Inside Macintosh: QuickDraw GX Objects /

Chapter 6 - Transform Objects / Transform Objects Reference

Functions / Transforming Shapes by Modifying Shape Geometries

GXSkewShape

You can use the GXSkewShape function to skew a shape about a specified origin by specified horizontal and vertical factors.

void GXSkewShape(gxShape target, Fixed xSkew, Fixed ySkew, 
               Fixed xOffset, Fixed yOffset);

target

A reference to the shape you want to skew.

hSkew

The amount to skew the shape horizontally.

vSkew

The amount to skew the shape vertically.

xOffset

The horizontal coordinate of the origin to skew the shape about.

yOffset

The vertical coordinate of the origin to skew the shape about.

DESCRIPTION

The GXSkewShape function skews the shape referenced by the target parameter horizontally by the factor specified in the hSkew parameter and vertically by the factor specified in the vSkew parameter. The skewing is centered about the origin specified in the xOffset and yOffset parameters. (The origin is the point whose coordinates do not change as a result of the skewing operation.)

The skew factors are expressed as a proportional amount of shift in one direction with distance in the perpendicular direction. A value of 0 for the hSkew or vSkew parameter indicates no skewing in the corresponding direction.

This function skews the target shape in one of two ways:

• If the target shape's gxMapTransformShape attribute is cleared, the function recalculates the control points of the shape's geometry to effect the skewing.
• If the target shape's gxMapTransformShape attribute is set, this function is identical to the GXSkewTransform function; it recalculates the mapping matrix of the target shape's transform object to effect the skewing. If the target shape shares this transform object with other shapes, QuickDraw GX makes a copy of the transform object, associates the copy with the target shape, and makes changes to the copy.

The target shape can be any shape type. However, if the target shape is an empty shape, a full shape, or a picture shape, this function has no effect unless the shape's gxMapTransformShape attribute is set.

The coordinates of the origin are specified in geometry space.

ERRORS, WARNINGS, AND NOTICES

Errors
out_of_memory
shape_is_nil
shape_access_not_allowed	(debugging version)
Warnings
skew_shape_out_of_range
graphic_type_cannot_be_moved
Notices (debugging version)
mapping_unaffected

SEE ALSO

For examples of the use of this function, see Listing 6-4 on page 6-25 and Listing 6-5 on page 6-27.

To skew a shape by altering the mapping property of its transform object, you can also use the GXSkewTransform function, described on page 6-63.