Computer generated pictures could be pixel-first or object-first. Yes, I made up those terms. Fractals are pixel-first. Pick a pixel, run the fractal calculation for the pixel to get a color, color the pixel, then move on to the next pixel.
This image consists of many small squares, and is drawn object-first. Pick a square, compute which pixels are on the square, color those pixels with the color of the selected square, and then move on to the next square.