WebGL Alpha Stencil Plus Graphics Overlay
Swipe Over the Canvas to Move the Cube
This Web page demonstrates
placing a stencil, with alpha transparency, over an image.
See a portion of the background
graphic, where a stencil masks
part of the cube.
The stencil applies transparency from
a GIF image. Transparent
portions of the texture mask portions of the cube,
allowing the background to show through.
Additionally non transparent areas of the
in front of the cube.
Each side of the cube is texture mapped with a different color. A large quad renders behind the cube. A small stationary stencil with transparent bars masks off the cube, as the cube passes over the stencil area. See a portion of the background quad through the cube, where the stencil masks the cube. Bars from the stationary graphic display over the cube as well.
This feature offers useful applications. Display complex elements with a simple quad of six vertices. For example display a fence in front of a landscape. Render the fence with transparency and map to a quad. Load six vertices rather than hundreds to model the shape of a fence.
Render complicated models with minimal vertices. Cut holes through three dimensional meshes with transparency.
Render the stencil with
gl.blendFunc( gl.ONE, gl.ONE_MINUS_SRC_ALPHA );
To render the cube
disable blend with