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The Anatomy of a Pattern

The pattern cell is the basic component of a pattern. The pattern cell for the pattern shown in Figure 6-1 is shown in Figure 6-2. The black rectangle is not part of the pattern; it’s drawn to show where the pattern cell ends.

The size of this particular pattern cell includes the area of the four colored rectangles and space above and to the right of the rectangles, as shown in Figure 6-3. The black rectangle surrounding each pattern cell in the figure is not part of the cell; it’s drawn to indicate the bounds of the cell. When you create a pattern cell, you define the bounds of the cell and draw within the bounds.

You can specify how far apart Quartz draws the start of each pattern cell from the next in the horizontal and vertical directions. The pattern cells in Figure 6-3 are drawn so that the start of one pattern cell is exactly a pattern width apart from the next pattern cell, resulting in each pattern cell abutting on the next. The pattern cells in Figure 6-4 have space added in both directions, horizontal and vertical. You can specify different spacing values for each direction. If you make the spacing less than the width or height of a pattern cell, the pattern cells overlap.

When you draw a pattern cell, Quartz uses pattern space as the coordinate system. Pattern space is an abstract space that maps to the default user space by the transformation matrix you specify when you create the pattern—the pattern matrix.

If you don’t want Quartz to transform the pattern cell, you can specify the identity matrix. However, you can achieve interesting effects by supplying a transformation matrix. Figure 6-5 shows the effect of scaling the pattern cell shown in Figure 6-2. Figure 6-6 demonstrates rotating the pattern cell. Translating the pattern cell is a bit more subtle. Figure 6-7 shows the origin of the pattern, with the pattern cell translated in both directions, horizontal and vertical, so that the pattern no longer abuts the window as it does in Figure 6-1.

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