content: /*
   * Copyright (C) 2013 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.rsen.github.easyandroidanimations;
  
  import android.content.Context;
  import android.graphics.Bitmap;
  import android.graphics.Canvas;
  import android.graphics.Color;
  import android.graphics.LinearGradient;
  import android.graphics.Matrix;
  import android.graphics.Paint;
  import android.graphics.Paint.Style;
  import android.graphics.Rect;
  import android.graphics.Shader.TileMode;
  import android.util.AttributeSet;
  import android.view.View;
  import android.view.ViewGroup;
  
  /**
   * The folding layout where the number of folds, the anchor point and the
   * orientation of the fold can be specified. Each of these parameters can
   * be modified individually and updates and resets the fold to a default
   * (unfolded) state. The fold factor varies between 0 (completely unfolded
   * flat image) to 1.0 (completely folded, non-visible image).
   *
   * This layout throws an exception if there is more than one child added to the view.
   * For more complicated view hierarchy's inside the folding layout, the views should all
   * be nested inside 1 parent layout.
   *
   * This layout folds the contents of its child in real time. By applying matrix
   * transformations when drawing to canvas, the contents of the child may change as
   * the fold takes place. It is important to note that there are jagged edges about
   * the perimeter of the layout as a result of applying transformations to a rectangle.
   * This can be avoided by having the child of this layout wrap its content inside a
   * 1 pixel transparent border. This will cause an anti-aliasing like effect and smoothen
   * out the edges.
   *
   */
  public class FoldLayout extends ViewGroup {
  
      public static enum Orientation {
          VERTICAL,
          HORIZONTAL
      }
  
      private final String FOLDING_VIEW_EXCEPTION_MESSAGE = "Folding Layout can only 1 child at " +
              "most";
  
      private final float SHADING_ALPHA = 0.8f;
      private final float SHADING_FACTOR = 0.5f;
      private final int DEPTH_CONSTANT = 1500;
      private final int NUM_OF_POLY_POINTS = 8;
  
      private Rect[] mFoldRectArray;
  
      private Matrix[] mMatrix;
  
      private Orientation mOrientation = Orientation.HORIZONTAL;
  
      private float mAnchorFactor = 0;
      private float mFoldFactor = 0;
  
      private int mNumberOfFolds = 2;
  
      private boolean mIsHorizontal = true;
  
      private int mOriginalWidth = 0;
      private int mOriginalHeight = 0;
  
      private float mFoldMaxWidth = 0;
      private float mFoldMaxHeight = 0;
      private float mFoldDrawWidth = 0;
      private float mFoldDrawHeight = 0;
  
      private boolean mIsFoldPrepared = false;
      private boolean mShouldDraw = true;
  
      private Paint mSolidShadow;
      private Paint mGradientShadow;
      private LinearGradient mShadowLinearGradient;
      private Matrix mShadowGradientMatrix;
  
      private float [] mSrc;
      private float [] mDst;
  
      private float mPreviousFoldFactor = 0;
  
      private Bitmap mFullBitmap;
      private Rect mDstRect;
  
      public FoldLayout(Context context) {
          super(context);
      }
  
      public FoldLayout(Context context, AttributeSet attrs) {
          super(context, attrs);
      }
  
      public FoldLayout(Context context, AttributeSet attrs, int defStyle) {
          super(context, attrs, defStyle);
      }
  
      @Override
      protected boolean addViewInLayout(View child, int index, LayoutParams params,
                                        boolean preventRequestLayout) {
          throwCustomException(getChildCount());
          boolean returnValue = super.addViewInLayout(child, index, params, preventRequestLayout);
          return returnValue;
      }
  
      @Override
      public void addView(View child, int index, LayoutParams params) {
          throwCustomException(getChildCount());
          super.addView(child, index, params);
      }
  
      @Override
      protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
          View child = getChildAt(0);
          measureChild(child,widthMeasureSpec, heightMeasureSpec);
          setMeasuredDimension(widthMeasureSpec, heightMeasureSpec);
      }
  
      @Override
      protected void onLayout(boolean changed, int l, int t, int r, int b) {
          View child = getChildAt(0);
          child.layout(0, 0, child.getMeasuredWidth(), child.getMeasuredHeight());
          updateFold();
      }
  
      /**
       * The custom exception to be thrown so as to limit the number of views in this
       * layout to at most one.
       */
      private class NumberOfFoldingLayoutChildrenException extends RuntimeException {
          public NumberOfFoldingLayoutChildrenException(String message) {
              super(message);
          }
      }
  
      /** Throws an exception if the number of views added to this layout exceeds one.*/
      private void throwCustomException (int numOfChildViews) {
          if (numOfChildViews == 1) {
              throw new NumberOfFoldingLayoutChildrenException(FOLDING_VIEW_EXCEPTION_MESSAGE);
          }
      }
  
