layout/doc/frame_reflow_debug.html@deefc01c0e14
layout/doc/frame_reflow_debug.html
Thu, 15 Jan 2015 21:03:48 +0100
- author
- Michael Schloh von Bennewitz <michael@schloh.com>
- date
- Thu, 15 Jan 2015 21:03:48 +0100
- branch
- TOR_BUG_9701
- changeset 11
- deefc01c0e14
- permissions
- -rw-r--r--
Integrate friendly tips from Tor colleagues to make (or not) 4.5 alpha 3;
This includes removal of overloaded (but unused) methods, and addition of
a overlooked call to DataStruct::SetData(nsISupports, uint32_t, bool.)
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5 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0//EN">
6 <html>
7 <head>
8 <meta http-equiv="content-type" content="text/html; charset=ISO-8859-1">
9 <style type="text/css">
10 body {font-family:arial}
11 .log {background-color:silver; color:blue}
12 </style>
13 <title> Debugging Frame Reflow</title>
14 </head>
15 <body>
16 <h1>Debugging Frame Reflow HowTo</h1>
17 <h2>General Overview</h2>
18 <p> The frame reflow can be logged with the debug capabilities implemented in <a href="http://lxr.mozilla.org/seamonkey/source/layout/html/base/src/nsFrame.cpp"><code>nsFrame.cpp</code></a>.
19 It provides the following information for each frame at the
20 start of its reflow
21 <ul>
22 <li>reflow reason
23 <li>available width, available height
24 <li>computed width, computed height
25 <li>the previous and the next frame in flow
26 <li>and a count number.
27 </ul>
28 <p>When the frame's reflow is finished the following information is displayed :</p>
29 <ul>
30 <li>reflow metric (desired) width, height
31 <li>max. element size (MES) width
32 <li>maximum Width
33 <li>frame status
34 <li>overflow area
35 </ul>
37 <h2>Getting the log</h2>
38 <ul>
39 <li>Make sure that your build is a <b>debug</b> build.
40 <li>Create a text file (for instance <code>reflow_rules.txt</code>).
41 <li>Enter this line in the text file <pre>* 1</pre>
42 <li>Save the text file in the <code>%DIST%</code> directory
43 <li>Go to the <code>%DIST%</code> directory
44 <li>enter from command line: <code>set GECKO_DISPLAY_REFLOW_RULES_FILE=reflow_rules.txt</code>
45 <li> Run <code>viewer > logfile.txt</code> and load your testcase. The
46 logfile will contain all the promised information.
47 </ul>
48 <h2>Log File analyis</h2>
49 <p>The logfile for a simple table like</p>
50 <pre>
51 <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
52 <html>
53 <head>
54 <meta http-equiv="content-type" content="text/html; charset=ISO-8859-1">
55 </head>
56 <body>
57 <table width="100">
58 <tbody>
59 <tr>
60 <td>foo</td>
61 </tr>
62 </tbody>
63 </table>
64 </body>
65 </html>
66 </pre>
68 <p> will create the following log:</p>
69 <table class="log"><tr><td>
70 <pre>
71 VP 00B97C30 r=0 a=9180,4470 c=9180,4470 cnt=856
72 scroll 00B97EE0 r=0 a=9180,4470 c=9180,4470 cnt=857
73 scroll 00B97EE0 r=0 a=9180,4470 c=9180,4470 cnt=858
74 canvas 00B97C6C r=0 a=9180,UC c=9180,4470 cnt=859
75 area 02D7AFE4 r=0 a=9180,UC c=9180,UC cnt=860
76 text 02D7B150 r=0 a=9180,UC c=UC,UC cnt=861
77 text 02D7B150 d=0,0
78 block 02D7B210 r=0 a=9180,UC c=8940,UC cnt=862
79 block 02D7B210 d=8940,0
80 area 02D7AFE4 d=9180,120
81 canvas 00B97C6C d=9180,4470
82 scroll 00B97EE0 d=9180,4470
83 scroll 00B97EE0 d=9180,4470
84 VP 00B97C30 d=9180,4470
85 VP 00B97C30 r=1 a=9180,4470 c=9180,4470 cnt=863
86 scroll 00B97EE0 r=1 a=9180,4470 c=9180,4470 cnt=864
87 scroll 00B97EE0 r=1 a=9180,4470 c=9180,4470 cnt=865
88 canvas 00B97C6C r=1 a=9180,UC c=9180,4470 cnt=866
