objective c - CoreGraphics draw an image on a white canvas -

i have source image has variable width , height, must show on fullscreen ipad uiimageview addition of borders around image itself. task create new image white border around it, not overlapping on image itself. i'm doing overlapping via code:

- (uiimage*)imagewithborderfromimage:(uiimage*)source {   cgsize size = [source size];   uigraphicsbeginimagecontext(size);   cgrect rect = cgrectmake(0, 0, size.width, size.height);   [source drawinrect:rect blendmode:kcgblendmodenormal alpha:1.0];    cgcontextref context = uigraphicsgetcurrentcontext();   cgcontextsetrgbstrokecolor(context, 1.0, 1.0, 1.0, 1.0);   cgcontextsetlinewidth(context, 40.0);   cgcontextstrokerect(context, rect);   uiimage *testimg =  uigraphicsgetimagefromcurrentimagecontext();   uigraphicsendimagecontext();   return testimg; } 

can tell me how first draw white canvas 40 pixels bigger in each direction source image , draw image on it?

i adjusted code make work. does:

1. set canvas size size of image + 2*margins
2. fill whole canvas background color (white in case)
3. draw image in appropriate rectangle (with initial size , required margins)

resulting code is:

- (uiimage*)imagewithborderfromimage:(uiimage*)source {     const cgfloat margin = 40.0f;     cgsize size = cgsizemake([source size].width + 2*margin, [source size].height + 2*margin);     uigraphicsbeginimagecontext(size);      [[uicolor whitecolor] setfill];     [[uibezierpath bezierpathwithrect:cgrectmake(0, 0, size.width, size.height)] fill];      cgrect rect = cgrectmake(margin, margin, size.width-2*margin, size.height-2*margin);     [source drawinrect:rect blendmode:kcgblendmodenormal alpha:1.0];      uiimage *testimg =  uigraphicsgetimagefromcurrentimagecontext();     uigraphicsendimagecontext();     return testimg; }