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LibWeb: Don't canonicalize linear easing function points until use time

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Canonicalization can require information that is only known after
compute time (i.e. resolved relative lengths within calcs).

This also allows us to get rid of the `had_explicit_input` flag and just
rely on whether Optional has a value
This commit is contained in:
Callum Law 2025-10-09 21:55:55 +13:00 • committed by Sam Atkins
commit 91925db9ca
Notes: github-actions[bot] 2025-10-20 10:29:40 +00:00
5 changed files with 67 additions and 67 deletions
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60
Libraries/LibWeb/CSS/EasingFunction.cpp
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@ -210,6 +210,61 @@ double StepsEasingFunction::evaluate_at(double input_progress, bool before_flag)
return current_step / jumps;
}
// https://drafts.csswg.org/css-easing/#linear-canonicalization
static Vector<LinearEasingFunction::ControlPoint> canonicalize_linear_easing_function_control_points(Vector<LinearEasingFunction::ControlPoint> control_points)
{
// To canonicalize a linear() function’s control points, perform the following:
Vector<LinearEasingFunction::ControlPoint> canonicalized_control_points = control_points;
// 1. If the first control point lacks an input progress value, set its input progress value to 0.
if (!canonicalized_control_points.first().input.has_value())
canonicalized_control_points.first().input = 0;
// 2. If the last control point lacks an input progress value, set its input progress value to 1.
if (!canonicalized_control_points.last().input.has_value())
canonicalized_control_points.last().input = 1;
// 3. If any control point has an input progress value that is less than
// the input progress value of any preceding control point,
// set its input progress value to the largest input progress value of any preceding control point.
double largest_input = 0;
for (auto& control_point : canonicalized_control_points) {
if (control_point.input.has_value()) {
if (control_point.input.value() < largest_input) {
control_point.input = largest_input;
} else {
largest_input = control_point.input.value();
}
}
}
// 4. If any control point still lacks an input progress value,
// then for each contiguous run of such control points,
// set their input progress values so that they are evenly spaced
// between the preceding and following control points with input progress values.
Optional<size_t> run_start_idx;
for (size_t idx = 0; idx < canonicalized_control_points.size(); idx++) {
auto& control_point = canonicalized_control_points[idx];
if (control_point.input.has_value() && run_start_idx.has_value()) {
// Note: this stop is immediately after a run
// set inputs of [start, idx-1] stops to be evenly spaced between start-1 and idx
auto start_input = canonicalized_control_points[run_start_idx.value() - 1].input.value();
auto end_input = canonicalized_control_points[idx].input.value();
auto run_stop_count = idx - run_start_idx.value() + 1;
auto delta = (end_input - start_input) / run_stop_count;
for (size_t run_idx = 0; run_idx < run_stop_count; run_idx++) {
canonicalized_control_points[run_idx + run_start_idx.value() - 1].input = start_input + delta * run_idx;
}
run_start_idx = {};
} else if (!control_point.input.has_value() && !run_start_idx.has_value()) {
// Note: this stop is the start of a run
run_start_idx = idx;
}
}
return canonicalized_control_points;
}
EasingFunction EasingFunction::from_style_value(StyleValue const& style_value)
{
if (style_value.is_easing()) {
@ -220,6 +275,11 @@ EasingFunction EasingFunction::from_style_value(StyleValue const& style_value)
for (auto const& control_point : linear.stops)
resolved_control_points.append({ control_point.input, control_point.output });
// https://drafts.csswg.org/css-easing-2/#funcdef-linear
// If an argument lacks a <percentage>, its input progress value is initially empty. This is corrected
// at used value time by linear() canonicalization.
resolved_control_points = canonicalize_linear_easing_function_control_points(resolved_control_points);
return LinearEasingFunction { resolved_control_points, linear.to_string(SerializationMode::ResolvedValue) };
},
[](EasingStyleValue::CubicBezier const& cubic_bezier) -> EasingFunction {