uiimage - iOS paint optimization -

hi working on app contains taking notes drawing. followed ray wenderlich tutorials , far i've got, ended code:

- (void)touchesbegan:(nsset *)touches withevent:(uievent *)event {      mouseswiped = no;     uitouch *touch = [touches anyobject];     lastpoint = [touch locationinview:self]; }   - (void)touchesmoved:(nsset *)touches withevent:(uievent *)event {     cgfloat red,green,blue,alpha;      mouseswiped = yes;     uitouch *touch = [touches anyobject];     cgpoint currentpoint = [touch locationinview:self];        uigraphicsbeginimagecontext(self.mainimage.frame.size);     [self.tempdrawimage.image drawinrect:cgrectmake(0, 0, self.mainimage.frame.size.width, self.mainimage.frame.size.height)];      cgcontextsetblendmode(uigraphicsgetcurrentcontext(),[self getblendmode]);      cgcontextmovetopoint(uigraphicsgetcurrentcontext(), lastpoint.x , lastpoint.y  );     cgcontextaddlinetopoint(uigraphicsgetcurrentcontext(), currentpoint.x , currentpoint.y  );     cgcontextsetlinecap(uigraphicsgetcurrentcontext(), kcglinecapround);     cgcontextsetlinewidth(uigraphicsgetcurrentcontext(), [self getbrushsize] );      [[self getpaintcolor] getred:&red green:&green blue:&blue alpha:&alpha];     cgcontextsetrgbstrokecolor(uigraphicsgetcurrentcontext(), red, green, blue, 1);      cgcontextsetblendmode(uigraphicsgetcurrentcontext(),[self getblendmode]);      cgcontextstrokepath(uigraphicsgetcurrentcontext());     self.tempdrawimage.image = uigraphicsgetimagefromcurrentimagecontext();     [self.tempdrawimage setalpha:[self getpaintalpha]];     uigraphicsendimagecontext();      lastpoint = currentpoint; }  - (void)touchesended:(nsset *)touches withevent:(uievent *)event {     cgfloat red,green,blue;      if(!mouseswiped) {          uigraphicsbeginimagecontext(self.mainimage.frame.size);         [self.tempdrawimage.image drawinrect:cgrectmake(0, 0, self.mainimage.frame.size.width, self.mainimage.frame.size.height)];         cgcontextsetlinecap(uigraphicsgetcurrentcontext(), kcglinecapround);         cgcontextsetlinewidth(uigraphicsgetcurrentcontext(), [self getbrushsize]);          [[self getpaintcolor] getred:&red green:&green blue:&blue alpha:nil];         cgcontextsetrgbstrokecolor(uigraphicsgetcurrentcontext(), red, green, blue, [self getpaintalpha]);         cgcontextmovetopoint(uigraphicsgetcurrentcontext(), lastpoint.x, lastpoint.y - self.mainimage.frame.origin.y);         cgcontextaddlinetopoint(uigraphicsgetcurrentcontext(), lastpoint.x, lastpoint.y - self.mainimage.frame.origin.y );         cgcontextstrokepath(uigraphicsgetcurrentcontext());         cgcontextflush(uigraphicsgetcurrentcontext());         self.tempdrawimage.image = uigraphicsgetimagefromcurrentimagecontext();         uigraphicsendimagecontext();     }      uigraphicsbeginimagecontext(self.mainimage.frame.size);      [self.mainimage.image drawinrect:cgrectmake(0, 0, self.mainimage.frame.size.width, self.mainimage.frame.size.height) blendmode:[self getblendmode] alpha:1.0];     [self.tempdrawimage.image drawinrect:cgrectmake(0, 0, self.mainimage.frame.size.width, self.mainimage.frame.size.height) blendmode:[self getblendmode] alpha:[self getpaintalpha]];     if(self.drawmode != draweraser)     {         self.mainimage.image = uigraphicsgetimagefromcurrentimagecontext();         self.tempdrawimage.image = nil;     }     uigraphicsendimagecontext();     mouseswiped = no; } 

this code working fine small frame when increased frame 2 times bigger before, unfortunately performance not good. thinking optimizing code. focused on touchesmoved method. far understand, draws whole image on context , changes , assigns context image. drawing whole image seemed overload. wondering, if can draw parts of image context , changes , draw part of context image.

you're right - redrawing whole image every time in touchesmoved bad idea. think should create , keep reference context @ beginning. in touches moved, should draw on , create image context. can use cgbitmapcontextcreate() create context instead of uigraphicsbeginimagecontext() , cgbitmapcontextcreateimage() create image context instead of uigraphicsgetimagefromcurrentimagecontext(). here documentation on how use (https://developer.apple.com/library/mac/#documentation/graphicsimaging/reference/cgbitmapcontext/reference/reference.html).