Android中的Interpolator

Interpolator用于动画中的时间插值，其作用就是把0到1的浮点值变化映射到另一个浮点值变化。

　　本文列出Android API提供的Interpolator的若干种实现，列出源码，并且用一个程序绘制出其数学曲线。（项目链接附在文后）。

 

AccelerateDecelerateInterpolator

/** * An interpolator where the rate of change starts and ends slowly but * accelerates through the middle. *  */public class AccelerateDecelerateInterpolator implements Interpolator {    public AccelerateDecelerateInterpolator() {    }        @SuppressWarnings({"UnusedDeclaration"})    public AccelerateDecelerateInterpolator(Context context, AttributeSet attrs) {    }        public float getInterpolation(float input) {        return (float)(Math.cos((input + 1) * Math.PI) / 2.0f) + 0.5f;    }}

 

 

AccelerateInterpolator

/** * An interpolator where the rate of change starts out slowly and  * and then accelerates. * */public class AccelerateInterpolator implements Interpolator {    private final float mFactor;    private final double mDoubleFactor;    public AccelerateInterpolator() {        mFactor = 1.0f;        mDoubleFactor = 2.0;    }        /**     * Constructor     *      * @param factor Degree to which the animation should be eased. Seting     *        factor to 1.0f produces a y=x^2 parabola. Increasing factor above     *        1.0f  exaggerates the ease-in effect (i.e., it starts even     *        slower and ends evens faster)     */    public AccelerateInterpolator(float factor) {        mFactor = factor;        mDoubleFactor = 2 * mFactor;    }        public AccelerateInterpolator(Context context, AttributeSet attrs) {        TypedArray a =            context.obtainStyledAttributes(attrs, com.android.internal.R.styleable.AccelerateInterpolator);                mFactor = a.getFloat(com.android.internal.R.styleable.AccelerateInterpolator_factor, 1.0f);        mDoubleFactor = 2 * mFactor;        a.recycle();    }        public float getInterpolation(float input) {        if (mFactor == 1.0f) {            return input * input;        } else {            return (float)Math.pow(input, mDoubleFactor);        }    }}

 

AnticipateInterpolator

/** * An interpolator where the change starts backward then flings forward. */public class AnticipateInterpolator implements Interpolator {    private final float mTension;    public AnticipateInterpolator() {        mTension = 2.0f;    }    /**     * @param tension Amount of anticipation. When tension equals 0.0f, there is     *                no anticipation and the interpolator becomes a simple     *                acceleration interpolator.     */    public AnticipateInterpolator(float tension) {        mTension = tension;    }    public AnticipateInterpolator(Context context, AttributeSet attrs) {        TypedArray a = context.obtainStyledAttributes(attrs,                com.android.internal.R.styleable.AnticipateInterpolator);        mTension =                a.getFloat(com.android.internal.R.styleable.AnticipateInterpolator_tension, 2.0f);        a.recycle();    }    public float getInterpolation(float t) {        // a(t) = t * t * ((tension + 1) * t - tension)        return t * t * ((mTension + 1) * t - mTension);    }}

 

 

AnticipateOvershootInterpolator

/** * An interpolator where the change starts backward then flings forward and overshoots * the target value and finally goes back to the final value. */public class AnticipateOvershootInterpolator implements Interpolator {    private final float mTension;    public AnticipateOvershootInterpolator() {        mTension = 2.0f * 1.5f;    }    /**     * @param tension Amount of anticipation/overshoot. When tension equals 0.0f,     *                there is no anticipation/overshoot and the interpolator becomes     *                a simple acceleration/deceleration interpolator.     */    public AnticipateOvershootInterpolator(float tension) {        mTension = tension * 1.5f;    }    /**     * @param tension Amount of anticipation/overshoot. When tension equals 0.0f,     *                there is no anticipation/overshoot and the interpolator becomes     *                a simple acceleration/deceleration interpolator.     * @param extraTension Amount by which to multiply the tension. For instance,     *                     to get the same overshoot as an OvershootInterpolator with     *                     a tension of 2.0f, you would use an extraTension of 1.5f.     */    public AnticipateOvershootInterpolator(float tension, float extraTension) {        mTension = tension * extraTension;    }    public AnticipateOvershootInterpolator(Context context, AttributeSet attrs) {        TypedArray a = context.obtainStyledAttributes(attrs, AnticipateOvershootInterpolator);        mTension = a.getFloat(AnticipateOvershootInterpolator_tension, 2.0f) *                a.getFloat(AnticipateOvershootInterpolator_extraTension, 1.5f);        a.recycle();    }    private static float a(float t, float s) {        return t * t * ((s + 1) * t - s);    }    private static float o(float t, float s) {        return t * t * ((s + 1) * t + s);    }    public float getInterpolation(float t) {        // a(t, s) = t * t * ((s + 1) * t - s)        // o(t, s) = t * t * ((s + 1) * t + s)        // f(t) = 0.5 * a(t * 2, tension * extraTension), when t < 0.5        // f(t) = 0.5 * (o(t * 2 - 2, tension * extraTension) + 2), when t <= 1.0        if (t < 0.5f) return 0.5f * a(t * 2.0f, mTension);        else return 0.5f * (o(t * 2.0f - 2.0f, mTension) + 2.0f);    }}

