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Getting the User to Device Space Transform

Typically when you draw with Quartz 2D, you need only to work in user space. Quartz takes care of transforming between user and device space for you. If your application needs to obtain the affine transform that Quartz uses to convert between user and device space, you can call the function CGContextGetUserSpaceToDeviceSpaceTransform. This function is available starting in Mac OS X v10.4.

Quartz adds a number of convenience functions in Mac OS X v10.4 to transform the following geometries between user space and device space. You might find these functions easier to use than applying the affine transform returned from the function CGContextGetUserSpaceToDeviceSpaceTransform.

• Points. The functions CGContextConvertPointToDeviceSpace and CGContextConvertPointToUserSpace transform a CGPoint data type from one space to the other.

• Sizes. The functions CGContextConvertSizeToDeviceSpace and CGContextConvertSizeToUserSpace transform a CGSize data type from one space to the other.

• Rectangles. The functions CGContextConvertRectToDeviceSpace and CGContextConvertRectToUserSpace transform a CGRect data type from one space to the other.

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