89 area 02D7AFE4 r=1 a=9180,UC c=9180,UC cnt=867
90 block 02D7B210 r=1 a=9180,UC c=8940,UC cnt=868
91 text 02D7B3F8 r=0 a=8940,UC c=UC,UC cnt=869
92 text 02D7B3F8 d=0,0
93 tblO 02D7B5F0 r=0 a=8940,UC c=0,0 cnt=870
94 tbl 02D7B7EC r=0 a=8940,UC c=1500,UC cnt=871
95 rowG 00B984A4 r=0 a=UC,UC c=UC,UC cnt=872
96 row 02D7BAF8 r=0 a=UC,UC c=UC,UC cnt=873
97 cell 02D7BC98 r=0 a=UC,UC c=UC,UC cnt=874
98 block 02D7BCF8 r=0 a=UC,UC c=UC,UC cnt=875
99 text 02D7BE84 r=0 a=UC,UC c=UC,UC cnt=876
100 text 02D7BE84 d=300,285 me=300
101 block 02D7BCF8 d=300,300 me=300
102 cell 02D7BC98 d=330,330 me=330
103 row 02D7BAF8 d=UC,330
104 rowG 00B984A4 d=UC,330
105 colG 02D7BFB0 r=0 a=UC,UC c=UC,UC cnt=877
106 col 02D7C0D8 r=0 a=0,0 c=1500,UC cnt=878
107 col 02D7C0D8 d=0,0
108 colG 02D7BFB0 d=0,0
109 rowG 00B984A4 r=2 a=1500,UC c=1500,UC cnt=879
110 row 02D7BAF8 r=2 a=1500,UC c=1500,UC cnt=880
111 cell 02D7BC98 r=2 a=1440,UC c=1410,UC cnt=881
112 block 02D7BCF8 r=2 a=1410,UC c=1410,UC cnt=882
113 block 02D7BCF8 d=1410,300
114 cell 02D7BC98 d=1440,330
115 row 02D7BAF8 d=1500,330
116 rowG 00B984A4 d=1500,330
117 colG 02D7BFB0 r=2 a=1500,UC c=1500,UC cnt=883
118 col 02D7C0D8 r=0 a=0,0 c=1500,UC cnt=884
119 col 02D7C0D8 d=0,0
120 colG 02D7BFB0 d=0,0
121 tbl 02D7B7EC d=1500,390
122 tblO 02D7B5F0 d=1500,390
123 text 02D7C130 r=0 a=8940,UC c=UC,UC cnt=885
124 text 02D7C130 d=0,0
125 block 02D7B210 d=8940,390
126 area 02D7AFE4 d=9180,630
127 canvas 00B97C6C d=9180,4470
128 scroll 00B97EE0 d=9180,4470
129 scroll 00B97EE0 d=9180,4470
130 VP 00B97C30 d=9180,4470
131 </pre>
132 </td></tr></table>
133 <p>
134 The first line shows the reflow of the viewport (<code class="log">VP</code>). This viewport has the address <code class="log">00B97C30</code>. It is the initial reflow: <code class="log">r=0</code>. Other reflow reasons are: </p>
135 <table>
136 <tr><td>1</td><td>incremental reflow</td></tr>
137 <tr><td>2</td><td>resize reflow</td></tr>
138 <tr><td>3</td><td>style change reflow</td></tr>
139 <tr><td>4</td><td>dirty reflow.</td></tr>
140 </table>
142 <p>The available width is 9180 twips. The available height is 4470 twips (<code class="log">a=9180,4470</code>). The computed width is 9180 twips. The computed height is 4470 twips (<code class="log">c=9180,4470</code>). The line count is 856 (<code class="log">cnt=856</code>).
143 <p>
144 Below this is a line that reads:<p><code class="log">tblO 02D7B5F0 r=0 a=8940,UC c=0,0 cnt=870</code></p><p> Here the <code class="log">UC</code> shows that on initial reflow the available height for the outer table frame is unconstrained.
145 <p>
146 The table cell requires its children to compute the MES. It is reported back from the block as:
147 <p><code class="log">block 02D7BCF8 d=300,300 me=300</code></p>
148 <p>The block max. element size is 300 twips.
149 <p> The second table reflow is started at
150 <p><code class="log">rowG 00B984A4 r=2 a=1500,UC c=1500,UC cnt=879</code></p>
151 <p>where the previous information is used.
152 The block has been required to compute the max. element size only once and it reports now:
153 <p> <code class="log">block 02D7BCF8 d=1410,300</code></p>
154 <p>The block shows the same address as the previous one.
155 <p>Frames with children that overflow the parent will return <code>PR_TRUE</code> from <code>HasOverflowRect()</code>. For these frames
156 the overflow area is displayed as <code class="log">block 025ED8F0 d=8940,1020 o=(0,0) 9180 x 1020</code>. The overflow area is specified as (x,y) origin and width x height.
