how to change UIKit UIImage:drawInRect method to AppKIt NSImage:drawInRect Method

Question

i'm porting an iphone app to Mac app,there i have to change all the UIKit related class to AppKit. if you can help me on this really appreciate. is this the best way to do below part..

Iphone App-->using UIKit

UIGraphicsPushContext(ctx);
[image drawInRect:rect];
UIGraphicsPopContext();

Mac Os--Using AppKit

[NSGraphicsContext saveGraphicsState];
NSGraphicsContext * nscg = [NSGraphicsContext graphicsContextWithGraphicsPort:ctx flipped:YES];
[NSGraphicsContext setCurrentContext:nscg];
NSRect rect = NSMakeRect(offset.x * scale, offset.y * scale, scale * size.width, scale * size.height);
[NSGraphicsContext restoreGraphicsState];

[image drawInRect:rect fromRect:NSMakeRect( 0, 0, [image size].width, [image size].height )
        operation:NSCompositeClear
         fraction:1.0];

Answer 1

The docs and the docs are your friends; they'll explain a lot of things that you're misusing here.

[NSGraphicsContext saveGraphicsState];
NSGraphicsContext * nscg = [NSGraphicsContext graphicsContextWithGraphicsPort:ctx flipped:YES];
[NSGraphicsContext setCurrentContext:nscg];

You save the graphics state in the current context, and then immediately create a new context and set it as current.

NSRect rect = NSMakeRect(offset.x * scale, offset.y * scale, scale * size.width, scale * size.height);

This is apparently all you gsaved for. Creating a rectangle is not affected by the gstate, since it isn't a drawing operation (the rectangle is just a set of numbers; you're not drawing a rectangle here).

Furthermore, you should use the current transformation matrix for the scale.

[NSGraphicsContext restoreGraphicsState];

And then you grestore in the context you created, not the one you gsaved in.

[Edit] Looking at this again a year and a half later, I think you misinterpreted the saveGraphicsState and restoreGraphicsState methods as a counterpart to UIGraphicsPushContext and UIGraphicsPopContext. They're not; saveGraphicsState and restoreGraphicsState push and pop the graphics state of the current context. The current context is separately controlled (setCurrentContext:) and does not have a push/pop API. [/Edit]

I'm assuming that you're in a CALayer's drawInContext: method? If this is in an NSView, then you already have a current context and don't need to (and shouldn't) create one.

[image drawInRect:rect fromRect:NSMakeRect( 0, 0, [image size].width, [image size].height )
        operation:NSCompositeClear
         fraction:1.0];

The NSCompositeClear operation clears the destination pixels, like the Eraser tool in your favorite paint program. It does not draw the image. You want the NSCompositeSourceOver operation.