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

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

@@ -1242,7 +1242,7 @@ fn gradient_midpoints(_: impl Ctx, mut gradient: 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(
 	ctx: impl Ctx + ExtractIndex + InjectIndex + Copy,
@@ -1255,8 +1255,9 @@ fn sample_gradient(
 		return Err(GraphError::past_end().into());
 	}
 
-	let spread_method = gradient.lane(0).attr::<GradientSpreadAttr>();
-	Ok(gradient.element_ref(0).evaluate(position, spread_method))
+	let gradient_spread = gradient.lane(0).attr::<GradientSpreadAttr>();
+	let gradient_interpolation = gradient.lane(0).attr::<GradientInterpolationAttr>();
+	Ok(gradient.element_ref(0).evaluate(position, gradient_spread, gradient_interpolation))
 }
 
 /// Constructs a footprint value which may be set to any transformation of a unit square describing a render area, and a render resolution at least 1x1 integer pixels.

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

@@ -37,13 +37,16 @@ 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

@@ -24,12 +24,13 @@ fn gradient_map<T: Adjust<Color> + Clone + Send + Sync + core_types::CacheHash +
 		return image;
 	}
 	let gradient_spread = gradient.lane(0).attr::<vector_types::markers::GradientSpread>();
+	let gradient_interpolation = gradient.lane(0).attr::<vector_types::markers::GradientInterpolation>();
 	let gradient = gradient.element_ref(0);
 
 	image.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

@@ -39,13 +39,13 @@ 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};
 
 /// The gradient color for one assign-colors position, replaying the
 /// randomized draws up to it.
-fn assign_color_at(gradient: &Gradient, position: usize, length: usize, randomize: bool, seed: SeedValue, repeat_every: u32) -> Color {
+fn assign_color_at(gradient: &Gradient, gradient_interpolation: vector_types::GradientInterpolation, position: usize, length: usize, randomize: bool, seed: SeedValue, repeat_every: u32) -> Color {
 	let factor = match randomize {
 		true => {
 			let mut rng = rand::rngs::StdRng::seed_from_u64(seed.into());
@@ -61,7 +61,7 @@ fn assign_color_at(gradient: &Gradient, position: usize, length: usize, randomiz
 			_ => position as f64 % repeat_every as f64 / (repeat_every - 1) as f64,
 		},
 	};
-	gradient.evaluate(factor, Default::default())
+	gradient.evaluate(factor, Default::default(), gradient_interpolation)
 }
 
 /// Uniquely sets the fill and/or stroke style of every vector element to individual colors sampled along a chosen gradient.
@@ -104,6 +104,7 @@ fn assign_colors<'e>(
 	if gradient.is_empty() {
 		return Ok((content.lane(lane).map_element(element), Attr(existing_fill), Attr(existing_stroke)));
 	}
+	let gradient_interpolation = gradient.lane(0).attr::<vector_types::markers::GradientInterpolation>();
 	let gradient_element = gradient.element_ref(0);
 	let reversed;
 	let gradient_element = match reverse {
@@ -114,7 +115,7 @@ fn assign_colors<'e>(
 		false => gradient_element,
 	};
 
-	let color = assign_color_at(gradient_element, lane, content.len(), randomize, seed, repeat_every);
+	let color = assign_color_at(gradient_element, gradient_interpolation, lane, content.len(), randomize, seed, repeat_every);
 	let paint = List::new_from_element(color).into_graphic_list();
 	let parked = park_paint(ctx.arena(), paint)?;
 
@@ -172,6 +173,7 @@ fn assign_colors_graphic<'e>(
 	if gradient.is_empty() {
 		return Ok(content.lane(lane).map_element(original.clone()));
 	}
+	let gradient_interpolation = gradient.lane(0).attr::<vector_types::markers::GradientInterpolation>();
 	let gradient_element = gradient.element_ref(0);
 	let reversed;
 	let gradient_element = match reverse {
@@ -217,7 +219,7 @@ fn assign_colors_graphic<'e>(
 		Some(mut rows) => {
 			for row in 0..rows.len() {
 				let has_stroke = rows.element(row).is_some_and(|vector| vector.stroke.is_some());
-				let color = assign_color_at(gradient_element, position + row, length, randomize, seed, repeat_every);
+				let color = assign_color_at(gradient_element, gradient_interpolation, position + row, length, randomize, seed, repeat_every);
 				let paint = List::new_from_element(color).into_graphic_list();
 				if fill {
 					set_paint_attribute_at(&mut rows, row, ATTR_FILL, paint.clone());