drawingcontext - WPF Clear Region on a Drawing Context? -

drawingcontext - WPF Clear Region on a Drawing Context? -

so producing transparent png using drawingcontext , drawingvisual.

inside drawingcontext, drew rectange.

i "cut out" circle within of rectangle. how do this? did not find functions in drawing context clear region.

you can seek using combinedgeometry combine 2 geometries (each time). has geometrycombinemode allowing specify logic combination. in case need geometrycombinemode.xor. intersection of rect , ellipse (cirlce) cut out. here simple code demonstrating it:

drawingvisual dv = new drawingvisual(); using (var dc = dv.renderopen()) { var rect = new rect(0, 0, 300, 200); var cb = new combinedgeometry(geometrycombinemode.xor, new rectanglegeometry(rect), new ellipsegeometry(new point(150, 100), 50, 50)); dc.drawgeometry(brushes.blue, null, cb); }

i hope know how render drawingvisual. can utilize rendertargetbitmap capture kind of bitmapsource , have many ways show bitmap.

here screenshot:

the black part means color transparent.

in case want cutting out complex image (such drawn text or image). can turn combinedgeometry kind of opacitymask (type of brush). can turn drawingbrush , brush can used opacitymask can passed drawingcontext.pushopacitymask method:

drawingvisual dv = new drawingvisual(); using (var dc = dv.renderopen()) { var rect = new rect(0, 0, 300, 200); var cb = new combinedgeometry(geometrycombinemode.xor, new rectanglegeometry(rect), new ellipsegeometry(new point(150, 100), 50, 50)); var mask = new drawingbrush(new geometrydrawing(brushes.blue, null, cb)); dc.pushopacitymask(mask); dc.drawimage(someimage, rect); dc.drawtext(new formattedtext("windows presentation foundation", system.globalization.cultureinfo.currentculture, system.windows.flowdirection.lefttoright, new typeface("lucida bright"), 30, brushes.red){ maxtextwidth = rect.width, maxtextheight = rect.height, textalignment = textalignment.center }, new point()); }

note rect should have size of whole drawing. positioning hole , other drawn stuff exact want.

finally drawingvisual has useful property called clip geometry. can prepare combinedgeometry , assign drawingvisual.clip property.

suppose have drawingvisual (with drawn stuff including text, images, ...). next code punch hole through it:

//prepare geometry, can considered puncher. var rect = new rect(0, 0, 300, 200); var cb = new combinedgeometry(geometrycombinemode.xor, new rectanglegeometry(rect), new ellipsegeometry(new point(150, 100), 50, 50)); //punch drawingvisual yourdrawingvisual.clip = cb;

wpf drawingcontext