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MIT License
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package com.qozix.widgets; //from w w w . j a v a 2 s .co m import android.content.Context; import android.hardware.SensorManager; import android.util.FloatMath; import android.view.ViewConfiguration; import android.view.animation.AnimationUtils; import android.view.animation.Interpolator; /** * This class encapsulates scrolling. The duration of the scroll * can be passed in the constructor and specifies the maximum time that * the scrolling animation should take. Past this time, the scrolling is * automatically moved to its final stage and computeScrollOffset() * will always return false to indicate that scrolling is over. */ public class Scroller { private int mMode; private int mStartX; private int mStartY; private int mFinalX; private int mFinalY; private int mMinX; private int mMaxX; private int mMinY; private int mMaxY; private int mCurrX; private int mCurrY; private long mStartTime; private int mDuration; private float mDurationReciprocal; private float mDeltaX; private float mDeltaY; private boolean mFinished; private Interpolator mInterpolator; private boolean mFlywheel; private float mVelocity; private static final int DEFAULT_DURATION = 250; private static final int SCROLL_MODE = 0; private static final int FLING_MODE = 1; private static float DECELERATION_RATE = (float) (Math.log(0.75) / Math.log(0.9)); private static float ALPHA = 800; // pixels / seconds private static float START_TENSION = 0.4f; // Tension at start: (0.4 * total T, 1.0 * Distance) private static float END_TENSION = 1.0f - START_TENSION; private static final int NB_SAMPLES = 100; private static final float[] SPLINE = new float[NB_SAMPLES + 1]; private float mDeceleration; private final float mPpi; static { float x_min = 0.0f; for (int i = 0; i <= NB_SAMPLES; i++) { final float t = (float) i / NB_SAMPLES; float x_max = 1.0f; float x, tx, coef; while (true) { x = x_min + (x_max - x_min) / 2.0f; coef = 3.0f * x * (1.0f - x); tx = coef * ((1.0f - x) * START_TENSION + x * END_TENSION) + x * x * x; if (Math.abs(tx - t) < 1E-5) break; if (tx > t) x_max = x; else x_min = x; } final float d = coef + x * x * x; SPLINE[i] = d; } SPLINE[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. */ public Scroller(Context context) { this(context, null); } public Scroller(Context context, Interpolator interpolator) { mFinished = true; mInterpolator = interpolator; mPpi = context.getResources().getDisplayMetrics().density * 160.0f; mDeceleration = computeDeceleration(ViewConfiguration.getScrollFriction()); } /** * The amount of friction applied to flings. The default value * is {@link ViewConfiguration#getScrollFriction}. * * @param friction A scalar dimension-less value representing the coefficient of * friction. */ public final void setFriction(float friction) { mDeceleration = computeDeceleration(friction); } private float computeDeceleration(float friction) { return SensorManager.GRAVITY_EARTH // g (m/s^2) * 39.37f // inch/meter * mPpi // pixels per inch * friction; } /** * * Returns whether the scroller has finished scrolling. * * @return True if the scroller has finished scrolling, false otherwise. */ public final boolean isFinished() { return mFinished; } /** * Force the finished field to a particular value. * * @param finished The new finished value. */ public final void forceFinished(boolean finished) { mFinished = finished; } /** * Returns how long the scroll event will take, in milliseconds. * * @return The duration of the scroll in milliseconds. */ public final int getDuration() { return mDuration; } /** * Returns the current X offset in the scroll. * * @return The new X offset as an absolute distance from the origin. */ public final int getCurrX() { return mCurrX; } /** * Returns the current Y offset in the scroll. * * @return The new Y offset as an absolute distance from the origin. */ public final int getCurrY() { return