On Monday, June 24, 2019 at 6:25:05 PM UTC+8, Nickolay Ilyushin wrote: > > While checking racket's gui possibilities, I've noticed that widgets (in > both amount and config) are limited - yes, they can do much enough, but > using somewhat different (yet minimalistic) style we can do way more while > dropping most of those widgets. > > Please note that this is only an idea which seems (at least for me) nice > enough to be implemented when you see such frameworks as Qt Quick or > Flutter. > > 1. Canvas/DC changes > > 1.1: Canvas clipping > Currently, if we want to limit our drawing to a square, we use bitmap-dc% > class, which creates a new bitmap which will be then blitted to the canvas > or another bitmap. > This can be simplified (for users though) by making a clip operation > similar to the one found in nanovg. > Ideally it would use opengl stencil buffer or similar techniques, so we > could clip non-square shapes, but as I can see, racket/gui's canvas does > not use low-level graphics APIs directly. > Although it is probably possible to allow non-rectangular shapes in other > way. >
The draw context for a canvas (which you can get via the `get-dc` canvas% method) has a `set-clipping-rect` and `set-clipping-region` methods to clip to a rectangle or an arbitrary path. > Ideally clip operations should be stored in a stack (aka list (push=cons, > peek=car, pop=cdr) in terms of lisp) so you could restore previous clip > state - that would allow making multiple widgets which clip their drawing > context. > There is no stack for the clipping regions, but each function that does some drawing could save the old clipping region, install a new one, than restore the old one once done: (let ((old-region (send dc get-clipping-region))) (send dc set-clipping-region new-region) ;; do the drawing here (send dc set-clipping-region old-region)) A similar approach can be used to set pens, brushes and other drawing resources and a lot of higher level drawing libraries already use this technique. Alex. -- You received this message because you are subscribed to the Google Groups "Racket Developers" group. To unsubscribe from this group and stop receiving emails from it, send an email to racket-dev+unsubscr...@googlegroups.com. To post to this group, send email to racket-dev@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/racket-dev/b0bd24bb-2802-45bd-9403-6fe108bcb11f%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
