Inside Macintosh: QuickTime Reference

Using QuickTime Vectors

This section explains how to create and manipulate QuickTime vectors. The examples use utility functions provided by the vector codec, described in "Vector Codec Component Functions" , that eliminate the need to work directly with the QuickTime atoms in a vector data stream. If your software edits or parses a great deal of vector data, it may be more efficient to work directly with the atoms. For descriptions of the atoms in a vector data stream, see "Vector QT Atom Container" . For information about working directly with QuickTime atoms, see "QuickTime Atoms" (page 47) .

There are several issues concerning the creation of curve movies that developers should be aware of. First, the most common mistake that developers may make when authoring a curve movie is to fail to place an "eraser shape" (usually white) of some kind behind the main shape. If an eraser shape is not placed behind the main shape, odd behaviors may occur:

Resizing/updating the window may result in the old size not being erased or "overlapped"
Curves that feature transfer modes blend and re-blend across themselves.

The second issue involves placing samples on top of another track (such as a movie). This works properly in only two cases:

If the user selects "composite mode" for the graphics mode of the curve track
If users place a white eraser rectangle and then use transparent mode.

Proper use of curves can produce QuickTime movies with spectacular effects, such as a red- blended curve with a video running underneath it. However, failure to use the proper mode may often result in confusion for the user.

Note that many of these problems do not occur when the user uses curves in a sprite track rather than directly in a video track.

Using QuickTime Vectors

Opening the Vector Codec Component

Creating a Vector Data Stream

Creating a Path Using Only Off-Curve Points

Creating Paths With Multiple Contours and Fills

Specifying Joins

Adding Gradients

Specifying a Color for a Path

Specifying a Transfer Mode

Hit-Testing a Path

Drawing Vectors