How to rotate OpenGL to fit iPhone Landscape mode?

Question

I am porting an existing cross-platform program I have made in C++ and with OpenGL/ES on the iPhone. Please keep in mind I do not know anything about Objective-C...

I have just briefly edited the Objective-C files of one of the tutorials to initialize OpenGL properly for the iPhone, and to simply call my C++ multi-platform code for everything else.

My program will only run in landscape mode, that is why I have set it as the only supported interface orientation (in the info.plist file).

What I want to know is how I should tell OpenGL to rotate according to the landscape mode. Currently I have added a glRotate that does it before draawing, but it is a dirty trick.

Another thing : I try to convert the touches into mouse click coordinates equivalent with another quick method, and I get a point located at a distance of 80 pixels on the X axis and 80 pixels on the Y axis. I added yet another dirty fix (with GlTranslatef) to this mess and I get the correct coordinates, except... color picking is broken.

To be clear, color picking does not detect anything on the 160 first pixels on the left (which is both 2 * 80 and 480 - 320, so, huh, 99% chance it is caused by my dirty code...)

What is the proper way of dealing with this ?

Answer 1

You shouldn't have to do anything to use OpenGL in landscape mode. I suspect you aren't actually going into landscape mode. You need to override shouldAutoRotateToInterfaceOrientation: in your view controller:

- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)orientation {
    return orientation == UIInterfaceOrientationLandscapeLeft; // Or ...Right
}

To verify that it's working, put some random controls (eg, empty buttons) in the corners of your view, with Interface Builder in landscape mode, and see where they pop up.

Answer 2

On iPhone 3G, this is a bad idea. Rotate using shouldAutoRotateToInterfaceOrientation use OpenGL hardware to perform this operation, so it is better to use a rotation in your OpenGL code. If you have no performance issue, keep it simple.