Android 动画总结(6) - 估值器

Android 动画总结(1) - 概述
Android 动画总结(2) - 帧动画
Android 动画总结(3) - 补间动画
Android 动画总结(4) - 插值器
Android 动画总结(5) - 属性动画
Android 动画总结(7) - ViewGroup 子元素间的动画
Android 动画总结(8) - Activity 转场动画
Android 动画总结(9) - 过渡动画

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插值器算出属性改变的百分比，Evaluator 估值器根据这个百分比算出属性值。

ArgbEvaluator

public class ArgbEvaluator implements TypeEvaluator {
    private static final ArgbEvaluator sInstance = new ArgbEvaluator();

    public static ArgbEvaluator getInstance() {
        return sInstance;
    }

    /**
     * fraction 是一个 0-1 的比例值，表示动画执行时间已经执行到了多少
     */
    public Object evaluate(float fraction, Object startValue, Object endValue) {
        int startInt = (Integer) startValue;
        float startA = ((startInt >> 24) & 0xff) / 255.0f;
        float startR = ((startInt >> 16) & 0xff) / 255.0f;
        float startG = ((startInt >>  8) & 0xff) / 255.0f;
        float startB = ( startInt        & 0xff) / 255.0f;

        int endInt = (Integer) endValue;
        float endA = ((endInt >> 24) & 0xff) / 255.0f;
        float endR = ((endInt >> 16) & 0xff) / 255.0f;
        float endG = ((endInt >>  8) & 0xff) / 255.0f;
        float endB = ( endInt        & 0xff) / 255.0f;

        // convert from sRGB to linear
        startR = (float) Math.pow(startR, 2.2);
        startG = (float) Math.pow(startG, 2.2);
        startB = (float) Math.pow(startB, 2.2);

        endR = (float) Math.pow(endR, 2.2);
        endG = (float) Math.pow(endG, 2.2);
        endB = (float) Math.pow(endB, 2.2);

        // compute the interpolated color in linear space
        float a = startA + fraction * (endA - startA);
        float r = startR + fraction * (endR - startR);
        float g = startG + fraction * (endG - startG);
        float b = startB + fraction * (endB - startB);

        // convert back to sRGB in the [0..255] range
        a = a * 255.0f;
        r = (float) Math.pow(r, 1.0 / 2.2) * 255.0f;
        g = (float) Math.pow(g, 1.0 / 2.2) * 255.0f;
        b = (float) Math.pow(b, 1.0 / 2.2) * 255.0f;

        return Math.round(a) << 24 | Math.round(r) << 16 | Math.round(g) << 8 | Math.round(b);
    }
}

IntEvaluator

public class IntEvaluator implements TypeEvaluator {

    public Integer evaluate(float fraction, Integer startValue, Integer endValue) {
        int startInt = startValue;
        return (int)(startInt + fraction * (endValue - startInt));
    }
}

IntArrayEvaluator

public class IntArrayEvaluator implements TypeEvaluator {

    private int[] mArray;

    public IntArrayEvaluator() {
    }

    public IntArrayEvaluator(int[] reuseArray) {
        mArray = reuseArray;
    }

    @Override
    public int[] evaluate(float fraction, int[] startValue, int[] endValue) {
        int[] array = mArray;
        if (array == null) {
            array = new int[startValue.length];
        }
        for (int i = 0; i < array.length; i++) {
            int start = startValue[i];
            int end = endValue[i];
            array[i] = (int) (start + (fraction * (end - start)));
        }
        return array;
    }
}

FloatEvaluator

public class FloatEvaluator implements TypeEvaluator {

    public Float evaluate(float fraction, Number startValue, Number endValue) {
        float startFloat = startValue.floatValue();
        return startFloat + fraction * (endValue.floatValue() - startFloat);
    }
}

FloatArrayEvaluator

public class FloatArrayEvaluator implements TypeEvaluator {

    private float[] mArray;
    public FloatArrayEvaluator() {
    }

    public FloatArrayEvaluator(float[] reuseArray) {
        mArray = reuseArray;
    }

    @Override
    public float[] evaluate(float fraction, float[] startValue, float[] endValue) {
        float[] array = mArray;
        if (array == null) {
            array = new float[startValue.length];
        }

        for (int i = 0; i < array.length; i++) {
            float start = startValue[i];
            float end = endValue[i];
            array[i] = start + (fraction * (end - start));
        }
        return array;
    }
}

PointFEvaluator

public class PointFEvaluator implements TypeEvaluator {

    private PointF mPoint;

    public PointFEvaluator() {
    }

    public PointFEvaluator(PointF reuse) {
        mPoint = reuse;
    }

    @Override
    public PointF evaluate(float fraction, PointF startValue, PointF endValue) {
        float x = startValue.x + (fraction * (endValue.x - startValue.x));
        float y = startValue.y + (fraction * (endValue.y - startValue.y));

        if (mPoint != null) {
            mPoint.set(x, y);
            return mPoint;
        } else {
            return new PointF(x, y);
        }
    }
}