157 <p> The reflow finishes at the same level where it started.
159 <h2>Advanced reflow debugging</h2>
160 <p>The previously described technique dumps the data for every frame. Sometimes the log is clearer if only the main frames are shown.
161 The entries in the reflow log can be controlled on a frame level. For instance adding <code>text 0</code> to the rules in <code>reflow_rules.txt</code> would hide the text entries from the reflow. The display of the following frames can be turned on by adding a line with the frame name and <code>1</code> or turned off by adding a line with the frame name and <code>0</code>:</p>
162 <table cellspacing="5">
163 <tr><th style="text-align:left">short name</th><th style="text-align:left">layout tag</th></tr>
164 <tr><td>area</td><td>area</td></tr>
165 <tr><td>block</td><td>block</td></tr>
166 <tr><td>br</td><td>br</td></tr>
167 <tr><td>bullet</td><td>bullet</td></tr>
168 <tr><td>button</td><td>gfxButtonControl</td></tr>
169 <tr><td>hr</td><td>hr</td></tr>
170 <tr><td>frameI</td><td>htmlFrameInner</td></tr>
171 <tr><td>frameO</td><td>htmlFrameOuter</td></tr>
172 <tr><td>img</td><td>image</td></tr>
173 <tr><td>inline</td><td>inline</td></tr>
174 <tr><td>letter</td><td>letter</td></tr>
175 <tr><td>line</td><td>line</td></tr>
176 <tr><td>select</td><td>select</td></tr>
177 <tr><td>obj</td><td>object</td></tr>
178 <tr><td>page</td><td>page</td></tr>
179 <tr><td>place</td><td>placeholder</td></tr>
180 <tr><td>canvas</td><td>canvas</td></tr>
181 <tr><td>root</td><td>root</td></tr>
182 <tr><td>scroll</td><td>scroll</td></tr>
183 <tr><td>caption</td><td>tableCaption</td></tr>
184 <tr><td>cell</td><td>tableCell</td></tr>
185 <tr><td>bcCell</td><td>bcTableCell</td></tr>
186 <tr><td>col</td><td>tableCol</td></tr>
187 <tr><td>colG</td><td>tableColGroup</td></tr>
188 <tr><td> tbl</td><td>table</td></tr>
189 <tr><td>tblO</td><td>tableOuter</td></tr>
190 <tr><td>rowG</td><td>tableRowGroup</td></tr>
191 <tr><td>row</td><td>tableRow</td></tr>
192 <tr><td>textCtl</td><td>textInput</td></tr>
193 <tr><td>text</td><td>text</td></tr>
194 <tr><td>VP</td><td>viewport</td></tr>
195 </table>
196 <p>Once the problem is reduced to a single frame level, placing a breakpoint at <code>DisplayReflowEnterPrint</code> in <a href="http://lxr.mozilla.org/seamonkey/source/layout/html/base/src/nsFrame.cpp"><code>nsFrame.cpp</code></a> is a very efficient way to step through
197 the reflow tree.
199 <h2>Other reflow debug options</h2>
201 <h3>GECKO_DISPLAY_REFLOW_FLAG_PIXEL_ERRORS</h3>
202 <p>
203 Setting this option via <code>set GECKO_DISPLAY_REFLOW_FLAG_PIXEL_ERRORS = 1</code> enables a verification for each coordinate value that the coordinates are aligned at pixel boundaries.
204 <table class="log"><tr><td>
205 <pre>
206 row 0268A594 r=0 a=UC,UC c=UC,20 cnt=870
207 VALUE 20 is not a whole pixel
208 cell 0268A6C0 r=0 a=UC,UC c=UC,15 cnt=871
209 block 0268A764 r=0 a=UC,UC c=UC,UC cnt=872
210 block 0268A764 d=0,0 me=0
211 cell 0268A6C0 d=0,0 me=0
212 row 0268A594 d=UC,20
213 VALUE 20 is not a whole pixel
214 rowG 0268A02C d=UC,695
215 VALUE 695 is not a whole pixel</pre>
216 </td></tr></table>
217 <p>
218 While unaligned values at the entrance of a frame reflow can be ignored, when they appear at the exit of a routine this can cause display errors like stray lines. OS2 is very vulnerable to pixel alignement errors as text is drawn on pixel boundaries.
220 <h3>GECKO_DISPLAY_REFLOW_INDENT_UNDISPLAYED_FRAMES</h3>
221 <p>
222 Setting this option via <code>set GECKO_DISPLAY_REFLOW_INDENT_UNDISPLAYED_FRAMES = 1</code> will cause an advance of the indent even for frames which are blocked via the reflow rules file.
223 </body>
224 </html>
