Re: mouse zoom centred on mouse position.

[Mojca M. <moj...@gm...>]

On Sat, Jun 23, 2012 at 11:23 PM, Petr Mikulik wrote:
> I have revised the mouse wheel zooming, see patch:
> https://sourceforge.net/tracker/?func=detail&aid=3537423&group_id=2055&atid=302055

Thank you.

However (the following comments are all unrelated to your specific
change), if revising the mouse, I would be very very very grateful if
functions would be modified in such a way that it would be possible to
specify the amount of zoom/scroll, not only large discrete steps.

Currently a single scroll event moves the graph for approximately
15-40 pixels, while macs allow precise scrolling with pixel precision.
On Mac mouse scrolling events return:
- scrolling direction (up/down or left/right)
- the number of pixels to scroll
and typically one gets several events one after another.

It is practically impossible, or at least very inconvenient to
generate one single scrolling event for one pixel. Usually one gets
2-5 steps with very very tiny movement. Last time when I tested, a
single swipe from left to right moved me from default (-10,10) to
somewhere around 2000. With a single movement!!! In a native mac
application that would correspond to a movement across the width of
the screen.

I volunteer to fix this behaviour in Qt & wxt, but there is no
suitable function to call directly. At the moment I can only "forward
wheel scrolling event", discarding the amount of scrolling (otherwise
it would behave even worse than it does now), but that makes
unproportional movement, depending on the speed of movement, not the
amount of movement.

So it would be very helpful to have not just
    zoom_around_mouse('+');
but rather something like
    zoom_around_mouse(1.134);

Also, as soon as one uses a scrolling event, the default behaviour is
the following (one example):

  if (((b == 5) && (modifier_mask & Mod_Shift)) || (b == 7)) {
    /* scroll right */
    xmin = rescale(FIRST_X_AXIS, .9, .1);
    ymin = rescale(FIRST_Y_AXIS, 1., 0.);
    x2min = rescale(SECOND_X_AXIS, .9, .1);
    y2min = rescale(SECOND_Y_AXIS, 1., 0.);

    xmax = rescale(FIRST_X_AXIS, -.1, 1.1);
    ymax = rescale(FIRST_Y_AXIS, 0., 1.);
    x2max = rescale(SECOND_X_AXIS, -.1, 1.1);
    y2max = rescale(SECOND_Y_AXIS, 0., 1.);
    do_zoom(xmin, ymin, x2min, y2min, xmax, ymax, x2max, y2max);

with hardcoded 10% movement. It would be a lot more useful to have a
finer control of the amount of zoom & movement than just discrete
hardcoded steps. I wanted to change the code, but I'm not sure where
to start. From Qt I can only forward scrolling event or do some other
dirty trickery without knowing much about gnuplot internals.



And related to your change: on Mac it is natural to use scrolling for
actually scrolling, since there are other events on trackpad which
allow zooming in (they work the same as maps on smart phones, using
two fingers and sliding them closer together or further apart).
Redefining the meaning of scrolling means a slightly unnatural
experience for mac users, but for the sake of all other more
widespread OS-es and hardware and for the sake of consistency of
gnuplot across platforms, it should be acceptable to use key
combinations that make sense elsewhere.

However ... if you redefine the meaning of scrolling event, then
please provide drag-and-drop to move around the graph.

Thank you,
    Mojca