Change color of mesh triangle based on Y position in world space

Question

Hi,

I have a mesh that I am trying to dynamically change the colors of the triangles based on their Y position in world space. I know that I have to apply the same color to the 3 vertices that make up a triangle, so that it is one solid color.

I've only just started working directly with meshes and made some progress, but the next stage is causing me problems.

How can I go through the whole mesh and apply to correct color to the 3 vertices so that each triangle is one solid color? The code below seems to get 'out of sequence' as triangle vertices have various colors applied:

 function MeshDetails(){
     meshFilter = gameObject.GetComponent(MeshFilter);
     
     mesh = meshFilter.mesh;
     vertices = mesh.vertices;
     vertexColors = mesh.colors;
     
     MeshDetailsGathered = true;
 }
 
 //-------------------------------------------------------------------------------------------------------
 //-------------------------------------------------------------------------------------------------------
 
 function ChangeColors()
 {
     
     //Iterate through vertices
     for(var i : int = 0; i <= vertices.Length - 3; ++i) //-3 as otherwise I get out of index errors
     {
 
         mesh.colors = vertexColors;
         //If vertices count matches the index (Triangle) number
         if(i == i){
             
             //Calculate Average Position for future color allocation
             //TransformPoint transforms a point from local coordinates to world coordinates wit respect to the transforms position/rotation/scale.
             var p1 : Vector3 = transform.TransformPoint(vertices[i]);
             var p2 : Vector3 = transform.TransformPoint(vertices[i+1]);
             var p3 : Vector3 = transform.TransformPoint(vertices[i+2]);
             
             //Calculate Center point
             var middlePositon = (p1 + p2 + p3) / 3;
             
             //Add Position to Debug list
             averagePositionsOfTriangles.Add(middlePositon);
 
             //Check positions and apply colors            
             if(middlePositon.y < level1Position){
                 //Apply new color and count up each time to fill the vertex range which makes up the triangle
                 vertexColors[i] = level1Color;
                 vertexColors[i+1] = level1Color;
                 vertexColors[i+2] = level1Color;
             }
              
             if(middlePositon.y > level1Position && middlePositon.y < level2Position){
                 //Apply new color and count up each time to fill the vertex range which makes up the triangle
                 vertexColors[i] = level2Color;
                 vertexColors[i+1] = level2Color;
                 vertexColors[i+2] = level2Color;
             }             
 
             if(middlePositon.y > level2Position && middlePositon.y < level3Position){
                 //Apply new color and count up each time to fill the vertex range which makes up the triangle
                 vertexColors[i] = level3Color;
                 vertexColors[i+1] = level3Color;
                 vertexColors[i+2] = level3Color;
             }              
 
             if(middlePositon.y > level3Position && middlePositon.y < level4Position){
                 //Apply new color and count up each time to fill the vertex range which makes up the triangle
                 vertexColors[i] = level4Color;
                 vertexColors[i+1] = level4Color;
                 vertexColors[i+2] = level4Color;
             } 
             
             if(middlePositon.y > level5Position){
                 //Apply new color and count up each time to fill the vertex range which makes up the triangle
                 vertexColors[i] = level5Color;
                 vertexColors[i+1] = level5Color;
                 vertexColors[i+2] = level5Color;
             }   
 
         }
     }
     
     //Update the vertex colors
     mesh.colors = vertexColors;
     
     //Sort array function
     averagePositionsOfTriangles.Sort(ByVector2Y);
     
     //Get Y min and max values
     maxYpositionUsed = averagePositionsOfTriangles[1].y;
     minYPOsitionUsed = averagePositionsOfTriangles[averagePositionsOfTriangles.Count-1].y;
 }

By the way I have rebuilt the mesh so that each triangle has unique vertices for the low-poly look

Am I at least on the right track?

Any suggestions are welcome!

Answer 1

Best Answer

Answer by robertbu · Aug 26, 2013 at 08:02 PM

Your approach looks like it will work, but you have an errors line 23:

   if(i == i){

That's always going to evaluate to 'true'. I recommend you change your 'for' loop as follows:

 for(var i : int = 0; i <= vertices.Length - 3; i = i + 3)

This will then count by 3s. Remove the if '(i == i)'.

There is also a minor hole in your 'if' logic in that (uncommon) situation where a value is exactly on a boundary, you won't set the color. Add some '

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robertbu · Aug 26, 2013 at 08:30 PM 0

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FYI: Vertex colors only work with a shader that supports vertex colors.

code-blep · Aug 26, 2013 at 08:33 PM 0

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Great points robertbu! The counting by 3 in a for loop kept tripping me up. Very useful! The code now works, although in the editor movement is quite jerky now compared to the original script I posted, which is odd. Any ideas?

robertbu · Aug 26, 2013 at 08:37 PM 0

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No specific ideas. Is the jerkiness due to a frame rate drop or something else?

code-blep · Aug 26, 2013 at 08:40 PM 0

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Framerate is good +150 fps. What is weird is if I go into the scene view after allocating the colors, do a quick camera movement, and go back into the game window, the movement is fine. It also compiles and runs fine as an exe.

Also if I remove the script after the color change, the movement is normal. I think the script is still in some kind of loop, Will start debugging and mark the question as answered.

Thanks!

code-blep · Aug 26, 2013 at 09:53 PM 0

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Found the problem. The array sort at the end is having to do a lot more work, will find another way to get the numbers I need.

Change color of mesh triangle based on Y position in world space

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