Re: [fltk.coredev] Gesture progress for 1.4?

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Re: Gesture progress for 1.4? Albrecht Schlosser 08:17 Oct 13 top right image
On 10/13/21 2:20 AM Rob McDonald wrote:
On Tuesday, October 12, 2021 at 3:13:23 PM UTC-7 Albrecht Schlosser wrote:
On 10/12/21 7:13 PM Rob McDonald wrote:

Yep, found it. The only "real" issue is in draw(): you're pushing the
matrix at the wrong place in the code. You need to move
'fl_push_matrix();' up before 'fl_translate(...);' and it should work
... with some minor issues. Cute!

That would have taken me a long time to figure out -- drawing the first time works, but I suppose it quickly out-runs the stack depth of 4 and stops working...

Hmm, not really. You can imagin fl_push_matrix as "save" and fl_pop_matrix as "restore" functions, respectively. There was nothing wrong with the stack (which is, BTW, 32 matrices deep, not only 4) because you used push and pop correctly in pairs. But you used transformation calls before you saved the current matrix and these transformations accumulated.

FLTK's fl_rotate() is positive CCW whereas FL_ROTATE_GESTURE is positive CW.  The sign flip is expected.

OK, I see.

The handling of FL_SCROLL_GESTURE had a negative inherited from the FL_MOUSEWHEEL code -- since it seemed quite counterintuitive for this use, I removed it there.

This one is tricky on macOS. You can use the system preferences for trackball and mouse, respectively, to enable "natural scrolling". No matter which one you use, both trackball and mouse are affected! I would have expected that these are different settings, and when I switched to "natural" my Mac did what I expected with the trackpad but the mouse scrolling change was not expected. With this *user preference* the sign of the scrolling delta is inverted (again, in both cases). It's not yet clear to me which sign convention we should apply taking this into account. Do (can) we access the system preference to compensate this? Is it useful to do so? I don't know.

I assume your setting is "natural" - please try to use your program after switching "natural scrollling" off. Is it still intuitive? I don't think so.

I've updated my branch with all these fixes together.  It makes for a little 2D app that responds in all the ways I would want it to -- rotate, pan, zoom.

Yep, that's great. Your addition is really helpful. Thanks. I pulled all your changes into my own fork.

It looks like MacOS and Windows both also support a swype gesture -- I hadn't looked into it because I don't see a use in my application.  However, as long as we're at it, we should probably be complete.

Yes, probably. My next step will be to add the Windows implementation. Once that is done we can see which sign conventions we should use and how "cross platform" compatible this all will be. Windows seem to call the swipe gesture "Flicks" if I interpret their docs correctly. It's hard for a non-native English speaker like me to interpret these gestures and the particular naming in the docs.

The macOS docs state: "Three fingers brushing across the trackpad surface in a common direction is a swipe gesture."

Finally, one important note: please don't rely on this experimental code for your "real" applications. I'm sure we will change the API before we go into production (release). For instance, one major change would be to add new Fl_event_*() accessor methods for a better interface to gestures. Some of these variables obviously need to be floats or doubles so the user doesn't need to divide by 1,000 or 100,000 or any other factor.

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