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Bug 1005660: Add an "early freeze" step, to freeze flex items that clearly can't grow (or shrink, if we're shrinking). r=mats

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This commit is contained in:
Daniel Holbert 2014-05-17 18:49:06 -07:00
parent 1b7d4536c1
commit de1b127bc9
3 changed files with 154 additions and 78 deletions
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2
layout/generic/crashtests/crashtests.list
View File

@ -523,7 +523,7 @@ test-pref(layout.css.sticky.enabled,true) load 914891.html
test-pref(layout.css.sticky.enabled,true) load 915475.xhtml
load 927558.html
load 943509-1.html
asserts(4-8) load 944909-1.html
asserts(3-6) load 944909-1.html
test-pref(layout.css.sticky.enabled,true) load 949932.html
load 973701-1.xhtml
load 973701-2.xhtml

76
layout/generic/nsFlexContainerFrame.cpp
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@ -458,8 +458,9 @@ public:
// Setters
// =======
// This sets our flex base size, and then updates the main size to the
// base size clamped to our main-axis [min,max] constraints.
// This sets our flex base size, and then sets our main size to the
// resulting "hypothetical main size" (the base size clamped to our
// main-axis [min,max] sizing constraints).
void SetFlexBaseSizeAndMainSize(nscoord aNewFlexBaseSize)
{
MOZ_ASSERT(!mIsFrozen || mFlexBaseSize == NS_INTRINSICSIZE,
@ -723,7 +724,9 @@ public:
friend class AutoFlexLineListClearer; // (needs access to mItems)
private:
// Helper for ResolveFlexibleLengths():
// Helpers for ResolveFlexibleLengths():
void FreezeItemsEarly(bool aIsUsingFlexGrow);
void FreezeOrRestoreEachFlexibleSize(const nscoord aTotalViolation,
bool aIsFinalIteration);
@ -1592,6 +1595,56 @@ nsFlexContainerFrame::SanityCheckAnonymousFlexItems() const
}
#endif // DEBUG
void
FlexLine::FreezeItemsEarly(bool aIsUsingFlexGrow)
{
// After we've established the type of flexing we're doing (growing vs.
// shrinking), and before we try to flex any items, we freeze items that
// obviously *can't* flex.
//
// Quoting the spec:
// # Freeze, setting its target main size to its hypothetical main size...
// # - any item that has a flex factor of zero
// # - if using the flex grow factor: any item that has a flex base size
// # greater than its hypothetical main size
// # - if using the flex shrink factor: any item that has a flex base size
// # smaller than its hypothetical main size
// http://dev.w3.org/csswg/css-flexbox/#resolve-flexible-lengths-flex-factors
//
// (NOTE: At this point, item->GetMainSize() *is* the item's hypothetical
// main size, since SetFlexBaseSizeAndMainSize() sets it up that way, and the
// item hasn't had a chance to flex away from that yet.)
// Since this loop only operates on unfrozen flex items, we can break as
// soon as we have seen all of them.
uint32_t numUnfrozenItemsToBeSeen = mNumItems - mNumFrozenItems;
for (FlexItem* item = mItems.getFirst();
numUnfrozenItemsToBeSeen > 0; item = item->getNext()) {
MOZ_ASSERT(item, "numUnfrozenItemsToBeSeen says items remain to be seen");
if (!item->IsFrozen()) {
numUnfrozenItemsToBeSeen--;
bool shouldFreeze = (0.0f == item->GetFlexFactor(aIsUsingFlexGrow));
if (!shouldFreeze) {
if (aIsUsingFlexGrow) {
if (item->GetFlexBaseSize() > item->GetMainSize()) {
shouldFreeze = true;
}
} else { // using flex-shrink
if (item->GetFlexBaseSize() < item->GetMainSize()) {
shouldFreeze = true;
}
}
}
if (shouldFreeze) {
// Freeze item! (at its hypothetical main size)
item->Freeze();
mNumFrozenItems++;
}
}
}
}
// Based on the sign of aTotalViolation, this function freezes a subset of our
// flexible sizes, and restores the remaining ones to their initial pref sizes.