BounceInterpolator

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CycleInterpolator

/** * Repeats the animation for a specified number of cycles. The * rate of change follows a sinusoidal pattern. * */public class CycleInterpolator implements Interpolator {    public CycleInterpolator(float cycles) {        mCycles = cycles;    }        public CycleInterpolator(Context context, AttributeSet attrs) {        TypedArray a =            context.obtainStyledAttributes(attrs, com.android.internal.R.styleable.CycleInterpolator);                mCycles = a.getFloat(com.android.internal.R.styleable.CycleInterpolator_cycles, 1.0f);                a.recycle();    }        public float getInterpolation(float input) {        return (float)(Math.sin(2 * mCycles * Math.PI * input));    }        private float mCycles;}

 

　　参数为2时的曲线：

 

DecelerateInterpolator

/** * An interpolator where the rate of change starts out quickly and  * and then decelerates. * */public class DecelerateInterpolator implements Interpolator {    public DecelerateInterpolator() {    }    /**     * Constructor     *      * @param factor Degree to which the animation should be eased. Setting factor to 1.0f produces     *        an upside-down y=x^2 parabola. Increasing factor above 1.0f makes exaggerates the     *        ease-out effect (i.e., it starts even faster and ends evens slower)     */    public DecelerateInterpolator(float factor) {        mFactor = factor;    }        public DecelerateInterpolator(Context context, AttributeSet attrs) {        TypedArray a =            context.obtainStyledAttributes(attrs, com.android.internal.R.styleable.DecelerateInterpolator);                mFactor = a.getFloat(com.android.internal.R.styleable.DecelerateInterpolator_factor, 1.0f);                a.recycle();    }        public float getInterpolation(float input) {        float result;        if (mFactor == 1.0f) {            result = (float)(1.0f - (1.0f - input) * (1.0f - input));        } else {            result = (float)(1.0f - Math.pow((1.0f - input), 2 * mFactor));        }        return result;    }        private float mFactor = 1.0f;}

 

LinearInterpolator

/** * An interpolator where the rate of change is constant * */public class LinearInterpolator implements Interpolator {    public LinearInterpolator() {    }        public LinearInterpolator(Context context, AttributeSet attrs) {    }        public float getInterpolation(float input) {        return input;    }}

 

OvershootInterpolator

/** * An interpolator where the change flings forward and overshoots the last value * then comes back. */public class OvershootInterpolator implements Interpolator {    private final float mTension;    public OvershootInterpolator() {        mTension = 2.0f;    }    /**     * @param tension Amount of overshoot. When tension equals 0.0f, there is     *                no overshoot and the interpolator becomes a simple     *                deceleration interpolator.     */    public OvershootInterpolator(float tension) {        mTension = tension;    }    public OvershootInterpolator(Context context, AttributeSet attrs) {        TypedArray a = context.obtainStyledAttributes(attrs,                com.android.internal.R.styleable.OvershootInterpolator);        mTension =                a.getFloat(com.android.internal.R.styleable.OvershootInterpolator_tension, 2.0f);        a.recycle();    }    public float getInterpolation(float t) {        // _o(t) = t * t * ((tension + 1) * t + tension)        // o(t) = _o(t - 1) + 1        t -= 1.0f;        return t * t * ((mTension + 1) * t + mTension) + 1.0f;    }}