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
; Draw a vertical line through the nearest datapoint.
PlotS, [datapt, datapt], !Y.CRange, Color=info.color
format = '(F4.1)'
XYOutS, datapt, 0.85, '(' + $
String(info.indep[datapt],Format=format) + $
',' + String(info.data[datapt],Format=format) + ')', $
Color=info.color
ENDCASE
ENDCASE
Widget_Control, event.top, Set_UValue=info, /No_Copy
END
PRO Example
; Fake data.
data = Findgen(11)
data = Sin(data*360*!RaDeg)
indep = Findgen(11)
; Create the widgets.
tlb = Widget_Base(Title='Example Program', Column=1)
drawID = Widget_Draw(tlb, XSize=500, YSize=500, $
Event_Pro='Draw_Widget_Events', Button_Events=1)
; Get the window index number.
Widget_Control, tlb, /Realize
Widget_Control, drawID, Get_Value=wid
WSet, wid
; Plot the data.
Plot, indep, data, PSym=-4, Position=[0.2, 0.2, 0.8, 0.8]
; Create a pixmap.
Window, /Free, /Pixmap, XSize=500, YSize=500
pixID = !D.Window
Plot, indep, data, PSym=-4, Position=[0.2, 0.2, 0.8, 0.8]
; The data step in the X direction. Assume regular steps.
step = indep[1] - indep[0]
TVLCT, 255, 255, 0, 1
color = 1
; Save information to run the program.
info = { indep:indep, $ ; Independent data.
data:data, $ ; Dependent data.
p:!P, $ ; Plotting system variable.
x:!X, $ ; X Axis system variable.
y:!Y, $ ; Y Axis system variable
wid:wid, $ ; Window index number.
pixID:pixID, $ ; The pixmap index number.
step:step, $ ; The step in independent data.
color:color, $ ; The line color.
last:N_Elements(indep)-1 $ ; Last element in array.
}
Widget_Control, tlb, Set_UValue=info, /No_Copy
XManager, 'example', tlb, /No_Block, Cleanup='Example_Cleanup'
END
-----------------------------------------------------------
David Fanning, Ph.D.
Fanning Software Consulting
E-Mail: davidf@dfanning.com
Phone: 970-221-0438
Coyote's Guide to IDL Programming: http://www.dfanning.com/
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