New nodes: 'Gradient Reverse', 'Gradient Shift', and 'Gradient Stretch' nodes for rearranging a ramp's stops (#4424)

* New nodes: 'Gradient Reverse', 'Gradient Shift', and 'Gradient Stretch' nodes for rearranging a ramp's stops

* Clip a lone out-of-range stop into the bake, and correct the docs that still promised edge-held stops

node-graph/nodes/math/src/lib.rs

@@ -1449,6 +1449,56 @@ fn gradient_midpoints(_: impl Ctx, gradient: Item<Gradient>, midpoints: List<f64
 	gradient
 }
 
+/// Reverses the order of each gradient's stops, moving the color at the start of the ramp to the end and vice versa.
+#[node_macro::node(category("Gradient"))]
+fn gradient_reverse(_: impl Ctx, gradient: Item<Gradient>) -> Item<Gradient> {
+	let settings = vector_types::GradientSettings::from(&gradient);
+	let mut gradient = gradient;
+	let reversed = gradient.element().reversed(settings.cyclic);
+	*gradient.element_mut() = reversed;
+	gradient
+}
+
+/// Shifts every stop along each gradient's ramp, sliding the colors within the gradient without moving the gradient itself.
+///
+/// The fraction is measured against the whole ramp. A cyclic gradient spins, wrapping past the end back around to the start so 1 is a full turn that lands where it began. A gradient that isn't cyclic has no loop to spin around, so its stops slide off the end and keep going, leaving the visible ramp to blend between whichever colors still span it.
+#[node_macro::node(category("Gradient"))]
+fn gradient_shift(
+	_: impl Ctx,
+	gradient: Item<Gradient>,
+	#[range]
+	#[soft(-1..1)]
+	fraction: Item<f64>,
+) -> Item<Gradient> {
+	let settings = vector_types::GradientSettings::from(&gradient);
+	let mut gradient = gradient;
+	gradient.element_mut().shift_positions(*fraction.element(), settings.cyclic);
+	gradient
+}
+
+/// Stretches or squeezes the spacing of each gradient's stops around a pivot, spreading the colors within the gradient without moving the gradient itself.
+///
+/// The factor multiplies every stop's distance from the pivot, so 2 spreads the ramp over twice its span while 0.5 packs it into half. A negative factor mirrors the stops across the pivot, reversing the order of the colors.
+///
+/// The pivot is the one point that stays put, measured against the whole ramp from 0 at the start to 1 at the end.
+#[node_macro::node(category("Gradient"))]
+fn gradient_stretch(
+	_: impl Ctx,
+	gradient: Item<Gradient>,
+	#[default(1.)]
+	#[unit("x")]
+	factor: Item<f64>,
+	#[default(0.5)]
+	#[range]
+	#[soft(0..1)]
+	pivot: Item<f64>,
+) -> Item<Gradient> {
+	let settings = vector_types::GradientSettings::from(&gradient);
+	let mut gradient = gradient;
+	gradient.element_mut().stretch_positions(*factor.element(), *pivot.element(), settings.cyclic);
+	gradient
+}
+
 /// Evaluates the color at the specified position along the gradient, given a position from 0 (left) to 1 (right). Positions beyond that range follow the gradient's `gradient_spread` attribute: Pad (default), Reflect, Repeat, or Clear. Colors between stops interpolate in the gradient's `gradient_space` color space.
 #[node_macro::node(category("Color"))]
 fn evaluate_gradient(