Inside Macintosh: QuickDraw GX Graphics /

Chapter 4 - Geometric Operations / Geometric Operations Reference

Functions / Finding Geometric Information About Shapes

GXGetShapeCenter

You can use the GXGetShapeCenter function to determine the center of a specified contour of a shape.

gxPoint *GXGetShapeCenter(gxShape source, long index, 
                          gxPoint *center);

source

A reference to the shape containing the contour whose center you want to find.

index

The number of the contour whose center you want to find. You may specify a value of 0 to indicate you want to find the center of the entire shape.

center

A pointer to a gxPoint structure. On return, this structure contains the point that falls at the center of the specified contour.

function result

The point that falls at the center of the specified contour. (This value is
the same as the value returned in the center parameter.)

DESCRIPTION

The GXGetShapeCenter function determines the point that falls at the center of the contour specified by the index parameter of the shape specified by the source parameter. If you specify a value of 0 for the index parameter, this function finds the center point of the entire source shape.

The center point of a shape is not merely the center of the shape's bounding rectangle; rather it is the "center of gravity" of a shape. QuickDraw GX guarantees the center point of a shape does not change even if the shape is rotated.

This function finds the center of a shape (or of a particular contour) as defined by the source shape's geometry; it does not consider shape fill or transformations to the shape made by the shape's transform. For point shapes, this function returns a copy of the point's geometry. For line and rectangle shapes, this function returns the midpoint of the geometry. For empty and full shapes, this function posts the error shape_does_not_have_length.

If you provide a target shape that is not one of the geometric shape types, this function performs the actions described in the following table:

Shape type	Action taken
bitmap	Returns midpoint of bounding rectangle
picture	Posts the error illegal_type_for_shape
text	Returns midpoint of the bounding rectangle of the specified glyph
glyph	Returns midpoint of the bounding rectangle of the specified glyph
layout	Converts to glyph shape and returns midpoint of the bounding rectangle of the specified glyph

ERRORS, WARNINGS, AND NOTICES

Errors
out_of_memory
shape_is_nil
parameter_is_nil	(debugging version
illegal_type_for_shape	(debugging version)
contour_less_than_zero	(debugging version)
graphic_type_does_not_contain_points	(debugging version)
Warnings
contour_out_of_range
unable_to_traverse_open_contour_that_starts_or_ends_off_the_curve
	(debugging version)

SEE ALSO

For examples using this function, see "Finding the Bounding Rectangle and Center Point of a Shape" beginning on page 4-43.

To find the bounding rectangle of a shape or a contour of a shape, use the GXGetShapeBounds function described on page 4-90.

Main | Page One | What's New | Apple Computer, Inc. | Find It | Contact Us | Help