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/* * Copyright 2008 Google Inc. * * 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.google.gwt.gen2.table.client; import java.util.*; /** * <p> * A helper class that distributes available width across a set of columns. * </p> * <p/> * <h3>The following algorithm is used to distribute the available width:</h3> * <ol> * <li>Calculate the percent difference between the current and preferred width * of each column</li> * <li>Order the columns in descending order according to their percent * differences from preferred width</li> * <li>For each iteration, distribute width into the first n columns such that * their percent difference now equals that of the n+1 column</li> * <li>If a column hits its minimum or maximum size, remove it from the list of * columns</li> * <li>If there are no more columns that can accept more/less width (they are * all at their boundaries), return the undistributed width.</li> * </ol> */ class ColumnResizer { /** * The resolution of the width of columns. The true target width of a column * is usually a decimal, but column widths can only be represented as integers * (ie. pixels). The resolution determines the maximum number of pixels that * the calculations can be off by. * <p/> * Increasing the resolution will increase the speed of the algorithm and * reduce the accuracy of the calculations. The resolution must be at least 1 * or errors will occur (because we cannot get perfect "0" accuracy). */ private static final int RESOLUTION = 1; /** * A class that contains the current and desired width of a column. */ static class ColumnWidthInfo { private int minWidth; private int maxWidth; private int preferredWidth; private int curWidth; /** * The new column width. */ private int newWidth = 0; /** * The required width to achieve the next level. */ private int requiredWidth; /** * Construct a new {@link ColumnWidthInfo}. * * @param minWidth the minimum width of the column * @param maxWidth the maximum width of the column * @param preferredWidth the preferred width of the column * @param curWidth the current width of the column */ public ColumnWidthInfo( int minWidth, int maxWidth, int preferredWidth, int curWidth ) { this.minWidth = minWidth; this.maxWidth = maxWidth; this.preferredWidth = preferredWidth; this.curWidth = curWidth; } public int getCurrentWidth() { return curWidth; } public int getMaximumWidth() { // For calculation purposes, ensure maxWidth >= minWidth if ( hasMaximumWidth() ) { return Math.max( maxWidth, minWidth ); } return maxWidth; } public int getMinimumWidth() { return minWidth; } public int getNewWidth() { return newWidth; } public int getPreferredWidth() { return preferredWidth; } public boolean hasMaximumWidth() { return maxWidth >= 0; } public boolean hasMinimumWidth() { return minWidth >= 0; } public void setCurrentWidth( int curWidth ) { this.curWidth = curWidth; } public void setMaximumWidth( int maxWidth ) { this.maxWidth = maxWidth; } public void setMinimumWidth( int minWidth ) { this.minWidth = minWidth; } public void setPreferredWidth( int preferredWidth ) { this.preferredWidth = preferredWidth; } /** * Get the percentage difference between the current column width and the * preferred column width. A negative value indicates that the current width * is less than the preferred width, while a positive value indicates that * the current width is above the preferred width. * * @return the percentage difference */ double getPercentageDifference() { return (newWidth - preferredWidth) / (double) preferredWidth; } int getRequiredWidth() { return requiredWidth; } void setNewWidth( int newWidth ) { this.newWidth = newWidth; } void setRequiredWidth( int requiredWidth ) { this.requiredWidth = requiredWidth; } } /** * Distribute some width across a list of columns, respecting the minimum and * maximum widths of the columns. The return value is the remaining width that * could not be distributed due to constraints. If the return value is 0, all * of the width has been distributed. * * @param columns the list of column width info * @param width the width to distribute * * @return the width that could not be distributed */ public int distributeWidth( List<ColumnWidthInfo> columns, int width ) { // The new width defaults to the current width, within min/max range for ( ColumnWidthInfo info : columns ) { int curWidth = info.getCurrentWidth(); if ( info.hasMinimumWidth() && curWidth < info.getMinimumWidth() ) { curWidth = info.getMinimumWidth(); } else if ( info.hasMaximumWidth() && curWidth > info.getMaximumWidth() ) { curWidth = info.getMaximumWidth(); } width -= (curWidth - info.getCurrentWidth()); info.setNewWidth( curWidth ); } // Do not modify widths