mCurrY; } /** * Returns the current velocity. * * @return The original velocity less the deceleration. Result may be * negative. */ public float getCurrVelocity() { return mVelocity - mDeceleration * timePassed() / 2000.0f; } /** * Returns the start X offset in the scroll. * * @return The start X offset as an absolute distance from the origin. */ public final int getStartX() { return mStartX; } /** * Returns the start Y offset in the scroll. * * @return The start Y offset as an absolute distance from the origin. */ public final int getStartY() { return mStartY; } /** * Returns where the scroll will end. Valid only for "fling" scrolls. * * @return The final X offset as an absolute distance from the origin. */ public final int getFinalX() { return mFinalX; } /** * Returns where the scroll will end. Valid only for "fling" scrolls. * * @return The final Y offset as an absolute distance from the origin. */ public final int getFinalY() { return mFinalY; } /** * Call this when you want to know the new location. If it returns true, * the animation is not yet finished. loc will be altered to provide the * new location. */ public boolean computeScrollOffset() { if (mFinished) { return false; } int timePassed = (int)(AnimationUtils.currentAnimationTimeMillis() - mStartTime); if (timePassed < mDuration) { switch (mMode) { case SCROLL_MODE: float x = timePassed * mDurationReciprocal; if (mInterpolator == null) x = viscousFluid(x); else x = mInterpolator.getInterpolation(x); mCurrX = mStartX + Math.round(x * mDeltaX); mCurrY = mStartY + Math.round(x * mDeltaY); break; case FLING_MODE: final float t = (float) timePassed / mDuration; final int index = (int) (NB_SAMPLES * t); final float t_inf = (float) index / NB_SAMPLES; final float t_sup = (float) (index + 1) / NB_SAMPLES; final float d_inf = SPLINE[index]; final float d_sup = SPLINE[index + 1]; final float distanceCoef = d_inf + (t - t_inf) / (t_sup - t_inf) * (d_sup - d_inf); mCurrX = mStartX + Math.round(distanceCoef * (mFinalX - mStartX)); // Pin to mMinX <= mCurrX <= mMaxX mCurrX = Math.min(mCurrX, mMaxX); mCurrX = Math.max(mCurrX, mMinX); mCurrY = mStartY + Math.round(distanceCoef * (mFinalY - mStartY)); // Pin to mMinY <= mCurrY <= mMaxY mCurrY = Math.min(mCurrY, mMaxY); mCurrY = Math.max(mCurrY, mMinY); if (mCurrX == mFinalX && mCurrY == mFinalY) { mFinished = true; } break; } } else { mCurrX = mFinalX; mCurrY = mFinalY; mFinished = true; } return true; } /** * Start scrolling by providing a starting point and the distance to travel. * The scroll will use the default value of 250 milliseconds for the * duration. * * @param startX Starting horizontal scroll offset in pixels. Positive * numbers will scroll the content to the left. * @param startY Starting vertical scroll offset in pixels. Positive numbers * will scroll the content up. * @param dx Horizontal distance to travel. Positive numbers will scroll the * content to the left. * @param dy Vertical distance to travel. Positive numbers will scroll the * content up. */ public void startScroll(int startX, int startY, int dx, int dy) { startScroll(startX, startY, dx, dy, DEFAULT_DURATION); } /** * Start scrolling by providing a starting point and the distance to travel. * * @param startX Starting horizontal scroll offset in pixels. Positive * numbers will scroll the content to the left. * @param startY Starting vertical scroll offset in pixels. Positive numbers * will scroll the content up. * @param dx Horizontal distance to travel. Positive numbers will scroll the * content to the left. * @param dy Vertical distance to travel. Positive numbers will scroll the * content up. * @param duration Duration of the scroll in milliseconds. */ public void startScroll(int startX, int startY, int dx, int dy, int duration) { mMode = SCROLL_MODE; mFinished = false; mDuration = duration; mStartTime = AnimationUtils.currentAnimationTimeMillis(); mStartX = startX; mStartY = startY; mFinalX = startX + dx; mFinalY = startY + dy; mDeltaX = dx; mDeltaY = dy; mDurationReciprocal = 1.0f / (float) mDuration; } /** * Start scrolling based on a fling gesture. The distance travelled will * depend on the initial velocity of the fling. * * @param startX Starting point of the scroll (X) * @param startY Starting point of the scroll (Y) * @param velocityX Initial velocity of the fling (X) measured in pixels per * second. * @param velocityY Initial velocity of the fling (Y) measured in pixels per * second * @param minX Minimum X value. The scroller will not scroll past this * point. * @param maxX Maximum X value. The scroller will not scroll past this * point. * @param minY Minimum Y value. The scroller will not scroll past this * point. * @param maxY Maximum Y value. The scroller will not scroll past this * point. */ public void fling(int startX, int startY, int velocityX, int velocityY, int minX, int maxX, int minY, int maxY) { // Continue a scroll or fling in progress if (mFlywheel && !mFinished) { float oldVel = getCurrVelocity(); float dx = (float) (mFinalX - mStartX); float dy = (float) (mFinalY - mStartY); float hyp = FloatMath.sqrt(dx * dx + dy * dy); float ndx = dx / hyp; float ndy = dy / hyp; float oldVelocityX = ndx * oldVel; float oldVelocityY = ndy * oldVel; if (Math.signum(velocityX) == Math.signum(oldVelocityX) && Math.signum(velocityY) == Math.signum(oldVelocityY)) { velocityX += oldVelocityX; velocityY += oldVelocityY; } } mMode = FLING_MODE; mFinished = false; float velocity = FloatMath.sqrt(velocityX * velocityX + velocityY * velocityY); mVelocity = velocity; final double l = Math.log(START_TENSION * velocity / ALPHA); mDuration = (int) (1000.0 * Math.exp(l / (DECELERATION_RATE - 1.0))); mStartTime = AnimationUtils.currentAnimationTimeMillis(); mStartX = startX; mStartY = startY; float coeffX = velocity == 0 ? 1.0f : velocityX / velocity; float coeffY = velocity == 0 ? 1.0f : velocityY / velocity; int totalDistance = (int) (ALPHA * Math.exp(DECELERATION_RATE / (DECELERATION_RATE - 1.0) * l)); mMinX = minX; mMaxX = maxX; mMinY = minY; mMaxY = maxY; mFinalX = startX + Math.round(totalDistance * coeffX); // Pin to mMinX <= mFinalX <= mMaxX mFinalX = Math.min(mFinalX, mMaxX); mFinalX = Math.max(mFinalX, mMinX); mFinalY = startY + Math.round(totalDistance * coeffY); // Pin to mMinY <= mFinalY <= mMaxY mFinalY = Math.min(mFinalY, mMaxY); mFinalY = Math.max(mFinalY, mMinY); } 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 * position * * @see #forceFinished(boolean) */ public void abortAnimation() { mCurrX = mFinalX; mCurrY = mFinalY; mFinished = true; } /** * Extend the scroll animation. This allows a running animation to scroll * further and longer, when used with {@link #setFinalX(int)} or {@link #setFinalY(int)}. * * @param extend Additional time to scroll in milliseconds. * @see #setFinalX(int) * @see #setFinalY(int) */ public void extendDuration(int extend) { int passed = timePassed(); mDuration = passed + extend; mDurationReciprocal = 1.0f / mDuration; mFinished = false; } /** * Returns the time elapsed since the beginning of the scrolling. * * @return The elapsed time in milliseconds. */ public int timePassed() { return (int)(AnimationUtils.currentAnimationTimeMillis() - mStartTime); } /** * Sets the final position (X) for this scroller. * * @param newX The new X offset as an absolute distance from the origin. * @see #extendDuration(int) * @see #setFinalY(int) */ public void setFinalX(int newX) { mFinalX = newX; mDeltaX = mFinalX - mStartX; mFinished = false; } /** * Sets the final position (Y) for this scroller. * * @param newY The new Y offset as an absolute distance from the origin. * @see #extendDuration(int) * @see #setFinalX(int) */ public void setFinalY(int newY) { mFinalY = newY; mDeltaY = mFinalY - mStartY; mFinished = false; } /** * @hide */ public boolean isScrollingInDirection(float xvel, float yvel) { return !mFinished && Math.signum(xvel) == Math.signum(mFinalX - mStartX) && Math.signum(yvel) == Math.signum(mFinalY - mStartY); } }