void
@ -1656,11 +1709,19 @@ void
FlexLine::ResolveFlexibleLengths(nscoord aFlexContainerMainSize)
{
PR_LOG(GetFlexContainerLog(), PR_LOG_DEBUG, ("ResolveFlexibleLengths\n"));
// Determine whether we're going to be growing or shrinking items.
const bool isUsingFlexGrow =
(mTotalOuterHypotheticalMainSize < aFlexContainerMainSize);
// Do an "early freeze" for flex items that obviously can't flex in the
// direction we've chosen:
FreezeItemsEarly(isUsingFlexGrow);
if (mNumFrozenItems == mNumItems) {
// All our items are frozen, so we have no flexible lengths to resolve.
return;
}
MOZ_ASSERT(!IsEmpty(), "empty lines should take the early-return above");
// Subtract space occupied by our items' margins/borders/padding, so we can
@ -1672,10 +1733,6 @@ FlexLine::ResolveFlexibleLengths(nscoord aFlexContainerMainSize)
nscoord spaceAvailableForFlexItemsContentBoxes =
aFlexContainerMainSize - spaceReservedForMarginBorderPadding;
// Determine whether we're going to be growing or shrinking items.
const bool isUsingFlexGrow =
(mTotalOuterHypotheticalMainSize < aFlexContainerMainSize);
nscoord origAvailableFreeSpace;
bool isOrigAvailFreeSpaceInitialized = false;
@ -1704,6 +1761,9 @@ FlexLine::ResolveFlexibleLengths(nscoord aFlexContainerMainSize)
// If sign of free space matches the type of flexing that we're doing, give
// each flexible item a portion of availableFreeSpace.
// XXXdholbert I think FreezeItemsThatAreObviouslyClamped might remove
// the need for this check. We can just check if availableFreeSpace is
// nonzero, and initialize origAvailableFreeSpace before we do that.
if ((availableFreeSpace > 0 && isUsingFlexGrow) ||
(availableFreeSpace < 0 && !isUsingFlexGrow)) {

154
layout/style/test/flexbox_layout_testcases.js
View File

@ -893,17 +893,19 @@ var gFlexboxTestcases =
]
},
// ...and now with a max-size smaller than our flex-basis:
// (This makes us freeze the second item right away, before we compute
// the initial free space.)
{
items:
[
{
"flex": "0.4 70px",
"_main-size": [ null, "110px" ] // +40% of free space
"_main-size": [ null, "118px" ] // +40% of 200px-70px-10px
},
{
"flex": "0.2 30px",
"_max-main-size": "10px",
"_main-size": [ null, "10px" ] // +20% free space, then clamped
"_main-size": [ null, "10px" ] // immediately frozen
},
]
},
@ -1006,21 +1008,20 @@ var gFlexboxTestcases =
]
},
// XXXdholbert The algorithm we're currently using has an unfortunate
// discontinuity between the following two cases, as described in bug 985304
// comment 28, due to when we determine the "original free space". We could
// fix this by always determining "original free space" up-front, but that
// causes other discontinuities. I'm waiting until the discussion sorts out a
// bit on www-style before deciding how to resolve this.
// Make sure we calculate "original free space" correctly when one of our
// flex items will be clamped right away, due to max-size preventing it from
// growing at all:
{
// First example:
// Here, we have an "original free space" of 2px, so our first item ends up
// getting 0.5 * 2px = 1px.