if there is nothing to distribute if ( width == 0 ) { return 0; } // Copy the list of columns List<ColumnWidthInfo> orderedColumns = new ArrayList<ColumnWidthInfo>( columns ); // Sort the list of columns if ( width > 0 ) { // Enlarge columns Comparator<ColumnWidthInfo> comparator = new Comparator<ColumnWidthInfo>() { public int compare( ColumnWidthInfo o1, ColumnWidthInfo o2 ) { double diff1 = o1.getPercentageDifference(); double diff2 = o2.getPercentageDifference(); if ( diff1 < diff2 ) { return -1; } else if ( diff1 == diff2 ) { return 0; } else { return 1; } } }; Collections.sort( orderedColumns, comparator ); } else if ( width < 0 ) { // Shrink columns Comparator<ColumnWidthInfo> comparator = new Comparator<ColumnWidthInfo>() { public int compare( ColumnWidthInfo o1, ColumnWidthInfo o2 ) { double diff1 = o1.getPercentageDifference(); double diff2 = o2.getPercentageDifference(); if ( diff1 > diff2 ) { return -1; } else if ( diff1 == diff2 ) { return 0; } else { return 1; } } }; Collections.sort( orderedColumns, comparator ); } // Distribute the width return distributeWidthImpl( orderedColumns, width ); } private int distributeWidthImpl( List<ColumnWidthInfo> columns, int width ) { // Iterate until width can not longer be distributed boolean growing = (width > 0); boolean fullySynced = false; int syncedColumns = 1; while ( columns.size() > 0 && width != 0 ) { // Calculate the target difference at the next level double targetDiff = getTargetDiff( columns, syncedColumns, width ); // Calculate the total required width to achieve the target difference int totalRequired = 0; for ( int curIndex = 0; curIndex < syncedColumns; curIndex++ ) { // Calculate the new width at the target diff ColumnWidthInfo curInfo = columns.get( curIndex ); int preferredWidth = curInfo.getPreferredWidth(); int newWidth = (int) (targetDiff * preferredWidth) + preferredWidth; // Compare the boundaries if ( growing ) { newWidth = Math.max( newWidth, curInfo.getCurrentWidth() ); if ( curInfo.hasMaximumWidth() ) { newWidth = Math.min( newWidth, curInfo.getMaximumWidth() ); } } else { newWidth = Math.min( newWidth, curInfo.getCurrentWidth() ); if ( curInfo.hasMinimumWidth() ) { newWidth = Math.max( newWidth, curInfo.getMinimumWidth() ); } } // Calculate the width required to achieve the new width curInfo.setRequiredWidth( newWidth - curInfo.getNewWidth() ); totalRequired += curInfo.getRequiredWidth(); } // Calculate the percent of the required width that is available double percentAvailable = 1.0; if ( totalRequired != 0 ) { percentAvailable = Math.min( 1.0, width / (double) totalRequired ); } for ( int curIndex = 0; curIndex < syncedColumns; curIndex++ ) { // Determine the true width to add to the column ColumnWidthInfo curInfo = columns.get( curIndex ); int required = (int) (percentAvailable * curInfo.getRequiredWidth()); // Make sure we get out of the loop by distributing at least 1 if ( fullySynced ) { if ( growing ) { required = Math.max( RESOLUTION, required ); } else { required = Math.min( -RESOLUTION, required ); } } // Don't distribute more than the available width if ( growing && required > width ) { required = width; } else if ( !growing && required < width ) { required = width; } // Set the new width of the column curInfo.setNewWidth( curInfo.getNewWidth() + required ); width -= required; // Remove the column if it has reached its maximum/minimum width boolean maxedOut = false; if ( growing && curInfo.hasMaximumWidth() ) { maxedOut = (curInfo.getNewWidth() >= curInfo.getMaximumWidth()); } else if ( !growing && curInfo.hasMinimumWidth() ) { maxedOut = (curInfo.getNewWidth() <= curInfo.getMinimumWidth()); } if ( maxedOut ) { columns.remove( curIndex ); curIndex--; syncedColumns--; } } // Increment the number of synced column if ( !fullySynced && syncedColumns < columns.size() ) { syncedColumns++; } else { fullySynced = true; } } // Return the undistributed width return width; } /** * Calculate the target percentage difference of the next level. * * @param columns the column width info * @param syncedColumns the number of synced columns * @param width the width to distribute */ private double getTargetDiff( List<ColumnWidthInfo> columns, int syncedColumns, int width ) { if ( syncedColumns < columns.size() ) { // Use the diff of the next un-synced column as the target return columns.get( syncedColumns ).getPercentageDifference(); } else { // Calculate the total diff after all width has been distributed int totalNewWidth = width; int totalPreferredWidth = 0; for ( ColumnWidthInfo info : columns ) { totalNewWidth += info.getNewWidth(); totalPreferredWidth += info.getPreferredWidth(); } return (totalNewWidth - totalPreferredWidth) / (double) totalPreferredWidth; } } } |