<!DOCTYPE html>
<link rel="help" href="https://html.spec.whatwg.org/#dom-offscreencanvas">
<canvas id="c1" width="100" height="100"></canvas>
<canvas id="c2" width="100" height="100"></canvas>
<canvas id="c3" width="100" height="100"></canvas>
<canvas id="c4" width="100" height="100"></canvas>
<script>
    const c1 = document.getElementById("c1");
    const gl1 = c1.getContext("webgl");
    gl1.clearColor(1, 0, 0, 1);
    gl1.clear(gl1.COLOR_BUFFER_BIT);

    const c2 = document.getElementById("c2");
    const gl2 = c2.getContext("webgl");
    gl2.clearColor(0, 1, 0, 1);
    gl2.clear(gl2.COLOR_BUFFER_BIT);

    const c3 = document.getElementById("c3");
    const gl3 = c3.getContext("webgl");
    gl3.clearColor(0, 0, 1, 1);
    gl3.clear(gl3.COLOR_BUFFER_BIT);
</script>