CanvasClear causes the application to crash

Question

I'm using a simple rectangular canvas-control with moving indicator(Vshape) which displays currently measured value.
The value is updated 10 - 14 times per second, and deliberately, I made these values fluctuate.
The canvas is filled with gradient colors (5 ranges) and the indicator moves up or down. In order to redraw the indicator,
I'm using CanvasClear with VAL_ENTIRE_OBJECT attribute and thereafter redraws its content.  Few days ago I noticed,
that the software crashed, when the panel, containing the canvas control, was behind another window (belonging to another SW,
say msword, or programmers notepad). I have been able to reproduce the crash, which does not occur immediately but
after the software has been running anywhere from 0.5 to 5 hours and the questionable control has been behind another window.
I also have been able to observe, before the crash, if  I move the covering window away from the canvas-control, covered rectangle
becomes black (in non-crashing mode, it remains white) and it takes several seconds to redraw the partial region.
Sometimes I have noticed irregular elements (a diagonal line, not intended, running from top left corner to bottom right).
Labwindows2010 IDE always indicates crash-point as a call to CanvasClear().
None of the functions, manipulating the canvas-control, return negative values, as the software does check for it and if found logs an
appropriate message. The canvas control has Draw Policy as mark for update.
Does anyone have any idea how to go around such an instability or how do fix it?
I also have been able to capture disassembly and call-stack:
Unhandled exception at 0x6850226E (cvirte.dll) in sw_dbg.exe: 0xC0000005: Access violation writing location 0x00000000.
6850226E
68502258  or          eax,0C00h
6850225D  mov         dword ptr [esp+50h],eax
68502261  fldcw       word ptr [esp+50h]
68502265  fistp       dword ptr [esp+50h]
68502269  movzx       eax,byte ptr [esp+50h]
6850226E  mov         byte ptr [esi],al                   // esi content is 0
68502270  movzx       ecx,byte ptr [edi]
68502273  fldcw       word ptr [esp+54h]
68502277  imul        ecx,ebx
6850227A  mov         dword ptr [esp+50h],ecx
6850227E  fild        dword ptr [esp+50h]
68502282  fdiv        qword ptr ds:[68802D40h]
68502288  fadd        qword ptr ds:[68802D38h]
6850228E  fstp        qword ptr [esp]
68502291  call        687D5950
Call-stack:
    cvirte.dll!6850226e()     
     [Frames below may be incorrect and/or missing, no symbols loaded for cvirte.dll]    
     cvirte.dll!684d149c()     
     cvirte.dll!687b036c()     
     cvirte.dll!687b09c2()     
     cvirte.dll!684d9759()     
     cvirte.dll!684d9981()     
     cvirte.dll!687b5850()     
     cvirte.dll!687bc167()     
     cvirte.dll!687bd40f()     
     user32.dll!7674c4e7()     
     user32.dll!7674c5e7()     
     user32.dll!7674c590()     
     user32.dll!76744f0e()     
     user32.dll!76744f7d()     
     ntdll.dll!779c6fce()     
     user32.dll!76744ec3()     
     user32.dll!76741be4()     
     user32.dll!7673ffcd()     
     cvirte.dll!687c13c1()     
     cvirte.dll!68483419()     
     cvirte.dll!68722687()     
     cvirte.dll!68729882()     
     cvirte.dll!68525b8b()     
     cvirte.dll!686042a6()     
     cvirte.dll!6846d7dd()     
     cvirte.dll!68557bcc()     
     sw_dbg.exe!00402470()
Solved!
Go to Solution.

Answer 1

In addition to this, you should take a look at the Color Ramp Settings for the Numeric Slide control. This allows you to convert a slide control into a color scale like you have implemented with the intensity plot and canvas. You may not be able to get it to look exactly like what you have created, but it might suit your needs and will be easier to maintain and less resource intensive. You can also configure it programmatically at run-time using the Color Ramp Functions library.
National Instruments
Product Support Engineer