Deprecated CIContext Methods

Discussion

After calling this method, Core Image draws content into the surface (drawable object) attached to the CGL context. A CGL context is an OS X OpenGL context. For more information, see OpenGL Programming Guide for Mac.

When you create a CIContext object using a CGL context, all OpenGL states set for the CGL context affect rendering to that context. That means that coordinate and viewport transformations set on the CGL context as well as the vertex color.

For best results, follow these guidelines when you use Core Image to render into an OpenGL context:

• Ensure that the a single unit in the coordinate space of the OpenGL context represents a single pixel in the output device.

• The Core Image coordinate space has the origin in the bottom left corner of the screen. You should configure the OpenGL context in the same way.

• The OpenGL context blending state is respected by Core Image. If the image you want to render contains translucent pixels, it’s best to enable blending using a blend function with the parameters GL_ONE, GL_ONE_MINUS_SRC_ALPHA, as shown in the following code example.

Some typical initialization code for a view with width W and height H is:

    glViewport (0, 0, W, H);

    glMatrixMode (GL_PROJECTION);

    glLoadIdentity ();

    glOrtho (0, W, 0, H, -1, 1);

    glMatrixMode (GL_MODELVIEW);

    glLoadIdentity ();

    glBlendFunc (GL_ONE, GL_ONE_MINUS_SRC_ALPHA);

    glEnable (GL_BLEND);