Add 'Gradient Map' adjustment node

node-graph/gcore/src/raster/adjustments.rs

@@ -5,6 +5,7 @@ use super::curve::{Curve, CurveManipulatorGroup, ValueMapperNode};
 #[cfg(feature = "alloc")]
 use super::ImageFrame;
 use super::{Channel, Color, Node, RGBMut};
+use crate::vector::style::GradientStops;
 use crate::vector::VectorData;
 use crate::GraphicGroup;
 
@@ -554,6 +555,21 @@ pub fn blend_colors(foreground: Color, background: Color, blend_mode: BlendMode,
 	background.alpha_blend(target_color.to_associated_alpha(opacity))
 }
 
+#[derive(Debug, Clone, Copy)]
+pub struct GradientMapNode<Gradient, Reverse> {
+	gradient: Gradient,
+	reverse: Reverse,
+	// TODO: Add support for dithering to break up gradient color banding
+	// TODO: Add support for controlling the gradient interpolation method (instead of always `luminance_srgb()`)
+}
+
+#[node_macro::node_fn(GradientMapNode)]
+fn gradient_map_node(color: Color, gradient: GradientStops, reverse: bool) -> Color {
+	let intensity = color.luminance_srgb();
+	let intensity = if reverse { 1. - intensity } else { intensity };
+	gradient.evalute(intensity as f64)
+}
+
 #[derive(Debug, Clone, Copy)]
 pub struct VibranceNode<Vibrance> {
 	vibrance: Vibrance,

node-graph/gcore/src/vector/style.rs

@@ -36,6 +36,32 @@ impl Default for GradientStops {
 	}
 }
 
+impl GradientStops {
+	pub fn evalute(&self, t: f64) -> Color {
+		if self.0.is_empty() {
+			return Color::BLACK;
+		}
+
+		if t <= self.0[0].0 {
+			return self.0[0].1;
+		}
+		if t >= self.0[self.0.len() - 1].0 {
+			return self.0[self.0.len() - 1].1;
+		}
+
+		for i in 0..self.0.len() - 1 {
+			let (t1, c1) = self.0[i];
+			let (t2, c2) = self.0[i + 1];
+			if t >= t1 && t <= t2 {
+				let normalized_t = (t - t1) / (t2 - t1);
+				return c1.lerp(&c2, normalized_t as f32);
+			}
+		}
+
+		Color::BLACK
+	}
+}
+
 /// A gradient fill.
 ///
 /// Contains the start and end points, along with the colors at varying points along the length.