Low fps on ios mobile with pixel ration set as window.devicePixelRatio

Hello guys, I’ve noticed that when I render a simple scene (just one mesh) with pixel ratio set as window.devicePixelRatio I got 40 fps on ios mobile devices (not tested on other mobile devices).

renderer.setPixelRatio( window.devicePixelRatio );

Basically even with an empty scene the fps don’t go up more than 40.
If I remove this line the fps go up to 60. I’ve tested this on an iphone and ipad.
Is this expected to happen?

threejs 98

Setting window.devicePixelRatio via WebGLRenderer.renderer.setPixelRatio() means your render in a much higher resolution. If the value is 2, the resolution is twice as high. Even with simple scenes this can kill performance.


Thank you @Mugen87. I was really surprised that even with an empty scene (just the axes helper) setting the pixel ratio causes the fps to go so low on mobile