Possible shader interference when updating matrix

Questions & Answers
1

Greetings,

I’m currently facing a problem regarding updating values of several arrays inside a list.
The basic setup is the following: a List containing 2 arrays each comprised of 16 float numbers.
Earlier I had a problem problem regarding the update of the each array: whenever I update one, it also instantly affects ALL other arrays present in the list, something that I didn’t want to happen.
Now the problem is somewhat similar except the update earlier mentioned doesn’t happen instantly, i.e.:

  1. The matrix present in matrixList[0] is updated with calculated values;
  2. matrixList[1] remains unchanged;
  3. Swap to matrixList[1] to update her with new calculated values. It copies the values from matrixList[0] instead of the new calculated values.

The code is as follows (for a matter of simplicity I omitted most of the code, however I can post more if needed):

enter code herepublic class Homography : MonoBehaviour {

            public float[] matrix;
            public const int arraySize = 16;
            public List<float[]> matrixList;
            
            void Start () {
            	InitMatrixList();
            }
            
            void InitMatrixList(){
            	
            	int numPlanes = manager.numExistPlanes;
            	matrixList = new List<float[]>();
            	for(int i = 0; i <= numPlanes; i++){
            		matrixList.Add(new float[16]);
            	}
            }
            
            void LateUpdate () {
            	
            	planeMatrixNum = manager.activePlaneNum;
            	matrix = matrixList[planeMatrixNum-1]; 
            	FindHomography(ref source, ref destination, ref matrix);
            	
            	meshMaterial.SetVector("matrixRow_1", new Vector4(matrix[0], matrix[4], matrix[8], matrix[12]));
            	meshMaterial.SetVector("matrixRow_2", new Vector4(matrix[1], matrix[5], matrix[9], matrix[13]));
            	meshMaterial.SetVector("matrixRow_3", new Vector4(matrix[2], matrix[6], matrix[10], matrix[14]));
            	meshMaterial.SetVector("matrixRow_4", new Vector4(matrix[3], matrix[7], matrix[11], matrix[15]));
            	
            }
            
}

About the desired process flow of this application:

  1. GameObject 1 is selected in the scene and has its position changed;
  2. matrixList[0] is selected and updated with new values based on the GO1 position changes;
  3. GameObject 2 is selected in the scene and has its position changed;
  4. matrixList[1] is selected and updated with new values based on the GO2 position changes;

This script (Homography.cs) is attached one gameobject only. However the changes done to each of the Matrix present in the matrixList affect other gameobjects. Through debugging I notice he does save the matrix values for GameObject 1, however the same does not happen for GameObject 2, he just copies the values obtained from the matrix of GameObject 1 and applies them to his own matrix.

Also I don’t really know if it’s relevant since I have very limited experience but these matrix values (matrixRow_X) are used within a shader (not written by me).

EDIT: Used an old version of the code by mistake. Also added more info.

2

You are putting the same matrix array into each slot - you mean to do this I think:

void InitMatrixList(){
 
    int numPlanes = manager.numExistPlanes;
    matrixList = new List<float[]>();
    for(int i = 0; i <= numPlanes; i++){
       matrixList.Add(new float[16]);
    }
}

But I’m not sure how any of that would refer to your matrix variable (the one you were repeatedly adding). No chance the shader is doing this - wish it could :slight_smile: