Small example of drawing colors using the C SDK for GameTank

gt_draw_colors.c

#include "gt/gfx/draw_queue.h"

char bx = 30, by = 20;
char dx = 1, dy = 1;

const int cw = 6, ch = 5;
const int sx = 8, sy = 6;

void update() {
  bx += dx;
  by += dy;

  if (bx == 1) {
    dx = 1;
  } else if (bx == 119) {
    dx = -1;
  }

  if (by == 8) {
    dy = 1;
  } else if (by == 112) {
    dy = -1;
  }
}

void draw() {
  queue_clear_screen(0x0);

  { // Draw colors
    int col, row;

    for (col = 0; col < 16; col++) {
      for (row = 0; row < 16; row++) {
        int x = 1 + (col * sx);
        int y = 1 + (row * sy);

        queue_draw_box(x, y, cw, ch, (col << 4) | row);
      }
    }
  }

  { // Bouncing box
    queue_draw_box(bx - 1, by - 1, 20, 10, 0xDE);
    queue_draw_box(bx, by, 18, 8, 0xDF);
  }

  { // Border
    queue_clear_border(0x0);
  }

  await_draw_queue();
  await_vsync(1);
  flip_pages();
}

int main() {
  while (1) { // Forever
    update();
    draw();
  }

  return 0;
}

https://github.com/clydeshaffer/gametank_sdk/