Changing the Actions in EventHandler

Question

I would like to be able to change which action specified events take depending on some condition. For example, I have established a SetterBar

SetterBar[Dynamic[setter], {Zoom, Pan}]

and created a graphic that I would like the left mouse button to cause to either zoom or pan, depending on what the value of setter is when the event occurs.

DynamicModule[{frac = 0, zoomval = 7*Pi/36, drag = {0, 0}, 
pt = CurrentValue[ImageSize], CurrentPosition = {1/2, 1/2}, 
panvalue = {0, 0}}, 
EventHandler[
Dynamic[Show[graphics, 
ViewCenter -> {{1/2, 1/2, 
   1/2}, {x = CurrentPosition[[1]] + panvalue[[1]], 
   y = CurrentPosition[[2]] - panvalue[[2]]}}, 
ViewAngle -> (Which[drag[[2]] > 0, 
   zoomval = Min[Pi*0.7, zoomval + frac*(Pi - zoomval)], 
   drag[[2]] < 0, 
   zoomval = Max[zoomval - frac*(Pi - zoomval), 0.2], 
   drag[[2]] == 0, zoomval = zoomval]), 
RotationAction -> "Clip"]], {{"MouseDown", 
 1} :> (a = CurrentValue[MousePosition]), {"MouseDragged", 
 1} :> {Which[
  setter == Zoom, {b = CurrentValue[MousePosition], drag = b - a, 
   frac = 0.5 Norm[drag]/Norm[pt]}, 
  setter == Pan, {b = CurrentValue[MousePosition], drag = b - a, 
   panvalue = {drag[[1]]/(pt[[1]]), 
     drag[[2]]/(pt[[2]])}}]}, {"MouseUp", 1} :> {frac = 0, 
 drag = {0, 0}, panvalue = {0, 0}, CurrentPosition[[1]] = x, 
 CurrentPosition[[2]] = y}}]]

This may be a little difficult to follow, but esentially I want the Which function to alter the action taken by the event "MouseDragged" depending on if setter is set to Zoom or Pan. Currently, everything works when the value is set to Zoom, but no action occurs upon setting the value to Pan.

Also, graphics is simply a red cylinder created for example.

graphics = Graphics3D[{Red, Cylinder[]}];

Answer 1

As your code doesn't appear to run and presents so much to decipher before anyone could usefully help you with it, consider this simpler alternative:

Manipulate[
 Graphics3D[{Red, Cylinder[]}, 
   ImageSize -> iSize, 
   ViewAngle -> vAngle \[Degree]], {{iSize, 250}, 50, 500, 25}, {{vAngle, 40}, 50, 10, 1}]

A couple of screen shots of the output follows:

The Manipulate simply enables one to dynamically change the ImageSize of the Graphics3D object and its ViewAngle. I've set an initial value of the variable for ImageSize to 250 and range it from 50 to 500 in steps of 25.

For ViewAngle, I've specified it in degrees, set a default as 40 and allow it to range from 50 to 10 with a step of 1.

Take a look at howto/RotateZoomAndPanGraphics

Note that Mathematica typically enables 3D graphic output for rotating. You may have to do a bit more thinking to incorporate Pan.

This approach may not do everything you want, but it may give you a different and simpler way to think about what you want to do.

Answer 2

Here is the minimal example what you are probably looking for.

Switching between zooming and rotating is handled in two places: If stops zooming unless zoom==True. PassEventsDown->!zoom prevents rotating when zooming is enabled.

DynamicModule[{y = .5, zoom},
 EventHandler[
              Column[{
                      Row[{Checkbox[Dynamic@zoom], "zoom"}],
                      Plot3D[Exp[-x^2 - y^2], {x, -4, 4}, {y, -4, 4}, PlotRange -> 1, 
                      ViewAngle -> Dynamic@y, ImageSize -> 400]
                    }]
              ,
       "MouseDown" :> If[zoom, init = y + Last@MousePosition["Graphics"]],
       "MouseDragged" :> If[zoom, y = Clip[init-Last@MousePosition["Graphics"], {.2, 1}]],
       PassEventsDown -> ! Dynamic@zoom
             ]
       , Initialization :> (zoom = False)
            ]

Answer 3

Using @Jagra's suggestion I was able to make a Manipulate function that was FAR neater than what I previously had (again, apologies for the unnecessarily long and messy code).

Manipulate[
Graphics3D[{Red, Cylinder[]}, ViewAngle -> Dynamic[vAngle \[Degree]],
ViewCenter -> {{1/2, 1/2, 1/2}, Dynamic[cen]}], {{vAngle, 30, 
"Zoom"}, 90, 10, 1}, {{cen, {1/2, 1/2}, "Pan"}, {0, 0}, {1, 1}}]

While this isn't exactly what I was going for, I think it's definitely something that I can work with, and maybe tweak a little.