gistfile1.txt

function circle(buffer, cx, cy, radius) {
    var error = -radius,
        x = radius,
        y = 0,
        lastY;

    while (x >= y) {
        lastY = y;

        error += y;
        ++y;
        error += y;

        plot4points(buffer, cx, cy, x, lastY);

        if (error >= 0) {
            if (x != lastY)
                plot4points(buffer, cx, cy, lastY, x);

            error -= x;
            --x;
            error -= x;
        }
    }
}

function plot4points(buffer, cx, cy, x, y) {
    horizontalLine(buffer, cx - x, cy + y, cx + x);
    if (x != 0 && y != 0)
        horizontalLine(buffer, cx - x, cy - y, cx + x);
}
function horizontalLine(buffer, fromX, y, toX) {
    for (var i = fromX; i < toX; i++) {
        buffer[y][i]++;
    }
}