Inside Macintosh: QuickDraw GX Graphics /

Chapter 4 - Geometric Operations / Geometric Operations Reference

Functions / Determining and Reversing Contour Direction

GXGetShapeDirection

You can use the GXGetShapeDirection function to determine whether a contour has a clockwise or counterclockwise direction.

gxContourDirection GXGetShapeDirection(gxShape source, 
                                       long contour);

source

A reference to the shape containing the contour.

contour

The contour index of the contour whose direction you want to determine.

function result

The direction of the contour, either gxClockwiseDirection or gxCounterclockwiseDirection.

DESCRIPTION

The GXGetShapeDirection function indicates whether QuickDraw GX considers the contour indicated by the contour parameter of the shape indicated by the source parameter to be clockwise or counterclockwise. You can use this information to determine how QuickDraw GX will draw a shape that has the gxInsideFrameStyle or gxOutsideFrameStyle style attribute set, or how the GXInsetShape function affects a shape.

For empty and full shapes, this function posts the error graphic_type_does_not_have_multiple_contours.

For point shapes and line shapes, this function always returns gxClockwiseDirection. Although the order of the geometric points in a line shape's geometry does not affect the result of this function, it may affect how QuickDraw GX draws the line. For example, if the line is dashed, the order of the geometric points determines the end of the line at which dashing begins. Also, if the line has a pen width and the gxInsideFrameStyle or gxOutsideFrameStyle style attribute is set, the order of the geometric points determines the side of the geometry on which QuickDraw GX draws the line.

For rectangle shapes, the result of this function is determined by examining which corners are specified by the geometric points. For a rectangle whose geometry includes the upper-left point and the lower-right point, this function returns gxClockwiseDirection, regardless of the order of the two points in the geometry. For a rectangle whose geometry includes the upper-right point and the lower-left point, this function returns gxCounterclockwiseDirection, again regardless of the order of the two points.

For curve shapes, polygon shapes, and path shapes, reversing the order of any contour's geometric points reverses the result of this function.

If you provide a source 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 graphic_type_does_not_have_multiple_contours
picture	Posts the error graphic_type_does_not_have_multiple_contours
text	Posts the error illegal_type_for_shape
glyph	Posts the error illegal_type_for_shape
layout	Posts the error illegal_type_for_shape

ERRORS, WARNINGS, AND NOTICES

Errors
out_of_memory
shape_is_nil
contour_is_less_than_zero	(debugging version)
illegal_type_for_shape	(debugging version)
graphic_type_does_not_have_multiple_contours	(debugging version)
Warnings
contour_out_of_range

SEE ALSO

For examples using this function, see "Determining and Reversing Contour Direction" beginning on page 4-23.

To reverse the order of geometric points in a shape's geometry, use the GXReverseShape function, described in the next section.

For a description of the GXInsetShape function, see page 4-94. For a description of the gxInsideFrameStyle and gxOutsideFrameStyle style attributes, see Chapter 3, "Geometric Styles," in this book.

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