colormapper.sol

// SPDX-License-Identifier: MIT

pragma solidity ^0.8.7;
pragma abicoder v2;


contract ArrayTest {
    
    function colourToString(uint r, uint g, uint b) private pure returns(string memory) {
        bytes memory alphabet = "0123456789abcdef";
        bytes memory str = new bytes(7);
        str[0] = '#';
        str[1] = alphabet[r >> 4];
        str[2] = alphabet[r & 0x0f];
        str[3] = alphabet[g >> 4];
        str[4] = alphabet[g & 0x0f];
        str[5] = alphabet[b >> 4];
        str[6] = alphabet[b & 0x0f];
        return string(str);
    }    
    

   function getColourMap(uint tokenId) public view returns (string[8] memory){
        uint8[100] memory array = [5,228,119,255,5,228,119,255,122,191,72,255,5,228,119,255,5,228,119,255,5,228,119,255,122,191,72,255,0,0,0,0,122,191,72,255,5,228,119,255,164,13,103,255,0,0,0,0,5,228,119,255,0,0,0,0,164,13,103,255,0,0,0,0,122,191,72,255,164,13,103,255,122,191,72,255,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0];//_pixelArrays[tokenId];
        // We limit to 8 colours per invader because EVM limitations of no dynamic arrays within the function scope
        string[8] memory colourmap;
        uint[8] memory found;
        string memory colourHex;
        uint existingIdx;
        

        // convert to hex, loop through pixels, check if new colour & add to list of hex #RRGGBB
        for (uint8 i=0; i<100 ; i+=4){
            uint r  = array[i];
            uint g  = array[i + 1];
            uint8 b  = array[i + 2];
            
            // colour as integer
            // add 0xff alpha so we distinguish 0x000000 black from unallocated memory
            uint binValue = r << 24 | g << 16 | b << 8 | 0xff;
           
            // colour as string
            colourHex = colourToString(r, g, b);
       
            
            // mapping() would be better, but mapping type is only supported for
            // storage and not available within the functions
            bool alreadyHas = false;
            for(existingIdx=0; existingIdx<found.length; existingIdx++) {
                if(found[existingIdx] == binValue) {
                    alreadyHas = true;
                }       
            }
            
            if(!alreadyHas) {
                for(existingIdx=0; existingIdx<found.length; existingIdx++) {
                    // 0x0 is the default unallocated memory in EVM
                    if(found[existingIdx] == 0) {
                        found[existingIdx] = binValue;
                        colourmap[existingIdx] = colourHex;
                        break;
                    }       
                }
    
            }
        }
        return colourmap;
    }

    
}