OpenGL Layer - Core Animation - page 134

In a CAOpenGLLayer , however, setting up and using a display link callback is com-
pletely unnecessary as this is provided for you in both -canDrawInCGLContext and
-drawInCGLContext . The time you use to check to see if a new frame is ready is provided
in the parameter called displayTime .

So, to render a movie into the CAOpenGLLayer , in the -canDrawInCGLContext :

1. Check to see if the movie is playing back; if not, return NO .

2. If the movie is playing back, check to see if the context for the movie has been set
up yet. If not, set it up with a call to -setupVisualContext .

3. Check to see if a new frame is ready.

4. If so, copy the current image into the image buffer.

5. If everything is successful, return YES .

6. If -canDrawInCGLContext returned YES , -drawInCGLContext gets called. Inside of that
method, draw the OpenGL quads for the movie's current texture images.

The implementation of -canDrawInCGLContext is in Listing 8-3.

LISTING 8-3 Implementation of Delegate -canDrawInCGLContext

- ( BOOL )canDrawInCGLContext:( CGLContextObj )glContext
pixelFormat:( CGLPixelFormatObj )pixelFormat
forLayerTime:( CFTimeInterval )timeInterval
displayTime:( const CVTimeStamp *)timeStamp

{

if ( ! qtVisualContext )
{

// If the visual context for the QTMovie has not been set up
// we initialize it now
[ self setupVisualContext :glContext withPixelFormat :pixelFormat];

}

// Check to see if a new frame (image) is ready to be drawn at
// the current time by passing NULL as the second param
if ( QTVisualContextIsNewImageAvailable ( qtVisualContext , NULL ))
{

// Release the previous frame
CVOpenGLTextureRelease ( currentFrame );

// Copy the current frame into the image buffer
QTVisualContextCopyImageForTime ( qtVisualContext ,
NULL ,
NULL ,
& currentFrame );