http://output.jsbin.com/watuhug/quiet

The above demo works at 60fps on a non-retina screen (at around 1080p), but totally dies on retina, even if the number of pixels being rendered is smaller.

However, if the zoom level is decreased (cmd & -), the frame-rate recovers, even though the number of pixels rendered remains the same.

https://www.youtube.com/watch?v=y5Zbzb_rv-o&feature=youtu.be shows:
Chrome (Canary) struggling at 100%
Hitting 60fps when zoom is decreased to 75% (although the text-shadow breaks)
Safari hitting 60fps at a larger size, no problem.

Attached traces for non-retina (hitting 60fps at around 1080p), and retina, where I follow the pattern in the video and decrease the zoom until the frame-rate hits 60fps.

From the trace, it appears that the GPU is the bottleneck. I suspect the zoom level is altering the texture sizes, making this switch from broken to working.

Force GPU rasterisation was enabled during the video capture & traces, but disabling it doesn't appear to make a difference. If I switch onto the integrated GPU in this macbook, performance increases compared to 100% zoom on the Nvidia, but it's still slow.

Machine is a 15" 2012 Macbook Pro, in case that matters.

 

Deleted: trace_non-retina.json.gz 1.6 MB

trace_non-retina.json.gz 1.6 MB Download

Deleted: trace_retina.json.gz 7.1 MB

trace_retina.json.gz 7.1 MB Download