Apple Newton Utilities Uživatelská příručka stáhnout pdf (Strana 536)

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101

CHAPTER 13

Drawing and Graphics

13-10 Using the Drawing Interface

If you want to redraw a view explicitly at any particular time, you need to send it

the

Dirty message. This message causes the system to add that view to the area of

the screen that it updates in the next event loop cycle. To make the update area

redraw before the next event loop cycle, you must call the

RefreshViews

function after sending the

Dirty message.

Drawing Immediately 13

If you want to draw in a view at times other than when the view is being opened

or redrawn automatically, you can execute drawing code outside of the

ViewDrawScript method by using DoDrawing. For example, you might need

to perform your own drawing operations immediately when the user taps in the view.

You can use the

DoDrawing method for this purpose. The DoDrawing method

calls another drawing method that you supply as one of its arguments.

▲ W ARNING

Do not directly use DrawShape to draw shapes outside

of your

ViewDrawScript. Standard drawing in

ViewDrawScript and DoDrawing automatically set

up the drawing environment. If you use

DrawShape without

setting up the drawing environment, your application could

accidentally draw on top of other applications, keyboards,

or ﬂoaters.

▲

Using Nested Arrays of Shapes 13

The DrawShape method can draw multiple shapes when passed an array of shapes

as its argument. Style frames may be included in the shape array to change the

drawing style used to image subsequent elements of the array. Each element of

the array can itself be an array as well; this section refers to such an array as a

nested array.

Styles are maintained on a per-array basis in nested arrays, and the

startStyle

parameter of

DrawShape is always treated as though it were the ﬁrst array

element of the topmost array. Therefore, compound shapes and multiple styles

remain intact when nested arrays are combined into larger groupings.

When the

DrawShape method processes a nested array, the shapes are drawn in

ascending element order and drawing begins with the style of the parent array.

Although the drawing style may change while processing the elements of an

individual array, that style applies only to the elements of that particular array.

Therefore, if an array happens to be an element of another array—that is, a nested

array—style changes in the nested array affect the processing of its subsequent

elements but the drawing style of the parent array is restored after the last element

of the nested array is processed.

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