Inconsistent resize behavior for plots

[Bromeon]

The resize behavior is different when a plot is "centered" (after double-click) vs. when the position is moved:

egui-resize-plot.mp4

To Reproduce
Steps to reproduce the behavior:

1. Open plot demo example
2. Resize horizontally or vertically -- the zoom doesn't change
3. Move plot slightly with left click
4. Resize again horizontally or vertically -- when reducing size, plot shrinks

Desktop

• OS: Windows 10
• egui master version, commit 3333d63

[saecki]

Also related to this. Changing the data_aspect when the Plot isn't centered will always zooms out.
The problem in both cases is that egui always tries to keep everything that was previously visble also visible after resizing/changing the aspect ratio, thus always expanding one axis.

I think it would be a better user experience to make sure that the same amount of data on one axis will be kept visible.
So when rapidly resizing like in the video, or trying to find the right data_aspect using a slider the plot wont zoom out further and further.

Either way I think it's more important that this is consistent across resize/aspect-ratio.
So when the behavior will be changed both should be changed.

The code regarding changing the aspect ratio is here

egui/egui/src/widgets/plot/transform.rs

Lines 279 to 285 in 4db6984

	if current_aspect < aspect - epsilon {
	self.bounds
	.expand_x((aspect / current_aspect - 1.0) * self.bounds.width() * 0.5);
	} else if current_aspect > aspect + epsilon {
	self.bounds
	.expand_y((current_aspect / aspect - 1.0) * self.bounds.height() * 0.5);
	}

Changing this would be trivial, and would simplify the code a bit by always expanding/shrinking one axis.

The code regarding resizing is a bit more complex:

egui/egui/src/widgets/plot/mod.rs

Lines 308 to 330 in 4db6984

	// Determine the size of the plot in the UI
	let size = {
	let width = width
	.unwrap_or_else(|| {
	if let (Some(height), Some(aspect)) = (height, view_aspect) {
	height * aspect
	} else {
	ui.available_size_before_wrap().x
	}
	})
	.at_least(min_size.x);
	let height = height
	.unwrap_or_else(|| {
	if let Some(aspect) = view_aspect {
	width / aspect
	} else {
	ui.available_size_before_wrap().y
	}
	})
	.at_least(min_size.y);
	vec2(width, height)
	};

But about the same would apply here.

[s-nie]

Just stumbled upon this issue. I think #1184 should fix it.

[saecki]

Yes that is pretty much exactly what I had in mind, and more.