integer offsets
 - Using a single channel stencil texture instead of a 4-channel one

modules/newhorizons/shaders/dilation_fs.glsl

@@ -30,6 +30,8 @@ out vec4 color;
 uniform sampler2D tex;
 uniform sampler2D stencil;
 
+// We conside the 8-neighborhood of a texel, so going a stepsize of '1' in both
+// directions
 vec2 offsets[8] = {
     vec2(-1.0, -1.0),
     vec2(-1.0,  0.0),
@@ -41,38 +43,52 @@ vec2 offsets[8] = {
     vec2(1.0,   1.0)
 };
 
-vec3 gatherColors(vec2 position) {
+// Collect the contributing colors from the neighboring texels and return the
+// averaged value of all texels that passed the masking test based on 'stencil'
+vec3 gatherNeighboringColors() {
     vec2 texSize = textureSize(tex, 0);
 
+    // The total number of contributing texels
     int nContributions = 0;
+
+    // The summed color of all contributing texels
     vec3 totalColor = vec3(0.0);
 
     for (int i = 0; i < 8; i++) {
+        // gl_FragCoord is in pixel coordinates; the ProjectionComponent sets
+        // the viewport such that pixels=texels, so we can use gl_FragCoord as an
+        // integer texel coordinate
+        // First offsetting them, then dividing by the texture size to get to [0,1]
         vec2 samplePosition = (gl_FragCoord.xy + offsets[i]) / texSize;
 
+        // The stencelling determines the areas that we have to enlarge, such that we
+        // do not enlarge a previously enlarged area
         if (texture(stencil, samplePosition).r != 0.0) {
-            vec3 c = texture(tex, samplePosition).rgb;
-            totalColor += c;
+            totalColor += texture(tex, samplePosition).rgb;
             nContributions++;
         }
     }
 
-    return totalColor / nContributions;
+    // GLSL normally doesn't have a problem taking vec3(0.0)/0.0 but we don't want to
+    // tempt the compiler gods
+    if (nContributions > 0) {
+        return totalColor / nContributions;
+    }
+    else {
+        return vec3(0.0);
+    }
+
 }
 
 void main() {
-    vec4 c = texture(tex, vs_uv); 
-    float s = texture(stencil, vs_uv).r;
-
-    if (s == 0.0) {
+    if (texture(stencil, vs_uv).r == 0.0) {
         // This means that the current fragment/texel we are looking at has not been
         // projected on and we only want to do the dilation into these texels
-
-        color = vec4(gatherColors(vs_uv), 1.0);
+        color = vec4(gatherNeighboringColors(), 1.0);
     }
     else {
         // We are in a region where an image has been projected, so we can reuse the
         // already sampled version
-        color = c;
+        color = texture(tex, vs_uv);
     }
-}
+}

modules/newhorizons/shaders/renderableModelProjection_fs.glsl

@@ -24,14 +24,14 @@
 
 #version __CONTEXT__
 
-#include "PowerScaling/powerScaling_vs.hglsl"
-
 in vec4 vs_position;
 in vec4 vs_normal;
 in vec2 vs_uv;
 in vec4 ProjTexCoord;
 
-layout (location = 0) out vec4 color; 
+layout (location = 0) out vec4 color;
+// Even though the stencel texture is only a single channel, we still need to
+// output a vec4, or the result will disappear
 layout (location = 1) out vec4 stencil;
 
 uniform sampler2D projectionTexture;

modules/newhorizons/util/projectioncomponent.cpp

@@ -558,7 +558,8 @@ bool ProjectionComponent::generateProjectionLayerTexture() {
 
         _dilation.stencilTexture = std::make_unique<ghoul::opengl::Texture>(
             glm::uvec3(maxSize, maxSize / 2, 1),
-            ghoul::opengl::Texture::Format::RGBA
+            ghoul::opengl::Texture::Format::Red,
+            ghoul::opengl::Texture::Format::Red
         );
 
         if (_dilation.stencilTexture) {