Hairline strokes under fractional display metrics

[Philip Race]

Indeed .. something very close to that is what is being proposed in a 
current PR here :
https://github.com/openjdk/jdk/pull/7449/files

Just bear in mind some of the same constraints and that if printed on a 
1200dpi printer
with a scale of 16.67 .. your one pixel line might be too thin to be 
seen at all.

I suggest you should have an upper limit on the unscaling.

I don't remember why the change a long time ago was backed out .. indeed I
am not sure I remember it will enough for it to be more than a figment 
of my imagination
but "0" used to have a special meaning in some graphics systems - X11 
took it to
mean "draw a line the fastest way you can, I do not care about accuracy".

-phil.

On 5/26/22 2:47 PM, Kirill Grouchnikov wrote:
> Haven't heard anything here, but in the meanwhile I got great pointers from
> Karl, the developer of JFormDesigner and FlatLaf over at
> https://github.com/kirill-grouchnikov/radiance/issues/39#issuecomment-1137649208
> and subsequent comments.
>
> The core of the idea is to force scale factor of 1.0 on the graphics
> context, compute new origin and bounding box similar to how it's done in
> the internals of Java2D, and then strokes with width of 1.0f will be
> treated as full pixels (if no VALUE_STROKE_PURE hint is set).
>
> On Tue, May 24, 2022 at 7:48 PM Kirill Grouchnikov <
> kirill.grouchnikov at gmail.com> wrote:
>
>> I'm trying to figure out what is the right way to draw paths such
>> rectangles or rounded rectangles, such that horizontal and vertical parts
>> always fall on a full pixel and are displayed at hairline stroke width.
>>
>> A long time ago there was an option to specify stroke width of 0 for that,
>> but then it was quickly reverted.
>>
>> My understanding is that I need to query scale x and scale y of the
>> device's config's transform, and use that to compute the stroke width.
>> Here's my code -
>> https://github.com/kirill-grouchnikov/radiance/blob/sunshine/demos/theming-demo/src/main/java/org/pushingpixels/radiance/demo/theming/main/Hairlines.java
>> (no dependency on anything from Radiance, just the core Swing / AWT stuff).
>>
>> Now, running this on a Windows 10 laptop with recommended / default 250%
>> scale factor gets the correct value of 2.5 as scale. But the visuals switch
>> between hairline and "smudged" as I horizontally resize the frame one pixel
>> at a time and the component shifts horizontally -
>> https://raw.githubusercontent.com/kirill-grouchnikov/radiance/sunshine/docs/images/hairlines.png
>> (and the horizontal lines are also not hairline)
>>
>> How do I make this work in Java2D across all display scale factors so that
>> I get consistent hairlines? I see the same behavior on Java 9 and Java 17
>>
>> Thanks
>> Kirill
>>