      /**
       * Sets the fold factor of the folding view and updates all the corresponding
       * matrices and values to account for the new fold factor. Once that is complete,
       * it redraws itself with the new fold. */
      public void setFoldFactor(float foldFactor) {
          if (foldFactor != mFoldFactor) {
              mFoldFactor = foldFactor;
              calculateMatrices();
              invalidate();
          }
      }
  
      public void setOrientation(Orientation orientation) {
          if (orientation != mOrientation) {
              mOrientation = orientation;
              updateFold();
          }
      }
  
      public void setAnchorFactor(float anchorFactor) {
          if (anchorFactor != mAnchorFactor) {
              mAnchorFactor = anchorFactor;
              updateFold();
          }
      }
  
      public void setNumberOfFolds(int numberOfFolds) {
          if (numberOfFolds != mNumberOfFolds) {
              mNumberOfFolds = numberOfFolds;
              updateFold();
          }
      }
  
      public float getAnchorFactor() {
          return mAnchorFactor;
      }
  
      public Orientation getOrientation() {
          return mOrientation;
      }
  
      public float getFoldFactor() {
          return mFoldFactor;
      }
  
      public int getNumberOfFolds() {
          return mNumberOfFolds;
      }
  
      private void updateFold() {
          prepareFold(mOrientation, mAnchorFactor, mNumberOfFolds);
          calculateMatrices();
          invalidate();
      }
  
      /**
       * This method is called in order to update the fold's orientation, anchor
       * point and number of folds. This creates the necessary setup in order to
       * prepare the layout for a fold with the specified parameters. Some of the
       * dimensions required for the folding transformation are also acquired here.
       *
       * After this method is called, it will be in a completely unfolded state by default.
       */
      private void prepareFold(Orientation orientation, float anchorFactor, int numberOfFolds) {
  
          mSrc = new float[NUM_OF_POLY_POINTS];
          mDst = new float[NUM_OF_POLY_POINTS];
  
          mDstRect = new Rect();
  
          mFoldFactor = 0;
          mPreviousFoldFactor = 0;
  
          mIsFoldPrepared = false;
  
          mSolidShadow = new Paint();
          mGradientShadow = new Paint();
  
          mOrientation = orientation;
          mIsHorizontal = (orientation == Orientation.HORIZONTAL);
  
          if (mIsHorizontal) {
              mShadowLinearGradient = new LinearGradient(0, 0, SHADING_FACTOR, 0, Color.BLACK,
                      Color.TRANSPARENT, TileMode.CLAMP);
          } else {
              mShadowLinearGradient = new LinearGradient(0, 0, 0, SHADING_FACTOR, Color.BLACK,
                      Color.TRANSPARENT, TileMode.CLAMP);
          }
  
          mGradientShadow.setStyle(Style.FILL);
          mGradientShadow.setShader(mShadowLinearGradient);
          mShadowGradientMatrix = new Matrix();
  
          mAnchorFactor = anchorFactor;
          mNumberOfFolds = numberOfFolds;
  
          mOriginalWidth = getMeasuredWidth();
          mOriginalHeight = getMeasuredHeight();
  
          mFoldRectArray = new Rect[mNumberOfFolds];
          mMatrix = new Matrix[mNumberOfFolds];
  
          for (int x = 0; x < mNumberOfFolds; x++) {
              mMatrix[x] = new Matrix();
          }
  
          int h = mOriginalHeight;
          int w = mOriginalWidth;
  
          int delta = Math.round(mIsHorizontal ? ((float) w) / ((float) mNumberOfFolds) :
                  ((float) h) /((float) mNumberOfFolds));
  
          /* Loops through the number of folds and segments the full layout into a number
           * of smaller equal components. If the number of folds is odd, then one of the
           * components will be smaller than all the rest. Note that deltap below handles
           * the calculation for an odd number of folds.*/
          for (int x = 0; x < mNumberOfFolds; x++) {
              if (mIsHorizontal) {
                  int deltap = (x + 1) * delta > w ? w - x * delta : delta;
                  mFoldRectArray[x] = new Rect(x * delta, 0, x * delta + deltap, h);
              } else {
                  int deltap = (x + 1) * delta > h ? h - x * delta : delta;
                  mFoldRectArray[x] = new Rect(0, x * delta, w, x * delta + deltap);
              }
          }
  
          if (mIsHorizontal) {
              mFoldMaxHeight = h;
              mFoldMaxWidth = delta;
          } else {
              mFoldMaxHeight = delta;
              mFoldMaxWidth = w;
          }
  
          mIsFoldPrepared = true;
      }
  
      /*
      * Calculates the transformation matrices used to draw each of the separate folding
      * segments from this view.
      */
      private void calculateMatrices() {
  
          mShouldDraw = true;
  
          if (!mIsFoldPrepared) {
              return;
          }
  
          /** If the fold factor is 1 than the folding view should not be seen
           * and the canvas can be left completely empty. */
          if (mFoldFactor == 1) {
              mShouldDraw = false;
              return;
          }
  
          mPreviousFoldFactor = mFoldFactor;
  
