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CSS: optimize pseudoclass nth-child() and friends
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The getUnboxedSibling calls are expensive, and we
can cache the resulting index of a node in its parent
children collection as it won't change.
We can cache these values in a node's RenderRectAccessor,
as it's not yet used at this point.
(On some books with a few dozens of p:nth-child(N)
rules, it can reduce the loading and rendering from
a few minutes to only a few seconds.)
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@poire-z
poire-z committed Jun 30, 2020
1 parent bcb8fa4 commit ff3640d
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Showing 4 changed files with 218 additions and 51 deletions.
1 change: 1 addition & 0 deletions crengine/include/lvrend.h
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Original file line number Diff line number Diff line change
Expand Up @@ -37,6 +37,7 @@
#define RENDER_RECT_FLAG_FINAL_FOOTPRINT_AS_SAVED_FLOAT_IDS 0x0040
#define RENDER_RECT_FLAG_FLOATBOX_IS_RIGHT 0x0080
#define RENDER_RECT_FLAG_NO_INTERLINE_SCALE_UP 0x0100 // for ruby elements to not scale up
#define RENDER_RECT_FLAG_TEMP_USED_AS_CSS_CHECK_CACHE 0x8000 // has been cleared and is used as a CSS checks cache

#define RENDER_RECT_SET_FLAG(r, f) ( r.setFlags( r.getFlags() | RENDER_RECT_FLAG_##f ) )
#define RENDER_RECT_UNSET_FLAG(r, f) ( r.setFlags( r.getFlags() & ~RENDER_RECT_FLAG_##f ) )
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2 changes: 2 additions & 0 deletions crengine/include/lvtinydom.h
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Original file line number Diff line number Diff line change
Expand Up @@ -986,6 +986,8 @@ struct ldomNode
void getAbsRect( lvRect & rect, bool inner=false );
/// sets node rendering structure pointer
void clearRenderData();
/// reset node rendering structure pointer for sub-tree
void clearRenderDataRecursive();
/// calls specified function recursively for all elements of DOM tree
void recurseElements( void (*pFun)( ldomNode * node ) );
/// calls specified function recursively for all elements of DOM tree matched by matchFun
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247 changes: 196 additions & 51 deletions crengine/src/lvstsheet.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -641,6 +641,122 @@ static bool match_nth_value( const lString16 value, int n)
return n % step == 0;
}

// For some expensive LVCssSelectorRule::check() checks, that might
// be done on a node for multiple rules and would give the same
// result, we can cache the result in the node's RenderRectAccessor(),
// which is not used at this point and will be reset and cleared after
// all styles have been applied, before rendering methods are set.
// This is mostly useful for the :zzz-child pseudoclasses checks
// that involve using the expensive getUnboxedSibling methods; we
// are sure that no boxing is done when applying stylesheets, so
// the position among the parent children collection is stable
// and can be cached.
// Note that we can't cache the value 0: a field with value 0 means
// it has not yet been cached (we could tweak it before caching if
// storing 0 is needed).
static void cache_node_checked_property( const ldomNode * node, int property, int value )
{
RenderRectAccessor fmt( (ldomNode*)node );
if ( !RENDER_RECT_HAS_FLAG(fmt, TEMP_USED_AS_CSS_CHECK_CACHE) ) {
// Clear it from past rendering stuff: we're processing stylesheets,
// which means we will soon re-render the whole DOM and have it cleared
// and updated. We can use it for caching other stuff until then.
fmt.clear();
RENDER_RECT_SET_FLAG(fmt, TEMP_USED_AS_CSS_CHECK_CACHE);
}
switch ( property ) {
// Positive integer >= 1: needs a int field
case csspc_nth_child:
fmt.setY(value);
break;
case csspc_nth_of_type:
fmt.setHeight(value);
break;
case csspc_nth_last_child:
fmt.setTopOverflow(value);
break;
case csspc_nth_last_of_type:
fmt.setBottomOverflow(value);
break;
// Boolean (1 means false, 2 means true): fine in a short int field
case csspc_first_child:
fmt.setX(value);
break;
case csspc_first_of_type:
fmt.setWidth(value);
break;
case csspc_last_child:
fmt.setInnerWidth(value);
break;
case csspc_last_of_type:
fmt.setInnerX(value);
break;
case csspc_only_child:
fmt.setInnerY(value);
break;
case csspc_only_of_type:
fmt.setBaseline(value);
break;
default:
break;
}
}

