Add pixelRatio to ol.source.Image#createImage
Add hidpi option to ol.source.ImageWMS constructor
Scale output canvas by devicePixelRatio
Pass pixel ratio to ol.render.canvas.ReplayGroup constructor
Pass pixel ratio to ol.render.canvas.Replay constructors
Scale line widths by pixel ratio in replay mode
Scale line widths by pixel ratio in immediate mode
Pass pixel ratio to ol.render.canvas.Immediate constructor
Simplify geometries to a tolerance of half a device pixel
Pass pixel ratio to ol.renderer.canvas.VectorLayer#renderFeature