          /* Reset all the transformation matrices back to identity before computing
           * the new transformation */
          for (int x = 0; x < mNumberOfFolds; x++) {
              mMatrix[x].reset();
          }
  
          float cTranslationFactor = 1 - mFoldFactor;
  
          float translatedDistance = mIsHorizontal ? mOriginalWidth * cTranslationFactor :
                  mOriginalHeight * cTranslationFactor;
  
          float translatedDistancePerFold = Math.round(translatedDistance / mNumberOfFolds);
  
          /* For an odd number of folds, the rounding error may cause the
           * translatedDistancePerFold to be grater than the max fold width or height. */
          mFoldDrawWidth = mFoldMaxWidth < translatedDistancePerFold ?
                  translatedDistancePerFold : mFoldMaxWidth;
          mFoldDrawHeight = mFoldMaxHeight < translatedDistancePerFold ?
                  translatedDistancePerFold : mFoldMaxHeight;
  
          float translatedDistanceFoldSquared = translatedDistancePerFold * translatedDistancePerFold;
  
          /* Calculate the depth of the fold into the screen using pythagorean theorem. */
          float depth = mIsHorizontal ?
                  (float) Math.sqrt((double)(mFoldDrawWidth * mFoldDrawWidth -
                          translatedDistanceFoldSquared)) :
                  (float) Math.sqrt((double)(mFoldDrawHeight * mFoldDrawHeight -
                          translatedDistanceFoldSquared));
  
          /* The size of some object is always inversely proportional to the distance
          *  it is away from the viewpoint. The constant can be varied to to affect the
          *  amount of perspective. */
          float scaleFactor = DEPTH_CONSTANT / (DEPTH_CONSTANT + depth);
  
          float scaledWidth, scaledHeight, bottomScaledPoint, topScaledPoint, rightScaledPoint,
                  leftScaledPoint;
  
          if (mIsHorizontal) {
              scaledWidth = mFoldDrawWidth * cTranslationFactor;
              scaledHeight = mFoldDrawHeight * scaleFactor;
          } else {
              scaledWidth = mFoldDrawWidth * scaleFactor;
              scaledHeight = mFoldDrawHeight * cTranslationFactor;
          }
  
          topScaledPoint = (mFoldDrawHeight - scaledHeight) / 2.0f;
          bottomScaledPoint = topScaledPoint + scaledHeight;
  
          leftScaledPoint = (mFoldDrawWidth - scaledWidth) / 2.0f;
          rightScaledPoint = leftScaledPoint + scaledWidth;
  
          float anchorPoint = mIsHorizontal ? mAnchorFactor * mOriginalWidth :
                  mAnchorFactor * mOriginalHeight;
  
          /* The fold along which the anchor point is located. */
          float midFold = mIsHorizontal ? (anchorPoint / mFoldDrawWidth) : anchorPoint /
                  mFoldDrawHeight;
  
          mSrc[0] = 0;
          mSrc[1] = 0;
          mSrc[2] = 0;
          mSrc[3] = mFoldDrawHeight;
          mSrc[4] = mFoldDrawWidth;
          mSrc[5] = 0;
          mSrc[6] = mFoldDrawWidth;
          mSrc[7] = mFoldDrawHeight;
  
          /* Computes the transformation matrix for each fold using the values calculated above. */
          for (int x = 0; x < mNumberOfFolds; x++) {
  
              boolean isEven = (x % 2 == 0);
  
              if (mIsHorizontal) {
                  mDst[0] = (anchorPoint > x * mFoldDrawWidth) ? anchorPoint + (x - midFold) *
                          scaledWidth : anchorPoint - (midFold - x) * scaledWidth;
                  mDst[1] = isEven ? 0 : topScaledPoint;
                  mDst[2] = mDst[0];
                  mDst[3] = isEven ? mFoldDrawHeight: bottomScaledPoint;
                  mDst[4] = (anchorPoint > (x + 1) * mFoldDrawWidth) ? anchorPoint + (x + 1 - midFold)
                          * scaledWidth : anchorPoint - (midFold - x - 1) * scaledWidth;
                  mDst[5] = isEven ? topScaledPoint : 0;
                  mDst[6] = mDst[4];
                  mDst[7] = isEven ? bottomScaledPoint : mFoldDrawHeight;
  
