draw :: (screen: *Screen, x: s64, y: s64, char: PIXEL_CHAR = .PIXEL_SOLID, color: COLOR = .FG_WHITE) {
    using screen;

    if x >= 0 && x < width && y >= 0 && y < height {
        buffer[y * width + x].char  = char;
        buffer[y * width + x].color = color;
    }
}

draw_line :: (screen: *Screen, x1: s64, y1: s64, x2: s64, y2: s64, char: PIXEL_CHAR = .PIXEL_SOLID, color: COLOR = .FG_WHITE) {
    x, y, dx, dy, dx1, dy1, xe, ye, px, py : s64;

    dx = x2 - x1;
    dy = y2 - y1;

    dx1 = abs(dx);
    dy1 = abs(dy);

    px = 2 * dy1 - dx1;
    py = 2 * dx1 - dy1;

    if dy1 <= dx1 {
        if dx >= 0 {
            x  = x1;
            y  = y1;
            xe = x2;
        } else {
            x  = x2;
            y  = y2;
            xe = x1;
        }

        draw(screen, x, y, char, color);

        for 0..xe {
            x = x + 1;

            if px < 0 {
                px = px + 2 * dy1;
            } else {
                if (dx < 0 && dy < 0) || (dx > 0 && dy > 0) then y = y + 1; else y = y - 1;
                px = px + 2 * (dy1 - dx1);
            }

            draw(screen, x, y, char, color);
        }
    } else {
        if dy >= 0 {
            x  = x1;
            y  = y1;
            ye = y2;
        } else {
            x  = x2;
            y  = y2;
            ye = y1;
        }

        draw(screen, x, y, char, color);

        for 0..ye {
            y = y + 1;

            if py <= 0 {
                py = py + 2 * dx1;
            } else {
                if (dx < 0 && dy < 0 ) || (dx > 0 && dy > 0) then x = x + 1; else x = x - 1;
                py = py + 2 * (dx1 - dy1);
            }

            draw(screen, x, y, char, color);
        }
    }
}

draw_triangle :: (screen: *Screen, x1: s64, y1: s64, x2: s64, y2: s64, x3: s64, y3: s64, char: PIXEL_CHAR = .PIXEL_SOLID, color: COLOR = .FG_WHITE) {
    draw_line(x1, y1, x2, y2, char, color);
    draw_line(x2, y2, x3, y3, char, color);
    draw_line(x3, y3, x1, y1, char, color);
}

clip :: (screen: *Screen, x: *s64, y: *s64) {
    using screen;

    if x.* < 0 then x.* = 0;
    if x.* >= width then x.* = width;
    if y.* < 0 then y.* = 0;
    if y.* >= height then y.* = height;
}

fill :: (screen: *Screen, x1: s64, y1: s64, x2: s64, y2: s64, char: PIXEL_CHAR = .PIXEL_SOLID, color: COLOR = .FG_WHITE) {
    clip(screen, *x1, *y1);
    clip(screen, *x2, *y2);

    for x: x1..x2 {
        for y: y1..y2 {
            draw(screen, x, y, char, color);
        }
    }
}

fill_entire_screen :: (screen: *Screen, char: PIXEL_CHAR = .PIXEL_SOLID, color: COLOR = .BG_BLACK) {
    fill(screen, 0, 0, screen.width, screen.height, char, color);
}

draw_string :: (screen: *Screen, x: s64, y: s64, text: string, c: COLOR = .FG_WHITE) {
    assert(false, "not implemented");
}