Blinking pic problem

[Jim Seekamp]

I am using gdiplus to draw a jpg image to the screen at wm_paint, then drawing lines on top of that using the Windows moveto and lineto. It works great, but the problem is that it blinks every time it redraws!! I don't see anywhere that the redrawing can be removed:

         call gdipcreatefromhdc(hdc&,graphics&)

         quality&=%qualitymodehigh

         call gdipgraphicsclear(graphics&,&hc0c0c0c0)
         call gdipsetinterpolationmode(graphics&,quality&)
         call gdipdrawimagerecti(graphics&,img&,0,0,xsz&,ysz&)

         call gdipdeletegraphics(graphics&)

Any ideas??

[Chris Holbrook]

try drawing onto a memory dc then bitblt the bitmap over in the wm_paint?

[Jim Seekamp]

Great idea (why didn't I think of that?)
Thanks

[Jim Seekamp]

Not working... not sure if I have to do a selectobject or not, but if so, I have no bitmap handle to select!!
Any ideas?

       case %wm_paint
         hdc&=beginpaint(hwnd&,ps)

         hbgdc&=createcompatibledc(hdc&)

         ''initialize graphics class
         call gdipcreatefromhdc(hbgdc&,graphics&)

         quality&=%qualitymodehigh

         call gdipgraphicsclear(graphics&,&hc0c0c0c0)
         call gdipsetinterpolationmode(graphics&,quality&)
         call gdipdrawimagerecti(graphics&,img&,0,0,xsz&,ysz&)

         call gdipdeletegraphics(graphics&)
         bitblt hdc&,0,0,xsz&,ysz&,hbgdc&,0,0,%srccopy
         deletedc hbgdc&

         ''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
         ''draw red square on top of image

         hpen&=createpen(%ps_solid,1,%red)
         selectobject hdc&,hpen&

         moveto hdc&,navrc.nleft,navrc.ntop
         lineto hdc&,navrc.nright,navrc.ntop
         lineto hdc&,navrc.nright,navrc.nbottom
         lineto hdc&,navrc.nleft,navrc.nbottom
         lineto hdc&,navrc.nleft,navrc.ntop

         deleteobject hpen&

         endpaint hwnd&,ps

[Chris Boss]

The problem is the WM_ERASEBKGND message.

When you process WM_PAINT, the BeginPaint API function generates the WM_ERASEBKGND message, where the windows background is drawn.

This is useful for controls like text controls, where the background is drawn during WM_ERASEBKGND and then WM_PAINT draws all the other stuff on top of the background.

You can handle it two ways.

Do your background drawing in WM_ERASEBKGND and simply do nothing in WM_PAINT

or

Trap WM_ERAASEBKGND and don't let it gets processed by Windows (ie. don't pass it to DefWindowProc or back to the dialog in a dialog procedure. Then do all your drawing in WM_PAINT.

[Patrice Terrier]

Or you could use a 32-bit DIB as double buffer.

...

[Jim Seekamp]

Now all I'm getting are the red lines drawn in wm_paint - nothing appears from wm_erasebkgnd

I first did it the way it is below without doing the background dc and the bitblt and it worked, but the blinking was still there, so I put the bitblt back in hoping to get rid of the blinking, but now nothing comes up from the background image...
Any ideas?

       case %wm_erasebkgnd
         hdc&=getdc(hwnd&)  ''beginpaint(hwnd&,ps)

         hbgdc&=createcompatibledc(hdc&)

         ''initialize graphics class
         call gdipcreatefromhdc(hbgdc&,graphics&)

         ''quality&=100
         quality&=%qualitymodehigh

         call gdipgraphicsclear(graphics&,&hc0c0c0c0)
         call gdipsetinterpolationmode(graphics&,quality&)
         call gdipdrawimagerecti(graphics&,img&,0,0,xsz&,ysz&)

         call gdipdeletegraphics(graphics&)

         bitblt hdc&,0,0,xsz&,ysz&,hbgdc&,0,0,%srccopy

         deletedc hdc&
         deletedc hbgdc&

         exit function
       case %wm_paint
         hdc&=beginpaint(hwnd&,ps)

         '''initialize graphics class
         'call gdipcreatefromhdc(hbgdc&,graphics&)
         '
         '''quality&=100
         'quality&=%qualitymodehigh
         '
         'call gdipgraphicsclear(graphics&,&hc0c0c0c0)
         'call gdipsetinterpolationmode(graphics&,quality&)
         'call gdipdrawimagerecti(graphics&,img&,0,0,xsz&,ysz&)
         '
         'call gdipdeletegraphics(graphics&)

         ''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
         ''draw red square representing position

         hpen&=createpen(%ps_solid,1,%red)
         selectobject hdc&,hpen&

         moveto hdc&,navrc.nleft,navrc.ntop
         lineto hdc&,navrc.nright,navrc.ntop
         lineto hdc&,navrc.nright,navrc.nbottom
         lineto hdc&,navrc.nleft,navrc.nbottom
         lineto hdc&,navrc.nleft,navrc.ntop

         deleteobject hpen&

         endpaint hwnd&,ps

[Chris Holbrook]

Jim, suggestion - post compileable source code. It would then take people 1 minute to get into test mode!

[Chris Holbrook]

Don't know if my old compileable example posted here will help (post #15). It does the drawing in WM_ERASEBKGND as Chris Boss suggested above.

[Jim Seekamp]

This is what ended up working... I had to do 2 things: use the device context passed by wm_erasebkgnd and I had to set %null as the window class's background. (wclass.hbrbackground=%null) Works like a charm with no blinking!
Thanks for the helpful insights Chris and Chris!
Jim

       case %wm_erasebkgnd
         hdc&=wparam&

         ''initialize graphics class
         call gdipcreatefromhdc(hdc&,graphics&)

         ''quality&=100
         quality&=%qualitymodehigh

         'call gdipgraphicsclear(graphics&,&hc0c0c0c0)
         call gdipsetinterpolationmode(graphics&,quality&)
         call gdipdrawimagerecti(graphics&,img&,0,0,xsz&,ysz&)

         call gdipdeletegraphics(graphics&)

         ''''''''''''''''''''''''''''''''''''''''''''''''
         ''draw red rectangle

         hpen&=createpen(%ps_solid,1,%red)
         selectobject hdc&,hpen&

         moveto hdc&,navrc.nleft,navrc.ntop
         lineto hdc&,navrc.nright,navrc.ntop
         lineto hdc&,navrc.nright,navrc.nbottom
         lineto hdc&,navrc.nleft,navrc.nbottom
         lineto hdc&,navrc.nleft,navrc.ntop

         deleteobject hpen&

         exit function
       case %wm_paint
         hdc&=beginpaint(hwnd&,ps)

         endpaint hwnd&,ps