              } else {
                  mDst[0] = isEven ? 0 : leftScaledPoint;
                  mDst[1] = (anchorPoint > x * mFoldDrawHeight) ? anchorPoint + (x - midFold) *
                          scaledHeight : anchorPoint - (midFold - x) * scaledHeight;
                  mDst[2] = isEven ? leftScaledPoint: 0;
                  mDst[3] = (anchorPoint > (x + 1) * mFoldDrawHeight) ? anchorPoint + (x + 1 -
                          midFold) * scaledHeight : anchorPoint - (midFold - x - 1) * scaledHeight;
                  mDst[4] = isEven ? mFoldDrawWidth : rightScaledPoint;
                  mDst[5] = mDst[1];
                  mDst[6] = isEven ? rightScaledPoint : mFoldDrawWidth;
                  mDst[7] = mDst[3];
              }
  
              /* Pixel fractions are present for odd number of folds which need to be
               * rounded off here.*/
              for (int y = 0; y < 8; y ++) {
                  mDst[y] = Math.round(mDst[y]);
              }
  
              /* If it so happens that any of the folds have reached a point where
              *  the width or height of that fold is 0, then nothing needs to be
              *  drawn onto the canvas because the view is essentially completely
              *  folded.*/
              if (mIsHorizontal) {
                  if (mDst[4] <= mDst[0] || mDst[6] <= mDst[2]) {
                      mShouldDraw = false;
                      return;
                  }
              } else {
                  if (mDst[3] <= mDst[1] || mDst[7] <= mDst[5]) {
                      mShouldDraw = false;
                      return;
                  }
              }
  
              /* Sets the shadow and bitmap transformation matrices.*/
              mMatrix[x].setPolyToPoly(mSrc, 0, mDst, 0, NUM_OF_POLY_POINTS / 2);
          }
          /* The shadows on the folds are split into two parts: Solid shadows and gradients.
           * Every other fold has a solid shadow which overlays the whole fold. Similarly,
           * the folds in between these alternating folds also have an overlaying shadow.
           * However, it is a gradient that takes up part of the fold as opposed to a solid
           * shadow overlaying the whole fold.*/
  
          /* Solid shadow paint object. */
          int alpha = (int) (mFoldFactor * 255 * SHADING_ALPHA);
  
          mSolidShadow.setColor(Color.argb(alpha, 0, 0, 0));
  
          if (mIsHorizontal) {
              mShadowGradientMatrix.setScale(mFoldDrawWidth, 1);
              mShadowLinearGradient.setLocalMatrix(mShadowGradientMatrix);
          } else {
              mShadowGradientMatrix.setScale(1, mFoldDrawHeight);
              mShadowLinearGradient.setLocalMatrix(mShadowGradientMatrix);
          }
  
          mGradientShadow.setAlpha(alpha);
      }
  
      @Override
      protected void dispatchDraw(Canvas canvas) {
          /** If prepareFold has not been called or if preparation has not completed yet,
           * then no custom drawing will take place so only need to invoke super's
           * onDraw and return. */
          if (!mIsFoldPrepared || mFoldFactor == 0) {
              super.dispatchDraw(canvas);
              return;
          }
  
          if (!mShouldDraw) {
              return;
          }
  
          Rect src;
           /* Draws the bitmaps and shadows on the canvas with the appropriate transformations. */
          for (int x = 0; x < mNumberOfFolds; x++) {
  
              src = mFoldRectArray[x];
              /* The canvas is saved and restored for every individual fold*/
              canvas.save();
  
              /* Concatenates the canvas with the transformation matrix for the
               *  the segment of the view corresponding to the actual image being
               *  displayed. */
              canvas.concat(mMatrix[x]);
              /* The same transformation matrix is used for both the shadow and the image
               * segment. The canvas is clipped to account for the size of each fold and
               * is translated so they are drawn in the right place. The shadow is then drawn on
               * top of the different folds using the sametransformation matrix.*/
              canvas.clipRect(0, 0, src.right - src.left, src.bottom - src.top);
  
              if (mIsHorizontal) {
                  canvas.translate(-src.left, 0);
              } else {
                  canvas.translate(0, -src.top);
              }
  
              super.dispatchDraw(canvas);
  
              if (mIsHorizontal) {
                  canvas.translate(src.left, 0);
              } else {
                  canvas.translate(0, src.top);
              }
              /* Draws the shadows corresponding to this specific fold. */
              if (x % 2 == 0) {
                  canvas.drawRect(0, 0, mFoldDrawWidth, mFoldDrawHeight, mSolidShadow);
              } else {
                  canvas.drawRect(0, 0, mFoldDrawWidth, mFoldDrawHeight, mGradientShadow);
              }
  
              canvas.restore();
          }
      }
  
  }