I can't stop my compute shader code from overwriting items in an array instead of using empty indices

Question

#pragma kernel CombTreeData;


bool SetEmptyIndex(int val) //write to an unwritten (-1) index and set it to val
{
    for (int i = 0; i < 10;i++)
    {
        if (emptyIndices[i] == -1)
        {
            emptyIndices[i] = val;
            return true;
        }
    }
    return false;
}

int GetAndClearEmptyIndex() //return first written index as val and clear that index to -1 (returns -1 if no index found)
{
    int val = 0;
    for (int i = 0; i < 10;i++)
    {
        if (emptyIndices[i] != -1)
        {
            val = emptyIndices[i];
            emptyIndices[i] = -1;
            return val;
        }
    }
    return -1;
}

[numthreads(1,1,1)]
void CombTreeData(uint3 id : SV_DispatchThreadID)
{
    for (int treePointer = 0; treePointer < 50000;treePointer++) // For all possiable trees, living or dead
    {
        if (Trees[treePointer].plantState == 0 && Trees[treePointer].growth > -1) // if the tree at index is dead
        {
            if (SetEmptyIndex(treePointer)) // Save the dead tree's index to the list of emptyIndices
            {
                Trees[treePointer].growth = -1; // Growth of -1 marks the index as already saved to the emptyIndices
            }
            
        }
        if (Trees[treePointer].plantState > 2) // if tree wants to create seeds
        {
            for (int i = 0; i < 4; i++) // Attempt 4 times
            {
                if (Trees[treePointer].plantState >2) // if tree still wants to create seeds
                {
                    int getEmptyVal = GetAndClearEmptyIndex(); // Find empty index and clear it
                    if (getEmptyVal != -1) // If empty index found succesfully
                    {
                        Trees[getEmptyVal].plantState = 1; // Empty tree index is now a seed
                        Trees[getEmptyVal].growth = 0; // with 0 growth
                        Trees[getEmptyVal].pos = Trees[treePointer].pos; // At the position of the seed-creating tree
                        Trees[treePointer].plantState -= 1; // The seed creating tree loses a seed
                    }
                }
            }
            
        }
        
    }
    
}

Hello, sorry for big code dump! Essentially, i have a list of ints set to -1 called emptyIndecies. I loop through a large array of trees, if a slot in the tree array is empty, I save that empty index to the emptyIndecies array for later use. If a tree wants to make new seeds, i search the emptyIndicies array for an empty tree array index to use, clear it from emptyIndecies and turn that index in the tree array into a seed.

This works great for the first batch of seeds, but after 10 or so trees (10 is the length of emptyIndecies), the new seeds seem to all overrite the same index, meaning they dissapear as soon as a new seed is spawned. I have no idea why!

I have looked through the code, checked the ifs and the loops. My best guess at this point is that I've done something the shader doesn't like, as i am very new to working with compute shaders. Either that or I've missed a silly error. My aim is to track a handfull of empty indecies in the tree array to be used for spawning new seeds.

Answer 1

I've found out that the problem stems from the compute shader not wanting to write an array at variable indices. However, it can accurately write to variable indices of a structured buffer that stores an array. So even though i don't plan to pass this data to a c# script, storing it as a buffer allows the shader to dynamically index to it and execute my code. (which is a bit pedantic of the shader imo)