Q:
I'm getting a list of QuickTime effects via the QTGetEffectsList
function. I will then pass this list to the QTCreateStandardParameterDialog
function to create a dialog so the user can choose an effect
from the list. However, I would like to be able to edit
the list beforehand so it only shows the effects I want.
Is this possible?
A: With QuickTime 6 you can use the nifty new function QTGetEffectsListExtended
to filter the effects which are placed into the effects list. Full documentation
for this function can be found in the "What's
New in QuickTime 6" document. We strongly urge developers to
use this technique as it will guarantee compatability with future versions
of QuickTime.
For example, here's how you would use this call to display only
multi-source transition effects:
QTAtomContainer effectsList;
OSErr err;
err = QTGetEffectsListExtended(
&effectsList,
2, /* minimum number of sources */
-1, /* no maximum number of sources */
0, /* getOptions - optional */
kTransitionMajorClass, /* filter multi-source morph effects */
kTransitionMinorClass, /* filter transitions */
0, /* optional filter procedure */
0); /* optional refcon for the filter procedure */
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Listing 1. Filtering the effects list using QTGetEffectsListExtended
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For QuickTime 5 and earlier, you'll need to manually walk the list of
effects returned by QTGetEffectsList and delete those effects from the
list you don't want shown. The list returned by QTGetEffectsList contains
two atoms for each effect component. The first atom, of type kEffectNameAtom
('name'), contains the name of the effect. The second atom, of type
kEffectTypeAtom ('type'), contains the type of the effect, which is
the sub-type of the effect component. Simply walk this list and remove
both the kEffectNameAtom and kEffectTypeAtom atom for those effects
you don't want shown. Here's a code snippet showing how it's done:
void BuildAndEditEffectsList() {
short childCount, index;
OSErr err;
QTAtomContainer effectsList, effectSample;
QTParameterDialog effectsDialog;
/* these are the only effects we'd like to
show up in the list */
const OSType supportedEffects[] = {
kBlurImageFilterType,
kBrightnessContrastImageFilterType
};
/* get the current list of effects */
/* min == max == -1, no min or max */
err = QTGetEffectsList( &effectsList, -1, -1, 0 );
if (err != noErr) goto bailError;
/* get a count of the number of effects in the list */
childCount = QTCountChildrenOfType(
effectsList, kParentAtomIsContainer, kEffectNameAtom );
/* iterate over each effect in the list, removing those
which don't match the ones in our pre-chosen list
from above */
for( index = childCount; index > 0 ; index -- )
{
QTAtom effectTypeAtom;
QTAtomID id;
long effectCodeSize;
Ptr effectCodePtr;
OSType effectCode;
short j;
Boolean effectIsSupported;
effectTypeAtom = QTFindChildByIndex( effectsList,
kParentAtomIsContainer,
kEffectTypeAtom, index, &id );
err = QTLockContainer( effectsList );
if (err != noErr) goto bailError;
err = QTGetAtomDataPtr( effectsList,
effectTypeAtom,
&effectCodeSize,
&effectCodePtr);
if (err != noErr) goto bailError;
/* grab the actual effect code */
effectCode = *(OSType *)effectCodePtr;
err = QTUnlockContainer( effectsList );
/* check to see if the current
effect is in our list */
for( j=0, effectIsSupported=false ;
j<sizeof(supportedEffects)/sizeof(OSType) ; j++ )
{
if ( effectCode == supportedEffects[j] )
{
effectIsSupported = true;
break;
}
}
/* delete the effect from the list if we didn't find a match
in our custom list */
if ( !effectIsSupported )
{
QTAtom effectNameAtom;
effectNameAtom = QTFindChildByIndex( effectsList,
kParentAtomIsContainer, kEffectNameAtom, index, &id );
err = QTRemoveAtom( effectsList, effectTypeAtom );
err = QTRemoveAtom( effectsList, effectNameAtom );
}
}
/* now use our newly built effects list to
create a dialog for later use... */
err = QTNewAtomContainer( &effectSample );
err = QTCreateStandardParameterDialog( effectsList,
effectSample, 0, &effectsDialog );
bailError:
return;
}
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Listing 2. Editing the list of effects returned by QTGetEffectsList
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[Sep 04 2002]
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