ArgbEvaluator.java

package carbon.internal;

import android.animation.TypeEvaluator;

public class ArgbEvaluator implements TypeEvaluator {

    /**
     * This function returns the calculated in-between value for a color
     * given integers that represent the start and end values in the four
     * bytes of the 32-bit int. Each channel is separately linearly interpolated
     * and the resulting calculated values are recombined into the return value.
     *
     * @param fraction   The fraction from the starting to the ending values
     * @param startValue A 32-bit int value representing colors in the separate bytes of the
     *                   parameter
     * @param endValue   A 32-bit int value representing colors in the separate bytes of the
     *                   parameter
     * @return A value that is calculated to be the linearly interpolated result, derived by
     * separating the start and end values into separate color channels and interpolating each one
     * separately, recombining the resulting values in the same way.
     */
    public Object evaluate(float fraction, Object startValue, Object endValue) {
        int startInt = (Integer) startValue;
        int startA = (startInt >> 24) & 0xff;
        int startR = (startInt >> 16) & 0xff;
        int startG = (startInt >> 8) & 0xff;
        int startB = startInt & 0xff;

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

        return (startA + (int) (fraction * (endA - startA))) << 24 |
                (startR + (int) (fraction * (endR - startR))) << 16 |
                (startG + (int) (fraction * (endG - startG))) << 8 |
                (startB + (int) (fraction * (endB - startB)));
    }
}