GlobalToLocal

GlobalToLocal Obtain local coordinates of global point

#include <Quickdraw.h> Quickdraw

void GlobalToLocal(thePoint );

Point *thePoint ; global Point; receives local coordinates

GlobalToLocal converts a point from global ( screen) coordinates to values

expressed in coordinates of the current GrafPort. It is used to obtain the local

address of a mouse-down event and as a step in converting between coordinates

of two different grafPorts.

thePoint is the address of a 4-byte Point structure, expressed in global

( screen) coordinates. Upon return, it will contain the coordinates of

that same position, expressed in the coordinate system of the current

Notes: The specified Point is converted, in place. Upon return, it is the same

physical location, expressed in global coordinates.

For instance, mouse-down events are reported in global coordinates, but

TextEdit and the Control Manager functions expect local ( window- relative)

coordinates. Thus, a typical sequence may include:

short ctlCode;

GetNextEvent( everyEvent, &myEvent );

if ( myEvent.what ) == mouseDown {

GlobalToLocal( &myEvent.where ); /* get local equivalent */

ctlCode=FindControl( myEvent.where, myWindow, &myCtl );

if ( ctlCode == inThumb )

/*. . . etc. . . */

}

This function is also used as an intermediate step in converting between

coordinates of two different grafPorts (e.g., windows). For instance, to

convert the position of rectangle theRect from the coordinates of windowA

to the coordinates of windowB :

SetPort( windowA );

LocalToGlobal( & topLeft( theRect ) );

LocalToGlobal( & botRight( theRect ) );

SetPort( windowB );

GlobalToLocal( & topLeft( theRect ) );

GlobalToLocal( & botRight( theRect ) );

To convert between the coordinates of regions and polygons, calculate the

difference between the coordinate systems and use OffsetRect, OffsetRgn,

and OffsetPoly. See LocalToGlobal for an example.

Referenced by (41):