Inside Macintosh: QuickDraw GX Graphics /

Chapter 4 - Geometric Operations / Geometric Operations Reference

Functions / Performing Geometric Arithmetic With Shapes

GXReverseDifferenceShape

You can use the GXReverseDifferenceShape function to find the geometric difference between two shapes.

void GXReverseDifferenceShape(gxShape target, gxShape operand);

target

On input, a reference to the shape to subtract. On output, a reference to a shape describing the difference between the two shapes.

operand

A reference to the shape to subtract from.

DESCRIPTION

The GXReverseDifferenceShape function subtracts the target shape from the operand shape and stores the result in the target shape.

The initial operand shape does not have to contain the target shape; the result of this function is the intersection of the target and operand shapes subtracted from the operand shape.

This function considers the shape fill, the style modifications, and the transform mapping of the target and operand shapes. Only areas that are drawn are considered when calculating the difference.

Neither the target shape nor the operand shape have one of the framed fills (open-frame or closed-frame).

If you provide a target or operand 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	Posts the error shape_operator_may_not_be_a_bitmap
picture	Posts the error shape_operator_may_not_be_a_picture
text	Converts to path shape if other parameter is not an empty shape or a full shape
glyph	Converts to path shape if other parameter is not an empty shape or a full shape
layout	Converts to path shape if other parameter is not an empty shape or a full shape

ERRORS, WARNINGS, AND NOTICES

Errors
out_of_memory
shape_is_nil
number_of_contours_exceeds_implementation_limit
number_of_points_exceeds_implementation_limit
size_of_path_exceeds_implementation_limit
size_of_polygon_exceeds_implementation_limit
fill_type_not_allowed	(debugging version)
shape_access_not_allowed	(debugging version)
clip_to_frame_shape_unimplemented	(debugging version)
shape_operator_may_not_be_a_bitmap	(debugging version)
shape_operator_may_not_be_a_picture	(debugging version)
Warnings
character_substitution_took_place
font_substitution_took_place
unable_to_traverse_open_contour_that_starts_or_ends_off_the_curve
	(debugging version)

SEE ALSO

For examples using this function, see "Performing Geometric Arithmetic With Shapes" beginning on page 4-60.

For a discussion of geometric arithmetic, see "Geometric Arithmetic" beginning on page 4-21.

For a discussion of shape fills, see Chapter 2, "Geometric Shapes," in this book.

For a discussion of style modifications, see Chapter 3, "Geometric Styles," in this book.

For a discussion of transform mappings, see the chapter "Transform Objects" in Inside Macintosh: QuickDraw GX Objects.

For information about related functions, see the description of the GXIntersectShape function on page 4-107, the GXUnionShape function on page 4-109, and the GXDifferenceShape function on page 4-110.

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