RFR: 8211294: [windows] TextArea content is blurry with 125% scaling

[Frederic Thevenet]

On Thu, 24 Sep 2020 18:57:13 GMT, Frederic Thevenet <fthevenet at openjdk.org> wrote:

> This PR aims to fix the blurriness to sometimes affects some controls (such as TextArea) in a scene when rendered with
> a scaling factor that is not an integer (typically when viewed on a HiDPI screen with a 125%, 150% or 175% output
> scaling).  Please note that regardless of what the JBS issue (and therefore the title of this PR) states, this does not
> appear to be a Windows only issue as I have observed the same issue on Linux (Ubuntu 20.04).
> The following conditions are necessary for the blurriness to appear, but do not guarantee that it will:
> 
> - The node, or one of its parents, must have set `Node::cacheProperty` to `true`
> 
> - The scaling factor (as detected automatically or explicitly set via glass.win/gtk.uiScale) must be a non integer number
>   (e.g. 1.25, 1.5, 175)
> 
> - The effective layout X or Y coordinates for the cached node must be != 0;
> 
> Under these conditions, the translate coordinates for the transform used when the cached image for a node is rendered
> to the screen may be non integer numbers, which is the cause for the blurriness.
> Based on these observations, this PR fixes the issue by simply rounding the translate coordinates (using `Math.round`)
> before the transform is applied in `renderCacheToScreen()` and as far as I can tell, it fixes the blurriness in all the
> previously affected applications (both trivial test cases or with complex scenegraphs) and does not appear to introduce
> other noticeable visual artifacts.  Still, there might be a better place somewhere else higher up in the call chain
> where this should be addressed as it could maybe be the root cause for other rendering glitches, though I'm not yet
> familiar enough with the code to see if it is really the case.

Also, I don't really have an idea on how this could be tested other than visually, so I'm open to suggestions.

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PR: https://git.openjdk.java.net/jfx/pull/308