In all of our previous examples, shapes were always drawn one on top of the other. This is more than adequate for most situations, but it limits the order in which composite shapes are built. We can, however, change this behavior by setting the globalCompositeOperation property. In addition, the clip property allows us to hide unwanted parts of shapes.
WebGL (Web Graphics Library) is a JavaScript API for rendering high-performance interactive 3D and 2D graphics within any compatible web browser without the use of plug-ins. WebGL does so by introducing an API that closely conforms to OpenGL ES 2.0 that can be used in HTML elements. This conformance makes it possible for the API to take advantage of hardware graphics acceleration ...
You cannot (ugh) access the DPI of a display of the current web page in any browser:
Detecting the system DPI/PPI from JS/CSS?
For printing: You most likely cannot set the DPI of exported <canvas>
https://gist.github.com/1245476
