Make gradient evaluation follow the ramp's interpolation space attribute (#4414)

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

@@ -1425,11 +1425,12 @@ fn gradient_midpoints(_: impl Ctx, gradient: Item<Gradient>, midpoints: List<f64
 	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.
+/// 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 blend in the gradient's `gradient_interpolation` color space.
 #[node_macro::node(category("Color"))]
 fn sample_gradient(_: impl Ctx, _primary: (), #[default(Color::BLACK, Color::WHITE)] gradient: Item<Gradient>, position: Item<Fraction>) -> Item<Color> {
 	let gradient_spread = gradient.attribute_cloned_or_default::<vector_types::GradientSpread>(core_types::ATTR_GRADIENT_SPREAD);
-	let color = gradient.element().evaluate(*position.element(), gradient_spread);
+	let gradient_interpolation = gradient.attribute_cloned_or_default::<vector_types::GradientInterpolation>(core_types::ATTR_GRADIENT_INTERPOLATION);
+	let color = gradient.element().evaluate(*position.element(), gradient_spread, gradient_interpolation);
 	Item::new_from_element(color)
 }
 

node-graph/nodes/raster/src/blending_nodes.rs

@@ -41,13 +41,16 @@ mod blend_std {
 		}
 	}
 	impl Blend<Color> for Gradient {
+		// TODO: This joining is unfaithful in several ways: it samples only at stop positions so midpoint curves flatten away;
+		// it evaluates both sources with the default spread and interpolation rather than their own attributes (which this
+		// element-level impl cannot read); and the output keeps over's attributes despite being sampled in the default space
 		fn blend(&self, under: &Self, blend_fn: impl Fn(Color, Color) -> Color) -> Self {
 			let mut combined_stops = self.positions().into_iter().chain(under.positions()).collect::<Vec<_>>();
 			combined_stops.sort_by(|a, b| a.partial_cmp(b).unwrap_or(Ordering::Equal));
 			combined_stops.dedup_by(|a, b| (*a - *b).abs() < 1e-6);
 			let stops = combined_stops.into_iter().map(|position| {
-				let over_color = self.evaluate(position, Default::default());
-				let under_color = under.evaluate(position, Default::default());
+				let over_color = self.evaluate(position, Default::default(), Default::default());
+				let under_color = under.evaluate(position, Default::default(), Default::default());
 				let color = blend_fn(over_color, under_color);
 				GradientStop { position, midpoint: 0.5, color }
 			});

node-graph/nodes/raster/src/gradient_map.rs

@@ -23,13 +23,14 @@ async fn gradient_map<T: Adjust<Color> + Send>(
 ) -> Item<T> {
 	let mut image = image;
 	let gradient_spread = gradient.attribute_cloned_or_default::<vector_types::GradientSpread>(core_types::ATTR_GRADIENT_SPREAD);
+	let gradient_interpolation = gradient.attribute_cloned_or_default::<vector_types::GradientInterpolation>(core_types::ATTR_GRADIENT_INTERPOLATION);
 	let gradient = gradient.into_element();
 	let reverse = reverse.into_element();
 
 	image.element_mut().adjust(|color| {
 		let intensity = color.luminance_rec_709();
 		let intensity = if reverse { 1. - intensity } else { intensity };
-		gradient.evaluate(intensity as f64, gradient_spread)
+		gradient.evaluate(intensity as f64, gradient_spread, gradient_interpolation)
 	});
 
 	image

node-graph/nodes/vector/src/vector_nodes.rs

@@ -3,7 +3,7 @@ use core::f64::consts::{PI, TAU};
 use core::hash::{Hash, Hasher};
 use core_types::blending::BlendMode;
 use core_types::bounds::{BoundingBox, RenderBoundingBox};
-use core_types::list::{ATTR_FILL, ATTR_STROKE, Item, ItemAttributeValues, List, ListDyn, NodeIdPath};
+use core_types::list::{ATTR_FILL, ATTR_GRADIENT_INTERPOLATION, ATTR_STROKE, Item, ItemAttributeValues, List, ListDyn, NodeIdPath};
 use core_types::registry::types::{Angle, Length, Multiplier, Percentage, PixelLength, Progression, SeedValue};
 use core_types::transform::{Footprint, Transform};
 use core_types::uuid::NodeId;
@@ -32,7 +32,7 @@ use vector_types::vector::misc::{
 	CentroidType, ExtrudeJoiningAlgorithm, HandleId, InterpolationDistribution, MergeByDistanceAlgorithm, PointSpacingType, RowsOrColumns, bezpath_from_manipulator_groups,
 	bezpath_to_manipulator_groups, handles_to_segment, is_linear, point_to_dvec2, segment_to_handles,
 };
-use vector_types::vector::style::{DashPattern, Gradient, PaintOrder, Stroke, StrokeAlign, StrokeCap, StrokeJoin};
+use vector_types::vector::style::{DashPattern, Gradient, GradientInterpolation, PaintOrder, Stroke, StrokeAlign, StrokeCap, StrokeJoin};
 use vector_types::vector::{FillId, PointId, RegionId, SegmentDomain, SegmentId, StrokeId, VectorExt};
 use vector_types::vector::{PointDomain, RegionDomain};
 
@@ -141,6 +141,7 @@ where
 
 	let mut content = content;
 	let length = content.vector_count();
+	let gradient_interpolation = gradient.attribute_cloned_or_default::<GradientInterpolation>(ATTR_GRADIENT_INTERPOLATION);
 	let element = gradient.into_element();
 	let gradient = if reverse { element.reversed() } else { element };
 
@@ -158,7 +159,8 @@ where
 				},
 			};
 
-			let color = gradient.evaluate(factor, Default::default());
+			// The factor spans 0..=1 inclusively, so the spread deliberately stays Pad (Repeat would wrap the final element onto the first stop's color)
+			let color = gradient.evaluate(factor, Default::default(), gradient_interpolation);
 			let paint = List::new_from_element(color).into_graphic_list();
 
 			if fill {