MapPt

MapPt Map point relative to two rectangles

#include <Quickdraw.h> Quickdraw

void MapPt(thePoint, srcRect, destRect );

Point *thePoint ; address of point to map; receives result

Rect *srcRect ; address of Rect to convert from

Rect *destRect ; address of Rect to convert to

MapPt maps a point within one rectangle to a similarly-located position in a

different rectangle. Use this to scale individual points of an object being moved

to a larger or smaller rectangle.

thePoint is the address of a 4-byte Point structure. On entry, it is the

coordinates of a point, relative to srcRect that you wish to convert;

upon return, it contains the coordinates of a point relative to the size

and position of destRect .

destRect are the addresses of two 8-byte Rect structures. For typical

operations, thePoint is an element of an object enclosed by srcRect .

It gets mapped to a similar position within destRect .

Notes: This function is typically used to convert individual points of an object

(e.g., a "freehand" drawing) within one rectangle to similar positions

within a larger or smaller rectangle. Other tools exist to scale rectangles

(MapRect), regions (MapRgn), and polygons (MapPoly).

For instance, a corner of srcRect will map exactly to the corresponding

corner of destRect ; similarly, the center of srcRect maps to the center of

destRect . Other points will be positioned at distances from the edges

relative to the ratio of the sizes of the rectangles.

srcRect Á destRect

It is OK if the two rectangles overlap, and thePoint need not be enclosed by

srcRect (in that case, its remapped position will be outside of destRect ).

This call is functionally equivalent to the long-winded:

h1=r1.bottom-r1.top; h2=r2.bottom - r2.top; /* calc heights */

w1=r1.right-r1.left; w2=r2.right - r2.left; /* and widths */

thePoint.h = (thePoint.h * w1) / w2; /* apply ratio of sizes */

thePoint.v = (thePoint.v * h1) / h2;

thePoint.h += (r2.left - r1.left); /* move to position ...*/

thePoint.v += (r2.top - r1.top); /* ... relative to destination */

Referenced by (6):