static bool get_cached_node_checked_property( const ldomNode * node, int property, int & value )
{
RenderRectAccessor fmt( (ldomNode*)node );
if ( !RENDER_RECT_HAS_FLAG(fmt, TEMP_USED_AS_CSS_CHECK_CACHE) )
return false; // nothing cached yet
bool res = false;
switch ( property ) {
// Positive integer >= 1
case csspc_nth_child:
value = fmt.getY();
res = value != 0;
break;
case csspc_nth_of_type:
value = fmt.getHeight();
res = value != 0;
break;
case csspc_nth_last_child:
value = fmt.getTopOverflow();
res = value != 0;
break;
case csspc_nth_last_of_type:
value = fmt.getBottomOverflow();
res = value != 0;
break;
// Boolean (1 means false, 2 means true)
case csspc_first_child:
value = fmt.getX();
res = value != 0;
break;
case csspc_first_of_type:
value = fmt.getWidth();
res = value != 0;
break;
case csspc_last_child:
value = fmt.getInnerWidth();
res = value != 0;
break;
case csspc_last_of_type:
value = fmt.getInnerX();
res = value != 0;
break;
case csspc_only_child:
value = fmt.getInnerY();
res = value != 0;
break;
case csspc_only_of_type:
value = fmt.getBaseline();
res = value != 0;
break;
default:
break;
}
return res;
}

