compact framework - Drawing control with transparent background -

i've been trying display image has transparent border background control.

unfortunately, transparent area creates hole in parent form follows:

in above image, form has red background i'd hoped see behind control in transparent areas.

the code used follows:

    protected override void onpaint(system.windows.forms.painteventargs e)     {         if (this.image != null)         {             graphics g = graphics.fromimage(this.image);              imageattributes attr = new imageattributes();              //set transparency based on top left pixel             attr.setcolorkey((this.image bitmap).getpixel(0, 0), (this.image bitmap).getpixel(0, 0));              //draw image using image attributes.             rectangle dstrect = new rectangle(0, 0, this.image.width, this.image.height);              e.graphics.drawimage(this.image, dstrect, 0, 0, this.image.width, this.image.height,                 graphicsunit.pixel, attr);         }         else         {             base.onpaint(e);         }     }      protected override void onpaintbackground(system.windows.forms.painteventargs e)     {         //base.onpaintbackground(e);     } 

this class inherited picturebox because needed control implements onmousemove , onmouseup events.

i've been researching of day without success testing out different ideas unfortunately work on full framework , not .net cf.

any ideas appreciated.

ah joys of cf transparency. go on , on (and have in blog , project resistance code did ages ago).

the gist this. child control has paint it's areas, first has call it's parent (the form in case) , tell redraw it's background image everywhere except in child's clipping region , draw on top of that. if sounds bit confusing it's because is.

for example, if @ project resistance, view (which control) draws resistor , bands. lies in form has image background, , background needs "show through" transparent areas of resistor:

so in drawing code of resistor this:

protected override void onpaint(painteventargs e) {     base.onpaint(e);      try     {         rect rect = new rect(this.bounds);          // draw blank         infrastructure.graphictools.drawtransparentbitmap(e.graphics, m_blankimage, bounds,                new rectangle(0, 0, m_blankimage.width, m_blankimage.height));          if (m_bandsimage != null)         {             // draw bands             infrastructure.graphictools.drawtransparentbitmap(e.graphics, m_bandsimage, bounds,                   new rectangle(0, 0, m_bandsimage.width, m_bandsimage.height));         }     }         {     }      if (!controller.touchmode)     {         // todo: draw in selection arrow         // controller.selectedband     } } 

which simple enough. key calls it's base onpaint, this:

protected override void onpaint(system.windows.forms.painteventargs e) {     // assumes we're in workspace, on mainform (the whole parent.parent thing)     ibackgroundpaintprovider bgpaintprovider = parent.parent ibackgroundpaintprovider;     if (bgpaintprovider != null)     {         rectangle rcpaint = e.cliprectangle;         // use parent, since it's workspace position in form want,          // not our position in workspace         rcpaint.offset(parent.left, parent.top);         bgpaintprovider.paintbackground(e.graphics, e.cliprectangle, rcpaint);     } } 

you can see it's calling paintbackground of containing form (it's parent.parent in case becuse control in container called workspace - wouldn't need walk twice in case). draws in background image in area you're seeing "hole"

public void paintbackground(graphics g, rectangle targetrect, rectangle sourcerect) {     g.drawimage(m_bmbuffer, targetrect, sourcerect, graphicsunit.pixel); }