No (supported) API to change the pixel_ratio

[hmaarrfk]

It would be good to be able to change the pixel ratio dynamically.

I feel like browsers do this with Ctrl+"=" and Ctrl+"-".

AI would recommend doing it as part of set_logical_size but perhaps another API is more useful.

[Korijn]

I feel like browsers do this with Ctrl+"=" and Ctrl+"-".

Can you confirm this? I don't think this is true.

[almarklein]

Can you confirm this? I don't think this is true.

>> devicePixelRatio
2 
# turn browser zoom to 110%
>> devicePixelRatio
2.222222222222223

Right now, the pixel ratio is the one reported by the native widget (which asks the OS in most cases). This is the same as the browser being on 100%.

I think a sensible API to support something similar is something like set_zoom(), which would (for higher values) decrease the logical size, which results in an increased pixel ratio.

Would also have to check the logic in PyGfx that uses the pixel-ratio to determine if a screen is hidpi; I think the assumptions we make there still hold, but worth checking.

[hmaarrfk]

I’ll try to share something with you both.

But as you “zoom” you want to maintain your same number of physical pixels to draw sharply right?

So you must change logical and pixel ratio correct?

[hmaarrfk]

I just now understood that >> is the prompt in the console for browsers… thx

[almarklein]

Oh wait, I realize there's different use-cases, and I'm not sure which one you mean.

1. Have a canvas using a glfw / qt window, and being able to "zoom", similar as in a browser, so the font gets larger, lines thicker etc. -> Yes, we could add that, I can see it being useful.

2. Having an offscreen canvas that you want to match some remote canvas. As the remote's pixel ratio changes, you want the offscreen canvas to do too. Right now, you can set the pixel ratio of the offscreen canvas when you create it, but not change it at runtime. I think it would be quite trivial to add this. Other canvases can change their pixel-ratio too, e..g as you move them from one monitor to another.

The 2nd case is quite easy to implement. The first is also worth implementing, but requires a bit more work.

[hmaarrfk]

I feel like doing 1 requires 2 to be implemented.

Then you bind a shortcut to it.

I’m ok with pyGFX not having shortcuts.

Tbh. Setting the _pixel_width directly seems to have few negative consequences.

I am primarily thinking of use case 2

[Korijn]

Please consider that the word "zoom" also implies viewport cropping usually. Pixel ratio is more about rendering at a higher/lower resolution/density.

[hmaarrfk]

sorry for the confusion.

[Korijn]

Don't get me wrong :) just trying to help you calibrate on a nice name for the functionality

[hmaarrfk]

One thing I’ve noticed from hacking this functionality in is that floating point math gets in the way.

Logical pixels seem to be integers.

Physical pixels seem to be integers.

Pixel ratio is a floating point number.

So without “nice rounding” we may be 1 pixel off. (This one pixel error is super annoying since it just creates an ugly seam somewhere in the display pipeline).

It may be nice to be able to set the physical pixels. And not the pixel ration.

[almarklein]

I called it "zoom", because that's what my browser calls it:

But within our context that term may indeed be a bit generic ...

Logical pixels seem to be integers.

Logical pixels are float.

[Korijn]

Your browser also crops the viewport though :)

[almarklein]

I would not call that cropping... It reduces the logical size, so the viewport (in logical pixels) becomes smaller, but it does not zoom into a subsection of the total page or something like that.