 // -- Init buffers
        var positions = new Float32Array([
            -1.0, -1.0,
             1.0, -1.0,
             1.0,  1.0,
             1.0,  1.0,
            -1.0,  1.0,
            -1.0, -1.0
        ]);
        var vertexPosBuffer = gl.createBuffer();
        gl.bindBuffer(gl.ARRAY_BUFFER, vertexPosBuffer);
        gl.bufferData(gl.ARRAY_BUFFER, positions, gl.STATIC_DRAW);
        gl.bindBuffer(gl.ARRAY_BUFFER, null);

        var texCoords = new Float32Array([
            0.0, 1.0,
         