Determining Whether One Shape Contains Another (IM: XG)

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

Determining Whether One Shape Contains Another
QuickDraw GX also provides three functions to help you determine whether one area contains another:

The GXContainsRectangle function determines whether one rectangle contains another.
The GXContainsBoundsShape function determines whether the area covered by a rectangle contains the area covered by a shape.
The GXContainsShape function determines whether the area covered by one shape contains the area covered by another shape.

The sample function in Listing 4-11 creates a small circular path and a larger, donut-shaped path to test for containment.
Listing 4-11 Creating a path shape with two contours and a smaller concentric rectangle shape
void CreateMultiplePaths(void)
{
   gxShape twoCircleShape, smallSquareShape;

   static rectangle smallSquareGeometry[] = {ff(90), ff(90),
                                             ff(110), ff(110)};


   static long twoCircleGeometry[] = {2, /* # of contours */
                                      4, /* # of points */
                                      0xF0000000, /* 1111 ... */
                                      ff(50), ff(50),    
                                      ff(150), ff(50), 
                                      ff(150), ff(150),  
                                      ff(50), ff(150),
                                      4, /* # of points */
                                      0xF0000000, /* 1111 ... */
                                      ff(65), ff(65),
                                      ff(65), ff(135) ,
                                      ff(135), ff(135),
                                      ff(135), ff(65)};


   twoCircleShape = GXNewPaths((gxPaths *) twoCircleGeometry);
   GXSetShapeFill(twoCircleShape, gxEvenOddFill);
   
   smallSquareShape = GXNewRectangle(&smallSquareGeometry);
   GXSetShapeFill(smallSquareShape, gxEvenOddFill);

   GXDrawShape(twoCircleShape);
   GXDisposeShape(twoCircleShape);
   GXDrawShape(smallSquareShape);
   GXDisposeShape(smallSquareShape);
}
The results of this sample function are shown in Figure 4-50.
Figure 4-50 A path shape with two contours and a smaller concentric rectangle shape

Since the GXContainsShape function considers shape fill when calculating whether one shape contains another, the following function call:
GXContainsShape(twoCircleShape, smallerCircleShape);
returns false; the area covered by the larger path does not contain the area covered by the smaller path.
For more information about the GXContainsShape function, see page 4-103.
The functions GXContainsRectangle and GXContainsBoundsShape work similarly to the GXContainsShape function, except the input parameters to these functions are rectangle geometries, rather than shapes. The GXContainsRectangle function compares two rectangle geometries and the GXContainsBoundsShape compares a rectangle geometry to a shape.
For more information about the GXContainsRectangle function and the GXContainsBoundsShape function, see page 4-100 and page 4-101, respectively.