// Here, the second flex item is effectively inflexible; it's
// immediately frozen at 40px since we're growing & this item's max size
// trivially prevents it from growing. This leaves us with an "original
// free space" of 60px. The first flex item takes half of that, due to
// its flex-grow value of 0.5.
items:
[
{
"flex": "0.5 100px",
"_main-size": [ null, "101px" ]
"_main-size": [ null, "130px" ]
},
{
"flex": "1 98px",
@ -1030,12 +1031,9 @@ var gFlexboxTestcases =
]
},
{
// Second example (with 2nd flex item having 3px larger flex-basis):
// Here, our "original free space" is negative, but we're using flex-grow
// based on the sum of the items' hypothetical main sizes -- so we wait to
// establish the "original free space" until after we've frozen the second
// item. At that point, we have 60px free space. So our first item ends up
// getting 0.5 * 60px = 30px.
// Same as previous example, but with a larger flex-basis on the second
// element (which shouldn't ultimately matter, because its max size clamps
// its size immediately anyway).
items:
[
{
@ -1050,25 +1048,21 @@ var gFlexboxTestcases =
]
},
// XXXdholbert Here's another pair of testcases where we have another
// discontinuity, mentioned at the end of bug 985304 comment 28. Here, the
// "original free space" is small, and then a flex item gets clamped, making
// more free space available. If our flex items' sum is < 1, then this new
// free space won't be distributed (since it's not part of the *original* free
// space). But if we tweak a flex-grow value to push the sum over 1, then
// suddenly this extra free space *will* be distributed. Hence, discontinuity.
{
// First example: flex items' sum is 0.9 (just under 1)
// We only distribute shares of the "original free space", which is 10px.
// Here, the third flex item is effectively inflexible; it's immediately
// frozen at 0px since we're growing & this item's max size trivially
// prevents it from growing. This leaves us with an "original free space" of
// 100px. The first flex item takes 40px, and the third takes 50px, due to
// their flex values of 0.4 and 0.5.
items:
[
{
"flex": "0.4 50px",
"_main-size": [ null, "54px" ]
"_main-size": [ null, "90px" ]
},
{
"flex": "0.5 50px",
"_main-size": [ null, "55px" ]
"_main-size": [ null, "100px" ]
},
{
"flex": "0 90px",
@ -1078,11 +1072,10 @@ var gFlexboxTestcases =
]
},
{
// Second example: flex items' sum is exactly 1.0
// We distribute all of the current free space, in each loop of the
// algorithm. (In particular, after we've clamped the third item & freed up
// some more space.) So, the first and second item end up substantially
// larger than in the previous example.
// Same as previous example, but with slightly larger flex-grow values on
// the first and second items, which sum to 1.0 and produce slightly larger
// main sizes. This demonstrates that there's no discontinuity between the
// "< 1.0 sum" to ">= 1.0 sum" behavior, in this situation at least.
items:
[
{
@ -1202,17 +1195,19 @@ var gFlexboxTestcases =
},
// ...now with min-size larger than our flex-basis:
// (This makes us freeze the second item right away, before we compute
// the initial free space.)
{
items:
[
{
"flex": "0 0.3 100px",
"_main-size": [ null, "70px" ]
"_main-size": [ null, "55px" ] // +30% of 200px-100px-250px
},
{
"flex": "0 0.1 200px",
"_min-main-size": "250px",
"_main-size": [ null, "250px" ]
"_main-size": [ null, "250px" ] // immediately frozen
}
]
// (Same as previous example, except the min-main-size prevents the
@ -1310,11 +1305,11 @@ var gFlexboxTestcases =
[
{
"flex": "0 0.3 100px",
"_main-size": [ null, "84px" ]
"_main-size": [ null, "76px" ]
},
{
"flex": "0 0.1 150px",
"_main-size": [ null, "142px" ]
"_main-size": [ null, "138px" ]
},
{
"flex": "0 0.8 10px",
@ -1323,60 +1318,81 @@ var gFlexboxTestcases =
}
]
// Notes:
// - For the first round of flexing, we shrink everything and trivially
// violate the third items' min-size. So we freeze it and restart.
