colorparse.c

#include <stdint.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>

// Parse dispmanx-safe colors from command-line arguments

typedef struct __attribute__((__packed__)) {
    uint8_t r;
    uint8_t g;
    uint8_t b;
    uint8_t x;
} rgbx_t;

rgbx_t parseColor(char* hexString)
{
    rgbx_t rgbx = {0, 0, 0, 0}; // Return black on error
    uint8_t* colorPtr = (uint8_t*) &rgbx;
    
    if (hexString[0] == '#')
    {
        hexString += 1;
    }
    if (strncmp(hexString, "0x", 2) == 0)
    {
        hexString += 2;
    }
    
    uint32_t colorInt = strtol(hexString, NULL, 16);
    if (strlen(hexString) == 6)
    {
        int i;
        for (i = 2; i >= 0; i--) {
            colorPtr[2 - i] = (uint8_t) (colorInt >> (i * 8));
        }
    }
    else if (strlen(hexString) == 3)
    {
        int i;
        for (i = 2; i >= 0; i--) {
            colorPtr[2 - i] = (uint8_t) (colorInt >> (i * 4)) & 0xF;
            colorPtr[2 - i] |= colorPtr[2 - i] << 4;
        }
    }
    
    return rgbx;
}

int main(int argc, char** argv) {
    
    char* hexString = "000000";
    
    char c;
    while ((c = getopt(argc, argv, "b:")) != -1)
    {
        switch (c)
        {
            case 'b':
                hexString = optarg;
                break;
        }
    }
    
    rgbx_t rgbx = parseColor(hexString);
    
    printf("Colors (RGBX): %x %x %x %x\n", rgbx.r & 0xFF, rgbx.g & 0xFF, rgbx.b & 0xFF, rgbx.x & 0xFF);
    
    return 0;
}