Stroke Headers

A stroke refers to the data points collected while the pen is in contact with the tablet. These are called pen-down points. When the user lifts the pen, the stroke ends. A new stroke begins when the pen next touches the tablet. Some tablets also support proximity strokes, which consist of points received when the pen is not in contact with the tablet but near enough for the tablet to sense the pen movement. Such points are called pen-up points; a stroke consisting of pen-up points is said to have a pen-up state.

As Figure 4.1 shows, a stroke header prefaces each collection of pen coordinates that make up a single stroke. Note that the structure of the stroke header in version 2.0 of the Pen API is different from the stroke header of version 1.0, because, instead of the STROKEINFO structure used in version 1.0, the stroke header now consists of a variable-length array . The current STROKEINFO structure is still compatible with version 1.0 stroke headers.

Figure 4.1 shows strokes of different sizes. This is because the pen can be in contact with the surface of the tablet for longer or shorter periods of time, resulting in more or fewer points of data. The length of a single stroke is limited only by the 64K maximum size of an HPENDATA memory block.

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