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DrawPicture |
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| Header: | Quickdraw.h | Carbon status: | Supported | |
Draws a picture on any type of output device.
void DrawPicture (
PicHandle myPicture,
const Rect *dstRect
);
A handle to the picture to be drawn. You must access a picture through its handle.
When creating pictures, the OpenCPicture and OpenPicture functions return their handles. You can use the GetPicture function to get a handle to a QuickDraw picture stored in a 'PICT' resource. To get a handle to a QuickDraw picture stored in a 'PICT' file, you must use File Manager functions. To get a picture stored in the scrap, use the Scrap Manager function GetScrap to get a handle to its data and then coerce this handle to one of type PicHandle.
A destination rectangle, specified in coordinates local to the current graphics port, in which to draw the picture. The DrawPicture function shrinks or expands the picture as necessary to align the borders of its bounding rectangle with the rectangle you specify in this parameter. To display a picture at a resolution other than that at which it was created, your application should compute an appropriate destination rectangle by scaling its width and height by the following factor:
scale factor = destination resolution / source resolution
For example, if a picture was created at 300 dpi and you want to display it at 75 dpi, then your application should compute the destination rectangle width and height as 1/4 of those of the picture’s bounding rectangle. Use the GetPictInfo function to gather information about a picture. The PictInfo structure returned by GetPictInfo returns the picture’s resolution in its hRes and vRes fields. The sourceRect field contains the bounding rectangle for displaying the image at its optimal resolution.
Within the rectangle that you specify in the dstRect parameter, the DrawPicture function draws the picture that you specify in the myPicture parameter.
The DrawPicture function passes any picture comments to the StdComment function pointed to by the commentProc field of the CQDProcs or QDProcs structure, which in turn is pointed to by the grafProcs field of a CGrafPort or GrafPort structure. The default StdComment function provided by QuickDraw does no comment processing whatsoever. If you want to process picture comments when drawing a picture, use the SetStdCProcs function to assist you in changing the CQDProcs structure and use the SetStdProcs function to assist you in changing the QDProcs structure.
Always use the ClipRect function to specify a clipping region appropriate for your picture before defining it with the OpenCPicture (or OpenPicture) function. If you do not use ClipRect to specify a clipping region, OpenCPicture uses the clipping region specified in the current graphics port. If the clipping region is very large (as it is when a graphics port is initialized) and you want to scale the picture, the clipping region can become invalid when DrawPicture scales the clipping region—in which case, your picture will not be drawn. On the other hand, if the graphics port specifies a small clipping region, part of your drawing may be clipped when DrawPicture draws it. Setting a clipping region equal to the port rectangle of the current graphics port always sets a valid clipping region.
When it scales, DrawPicture changes the size of the font instead of scaling the bits. However, the widths used by bitmap fonts are not always linear. For example, the 12-point width isn’t exactly 1/2 of the 24-point width. This can cause lines of text to become slightly longer or shorter as the picture is scaled. The difference is often insignificant, but if you are trying to draw a line of text that fits exactly into a box (a spreadsheet cell, for example), the difference can become noticeable to the user—most typically, at print time. The easiest way to avoid such problems is to specify a destination rectangle that is the same size as the bounding rectangle for the picture. Otherwise, your application may need to directly process the opcodes in the picture instead of using DrawPicture.
You may also have disappointing results if the fonts contained in an image are not available on the user’s system. Before displaying a picture, your application may want to use the Picture Utilities to determine what fonts are contained in the picture, and then use Font Manager functions to determine whether the fonts are available on the user’s system. If they are not, you can use Dialog Manager functions to display an alert box warning the user of display problems.
If there is insufficient memory to draw a picture in Color QuickDraw, the QDError function returns the result code noMemForPictPlaybackErr.
The DrawPicture function may move or purge memory.
Supported in Carbon. Available in Carbon 1.0.2 and later when running Mac OS 8.1 or later.
© 2000 Apple Computer, Inc. (Last Updated 6/30/2000)