Inside Macintosh: QuickDraw GX Graphics /

Chapter 2 - Geometric Shapes / Geometric Shapes Reference

Functions / Editing Shape Geometries

GXGetPolygonParts

You can use the GXGetPolygonParts function to copy a specified range of geometric points from the geometry of a polygon shape and then put these points into a polygon structure.

long GXGetPolygonParts(gxShape source, long index, long count,
                       gxPolygons *data);

source

A reference to the polygon shape containing the desired geometric points.

index

The geometry index of the first geometric point to copy.

count

The number of the geometric points to copy. You may provide the gxSelectToEnd constant for this parameter.

data

A pointer to a polygon structure to hold the copied geometric information.

function result

The number of bytes required to hold the information returned in the data parameter.

DESCRIPTION

The GXGetPolygonParts function copies geometry information from the source polygon shape into the polygon structure specified by the data parameter. This function copies all of the geometry information starting with the geometric point indicated by the index parameter and continuing for as many geometric points as indicated by the count parameter. This function copies the values of the indicated geometric points and retains the information about contour breaks from the original geometry. The function result is the length in bytes of the information returned in the data parameter.

Both the index and the count parameters must be greater than 0, although you can provide the gxSelectToEnd constant for the count parameter, which indicates that you want a copy of all the geometric points starting with the point indicated by the index parameter.

You may pass nil for the data parameter. In this case, the function still returns the byte length as the function result, but does not copy any geometry information.

Typically, to use this function, you go through these steps:

1. Determine the byte length needed to store the copied geometry information by calling this function, passing nil for the data parameter.
2. Allocate enough memory to hold the copied geometric information.
3. Call this function again, passing a pointer to the allocated memory in the data parameter.

ERRORS, WARNINGS, AND NOTICES

Errors
out_of_memory
shape_is_nil
illegal_type_for_shape	(debugging version)
index_is_less_than_one	(debugging version)
count_is_less_than_one	(debugging version)
Warnings
index_out_of_range
count_out_of_range

SEE ALSO

For an example that uses this function, see "Editing Polygon Parts" beginning on page 2-82.

For a discussion of polygons, see "Polygon Shapes" on page 2-22.

For the definition of the gxPolygons structure, see page 2-106.

For information about other functions that allow you to extract information from shape geometries, see the description of the GXGetShapePoints function on page 2-140 and the description of the GXGetShapeParts function on page 2-152.

To replace parts of a polygon shape's geometry, use the GXSetPolygonParts function, which is described in the next section.

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