Support responsive scaling

[Kobzol]

It is useful to have the ability to re-scale the whole slide deck to a different resolution and/or ratio (e.g. 4:3, 16:9, etc.). While this can be done manually in the Python code, e.g. like this:

foo.box(width=scale_width(500), height=scale_height(500))

The way I do it is that I have some reference resolution (e.g. FullHD), against which I code the contents of my slides, and then some actual resolution, which is rendered by elsie. Before rendering, I recompute all of the values essentially just by dividing FullHD with the actual resolution, to get the final scaled value. In this way I can modify the target render resolution with a one-line change, without modifying the contents of the slides.

However, it is a bit annoying if we have to scale all the values of presentations with my own functions everywhere.

It would be nice if there was some was to hook into nelsie, so that we could automatically rescale all values, like X, Y, width, height etc., before rendering, or if nelsie had this built-in, so that you could specify a source (logical) resolution, and a target render resolution.

A related alternative is to allow specifying all values as relative, e.g. as percentages.

[spirali]

Percentage specification is allowed. What is not sufficient on this approach?

[Kobzol]

A few reasons:

• For me, it is easier to think about absolute numbers w.r.t. a reference resolution, than with percents. Percents are also not very granular, i.e. 80% vs 81% is a much larger difference than 1000 vs 1010 pixels (and I don't really want to use decimal points for percents :) ). In general, I would rather use integers than floating point numbers for this.
• Percents are relative to the parent (AFAIK?). But I usually want to scale the whole slide, relative to the dimension of the whole slide, not relative to the dimension of the parent of the thing that I'm scaling (for that, percents are indeed useful!).
• Percents probably cannot be used everywhere? E.g. in font size, which I want to scale almost everywhere.

[spirali]

I will think about it, but actually fonts is something that cannot be naively scaled in this way, as you have just one parameter for fonts (i.e. text are objects with a fixed aspect ratio). If you are rescaling a slide to different aspect ratio, you cannot rescale fonts to new ratio of width and height at same time.

[Kobzol]

I know, it's not perfect, but it's still better to have a somewhat scaled font than to not see the text at all if I change the resolution a lot :)