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Bug 295767. Simplify and thoroughly analyze previous-margin-dirty determination. r+sr=dbaron

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roc+%cs.cmu.edu 2005-08-21 23:18:11 +00:00
parent e1db238bf1
commit 3621391cc9
1 changed files with 34 additions and 18 deletions
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52
layout/generic/nsBlockFrame.cpp
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@ -2253,24 +2253,40 @@ nsBlockFrame::ReflowDirtyLines(nsBlockReflowState& aState, PRBool aTryPull)
break;
}
if (line.next() != end_lines() &&
// Check if the line might be empty, so the previous dirty
// margin might carry through to the next line.
((line->mBounds.height == 0 && previousMarginWasDirty) ||
// Check if the current line might have just been reflowed
// for the first time.
maybeReflowingForFirstTime ||
// Check if the current line might have been tested in a
// subsequent line's ShouldApplyTopMargin
(oldY == 0 && line->mBounds.y == 0 &&
// EXCEPT if it wasn't empty before and it wasn't empty
// now, nothing has changed that could affect
// ShouldApplyTopMargin
!(oldYMost != 0 && line->mBounds.height != 0)))) {
// In all these cases we must mark the the previous margin of
// the next line dirty.
line.next()->MarkPreviousMarginDirty();
// since it's marked dirty, nobody will care about |deltaY|
// Test to see whether the margin that should be carried out
// to the next line (NL) might have changed. In ReflowBlockFrame
// we call nextLine->MarkPreviousMarginDirty if the block's
// actual carried-out bottom margin changed. So here we only
// need to worry about the following effects:
// 1) the line was just created, and it might now be blocking
// a carried-out bottom margin from previous lines that
// used to reach NL from reaching NL
// 2) the line used to be empty, and is now not empty,
// thus blocking a carried-out bottom margin from previous lines
// that used to reach NL from reaching NL
// 3) the line wasn't empty, but now is, so a carried-out
// bottom margin from previous lines that didn't used to reach NL
// now does
// 4) the line might have changed in a way that affects NL's
// ShouldApplyTopMargin decision. The three things that matter
// are the line's emptiness, its adjacency to the top of the block,
// and whether it has clearance (the latter only matters if the block
// was and is adjacent to the top and empty).
//
// If the line is empty now, we can't reliably tell if the line was empty
// before, so we just assume it was and do nextLine->MarkPreviousMarginDirty.
// This means the checks in 4) are redundant; if the line is empty now
// we don't need to check 4), but if the line is not empty now and we're sure
// it wasn't empty before, any adjacency and clearance changes are irrelevant
// to the result of nextLine->ShouldApplyTopMargin.
if (line.next() != end_lines()) {
PRBool maybeWasEmpty = oldY == oldYMost;
PRBool isEmpty = line->mBounds.height == 0 && line->CachedIsEmpty();
if (maybeReflowingForFirstTime /*1*/ ||
(isEmpty || maybeWasEmpty) /*2/3/4*/) {
line.next()->MarkPreviousMarginDirty();
// since it's marked dirty, nobody will care about |deltaY|
}
}
// If the line was just reflowed for the first time, then its