Inside Macintosh: QuickDraw GX Graphics /

Chapter 4 - Geometric Operations / Geometric Operations Reference

Functions / Performing Geometric Arithmetic With Shapes

GXIntersectShape

You can use the GXIntersectShape function to find the intersection of two shapes.

void GXIntersectShape(gxShape target, gxShape operand);

target

On input, a reference to one of the shapes to intersect. On output, a reference to the intersection of the input target shape and the operand shape.

operand

A reference to the other shape to intersect.

DESCRIPTION

The GXIntersectShape function finds the intersection of the target shape and the operand shape, reduces and simplifies the result, and stores it in the target shape. If the original target shape and the operand shape do not intersect, the resulting target shape is an empty shape.

If the target shape and the operand shape share only an edge, and if both have a solid fill, the resulting target shape is an empty shape. However, you can provide a framed target shape and a solid operand shape--the result being a framed 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 determining intersection.

Implementation Note

Due to an implementation limit with QuickDraw GX version 1.0, you can find the intersection of two framed shapes only if the shapes are points, lines, or curves.

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 an example 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.

To determine if two shapes touch, use the GXTouchesShape function, described on page 4-98.

To find the union of two shapes, use the GXUnionShape function, described in the next section.

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