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Axial and Radial Gradient Examples

Quartz functions provide a rich vocabulary for creating gradient effects. This section shows some of the results you can achieve. The axial gradient in Figure 8-1 varies between one endpoint that is a shade of orange and another that is a shade of yellow. In this case, the axis is at a 45 degree angle with respect to the origin.

Quartz also lets you specify colors and locations along an axis to create more complex axial gradients, as shown in Figure 8-2. The color at the starting point is a shade of red and the color at the ending point is a shade of violet. However, there are also five locations on the axis whose color is set to orange, yellow, green, blue, and indigo, respectively. You can think of the result as six sequential linear gradients along the same axis. Although the axis used here is the same as that used in Figure 8-1 (45 degree angle), it doesn’t have to be. The angle of the axis is defined by the starting and ending point that you provide.

Figure 8-3 shows a radial gradient that varies between a small, bright red circle and a larger black one.

With Quartz, you are not restricted to creating gradients based on color changes; you can vary only the alpha, or you can vary the alpha along with the other color components. Figure 8-4 shows a gradient whose red, green, and blue components remain constant as the alpha value varies from 1.0 to 0.1.

You can position the circles in a radial gradient to create a variety of shapes. If one circle is partially or fully outside the other, Quartz creates a conical surface for circles that have unequal circumferences, and a cylindrical surface for circles that have equal circumferences. A common use of a radial gradient is to create a shaded sphere, as shown in Figure 8-5. In this case, a single point (a circle with a radius of 0) lies within a larger circle.

You can create more complex effects by nesting several radial gradients similar to that shown in Figure 8-6. The toroidal portion of the shape is created using concentric circles.

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