FormAttachment


1   /*******************************************************************************
2    * Copyright (c) 2000, 2006 IBM Corporation and others.
3    * All rights reserved. This program and the accompanying materials
4    * are made available under the terms of the Eclipse Public License v1.0
5    * which accompanies this distribution, and is available at
6    * http://www.eclipse.org/legal/epl-v10.html
7    *
8    * Contributors:
9    *     IBM Corporation - initial API and implementation
10   *******************************************************************************/
11  package org.eclipse.swt.layout;
12  
13  import org.eclipse.swt.*;
14  import org.eclipse.swt.widgets.*;
15  
16  /**
17   * Instances of this class are used to define the edges of a control
18   * within a <code>FormLayout</code>. 
19   * <p>
20   * <code>FormAttachments</code> are set into the top, bottom, left,
21   * and right fields of the <code>FormData</code> for a control.
22   * For example:
23   * <pre>
24   *      FormData data = new FormData();
25   *      data.top = new FormAttachment(0,5);
26   *      data.bottom = new FormAttachment(100,-5);
27   *      data.left = new FormAttachment(0,5);
28   *      data.right = new FormAttachment(100,-5);
29   *      button.setLayoutData(data);
30   * </pre>
31   * </p>
32   * <p>
33   * A <code>FormAttachment</code> defines where to attach the side of
34   * a control by using the equation, y = ax + b. The "a" term represents 
35   * a fraction of the parent composite's width (from the left) or height
36   * (from the top). It can be defined using a numerator and denominator,
37   * or just a percentage value. If a percentage is used, the denominator 
38   * is set to 100. The "b" term in the equation represents an offset, in
39   * pixels, from the attachment position. For example:
40   * <pre>
41   *      FormAttachment attach = new FormAttachment (20, -5);
42   * </pre>
43   * specifies that the side to which the <code>FormAttachment</code>
44   * object belongs will lie at 20% of the parent composite, minus 5 pixels.
45   * </p>
46   * <p>
47   * Control sides can also be attached to another control.
48   * For example:
49   * <pre>
50   *      FormAttachment attach = new FormAttachment (button, 10);
51   * </pre>
52   * specifies that the side to which the <code>FormAttachment</code>
53   * object belongs will lie in the same position as the adjacent side of 
54   * the <code>button</code> control, plus 10 pixels. The control side can 
55   * also be attached to the opposite side of the specified control.
56   * For example:
57   * <pre>
58   *      FormData data = new FormData ();
59   *      data.left = new FormAttachment (button, 0, SWT.LEFT);
60   * </pre>
61   * specifies that the left side of the control will lie in the same position
62   * as the left side of the <code>button</code> control. The control can also 
63   * be attached in a position that will center the control on the specified 
64   * control. For example:
65   * <pre>
66   *      data.left = new FormAttachment (button, 0, SWT.CENTER);
67   * </pre>
68   * specifies that the left side of the control will be positioned so that it is
69   * centered between the left and right sides of the <code>button</code> control.
70   * If the alignment is not specified, the default is to attach to the adjacent side.
71   * </p>
72   * 
73   * @see FormLayout
74   * @see FormData
75   * 
76   * @since 2.0
77   */
78  public final class FormAttachment {
79      /**
80       * numerator specifies the numerator of the "a" term in the
81       * equation, y = ax + b, which defines the attachment.
82       */
83      public int numerator;
84      
85      /**
86       * denominator specifies the denominator of the "a" term in the
87       * equation, y = ax + b, which defines the attachment.
88       * 
89       * The default value is 100.
90       */
91      public int denominator = 100;
92      
93      /**
94       * offset specifies the offset, in pixels, of the control side
95       * from the attachment position.
96       * If the offset is positive, then the control side is offset
97       * to the right of or below the attachment position. If it is
98       * negative, then the control side is offset to the left of or
99       * above the attachment position.
100      * 
101      * This is equivalent to the "b" term in the equation y = ax + b.
102      * The default value is 0.
103      */
104     public int offset;
105     
106     /**
107      * control specifies the control to which the control side is
108      * attached.
109      */
110     public Control control;
111     
112     /**
113      * alignment specifies the alignment of the control side that is
114      * attached to a control.
115      * <p>
116      * For top and bottom attachments, TOP, BOTTOM and CENTER are used. For left 
117      * and right attachments, LEFT, RIGHT and CENTER are used. If any other case
118      * occurs, the default will be used instead.
119      * </p>
120      * 
121      * <br>Possible values are: <ul>
122      *    <li>TOP: Attach the side to the top side of the specified control.</li>
123      *    <li>BOTTOM : Attach the side to the bottom side of the specified control.</li>
124      *    <li>LEFT: Attach the side to the left side of the specified control.</li>
125      *    <li>RIGHT: Attach the side to the right side of the specified control.</li>
126      *    <li>CENTER: Attach the side at a position which will center the control on the specified control.</li>
127      *    <li>DEFAULT: Attach the side to the adjacent side of the specified control.</li>
128      * </ul>
129      */
130     public int alignment;
131 
132 /**
133  * Constructs a new instance of this class.
134  * Since no numerator, denominator or offset is specified,
135  * the attachment is treated as a percentage of the form.
136  * The numerator is zero, the denominator is 100 and the
137  * offset is zero.
