double
ComputedTimingFunction::GetValue(double aPortion) const
{
switch (mType) {
case nsTimingFunction::Function:
return mTimingFunction.GetSplineValue(aPortion);
case nsTimingFunction::StepStart:
// There are diagrams in the spec that seem to suggest this check
// and the bounds point should not be symmetric with StepEnd, but
// should actually step up at rather than immediately after the
// fraction points. However, we rely on rounding negative values
// up to zero, so we can't do that. And it's not clear the spec
// really meant it.
return 1.0 - StepEnd(mSteps, 1.0 - aPortion);
default:
NS_ABORT_IF_FALSE(false, "bad type");
// fall through
case nsTimingFunction::StepEnd:
return StepEnd(mSteps, aPortion);
}
}
double
ComputedTimingFunction::GetValue(double aPortion) const
{
if (HasSpline()) {
// Check for a linear curve.
// (GetSplineValue(), below, also checks this but doesn't work when
// aPortion is outside the range [0.0, 1.0]).
if (mTimingFunction.X1() == mTimingFunction.Y1() &&
mTimingFunction.X2() == mTimingFunction.Y2()) {
return aPortion;
}
// For negative values, try to extrapolate with tangent (p1 - p0) or,
// if p1 is coincident with p0, with (p2 - p0).
if (aPortion < 0.0) {
if (mTimingFunction.X1() > 0.0) {
return aPortion * mTimingFunction.Y1() / mTimingFunction.X1();
} else if (mTimingFunction.Y1() == 0 && mTimingFunction.X2() > 0.0) {
return aPortion * mTimingFunction.Y2() / mTimingFunction.X2();
}
// If we can't calculate a sensible tangent, don't extrapolate at all.
return 0.0;
}
// For values greater than 1, try to extrapolate with tangent (p2 - p3) or,
// if p2 is coincident with p3, with (p1 - p3).
if (aPortion > 1.0) {
if (mTimingFunction.X2() < 1.0) {
return 1.0 + (aPortion - 1.0) *
(mTimingFunction.Y2() - 1) / (mTimingFunction.X2() - 1);
} else if (mTimingFunction.Y2() == 1 && mTimingFunction.X1() < 1.0) {
return 1.0 + (aPortion - 1.0) *
(mTimingFunction.Y1() - 1) / (mTimingFunction.X1() - 1);
}
// If we can't calculate a sensible tangent, don't extrapolate at all.
return 1.0;
}
return mTimingFunction.GetSplineValue(aPortion);
}
// Since we use endpoint-exclusive timing, the output of a steps(start) timing
// function when aPortion = 0.0 is the top of the first step. When aPortion is
// negative, however, we should use the bottom of the first step. We handle
// negative values of aPortion specially here since once we clamp aPortion
// to [0,1] below we will no longer be able to distinguish to the two cases.
if (aPortion < 0.0) {
return 0.0;
}
// Clamp in case of steps(end) and steps(start) for values greater than 1.
aPortion = clamped(aPortion, 0.0, 1.0);
if (mType == nsTimingFunction::Type::StepStart) {
// There are diagrams in the spec that seem to suggest this check
// and the bounds point should not be symmetric with StepEnd, but
// should actually step up at rather than immediately after the
// fraction points. However, we rely on rounding negative values
// up to zero, so we can't do that. And it's not clear the spec
// really meant it.
return 1.0 - StepEnd(mSteps, 1.0 - aPortion);
}
MOZ_ASSERT(mType == nsTimingFunction::Type::StepEnd, "bad type");
return StepEnd(mSteps, aPortion);
}