// We also establish a "original free space" of -60px.
// - We immediately freeze the 3rd item, since we're shrinking and its
// min size obviously prevents it from shrinking at all. This leaves
// 200px - 100px - 150px - 40px = -90px of "initial free space".
//
// - For the second round, we have -40px of free space, and a total
// flex-shrink of 0.4, and -60px *original* free space.
// So our remaining items will collectively shrink by
// 0.4 * -60px = -24px.
// - Our remaining flexible items have a total flex-shrink of 0.4,
// so we can distribute a total of 0.4 * -90px = -36px
//
// - 1st item's scaled flex factor: 0.3 * 100px = 30
// - 2nd item's scaled flex factor: 0.1 * 150px = 15
//
// - 1st item's share of distributed free space: 30/(30+15) = 2/3
// - 2nd item's share of distributed free space: 15/(30+15) = 1/3
// - We distribute that space using *scaled* flex factors:
// * 1st item's scaled flex factor: 0.3 * 100px = 30
// * 2nd item's scaled flex factor: 0.1 * 150px = 15
// ...which means...
// * 1st item's share of distributed free space: 30/(30+15) = 2/3
// * 2nd item's share of distributed free space: 15/(30+15) = 1/3
//
// SO:
// - 1st item gets 2/3 * -24px = -16px. 100px - 16px = 84px
// - 2nd item gets 1/3 * -24px = -8px. 150px - 8px = 142px
// - 1st item gets 2/3 * -36px = -24px. 100px - 24px = 76px
// - 2nd item gets 1/3 * -36px = -12px. 150px - 12px = 138px
},
// In this case, the items' flexibilities sum to > 1, in part due to an item
// that *can't actually shrink* due to its 0 flex-basis (which gives it a
// "scaled flex factor" of 0). So that item can't shrink, but it does prevent
// the others from getting the "flex-shrink sum less than 1" code-path.
// "scaled flex factor" of 0). This prevents us from triggering the special
// behavior for flexibilities that sum to less than 1, and as a result, the
// first item ends up absorbing all of the free space.
{
items:
[
{
"flex": "0 .3 150px",
"_main-size": [ null, "90px" ]
"flex": "0 .5 300px",
"_main-size": [ null, "200px" ]
},
{
"flex": "0 .2 150px",
"_main-size": [ null, "110px" ]
},
{
"flex": "0 2 0px",
"flex": "0 5 0px",
"_main-size": [ null, "0px" ]
}
]
},
// For comparison, the above testcase should behave just like this one with
// all >1 flex-shrink values (it shouldn't trigger any special <1 behavior):
// This case is similar to the one above, but with a *barely* nonzero base
// size for the second item. This should produce a result similar to the case
// above. (In particular, we should first distribute a very small amount of
// negative free space to the second item, getting it to approximately zero,
// and distribute the bulk of the negative free space to the first item,
// getting it to approximately 200px.)
{
items:
[
{
"flex": "0 3 150px",
"_main-size": [ null, "90px" ]
"flex": "0 .5 300px",
"_main-size": [ null, "200px" ]
},
{
"flex": "0 2 150px",
"_main-size": [ null, "110px" ]
},
]
"flex": "0 1 0.01px",
"_main-size": [ null, "0px" ]
}
]
},
// This case is similar to the ones above, but now we've increased the
// flex-shrink value on the second-item so that it claims enough of the
// negative free space to go below its min-size (0px). So, it triggers a min
// violation & is frozen. For the loop *after* the min violation, the sum of
// the remaining flex items' flex-shrink values is less than 1, so we trigger
// the special <1 behavior and only distribute half of the remaining
// (negative) free space to the first item (instead of all of it).
{
items:
[
{
"flex": "0 .5 300px",
"_main-size": [ null, "250px" ]
},
{
"flex": "0 5 0.01px",
"_main-size": [ null, "0px" ]
}
]
},
];