3Dcompass© (augmented reality) 0.8.5 - fit camera preview to fullscreen

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There were little trick to do during the scaling of the camera preview mentioned in the previous post. The only way to transform the camera preview is to assign a CGAffineTransform to the UIImagePickerController's cameraViewTransform property.

Knowing that the camera view (320x427) gets scaled from its center as a pivot point, it needs to be adjusted vertically since it is aligned top initially (its frame is 0,0,320,427). Thus we have to do a scale, and a translate in one step (must define it in one single CGAffineTransform matrix).

As I realized the camera preview has to be scaled to 480/427 and shifted down by (480-427)/2 to fit the entire screen (with a slight 6% crop by each side).

As I read the CGAffineTransform description carefully, and planned the transformation carefully above, creating the matrix wasn't a big deal (thanks for OpenGL to introducing me the idea of matrices). As the device/camera has fixed dimensions, we can calculate the constants to work with, the code goes below.

#define kCameraScale 1.12412178 //= 480 / 427
#define kCameraOffset 26.5 //= (480 - 427) / 2
	
//Make camera view full screen.
picker.wantsFullScreenLayout = YES;
picker.cameraViewTransform = CGAffineTransformMake(kCameraScale, 0.0f,
                                                   0.0f,         kCameraScale,
                                                   0.0f,         kCameraOffset);

It gives a pretty fullscreen camera preview with only a 12% zoom and without any distortion. It crops only 6% on each side, and there is no offset relative to the OpenGL overlay now.

Tomorrow I'm gonna do some interface/design/marketing stuff. As the app 3Dcompass© will be completed soon it needs a coherent identy.