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      1 /**
      2  * Copyright (C) 2015 The Android Open Source Project
      3  *
      4  * Licensed under the Apache License, Version 2.0 (the "License");
      5  * you may not use this file except in compliance with the License.
      6  * You may obtain a copy of the License at
      7  *
      8  *      http://www.apache.org/licenses/LICENSE-2.0
      9  *
     10  * Unless required by applicable law or agreed to in writing, software
     11  * distributed under the License is distributed on an "AS IS" BASIS,
     12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     13  * See the License for the specific language governing permissions and
     14  * limitations under the License.
     15  */
     16 
     17 package com.android.launcher3.folder;
     18 
     19 public class StackFolderIconLayoutRule implements FolderIcon.PreviewLayoutRule {
     20 
     21     static final int MAX_NUM_ITEMS_IN_PREVIEW = 3;
     22 
     23     // The degree to which the item in the back of the stack is scaled [0...1]
     24     // (0 means it's not scaled at all, 1 means it's scaled to nothing)
     25     private static final float PERSPECTIVE_SCALE_FACTOR = 0.35f;
     26 
     27     // The amount of vertical spread between items in the stack [0...1]
     28     private static final float PERSPECTIVE_SHIFT_FACTOR = 0.18f;
     29 
     30     private float mBaselineIconScale;
     31     private int mBaselineIconSize;
     32     private int mAvailableSpaceInPreview;
     33     private float mMaxPerspectiveShift;
     34 
     35     @Override
     36     public void init(int availableSpace, float intrinsicIconSize, boolean rtl) {
     37         mAvailableSpaceInPreview = availableSpace;
     38 
     39         // cos(45) = 0.707  + ~= 0.1) = 0.8f
     40         int adjustedAvailableSpace = (int) ((mAvailableSpaceInPreview / 2) * (1 + 0.8f));
     41 
     42         int unscaledHeight = (int) (intrinsicIconSize * (1 + PERSPECTIVE_SHIFT_FACTOR));
     43 
     44         mBaselineIconScale = (1.0f * adjustedAvailableSpace / unscaledHeight);
     45 
     46         mBaselineIconSize = (int) (intrinsicIconSize * mBaselineIconScale);
     47         mMaxPerspectiveShift = mBaselineIconSize * PERSPECTIVE_SHIFT_FACTOR;
     48     }
     49 
     50     @Override
     51     public PreviewItemDrawingParams computePreviewItemDrawingParams(int index, int curNumItems,
     52             PreviewItemDrawingParams params) {
     53         float scale = scaleForItem(index, curNumItems);
     54 
     55         index = MAX_NUM_ITEMS_IN_PREVIEW - index - 1;
     56         float r = (index * 1.0f) / (MAX_NUM_ITEMS_IN_PREVIEW - 1);
     57 
     58         float offset = (1 - r) * mMaxPerspectiveShift;
     59         float scaledSize = scale * mBaselineIconSize;
     60         float scaleOffsetCorrection = (1 - scale) * mBaselineIconSize;
     61 
     62         // We want to imagine our coordinates from the bottom left, growing up and to the
     63         // right. This is natural for the x-axis, but for the y-axis, we have to invert things.
     64         float transY = mAvailableSpaceInPreview - (offset + scaledSize + scaleOffsetCorrection);
     65         float transX = (mAvailableSpaceInPreview - scaledSize) / 2;
     66         float totalScale = mBaselineIconScale * scale;
     67         final float overlayAlpha = (80 * (1 - r)) / 255f;
     68 
     69         if (params == null) {
     70             params = new PreviewItemDrawingParams(transX, transY, totalScale, overlayAlpha);
     71         } else {
     72             params.update(transX, transY, totalScale);
     73             params.overlayAlpha = overlayAlpha;
     74         }
     75         return params;
     76     }
     77 
     78     @Override
     79     public int maxNumItems() {
     80         return MAX_NUM_ITEMS_IN_PREVIEW;
     81     }
     82 
     83     @Override
     84     public float getIconSize() {
     85         return mBaselineIconSize;
     86     }
     87 
     88     @Override
     89     public float scaleForItem(int index, int numItems) {
     90         // Scale is determined by the position of the icon in the preview.
     91         index = MAX_NUM_ITEMS_IN_PREVIEW - index - 1;
     92         float r = (index * 1.0f) / (MAX_NUM_ITEMS_IN_PREVIEW - 1);
     93         return (1 - PERSPECTIVE_SCALE_FACTOR * (1 - r));
     94     }
     95 
     96     @Override
     97     public boolean clipToBackground() {
     98         return false;
     99     }
    100 
    101     @Override
    102     public boolean hasEnterExitIndices() {
    103         return false;
    104     }
    105 
    106     @Override
    107     public int getExitIndex() {
    108         throw new RuntimeException("hasEnterExitIndices not supported");
    109     }
    110 
    111     @Override
    112     public int getEnterIndex() {
    113         throw new RuntimeException("hasEnterExitIndices not supported");
    114     }
    115 }
    116