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Re: Interactive 2d zoom and some Dynamic questions

  • To: mathgroup at smc.vnet.net
  • Subject: [mg84572] Re: Interactive 2d zoom and some Dynamic questions
  • From: dh <dh at metrohm.ch>
  • Date: Fri, 4 Jan 2008 05:40:34 -0500 (EST)
  • References: <flfaf0$a9e$1@smc.vnet.net>


Hi Szabolcs,

nice little tool. If you don't mind, I like to propose to add axes to 

the zoomed picture by adding:

AxesOrigin -> {Min[range[[1]]], Min[range[[2]]]}

to your graphics.

happy New Year, Daniel



Szabolcs Horvát wrote:

> Happy new year, MathGroup!

> 

> And now, the question:

> 

> First of all, those people who haven't seen it yet should definitely 

> check out Daniel Huber's very nice Zoom2D palette:

> http://groups.google.com/group/comp.soft-sys.math.mathematica/browse_thread/thread/58c77e4614440e57/5876f0611112765e

> 

> But I would like to have something simpler, a "quick and dirty" zoom 

> that has the simplest possible UI, and keeps the graphic in the 

> notebook.  So I came up with this:

> 

> zoomGraphics[graph_Graphics] :=

>      With[

>         {gr = First[graph],

>          opt = DeleteCases[Options[graph], PlotRange -> _],

>          plr = PlotRange /. Options[graph, PlotRange],

>          rectangle = {Dashing[Small],

>            Line[{#1, {First[#2], Last[#1]}, #2,

>                  {First[#1], Last[#2]}, #1}]} & },

>          DynamicModule[{dragging = False, first, second, range = plr},

>              Panel@EventHandler[

>                  Dynamic@Graphics[

>                      If[dragging, {gr, rectangle[first, second]}, gr],

>                      PlotRange -> range, Sequence @@ opt

>                  ],

>                 {{"MouseDown", 1} :> (first = MousePosition["Graphics"]),

>                  {"MouseDragged", 1} :>

>                     (dragging = True;

>                      second = MousePosition["Graphics"]),

>                  {"MouseUp", 1} :>

>                      If[dragging,

>                         dragging = False;

>                         range = Transpose@{first, second}, range = plr] }

>                  ]

>          ]]

> 

> Usage example:

> 

> Plot[1/x, {x, 0, 1}] // zoomGraphics

> 

> Drag to zoom, click to reset.  Remove Panel if you don't like it (or 

> replace it with Framed).  It's there to show the active ("draggable") area.

> 

> I do not understand Dynamic things well, so comments, suggestions (e.g. 

> for improving performance), problem cases where zoomGraphics fails are 

> most welcome.

> 

> One of the biggest problems with this is that EvantHandler prevents 

> resizing the graphic from working.  This is unacceptable because if we 

> want to zoom, most likely we also want to keep the resize functionality.

> 

> It also prevents dynamic things, like Locators from working properly.  I 

> could set PassEventsDown -> True in EventHandler, but zooming would 

> still interfere with resizing or moving a Locator (and other strange 

> behaviour appears too.)  One solution that I can imagine is to zoom only 

> while CTRL (or some other modifier key) is pressed.  But I do not know 

> how to implement this properly.  This is what I have so far:

> 

> zoomGraphics[graph_Graphics] :=

>   With[

>    {gr = First[graph],

>     opt = DeleteCases[Options[graph], PlotRange -> _],

>     plr = PlotRange /. Options[graph, PlotRange],

>     rectangle = {Dashing[Small],

>        Line[{#1, {First[#2], Last[#1]}, #2, {First[#1],

>           Last[#2]}, #1}]} &,

>     keyCheck =

>      Function[{arg}, If[CurrentValue["ControlKey"], arg], HoldAll]},

>    DynamicModule[{dragging = False, first, second, range = plr},

>     Panel@EventHandler[

>       Dynamic[

>        Graphics[

>         If[dragging, {gr, rectangle[first, second]}, gr],

>         PlotRange -> range, Sequence @@ opt

>         ]],

>       {{"MouseDown", 1} :>

>         keyCheck[first = MousePosition["Graphics"]],

>        {"MouseDragged", 1} :>

>         keyCheck[dragging = True; second = MousePosition["Graphics"]],

>        {"MouseUp", 1} :>

>         keyCheck@

>          If[dragging, dragging = False;

>           range = Transpose@{first, second}, range = plr]}]

>     ]]

> 

> OK, now zooming only works while CTRL is pressed.  Now it is somewhat 

> safer to set PassEventsDown -> True, and resizing works when CTRL is not 

> pressed.  But resizing and selecting graphics interferes with zooming 

> when CTRL is pressed.  The zoom level is also often reset unexpectedly 

> if CTRL is not released (and pressed again), and the graphics are not 

> deselected, between consecutive zoom attempts.  I don't completely 

> understand what is happening here.  Is it possible to somehow set 

> PassEventsDown -> True only when CTRL is not pressed?  As a desperate 

> attempt, I tried PassEventsDown -> 

> Dynamic@Not@CurrentValue["ControlKey"], but, unsurprisingly, it does not 

> work.

> 

> As an alternative solution, I also tried using 

> GraphicsGrid[{{zoomGraphics[someGraphic]}}] with the original version of 

> zoomGraphics to enable resizing (not moving Locators), but now the 

> events don't seem to reach the EventHandler.

> 

> Another question:  Could someone please explain, preferably with a 

> working example, what PassEventsUp is for?

> 

> Szabolcs

> 




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