Question

I get the context with [NSGraphicsContext currentContext], how do I get the NSAffineTransform currently applied to it?

I need this for implementing my own transformation stack where I can perform push and pop actions just like glPushMatrix() and glPopMatrix() in OpenGl.

[NSGraphicsContext saveGraphicsState] doesn’t do it for me because it isn’t stackable, or is it?

Answer 1

It is. Save the graphic state before you apply your changes to the context and restore the state after. Each saveGraphicsState must be paired with corresponding restoreGraphicsState call.

// Initial state

[NSGraphicsContext saveGraphicsState];

[transform1 concat];
// State 1.
//Draw with transform1 concatenated with the current transform of the context

[NSGraphicsContext saveGraphicsState];

[transform2 set];
// State 2
// draw with transform2 that replaces the transform of the context

[NSGraphicsContext restoreGraphicsState];

// now we have State 1 again

[NSGraphicsContext restoreGraphicsState];

// We came back to the initial state