struct standard_color_t
{
const char * name;
Expand Down Expand Up @@ -3321,85 +3437,114 @@ bool LVCssSelectorRule::check( const ldomNode * & node )
case csspc_first_child:
case csspc_first_of_type:
{
if ( _attrid == csspc_first_of_type )
nodeId = node->getNodeId();
const ldomNode * elem = node;
for (;;) {
elem = elem->getUnboxedPrevSibling(true); // skip text nodes
if (!elem)
break;
// We have a previous sibling
if (_attrid == csspc_first_child || elem->getNodeId() == nodeId)
return false;
int n; // 1 = false, 2 = true (should not be 0 for caching)
if ( !get_cached_node_checked_property(node, _attrid, n) ) {
n = 2; // true
if ( _attrid == csspc_first_of_type )
nodeId = node->getNodeId();
const ldomNode * elem = node;
for (;;) {
elem = elem->getUnboxedPrevSibling(true); // skip text nodes
if (!elem)
break;
// We have a previous sibling
if (_attrid == csspc_first_child || elem->getNodeId() == nodeId) {
n = 1; // false, we're not the first
break;
}
}
cache_node_checked_property(node, _attrid, n);
}
return true;
return n == 2;
}
break;
case csspc_last_child:
case csspc_last_of_type:
{
if ( _attrid == csspc_last_of_type )
nodeId = node->getNodeId();
const ldomNode * elem = node;
for (;;) {
elem = elem->getUnboxedNextSibling(true); // skip text nodes
if (!elem)
break;
// We have a next sibling
if (_attrid == csspc_last_child || elem->getNodeId() == nodeId)
return false;
int n; // 1 = false, 2 = true (should not be 0 for caching)
if ( !get_cached_node_checked_property(node, _attrid, n) ) {
n = 2; // true
if ( _attrid == csspc_last_of_type )
nodeId = node->getNodeId();
const ldomNode * elem = node;
for (;;) {
elem = elem->getUnboxedNextSibling(true); // skip text nodes
if (!elem)
break;
// We have a next sibling
if (_attrid == csspc_last_child || elem->getNodeId() == nodeId) {
n = 1; // false, we're not the last
break;
}
}
cache_node_checked_property(node, _attrid, n);
}
return true;
return n == 2;
}
break;
case csspc_nth_child:
case csspc_nth_of_type:
{
if ( _attrid == csspc_nth_of_type )
nodeId = node->getNodeId();
const ldomNode * elem = node;
int n = 1;
for (;;) {
elem = elem->getUnboxedPrevSibling(true); // skip text nodes
if (!elem)
break;
if (_attrid == csspc_nth_child || elem->getNodeId() == nodeId)
n++;
int n;
if ( !get_cached_node_checked_property(node, _attrid, n) ) {
if ( _attrid == csspc_nth_of_type )
nodeId = node->getNodeId();
const ldomNode * elem = node;
n = 1;
for (;;) {
elem = elem->getUnboxedPrevSibling(true); // skip text nodes
if (!elem)
break;
if (_attrid == csspc_nth_child || elem->getNodeId() == nodeId)
n++;
}
cache_node_checked_property(node, _attrid, n);
}
return match_nth_value(_value, n);
}
break;
case csspc_nth_last_child:
case csspc_nth_last_of_type:
{
if ( _attrid == csspc_nth_last_of_type )
nodeId = node->getNodeId();
const ldomNode * elem = node;
int n = 1;
for (;;) {
elem = elem->getUnboxedNextSibling(true); // skip text nodes
if (!elem)
break;
if (_attrid == csspc_nth_last_child || elem->getNodeId() == nodeId)
n++;
int n;
if ( !get_cached_node_checked_property(node, _attrid, n) ) {
if ( _attrid == csspc_nth_last_of_type )
nodeId = node->getNodeId();
const ldomNode * elem = node;
n = 1;
for (;;) {
elem = elem->getUnboxedNextSibling(true); // skip text nodes
if (!elem)
break;
if (_attrid == csspc_nth_last_child || elem->getNodeId() == nodeId)
n++;
}
cache_node_checked_property(node, _attrid, n);
}
return match_nth_value(_value, n);
}
break;
case csspc_only_child:
case csspc_only_of_type:
{
if ( _attrid == csspc_only_of_type )
nodeId = node->getNodeId();
const ldomNode * elem = node->getUnboxedParent()->getUnboxedFirstChild(true);
while (elem) {
if (elem != node) {
if (_attrid == csspc_only_child || elem->getNodeId() == nodeId)
return false; // we're not alone
int n; // 1 = false, 2 = true (should not be 0 for caching)
if ( !get_cached_node_checked_property(node, _attrid, n) ) {
n = 2; // true
if ( _attrid == csspc_only_of_type )
nodeId = node->getNodeId();
const ldomNode * elem = node->getUnboxedParent()->getUnboxedFirstChild(true);
while (elem) {
if (elem != node) {
if (_attrid == csspc_only_child || elem->getNodeId() == nodeId) {
n = 1; // false, we're not alone
break;
}
}
elem = elem->getUnboxedNextSibling(true);
}
elem = elem->getUnboxedNextSibling(true);
cache_node_checked_property(node, _attrid, n);
}
return true;
return n == 2;
}
break;
}
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19 changes: 19 additions & 0 deletions crengine/src/lvtinydom.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -4519,6 +4519,9 @@ bool ldomDocument::render( LVRendPageList * pages, LVDocViewCallback * callback,
// is invalid (should happen now only when EPUB has embedded fonts
// or some pseudoclass like :last-child has been met).
printf("CRE: styles re-init needed after load, re-rendering\n");
// We should clear RenderRectAccessor, that may have been used for
// caching CSS checks results (i.e. :nth-child(), :last-of-type...)
getRootNode()->clearRenderDataRecursive();
}
CRLog::info("rendering context is changed - full render required...");
// Clear LFormattedTextRef cache
Expand Down Expand Up @@ -15559,6 +15562,22 @@ void ldomNode::clearRenderData()
lvdomElementFormatRec rec;
getDocument()->_rectStorage.setRendRectData(_handle._dataIndex, &rec);
}
/// reset node rendering structure pointer for sub-tree
void ldomNode::clearRenderDataRecursive()
{
ASSERT_NODE_NOT_NULL;
if ( !isElement() )
return;
lvdomElementFormatRec rec;
getDocument()->_rectStorage.setRendRectData(_handle._dataIndex, &rec);
int cnt = getChildCount();
for (int i=0; i<cnt; i++) {
ldomNode * child = getChildNode( i );
if ( child->isElement() ) {
child->clearRenderDataRecursive();
}
}
}
#endif

/// calls specified function recursively for all elements of DOM tree, children before parent
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