Improve overlay rendering for DPI scaling

[Zamoca42]

Fixes #1688

Changes

Apply the following changes to the overlay using device_pixel_ratio:

1. Pixel alignment
2. Grid spacing adjustment
3. Dot size adjustment

Preview

dpr 1

dpr 2

dpr 3

[Keavon]

Thanks! Just an observation from the screenshots, it looks like the stroke diameter gets smaller and smaller but should be rounded to the nearest pixel scale.

[Zamoca42]

Yeah, I changed the outline to a linear scale based on DPR, but it caused dramatic of a change. So, I applied pixel scaling by rounding to the first decimal place on the root scale instead.

0. DPR 1
   

1. Linear scale at DPR 3
   

2. Square root scale at DPR 3
   

[Zamoca42]

I have a question while implementing this.

Is it necessary to change the size of the Overlay Canvas based on DPR (Device Pixel Ratio)?

I thought that simply increasing the physical pixel count of the Overlay Canvas would result in a clearer overlay, but this creates size and position discrepancies with the regular canvas.

[Keavon]

I don't recall off-hand if that is necessary but it could be worth attempting. I'll delegate that to you as a research/experiment and I can code review it afterwards to sanity check. If you get really stuck on that, I can try to find a bit of time to help research it.

[Zamoca42]

Thanks! What I tried was simply converting logical pixels to physical pixels on the canvas and applying the scale in the context. However, it seems that the scale in the context isn’t applied during resize or move. Is there a way to apply the scale to the overlay’s events as well?

Edit: When running in the development environment, I noticed a "Snap candidate overflow" occurring at /src/messages/tool/common_functionality/snapping.rs:349, which appears to prevent context.scale from being applied correctly. This issue occurs even without physical pixel adjustments on the overlay canvas, so the logic in snapping.rs needs to be revised.

I’m attaching a video of the overlay canvas with physical pixels applied.

resize.mov

[Zamoca42]

Applying physical pixels did not result in noticeable rendering differences, and I also identified an issue with inaccuracies occurring during the context.scale configuration of the overlay.

Given this, I concluded that applying physical pixels does not provide substantial improvements to the project and could add unnecessary complexity from a maintenance perspective.

Therefore, I have determined that applying physical pixels is not necessary at this stage.

Thank you for giving me the time to review this.