add comment in depth image projection shader for clarification

Author: mohammedari

opengl_ros_lib/shader/fs_depth_image_projection.glsl

@@ -37,7 +37,7 @@ void main(void)
         accumulatedProbability = gridMapAccumulationWeight;
 
     //store accumulated value in R channel
-    //store 1.0 in G channel if the pixel is on the line
+    //store 1.0 in G channel if valid depth is measured at the line
     //always store 1.0 in B channel 
     fragmentColor = vec3(accumulatedProbability, validDepthMeasured, 1.0); 
 }

opengl_ros_lib/shader/gs_depth_image_projection.glsl

@@ -11,8 +11,8 @@ in vertex
     float depth;
 } input_vertices[1];
 
-out float depth;
-out float hitDepth;
+out float depth;    //depth value of the pixel on the line
+out float hitDepth; //depth value of the end of the line
 
 void main(void)
 {

opengl_ros_lib/shader/vs_depth_image_projection.glsl

@@ -45,10 +45,9 @@ void main(void)
     );
     float depth = texelFetch(depthTexture, depthUV, 0).x * depthUnit; //convert to meter scale
 
+    //If valid depth is not measured at that pixel, treat as maximum depth is measured
     if (depth < validDepthInMeter.x || validDepthInMeter.y < depth)
-    {
-        depth = validDepthInMeter.y; //set to the max value
-    }
+        depth = validDepthInMeter.y;
 
     //Now, convert image pixel (ix, iy, iz) to point in the optical frame (px, py, pz).
     //First, calculate px/pz and px/pz from ix/iz and iy/iz using projection matrix. 
@@ -66,7 +65,7 @@ void main(void)
     //Projecting the point to the occupancy grid plane, in top down orthognal projection
     output_vertex.position = vec4(
         p.x / gridMapResolution / gridMapSize.x * 2,     //convert to -1 to 1
-        p.y / gridMapResolution / gridMapSize.y * 2,     //set the origin on the bottom and flip upside down
+        p.y / gridMapResolution / gridMapSize.y * 2,     //set the origin at the center and flip upside down
         p.z / (gridMapLayerHeight / 2),                  //mapping -height/2 to height/2, to -1 to 1
         1.0
     );