It's done at HTML level with canvas.clearRect() BUG=webp:261 Change-Id: I83c73791f5922cd1f426f19faf856fa1cf8f0311
The build is based on CMake. There is a demo HTML page under webp_js/index.html See README.webp_js file. BUG=webp:261 Change-Id: I6612378b89907efd7b863720c6becf98385fc406