The frame reflow can be logged with the debug capabilities implemented in nsFrame.cpp.
+It provides the following information for each frame at the
+start of its reflow
+
When the frame's reflow is finished the following information is displayed :
+reflow_rules.txt).
+* 1+
%DIST% directory
+%DIST% directory
+set GECKO_DISPLAY_REFLOW_RULES_FILE=reflow_rules.txt
+viewer > logfile.txt and load your testcase. The
+logfile will contain all the promised information.
+The logfile for a simple table like
++<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> +<html> +<head> + <meta http-equiv="content-type" content="text/html; charset=ISO-8859-1"> +</head> +<body> +<table width="100"> + <tbody> + <tr> + <td>foo</td> + </tr> + </tbody> +</table> +</body> +</html> ++ +
will create the following log:
+
++VP 00B97C30 r=0 a=9180,4470 c=9180,4470 cnt=856 + scroll 00B97EE0 r=0 a=9180,4470 c=9180,4470 cnt=857 + scroll 00B97EE0 r=0 a=9180,4470 c=9180,4470 cnt=858 + canvas 00B97C6C r=0 a=9180,UC c=9180,4470 cnt=859 + area 02D7AFE4 r=0 a=9180,UC c=9180,UC cnt=860 + text 02D7B150 r=0 a=9180,UC c=UC,UC cnt=861 + text 02D7B150 d=0,0 + block 02D7B210 r=0 a=9180,UC c=8940,UC cnt=862 + block 02D7B210 d=8940,0 + area 02D7AFE4 d=9180,120 + canvas 00B97C6C d=9180,4470 + scroll 00B97EE0 d=9180,4470 + scroll 00B97EE0 d=9180,4470 +VP 00B97C30 d=9180,4470 +VP 00B97C30 r=1 a=9180,4470 c=9180,4470 cnt=863 + scroll 00B97EE0 r=1 a=9180,4470 c=9180,4470 cnt=864 + scroll 00B97EE0 r=1 a=9180,4470 c=9180,4470 cnt=865 + canvas 00B97C6C r=1 a=9180,UC c=9180,4470 cnt=866 + area 02D7AFE4 r=1 a=9180,UC c=9180,UC cnt=867 + block 02D7B210 r=1 a=9180,UC c=8940,UC cnt=868 + text 02D7B3F8 r=0 a=8940,UC c=UC,UC cnt=869 + text 02D7B3F8 d=0,0 + tblO 02D7B5F0 r=0 a=8940,UC c=0,0 cnt=870 + tbl 02D7B7EC r=0 a=8940,UC c=1500,UC cnt=871 + rowG 00B984A4 r=0 a=UC,UC c=UC,UC cnt=872 + row 02D7BAF8 r=0 a=UC,UC c=UC,UC cnt=873 + cell 02D7BC98 r=0 a=UC,UC c=UC,UC cnt=874 + block 02D7BCF8 r=0 a=UC,UC c=UC,UC cnt=875 + text 02D7BE84 r=0 a=UC,UC c=UC,UC cnt=876 + text 02D7BE84 d=300,285 me=300 + block 02D7BCF8 d=300,300 me=300 + cell 02D7BC98 d=330,330 me=330 + row 02D7BAF8 d=UC,330 + rowG 00B984A4 d=UC,330 + colG 02D7BFB0 r=0 a=UC,UC c=UC,UC cnt=877 + col 02D7C0D8 r=0 a=0,0 c=1500,UC cnt=878 + col 02D7C0D8 d=0,0 + colG 02D7BFB0 d=0,0 + rowG 00B984A4 r=2 a=1500,UC c=1500,UC cnt=879 + row 02D7BAF8 r=2 a=1500,UC c=1500,UC cnt=880 + cell 02D7BC98 r=2 a=1440,UC c=1410,UC cnt=881 + block 02D7BCF8 r=2 a=1410,UC c=1410,UC cnt=882 + block 02D7BCF8 d=1410,300 + cell 02D7BC98 d=1440,330 + row 02D7BAF8 d=1500,330 + rowG 00B984A4 d=1500,330 + colG 02D7BFB0 r=2 a=1500,UC c=1500,UC cnt=883 + col 02D7C0D8 r=0 a=0,0 c=1500,UC cnt=884 + col 02D7C0D8 d=0,0 + colG 02D7BFB0 d=0,0 + tbl 02D7B7EC d=1500,390 + tblO 02D7B5F0 d=1500,390 + text 02D7C130 r=0 a=8940,UC c=UC,UC cnt=885 + text 02D7C130 d=0,0 + block 02D7B210 d=8940,390 + area 02D7AFE4 d=9180,630 + canvas 00B97C6C d=9180,4470 + scroll 00B97EE0 d=9180,4470 + scroll 00B97EE0 d=9180,4470 +VP 00B97C30 d=9180,4470 ++ |
+The first line shows the reflow of the viewport (VP). This viewport has the address 00B97C30. It is the initial reflow: r=0. Other reflow reasons are:
| 1 | incremental reflow |
| 2 | resize reflow |
| 3 | style change reflow |
| 4 | dirty reflow. |
The available width is 9180 twips. The available height is 4470 twips (a=9180,4470). The computed width is 9180 twips. The computed height is 4470 twips (c=9180,4470). The line count is 856 (cnt=856).
