1 files changed, 112 insertions, 0 deletions
diff --git a/src/com/android/gallery3d/ui/Paper.java b/src/com/android/gallery3d/ui/Paper.java
new file mode 100644
index 000000000..641fc2c8e
--- /dev/null
+++ b/src/com/android/gallery3d/ui/Paper.java
@@ -0,0 +1,112 @@
+/*
+ * Copyright (C) 2010 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.android.gallery3d.ui;
+
+import com.android.gallery3d.ui.PositionRepository.Position;
+import com.android.gallery3d.util.GalleryUtils;
+
+import android.opengl.Matrix;
+
+import javax.microedition.khronos.opengles.GL11;
+import javax.microedition.khronos.opengles.GL11ExtensionPack;
+
+// This class does the overscroll effect.
+class Paper {
+    private static final String TAG = "Paper";
+    private static final int ROTATE_FACTOR = 4;
+    private OverscrollAnimation mAnimationLeft = new OverscrollAnimation();
+    private OverscrollAnimation mAnimationRight = new OverscrollAnimation();
+    private int mWidth, mHeight;
+    private float[] mMatrix = new float[16];
+
+    public void overScroll(float distance) {
+        if (distance < 0) {
+            mAnimationLeft.scroll(-distance);
+        } else {
+            mAnimationRight.scroll(distance);
+        }
+    }
+
+    public boolean advanceAnimation(long currentTimeMillis) {
+        return mAnimationLeft.advanceAnimation(currentTimeMillis)
+            | mAnimationRight.advanceAnimation(currentTimeMillis);
+    }
+
+    public void setSize(int width, int height) {
+        mWidth = width;
+        mHeight = height;
+    }
+
+    public float[] getTransform(Position target, Position base,
+            float scrollX, float scrollY) {
+        float left = mAnimationLeft.getValue();
+        float right = mAnimationRight.getValue();
+        float screenX = target.x - scrollX;
+        float t = ((mWidth - screenX) * left - screenX * right) / (mWidth * mWidth);
+        // compress t to the range (-1, 1) by the function
+        // f(t) = (1 / (1 + e^-t) - 0.5) * 2
+        // then multiply by 90 to make the range (-45, 45)
+        float degrees =
+                (1 / (1 + (float) Math.exp(-t * ROTATE_FACTOR)) - 0.5f) * 2 * -45;
+        Matrix.setIdentityM(mMatrix, 0);
+        Matrix.translateM(mMatrix, 0, mMatrix, 0, base.x, base.y, base.z);
+        Matrix.rotateM(mMatrix, 0, degrees, 0, 1, 0);
+        Matrix.translateM(mMatrix, 0, mMatrix, 0,
+                target.x - base.x, target.y - base.y, target.z - base.z);
+        return mMatrix;
+    }
+}
+
+class OverscrollAnimation {
+    private static final String TAG = "OverscrollAnimation";
+    private static final long START_ANIMATION = -1;
+    private static final long NO_ANIMATION = -2;
+    private static final long ANIMATION_DURATION = 500;
+
+    private long mAnimationStartTime = NO_ANIMATION;
+    private float mVelocity;
+    private float mCurrentValue;
+
+    public void scroll(float distance) {
+        mAnimationStartTime = START_ANIMATION;
+        mCurrentValue += distance;
+    }
+
+    public boolean advanceAnimation(long currentTimeMillis) {
+        if (mAnimationStartTime == NO_ANIMATION) return false;
+        if (mAnimationStartTime == START_ANIMATION) {
+            mAnimationStartTime = currentTimeMillis;
+            return true;
+        }
+
+        long deltaTime = currentTimeMillis - mAnimationStartTime;
+        float t = deltaTime / 100f;
+        mCurrentValue *= Math.pow(0.5f, t);
+        mAnimationStartTime = currentTimeMillis;
+
+        if (mCurrentValue < 1) {
+            mAnimationStartTime = NO_ANIMATION;
+            mCurrentValue = 0;
+            return false;
+        }
+        return true;
+    }
+
+    public float getValue() {
+        return mCurrentValue;
+    }
+}