138  * 
139  * @since 3.2
140  */
141 public FormAttachment () {
142 }
143 
144 /**
145  * Constructs a new instance of this class given a numerator
146  * Since no denominator or offset is specified, the default
147  * is to treat the numerator as a percentage of the form, with a 
148  * denominator of 100. The offset is zero.
149  * 
150  * @param numerator the percentage of the position
151  * 
152  * @since 3.0
153  */
154 public FormAttachment (int numerator) {
155     this (numerator, 100, 0);
156 }
157 
158 /**
159  * Constructs a new instance of this class given a numerator
160  * and an offset. Since no denominator is specified, the default
161  * is to treat the numerator as a percentage of the form, with a 
162  * denominator of 100.
163  * 
164  * @param numerator the percentage of the position
165  * @param offset the offset of the side from the position
166  */
167 public FormAttachment (int numerator, int offset) {
168     this (numerator, 100, offset);
169 }
170 
171 /**
172  * Constructs a new instance of this class given a numerator 
173  * and denominator and an offset. The position of the side is
174  * given by the fraction of the form defined by the numerator
175  * and denominator.
176  *
177  * @param numerator the numerator of the position
178  * @param denominator the denominator of the position
179  * @param offset the offset of the side from the position
180  */
181 public FormAttachment (int numerator, int denominator, int offset) {
182     if (denominator == 0) SWT.error (SWT.ERROR_CANNOT_BE_ZERO);
183     this.numerator = numerator;
184     this.denominator = denominator;
185     this.offset = offset;
186 }
187 
188 /**
189  * Constructs a new instance of this class given a control.
190  * Since no alignment is specified, the default alignment is
191  * to attach the side to the adjacent side of the specified 
192  * control. Since no offset is specified, an offset of 0 is
193  * used.
194  * 
195  * @param control the control the side is attached to
196  */
197 public FormAttachment (Control control) {
198     this (control, 0, SWT.DEFAULT);
199 }
200 
201 /**
202  * Constructs a new instance of this class given a control
203  * and an offset. Since no alignment is specified, the default
204  * alignment is to attach the side to the adjacent side of the 
205  * specified control.
206  * 
207  * @param control the control the side is attached to
208  * @param offset the offset of the side from the control
209  */
210 public FormAttachment (Control control, int offset) {
211     this (control, offset, SWT.DEFAULT);
212 }
213 
214 /**
215  * Constructs a new instance of this class given a control,
216  * an offset and an alignment.
217  * 
218  * @param control the control the side is attached to
219  * @param offset the offset of the side from the control
220  * @param alignment the alignment of the side to the control it is attached to
221  */
222 public FormAttachment (Control control, int offset, int alignment) {
223     this.control = control;
224     this.offset = offset;
225     this.alignment = alignment;
226 }
227 
228 FormAttachment divide (int value) {
229     return new FormAttachment (numerator, denominator * value, offset / value);
230 }
231 
232 int gcd (int m, int n) {
233     int temp;
234     m = Math.abs (m);
235     n = Math.abs (n);
236     if (m < n) {
237         temp = m;
238         m = n;
239         n = temp;
240     }
241     while (n != 0){
242         temp = m;
243         m = n;
244         n = temp % n;
245     }
246     return m;
247 }
248 
249 FormAttachment minus (FormAttachment attachment) {
250     FormAttachment solution = new FormAttachment ();
251     solution.numerator = numerator * attachment.denominator - denominator * attachment.numerator;
252     solution.denominator = denominator * attachment.denominator;
253     int gcd = gcd (solution.denominator, solution.numerator);
254     solution.numerator = solution.numerator / gcd;
255     solution.denominator = solution.denominator / gcd;
256     solution.offset = offset - attachment.offset;
257     return solution;
258 }
259 
260 FormAttachment minus (int value) {
261     return new FormAttachment (numerator, denominator, offset - value);
262 }
263 
264 FormAttachment plus (FormAttachment attachment) {
265     FormAttachment solution = new FormAttachment ();
266     solution.numerator = numerator * attachment.denominator + denominator * attachment.numerator;
267     solution.denominator = denominator * attachment.denominator;
268     int gcd = gcd (solution.denominator, solution.numerator);
269     solution.numerator = solution.numerator / gcd;
270     solution.denominator = solution.denominator / gcd;
271     solution.offset = offset + attachment.offset;
272     return solution;
273 }
274 
275 FormAttachment plus (int value) {
276     return new FormAttachment (numerator, denominator, offset + value);
277 }
278 
279 int solveX (int value) {
280     if (denominator == 0) SWT.error (SWT.ERROR_CANNOT_BE_ZERO);
281     return ((numerator * value) / denominator) + offset;
282 }
283 
284 int solveY (int value) {
285     if (numerator == 0) SWT.error (SWT.ERROR_CANNOT_BE_ZERO);
286     return (value - offset) * denominator / numerator;
287 }
288     
289 /**
290  * Returns a string containing a concise, human-readable
291  * description of the receiver.
292  *
293  * @return a string representation of the FormAttachment
294  */
295 public String   toString () {
296     String   string = control != null ? control.toString () : numerator + "/" + denominator;
297     return "{y = (" + string + (offset >= 0 ? ")x + " + offset: ")x - " + (-offset))+"}";
298 }
299 
300 }
301
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