+
+Below this is a line that reads:
tblO 02D7B5F0 r=0 a=8940,UC c=0,0 cnt=870
Here the UC shows that on initial reflow the available height for the outer table frame is unconstrained.
+
+The table cell requires its children to compute the MES. It is reported back from the block as: +
block 02D7BCF8 d=300,300 me=300
The block max. element size is 300 twips. +
The second table reflow is started at +
rowG 00B984A4 r=2 a=1500,UC c=1500,UC cnt=879
where the previous information is used. +The block has been required to compute the max. element size only once and it reports now: +
block 02D7BCF8 d=1410,300
The block shows the same address as the previous one. +
Frames with children that overflow the parent will return PR_TRUE from HasOverflowRect(). For these frames
+the overflow area is displayed as block 025ED8F0 d=8940,1020 o=(0,0) 9180 x 1020. The overflow area is specified as (x,y) origin and width x height.
+
The reflow finishes at the same level where it started. + +
The previously described technique dumps the data for every frame. Sometimes the log is clearer if only the main frames are shown.
+The entries in the reflow log can be controlled on a frame level. For instance adding text 0 to the rules in reflow_rules.txt 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 1 or turned off by adding a line with the frame name and 0:
| short name | layout tag |
|---|---|
| area | area |
| block | block |
| br | br |
| bullet | bullet |
| button | gfxButtonControl |
| hr | hr |
| frameI | htmlFrameInner |
| frameO | htmlFrameOuter |
| img | image |
| inline | inline |
| letter | letter |
| line | line |
| select | select |
| obj | object |
| page | page |
| place | placeholder |
| canvas | canvas |
| root | root |
| scroll | scroll |
| caption | tableCaption |
| cell | tableCell |
| bcCell | bcTableCell |
| col | tableCol |
| colG | tableColGroup |
| tbl | table |
| tblO | tableOuter |
| rowG | tableRowGroup |
| row | tableRow |
| textCtl | textInput |
| text | text |
| VP | viewport |
Once the problem is reduced to a single frame level, placing a breakpoint at DisplayReflowEnterPrint in nsFrame.cpp is a very efficient way to step through
+ the reflow tree.
+
+
+Setting this option via set GECKO_DISPLAY_REFLOW_FLAG_PIXEL_ERRORS = 1 enables a verification for each coordinate value that the coordinates are aligned at pixel boundaries.
+
++ row 0268A594 r=0 a=UC,UC c=UC,20 cnt=870 +VALUE 20 is not a whole pixel + cell 0268A6C0 r=0 a=UC,UC c=UC,15 cnt=871 + block 0268A764 r=0 a=UC,UC c=UC,UC cnt=872 + block 0268A764 d=0,0 me=0 + cell 0268A6C0 d=0,0 me=0 + row 0268A594 d=UC,20 +VALUE 20 is not a whole pixel + rowG 0268A02C d=UC,695 +VALUE 695 is not a whole pixel+ |
+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. + +
+Setting this option via set GECKO_DISPLAY_REFLOW_INDENT_UNDISPLAYED_FRAMES = 1 will cause an advance of the indent even for frames which are blocked via the reflow rules file.
+
+