Android动画之Interpolator
16lz
2021-01-23
Android源码中,有两个Interpolator。一个是frameworks/base/graphics/java/android/graphics/Interpolator.java。另一个是
frameworks/base/core/java/android/view/animation/Interpolator.java。今天想要聊的是后者。
frameworks/base/core/java/android/view/animation/Interpolator.java的源码如下:
/** * An interpolator defines the rate of change of an animation. This allows * the basic animation effects (alpha, scale, translate, rotate) to be * accelerated, decelerated, repeated, etc. */public interface Interpolator extends TimeInterpolator { // A new interface, TimeInterpolator, was introduced for the new android.animation // package. This older Interpolator interface extends TimeInterpolator so that users of // the new Animator-based animations can use either the old Interpolator implementations or // new classes that implement TimeInterpolator directly.}
Android在3.0引入属性动画时,加入了TimeInterpolator接口。Interpolator变成与之(TimeInterpolator)对应的旧接口。Interpolator继承TimeInterpolator,可以兼容旧代码。建议开发者在开发新代码的时候,直接实现TimeInterpolator接口。所以,我们需要再看一下TimeInterpolator的源码。
frameworks/base/core/java/android/animation/TimeInterpolator.java的源码如下:
/** * A time interpolator defines the rate of change of an animation. This allows animations * to have non-linear motion, such as acceleration and deceleration. */public interface TimeInterpolator { /** * Maps a value representing the elapsed fraction of an animation to a value that represents * the interpolated fraction. This interpolated value is then multiplied by the change in * value of an animation to derive the animated value at the current elapsed animation time. * * @param input A value between 0 and 1.0 indicating our current point * in the animation where 0 represents the start and 1.0 represents * the end * @return The interpolation value. This value can be more than 1.0 for * interpolators which overshoot their targets, or less than 0 for * interpolators that undershoot their targets. */ float getInterpolation(float input);}
TimeInterpolator定义了动画变化的接口。float getInterpolation(float input)的输入是[0, 1.0],是动画插值器的归一化时间,0表示开始,1.0表示结束。返回值是动画插值器的归一化结果[0, 1.0],但是,返回值在超越目标(overshoot their targets)的时候,也可以<0或者>1.0。
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