| Re: Button_events and data [message #11163 is a reply to message #10980] |
Thu, 26 February 1998 00:00   |
J.D. Smith
Messages: 214
Registered: August 1996
|
Senior Member |
|
|
David Fanning wrote:
>
> Bernard Puc (puc@gsfc.nasa.gov) writes:
>
>> I'm looking for pointers on how to do the following: I have a line
>> plot in a draw widget. I want to click the pointer on the plot and have
>> a vertical line drawn at the nearest datapoint to the mouseclick.
>> widget_draw returns the cursor location in device coordinates and I
>> need to translate that into dataspace coordinates.
>> Going one step further, ideally, I'd like to have a vertical line
>> follow the cursor around the draw widget at all times, jumping from
>> datapoint to datapoint. I suspect someone has already written such a
>> thing...
>
> Well, you hit me in a moment of weakness. :-)
>
> I've been writing a program today that is out there on the
> edge of my knowledge and experience. Writing something I
> *know* how to write seemed kind of relaxing. I did this over
> a couple of beers, so it may not be my *best* work. ;-)
>
> The way I chose to implement your requirements is to draw
> the vertical line as long as you hold the cursor down in the
> draw widget. The program assumes regular "steps" in the
> X direction, but the algorithm could easily be changed
> to accommodate irregular steps.
>
> Here you go. Save the code below as "example.pro". Type
> "example" to see it work.
>
> Cheers,
>
> David
>
> PRO Example_Cleanup, id
> Widget_Control, id, Get_UValue=info, /No_Copy
> IF N_Elements(info) NE 0 THEN WDelete, info.pixID
> END
>
> PRO Draw_Widget_Events, event
>
> ; Deal only with button up, button down, and motion events.
>
> IF event.type GT 2 THEN RETURN
>
> ; What kind of event is this?
>
> Widget_Control, event.top, Get_UValue=info, /No_Copy
> eventType = ['Button Down', 'Button Up', 'Motion Events']
> thisEvent = eventType(event.type)
>
> CASE thisEvent OF
>
> 'Button Down': BEGIN
>
> ; Turn motion events on.
>
> Widget_Control, event.id, Draw_Motion_Events=1
> ENDCASE
>
> 'Button Up': BEGIN
>
> ; Turn motion events off.
>
> Widget_Control, event.id, Draw_Motion_Events=0
>
> ; Erase the last line.
>
> WSet, info.wid
> Device, Copy=[0,0,400,400,0,0,info.pixID]
>
> ENDCASE
>
> 'Motion Events': BEGIN
>
> ; Erase the previous line.
>
> WSet, info.wid
> Device, Copy=[0,0,500,500,0,0,info.pixID]
>
> ; Set up plot and axes scaling.
>
> !P = info.p
> !X = info.x
> !Y = info.y
>
> ; Convert cursor location to data coordinates.
>
> coords = Convert_Coord(event.x, event.y, /Device, /To_Data)
> x = coords[0]
> y = coords[1]
>
> ; Make sure X value is within plot limits.
>
> x = !X.crange[0] > x
> x = !X.crange[1] < x
>
> ; Find the nearest data point.
>
> nearest = WHERE(info.indep GE (x - (info.step/2.0)), count)
> IF count EQ 0 THEN datapt = info.indep[info.last] ELSE BEGIN
> nearest = nearest[0]
> IF nearest EQ 0 THEN datapt = info.indep[0] ELSE $
> datapt = info.indep[nearest]
> ENDELSE
I think perhaps he wants the actual nearest point, not the point at the
nearest x... how about:
tmp=min((info.indep-x)^2+(info.data-y)^2,near)
nearpt=[info.indep[near],info.data[near]]
This would also relieve the need for a regular grid of x values.
JD
--
J.D. Smith |*| WORK: (607) 255-5842
Cornell University Dept. of Astronomy |*| (607) 255-4083
206 Space Sciences Bldg. |*| FAX: (607) 255-5875
Ithaca, NY 14853 |*|
|
|
|
|
comp.lang.idl-pvwave archive
Members
Search
Help
Login
Home
