Subpixel Layout

Started by Google 2 years ago

• to do better space distribution in the short term
  • sub pixel layout

• support hiDPI displays by painting on odd device pixels in the long term
  • sub pixel painting

Subpixel Layout works right now has some directional rounding errors for non-horizontal-tb flows Subpixel painting/rendering work in progress

how does it work?

what is a layout unit

• made integer based to support fractional values without the burden of float arithmetic
• 1 layout unit == 1/64 CSS pixels

• Layout units are not rounded/etc during layout except in some cases, like in RenderLayer

• value is snapped during painting time

how does snapping work?

• float value gets snapped to device pixel boundary, still a float after being snapped
• this mostly happens in paint() in RenderObject classes
• can't do in GraphicsContext since sometimes you need to do floor or ceil instead of rounding
  • border types like groove, ridge, double require floor/ceil to keep the spacing

Testing

• prefix test case with 'hidpi-'
  • that will cause the test framework to switch to hidpi mode