MICROSOFT_PRESS_EBOOK_PROGRAMMING_WINDOWS_8_APPS_WITH_HTML_CSS_AND_JAVASCRIPT_PDF

Inking
Beyond the built-in soft keyboard/handwriting pane, an app might also want to provide a surface on
which it can directly accept pointer input as ink. By this I mean more than just having a canvas element
and processing MSPointer* events to draw on it to produce a raster bitmap. Ink is a data structure that
maintains the actual input data (including pressure, angle, and velocity if the hardware supports it)
which allows for handwriting recognition and other higher-level processing that isn’t possible with
raster data. Ink, in other words, remembers how an image was drawn, not just the final image itself, and
it works with all types of pointer input.
Ink support in WinRT is found in the Windows.UI.Input.Inking namespace. This API doesn’t
depend on any particular presentation framework, nor does it provide for rendering: it deals only with
the managing data structures that an app can then render itself to a drawing surface such as a canvas.
Here’s its basic function:
• Create an instance of the manager object with new Windows.UI.Input.Inking.InkManager().
• Assign any drawing attributes by creating a Windows.UI.Input.Inking.InkDrawing-Attributes
object and settings attributes like the ink color, fitToCurve (as opposed to the default straight
lines), ignorePressure, penTip (Windows.UI.Input.Inking.PenTipShape.circle or rectangle),
and size (a Windows.Foundation.Size object with height and width).
• For the input element, listen for the MSPointerDown, MSPointerMove, and MSPointerUp events,
which you generally need to handle for display purposes already. The eventArgs.currentPoint is
a Windows.UI.Input.PointerPoint object that contains a pointer id, point coordinates, and
properties like pressure, tilt, and twist.
• Pass that PointerPoint object to the ink manager’s processPointerDown,
process-PointerUpdate, and processPointerUp methods, respectively.
• After processPointerUp, the ink manager will create a Windows.UI.Input.Inking.InkStroke
object for that path. Those strokes can then be obtained through the ink manager’s getStrokes
method and rendered as desired.
• Higher-order gestures can be also converted into InkStroke objects directly and given to the
manager through its addStroke method. Stroke objects can also be deleted with deleteStroke.
The ink manager also provides methods for performing handwriting recognition with its contained
strokes, saving and loading the data, and handling different modes like draw and erase. For a complete
demonstration, check out the Input Ink sample that is shown in Figure 9-9. This sample lets you see the
full extent of inking capabilities, including handwriting recognition.
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