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Commit d75e2539 authored by Alan Viverette's avatar Alan Viverette
Browse files

Move viscous fluid interpolator to its own class

Change-Id: If7dcc968895ba9200b40fbc7d7aded6e6bbf6ff7
parent 24029435
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+45 −33
Original line number Diff line number Diff line
@@ -61,6 +61,8 @@ import android.view.animation.Interpolator;
 * }</pre>
 */
public class Scroller  {
    private final Interpolator mInterpolator;

    private int mMode;

    private int mStartX;
@@ -81,7 +83,6 @@ public class Scroller {
    private float mDeltaX;
    private float mDeltaY;
    private boolean mFinished;
    private Interpolator mInterpolator;
    private boolean mFlywheel;

    private float mVelocity;
@@ -142,18 +143,8 @@ public class Scroller {
            SPLINE_TIME[i] = coef * ((1.0f - y) * P1 + y * P2) + y * y * y;
        }
        SPLINE_POSITION[NB_SAMPLES] = SPLINE_TIME[NB_SAMPLES] = 1.0f;

        // This controls the viscous fluid effect (how much of it)
        sViscousFluidScale = 8.0f;
        // must be set to 1.0 (used in viscousFluid())
        sViscousFluidNormalize = 1.0f;
        sViscousFluidNormalize = 1.0f / viscousFluid(1.0f);

    }

    private static float sViscousFluidScale;
    private static float sViscousFluidNormalize;

    /**
     * Create a Scroller with the default duration and interpolator.
     */
@@ -178,7 +169,11 @@ public class Scroller {
     */
    public Scroller(Context context, Interpolator interpolator, boolean flywheel) {
        mFinished = true;
        if (interpolator == null) {
            mInterpolator = new ViscousFluidInterpolator();
        } else {
            mInterpolator = interpolator;
        }
        mPpi = context.getResources().getDisplayMetrics().density * 160.0f;
        mDeceleration = computeDeceleration(ViewConfiguration.getScrollFriction());
        mFlywheel = flywheel;
@@ -312,13 +307,7 @@ public class Scroller {
        if (timePassed < mDuration) {
            switch (mMode) {
            case SCROLL_MODE:
                float x = timePassed * mDurationReciprocal;
    
                if (mInterpolator == null)
                    x = viscousFluid(x); 
                else
                    x = mInterpolator.getInterpolation(x);
    
                final float x = mInterpolator.getInterpolation(timePassed * mDurationReciprocal);
                mCurrX = mStartX + Math.round(x * mDeltaX);
                mCurrY = mStartY + Math.round(x * mDeltaY);
                break;
@@ -499,20 +488,6 @@ public class Scroller {
        return mFlingFriction * mPhysicalCoeff * Math.exp(DECELERATION_RATE / decelMinusOne * l);
    }

    static float viscousFluid(float x)
    {
        x *= sViscousFluidScale;
        if (x < 1.0f) {
            x -= (1.0f - (float)Math.exp(-x));
        } else {
            float start = 0.36787944117f;   // 1/e == exp(-1)
            x = 1.0f - (float)Math.exp(1.0f - x);
            x = start + x * (1.0f - start);
        }
        x *= sViscousFluidNormalize;
        return x;
    }
    
    /**
     * Stops the animation. Contrary to {@link #forceFinished(boolean)},
     * aborting the animating cause the scroller to move to the final x and y
@@ -583,4 +558,41 @@ public class Scroller {
        return !mFinished && Math.signum(xvel) == Math.signum(mFinalX - mStartX) &&
                Math.signum(yvel) == Math.signum(mFinalY - mStartY);
    }

    private static class ViscousFluidInterpolator implements Interpolator {
        /** Controls the viscous fluid effect (how much of it). */
        private static final float VISCOUS_FLUID_SCALE = 8.0f;

        private static final float VISCOUS_FLUID_NORMALIZE;
        private static final float VISCOUS_FLUID_OFFSET;

        static {

            // must be set to 1.0 (used in viscousFluid())
            VISCOUS_FLUID_NORMALIZE = 1.0f / viscousFluid(1.0f);
            // account for very small floating-point error
            VISCOUS_FLUID_OFFSET = 1.0f - VISCOUS_FLUID_NORMALIZE * viscousFluid(1.0f);
        }

        private static float viscousFluid(float x) {
            x *= VISCOUS_FLUID_SCALE;
            if (x < 1.0f) {
                x -= (1.0f - (float)Math.exp(-x));
            } else {
                float start = 0.36787944117f;   // 1/e == exp(-1)
                x = 1.0f - (float)Math.exp(1.0f - x);
                x = start + x * (1.0f - start);
            }
            return x;
        }

        @Override
        public float getInterpolation(float input) {
            final float interpolated = VISCOUS_FLUID_NORMALIZE * viscousFluid(input);
            if (input > 0) {
                return input + VISCOUS_FLUID_OFFSET;
            }
            return input;
        }
    }
}