Incorrect translation in canvas component

[brads55]

The canvas component does a translation of visible_area().min() to place the drawn elements relative to the component position, however it does this after the canvas has been scaled with the scale factor, which means for scale factors != 1.0 the translation is incorrect. The translation amount should also take into account the scale factor, or happen before the scaling does.

freya/crates/freya-components/src/canvas.rs

Lines 151 to 154 in cde94c1

	context
	.canvas
	.scale((context.scale_factor as f32, context.scale_factor as f32));
	context.canvas.translate((area.min_x(), area.min_y()));

Also it might be helpful if examples/feature_canvas.rs made it clear that the drawing being done will be scaled after being drawn, for example by doing something such as:

let area = context.layout_node.visible_area() / ctx.scale_factor as f32;

in place of:

freya/examples/feature_canvas.rs

Lines 16 to 18 in cde94c1

	canvas(RenderCallback::new(|context| {
	let area = context.layout_node.visible_area();
	let center_x = area.center().x;

[brads55]

Thinking about this some more, I think there is actually a good argument to be made that the cavans component shouldn't be doing this scaling at all; letting the render callback draw in physical space and manually do the scaling if it wants to, especially given the layout area it is given is in physical space.

In my use case I'm trying to do pixel perfect rendering within the canvas and this scaling messes with that due to rounding errors. I just end up scaling the canvas with 1 / scale to undo what this component does (which in itself feels like it might introduce rounding issues).