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Heuristics for skipping calls to the measure function

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Introduced heuristics that enable css-layout to avoid
calling measure functions under a number of conditions.
This enables us to save time by skipping unnecessary
measurements.
This commit is contained in:
Adam Comella
2016-05-10 13:56:08 -07:00
parent 8779d942ea
commit 8177bfe702
11 changed files with 514 additions and 14 deletions
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53
src/Layout.c
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@@ -1516,6 +1516,37 @@ static const char* getModeName(css_measure_mode_t mode, bool performLayout) {
return performLayout? kLayoutModeNames[mode] : kMeasureModeNames[mode];
}
static bool canUseCachedMeasurement(float availableWidth, float availableHeight,
float marginRow, float marginColumn,
css_measure_mode_t widthMeasureMode, css_measure_mode_t heightMeasureMode,
css_cached_measurement_t cachedLayout) {
// Is it an exact match?
if (eq(cachedLayout.available_width, availableWidth) &&
eq(cachedLayout.available_height, availableHeight) &&
cachedLayout.width_measure_mode == widthMeasureMode &&
cachedLayout.height_measure_mode == heightMeasureMode) {
return true;
}
// If the width is an exact match, try a fuzzy match on the height.
if (cachedLayout.width_measure_mode == widthMeasureMode &&
eq(cachedLayout.available_width, availableWidth) &&
heightMeasureMode == CSS_MEASURE_MODE_EXACTLY &&
eq(availableHeight - marginColumn, cachedLayout.computed_height)) {
return true;
}
// If the height is an exact match, try a fuzzy match on the width.
if (cachedLayout.height_measure_mode == heightMeasureMode &&
eq(cachedLayout.available_height, availableHeight) &&
widthMeasureMode == CSS_MEASURE_MODE_EXACTLY &&
eq(availableWidth - marginRow, cachedLayout.computed_width)) {
return true;
}
return false;
}
//
// This is a wrapper around the layoutNodeImpl function. It determines
@@ -1548,7 +1579,27 @@ bool layoutNodeInternal(css_node_t* node, float availableWidth, float availableH
// and dimensions for nodes in the subtree. The algorithm assumes that each node
// gets layed out a maximum of one time per tree layout, but multiple measurements
// may be required to resolve all of the flex dimensions.
if (performLayout) {
// We handle nodes with measure functions specially here because they are the most
// expensive to measure, so it's worth avoiding redundant measurements if at all possible.
if (isMeasureDefined(node)) {
float marginAxisRow = getMarginAxis(node, CSS_FLEX_DIRECTION_ROW);
float marginAxisColumn = getMarginAxis(node, CSS_FLEX_DIRECTION_COLUMN);
// First, try to use the layout cache.
if (canUseCachedMeasurement(availableWidth, availableHeight, marginAxisRow, marginAxisColumn,
widthMeasureMode, heightMeasureMode, layout->cached_layout)) {
cachedResults = &layout->cached_layout;
} else {
// Try to use the measurement cache.
for (int i = 0; i < layout->next_cached_measurements_index; i++) {
if (canUseCachedMeasurement(availableWidth, availableHeight, marginAxisRow, marginAxisColumn,
widthMeasureMode, heightMeasureMode, layout->cached_measurements[i])) {
cachedResults = &layout->cached_measurements[i];
break;
}
}
}
} else if (performLayout) {
if (eq(layout->cached_layout.available_width, availableWidth) &&
eq(layout->cached_layout.available_height, availableHeight) &&
layout->cached_layout.width_measure_mode == widthMeasureMode &&