draw rounded edges in Rectangle

[MJacred]

Is your feature request related to a problem? Please describe:

For better readability and a more diverse collection of shapes. Different Components in Material Design have them, like Material buttons, tags/chips, cards, ...

Is it possible to construct a solution with the existing API?

desired outcome not possible at this time

Describe the solution you'd like to see:

define in canvas/Rectangle.go Rectangle struct additional members: cornerX1, cornerX2, cornerY1, cornerY2,
then define defaults in theme/theme.go per Widget: Makes sense for Button, Entry, Select, PopUp, TabContainer Button, ProgressBar, Spinner (wip). And other widgets which will probably come later: Frame, Switch.
Maybe let the user overwrite them in code?

see border radius in CSS

[andydotxyz]

I’m a little torn here on whether the individual corner configuration is needed? Adding “CornerRadius” to Rectangle could be a nice addition. However if it was to be 4 new fields then it might hint towards a RoundedRectangle type that offers more flexibility?

Just some thoughts really - no conclusion other than it sounds like a good idea in principle.

[MJacred]

Hm.. one CornerRadius probably suffices. I proposed the 4 for maximum configuration possibility.

I'd have no problem with an extra RoundedRectangle, which embeds Rectangle. So that both work harmoniously together, we'd probably need a Rect interface which both rectangle structs implement?

[andydotxyz]

The way that we add APIs here is based on a user requirement and exposing the least possible changes to support that - so maximum configuration isn't really a mantra we follow. If such configuration is needed we could add it as long as the API is kept clean and simple.

The canvas package uses only concrete types as they are used to pass through to a rendering engine so in that space interfaces don't usually work. With Go a Rectangle type could be embedded inside a RoundedRectangle - though whether that is cleaner than a small amount of duplication might be up for debate.

[fpabl0]

@andydotxyz Isn't it possible to just add a new field to canvas.Rectangle called BorderRadius? Then the canvas.Rectangle could be any kind of rectangle rounded or not. BorderRadius could be private and defined from Theme API. I am not sure how this can be implemented but looking at internal/painter/draw.go the method DrawRectangle could use rasterx.AddRoundRect instead of rasterx.AddRect to enable border radius. This feature would be very helpful to make the current widgets more beautiful :)

[jtlapp]

Would the dev need to implement anti-aliasing for this, or does a suitable API already exist?

I'm still making a go/no-go decision about whether to implement my app in Go + Fyne. It's possible that I could add this feature, if it isn't done by then.

[andydotxyz]

To add new canvas primitives (or features to them) we need to add in the software and OpenGL renderers.
The way that antialias works varies in this case. For the software renderer you can use any drawing API that can do curved corners and that will probably anti-alias. For the OpenGL it would mean replacing the simple rectangle draw with a shader (similar to the line implementation).
You can see these things in action at internal/painter/*

[renlite]

In draw.go you are using module rasterx to draw Line, Rect and Circle.
Would it work, to extend draw.go with func DrawRoundedRectangle(...), which calls the func DrawRectangle(...), if no corner radius (1,2,3,4) are set as parameter?
The module rasterx has a func AddRoundRect(minX, minY, maxX, maxY, rx, ry, rot float64, gf GapFunc, p Adder) {...} which offers the functionality. (AddCircle() is already in use)