程式學習紀錄

@HasNativeInterpolator
public class AnticipateInterpolator extends BaseInterpolator implements NativeInterpolatorFactory {
    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) {
        this(context.getResources(), context.getTheme(), attrs);
    }


    public AnticipateInterpolator(Resources res, Theme theme, AttributeSet attrs) {
        TypedArray a;
        if (theme != null) {
            a = theme.obtainStyledAttributes(attrs, R.styleable.AnticipateInterpolator, 0, 0);
        } else {
            a = res.obtainAttributes(attrs, R.styleable.AnticipateInterpolator);
        }

        mTension = a.getFloat(R.styleable.AnticipateInterpolator_tension, 2.0f);
        setChangingConfiguration(a.getChangingConfigurations());
        a.recycle();
    }

    public float getInterpolation(float t) {
        // a(t) = t * t * ((tension + 1) * t - tension)
        return t * t * ((mTension + 1) * t - mTension);  
        // y = (T+1)*t^3 - T*t^2
    }

    /** @hide */
    @Override
    public long createNativeInterpolator() {
        return NativeInterpolatorFactoryHelper.createAnticipateInterpolator(mTension);
    }
}