I've just tested with High DPI in C2 and compiled with Intel XDK using the canary beta option. It broke my WebGL effect "Glass" (from C2's default effects), it works fine with High DPI is set to No in C2. Quite strange.
All it is is a 128 x 128 white sprite with Glass effect, set to grow by 20 pixels height and width every frame.
The phenomenon I observed is, the 'Glass' effect is broken on a 256x256 sprite with nothing is painted for the sprite, regardless of whether high dpi is on or not. But it works if WebGL is off by C2, says canvas 2d renderer is used instead.
As for the High DPI setting itself, it works at making the image much better quality (same as CocoonJS). There is a noticeable drop in performance, I am doing more tests now to give you an exact performance loss figure.
Edit: Seems to go from an average fps of 45 to 40 with the DPI settings but on high DPI, it has more drops down to 30 fps. CocoonJS is most of the time 60 fps, with dips to 50. This is on my LG G-Pad with Snapdragon S600.
Really thanks for your update, and I think it is very important for Crosswalk. As I know, CJS has a special native implementation for canvas, called direct canvas (canvas+), which shortcuts a general rendering pipeline for web page layout and rendering. The thing I am interesting in is, the performance of high dpi is heavily impacted, which is beyond my expectation. For such performance issue, I am afraid it is not easy to reproduce without your case. So would you mind to share your capx file to me? I'd like to help profile and optimize it, from Crosswalk internal and app level. Thanks in advance.