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Gradients

Quartz provides two opaque data types for creating gradients—CGShadingRef and CGGradientRef. You can use either of these to create axial or radial gradients. A gradient is a fill that varies from one color to another. An axial gradient (also called a linear gradient) varies along an axis between two defined end points. All points that lie on a line perpendicular to the axis have the same color value.

A radial gradient is a fill that varies radially along an axis between two defined ends, which typically are both circles. Points share the same color value if they lie on the circumference of a circle whose center point falls on the axis. The radius of the circular sections of the gradient are defined by the radii of the end circles; the radius of each intermediate circle varies linearly from one end to the other.

This chapter provides examples of the sorts of linear and radial gradients you can create with Quartz, compares the two approaches you can take to painting gradients, and then shows how to use each opaque data type to create a gradient.

Contents:

Axial and Radial Gradient Examples
A Comparison of CGShading and CGGradient Objects
Extending Color Beyond the End of a Gradient
Using a CGGradient Object
Using a CGShading Object
See Also

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