Move client/{base, observable, layout, touch, util, view} to samples/ui_lib .

client/view/MeasureText.dart

-// Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
-// for details. All rights reserved. Use of this source code is governed by a
-// BSD-style license that can be found in the LICENSE file.
-
-// TODO(jacobr): handle splitting lines on symbols such as '-' that aren't
-// whitespace but are valid word breaking points.
-/**
- * Utility class to efficiently word break and measure text without requiring
- * access to the DOM.
- */
-class MeasureText {
-  static CanvasRenderingContext2D _context;
-
-  final String font;
-  num _spaceLength;
-  num _typicalCharLength;
-
-  static final String ELLIPSIS = '...';
-
-  MeasureText(this.font) {
-    if (_context === null) {
-      CanvasElement canvas = new Element.tag('canvas');
-      _context = canvas.getContext('2d');
-    }
-    if (_spaceLength === null) {
-      _context.font = font;
-      _spaceLength = _context.measureText(' ').width;
-      _typicalCharLength = _context.measureText('k').width;
-    }
-  }
-
-  // TODO(jacobr): we are DOA for i18N...
-  // the right solution is for the server to send us text perparsed into words
-  // perhaps even with hints on the guess for the correct breaks so on the
-  // client all we have to do is verify and fix errors rather than perform the
-  // full calculation.
-  static bool isWhitespace(String character) {
-    return character == ' ' || character == '\t' || character == '\n';
-  }
-
-  num get typicalCharLength() {
-    return _typicalCharLength;
-  }
-
-  String quickTruncate(String text, num lineWidth, int maxLines) {
-    int targetLength = (lineWidth * maxLines / _typicalCharLength).toInt();
-    // Advance to next word break point.
-    while(targetLength < text.length && !isWhitespace(text[targetLength])) {
-      targetLength++;
-    }
-
-    if (targetLength < text.length) {
-      return text.substring(0, targetLength) + ELLIPSIS;
-    } else {
-      return text;
-    }
-  }
-
-  /**
-   * Add line broken text as html separated by <br> elements.
-   * Returns the number of lines in the output.
-   * This function is safe to call with [:sb === null:] in which case just the
-   * line count is returned.
-   */
-  int addLineBrokenText(StringBuffer sb, String text, num lineWidth,
-                        int maxLines) {
-    // Strip surrounding whitespace. This ensures we create zero lines if there
-    // is no visible text.
-    text = text.trim();
-
-    // We can often avoid performing a full line break calculation when only
-    // the number of lines and not the actual linebreaks is required.
-    if (sb === null) {
-      _context.font = font;
-      int textWidth = _context.measureText(text).width.toInt();
-      // By the pigeon hole principle, the resulting text will require at least
-      // maxLines if the raw text is longer than the amount of text that will
-      // fit on maxLines - 1.  We add the length of a whitespace
-      // character to the lineWidth as each line is separated by a whitespace
-      // character. We assume all whitespace characters have the same length.
-      if (textWidth >= (lineWidth + _spaceLength) * (maxLines - 1)) {
-        return maxLines;
-      } else if (textWidth == 0) {
-        return 0;
-      } else if (textWidth < lineWidth) {
-        return 1;
-      }
-      // Fall through to the regular line breaking calculation as the number
-      // of lines required is unclear.
-    }
-    int lines = 0;
-    lineBreak(text, lineWidth, maxLines, (int start, int end, num width) {
-      lines++;
-      if (lines == maxLines) {
-        // Overflow case... there may be more lines of text than we can handle.
-        // Add a few characters to the last line so that the browser will
-        // render ellipses correctly.
-        // TODO(jacobr): make this optional and only add characters until
-        // the first whitespace character encountered.
-        end = Math.min(end + 50, text.length);
-      }
-      if (sb !== null) {
-        if (lines > 1) {
-          sb.add('<br>');
-        }
-        // TODO(jacobr): HTML escape this text.
-        sb.add(text.substring(start, end));
-      }
-    });
-    return lines;
-  }
-
-  void lineBreak(String text, num lineWidth, int maxLines,
-                 Function callback) {
-    _context.font = font;
-    int lines = 0;
-    num currentLength = 0;
-    int startIndex = 0;
-    int wordStartIndex = null;
-    int lastWordEndIndex = null;
-    bool lastWhitespace = true;
-    // TODO(jacobr): optimize this further.
-    // To simplify the logic, we simulate injecting a whitespace character
-    // at the end of the string.
-    for (int i = 0, len = text.length; i <= len; i++) {
-      // Treat the char after the end of the string as whitespace.
-      bool whitespace = i == len || isWhitespace(text[i]);
-      if (whitespace && !lastWhitespace) {
-        num wordLength = _context.measureText(text.substring(
-            wordStartIndex, i)).width;
-        // TODO(jimhug): Replace the line above with this one to workaround
-        //               dartium bug - error: unimplemented code
-        // num wordLength = (i - wordStartIndex) * 17;
-        currentLength += wordLength;
-        if (currentLength > lineWidth) {
-          // Edge case:
-          // It could be the very first word we ran into was too long for a
-          // line in which case  we let it have its own line.
-          if (lastWordEndIndex !== null) {
-            lines++;
-            callback(startIndex, lastWordEndIndex, currentLength - wordLength);
-          }
-          if (lines == maxLines) {
-            return;
-          }
-          startIndex = wordStartIndex;
-          currentLength = wordLength;
-        }
-        lastWordEndIndex = i;
-        currentLength += _spaceLength;
-        wordStartIndex = null;
-      } else if (wordStartIndex === null && !whitespace) {
-        wordStartIndex = i;
-      }
-      lastWhitespace = whitespace;
-    }
-    if (currentLength > 0) {
-      callback(startIndex, text.length, currentLength);
-    }
-  }
-}