clear method
Clears the current target with a given color.
Implementation
@override
void clear(double red, double green, double blue, double alpha) {
_context.clearColor(red, green, blue, alpha);
_context.clear(web_gl.WebGL.COLOR_BUFFER_BIT |
web_gl.WebGL.DEPTH_BUFFER_BIT |
web_gl.WebGL.STENCIL_BUFFER_BIT);
}