c# - Snap window size to fixed multiples -

the windows command console allows resize window multiple of character size. "snapping" of window size instantaneous , not flicker. in native code, done processing wm_sizing message , modifying rect structure accordingly.

in c#, tried overriding onresize method, computing "snapped" size, , setting form's clientsize property accordingly. unfortunately, size keeps jumping between snapped size , whatever size cursor dictates.

protected override void onresize(eventargs e) {     int tgtcols = (clientsize.width + 4) / 8;     int tgtlines = (clientsize.height + 8) / 15;     if (cols != tgtcols || lines != tgtlines)     {         cols = tgtcols;         lines = tgtlines;         int tgtwidth = cols * 8;         int tgtheight = lines * 15;         //clientsize = new size(tgtwidth, tgtheight);         size = new size(tgtwidth + exwidth, tgtheight + exheight);     }     base.onresize(e); } 

as can see, i've tried using both size , clientsize properties, both yield same effect. there better way of constraining size? or need manually intercept wm_sizing message?

edit: tried manually intercepting wm_sizing, same result:

protected override void wndproc(ref message m) {     switch (m.msg)     {         case wm_sizing:             dosizesnap(ref m);             m.result = new intptr(1);             break;          default:             base.wndproc(ref m);             break;     } }  private unsafe void dosizesnap(ref message m) {     int edge = m.wparam.toint32();     rect *prect = (rect *)m.lparam.topointer();     int tgtcols = (prect->right - prect->left - exwidth + 4) / 8;     int tgtlines = (prect->bottom - prect->top - exheight + 8) / 15;     if (cols != tgtcols || lines != tgtlines)     {         cols = tgtcols;         lines = tgtlines;         int tgtwidth = cols * 8;         int tgtheight = lines * 15;         // todo: handle edge         prect->right = prect->left + tgtwidth + exwidth;         prect->bottom = prect->top + tgtheight + exheight;     } } 

subscribing resize event doesn't work either.

the problem statement if (cols != tgtcols || lines != tgtlines). causes size snapping occur when target lines/columns changes, not when window width/height changes. prevent infinite recursion, resize event not fired if size not change, if statement unnecessary.