Using Geometric Operations (IM: XG)

Inside Macintosh: QuickDraw GX Graphics /: Chapter 4 - Geometric Operations

Using Geometric Operations
This section shows you how to apply geometric operations to shapes. In particular, this section shows you how to

determine and reverse the contour direction of a shape's contours
break a contour into multiple contours
reduce and simplify the geometric description of a shape
incorporate style information into a shape's geometry
obtain geometric information about a shape's geometry, such as contour length and area
determine and alter the bounding rectangle of a shape
inset a shape's geometry
determine if two shapes touch
determine if one shape contains another
perform geometric arithmetic, such as intersection and union, on shapes

Many of the sample functions in this section create geometric shapes, and to do so, they specify geometric points for the shapes' geometries. Since a geometric point contains two fixed-point values, the sample functions in this section must convert integer constants to fixed-point constants when specifying a geometric point. QuickDraw GX provides the GXIntToFixed macro, which performs this conversion by shifting the integer value 16 bits to the left:
#define GXIntToFixed(a)  ((Fixed) (a) << 16)
QuickDraw GX also provides the ff macro as a convenient alias:
#define ff(a)  GXIntToFixed(a)
The ff macro is used throughout this section.

Subtopics

Determining and Reversing Contour Direction

Breaking Shape Contours

Eliminating Unnecessary Geometric Points

Simplifying Shapes

Converting a Shape to Primitive Form

Finding Geometric Information About a Shape

Setting a Shape's Bounding Rectangle

Insetting Shapes

Determining Whether Two Shapes Touch

Determining Whether One Shape Contains Another

Performing Geometric Arithmetic With Shapes