vertexArray);

        var vertexPosLocation = 0;  // set with GLSL layout qualifier
        gl.enableVertexAttribArray(vertexPosLocation);
        gl.vertexAttribPointer(vertexPosLocation, 2, gl.FLOAT, false, 0, 0);

        gl.bindVertexArray(null);

        // -- Render
        gl.clearColor(0, 0, 0, 1);
        gl.clear(gl.COLOR_BUFFER_BIT);

        gl.bindVertexArray(vertexArray);

        gl.viewport(0, 0, canvas.width / 2, canvas.height);
        gl.drawArraysInstanced(gl.TRIANGLES, 0, vertexCount /