Shaders: graster-nodes no-std prep (#2924)

* raster-nodes: remove commented out index node * raster-nodes: move `CubicSplines` to separate mod * raster-nodes: create `mod blending_nodes` and move assoc nodes * raster-nodes: move node `gradient_map` to its own mod
2026-09-27 17:48:12 +08:00 · 2025-07-24 13:32:10 +00:00
parent 59f3835c5d
commit e7b8b5a3b6
9 changed files with 426 additions and 421 deletions
@@ -0,0 +1,118 @@
+#[derive(Debug)]
+pub struct CubicSplines {
+	pub x: [f32; 4],
+	pub y: [f32; 4],
+}
+
+impl CubicSplines {
+	pub fn solve(&self) -> [f32; 4] {
+		let (x, y) = (&self.x, &self.y);
+
+		// Build an augmented matrix to solve the system of equations using Gaussian elimination
+		let mut augmented_matrix = [
+			[
+				2. / (x[1] - x[0]),
+				1. / (x[1] - x[0]),
+				0.,
+				0.,
+				// |
+				3. * (y[1] - y[0]) / ((x[1] - x[0]) * (x[1] - x[0])),
+			],
+			[
+				1. / (x[1] - x[0]),
+				2. * (1. / (x[1] - x[0]) + 1. / (x[2] - x[1])),
+				1. / (x[2] - x[1]),
+				0.,
+				// |
+				3. * ((y[1] - y[0]) / ((x[1] - x[0]) * (x[1] - x[0])) + (y[2] - y[1]) / ((x[2] - x[1]) * (x[2] - x[1]))),
+			],
+			[
+				0.,
+				1. / (x[2] - x[1]),
+				2. * (1. / (x[2] - x[1]) + 1. / (x[3] - x[2])),
+				1. / (x[3] - x[2]),
+				// |
+				3. * ((y[2] - y[1]) / ((x[2] - x[1]) * (x[2] - x[1])) + (y[3] - y[2]) / ((x[3] - x[2]) * (x[3] - x[2]))),
+			],
+			[
+				0.,
+				0.,
+				1. / (x[3] - x[2]),
+				2. / (x[3] - x[2]),
+				// |
+				3. * (y[3] - y[2]) / ((x[3] - x[2]) * (x[3] - x[2])),
+			],
+		];
+
+		// Gaussian elimination: forward elimination
+		for row in 0..4 {
+			let pivot_row_index = (row..4)
+				.max_by(|&a_row, &b_row| augmented_matrix[a_row][row].abs().partial_cmp(&augmented_matrix[b_row][row].abs()).unwrap_or(std::cmp::Ordering::Equal))
+				.unwrap();
+
+			// Swap the current row with the row that has the largest pivot element
+			augmented_matrix.swap(row, pivot_row_index);
+
+			// Eliminate the current column in all rows below the current one
+			for row_below_current in row + 1..4 {
+				assert!(augmented_matrix[row][row].abs() > f32::EPSILON);
+
+				let scale_factor = augmented_matrix[row_below_current][row] / augmented_matrix[row][row];
+				for col in row..5 {
+					augmented_matrix[row_below_current][col] -= augmented_matrix[row][col] * scale_factor
+				}
+			}
+		}
+
+		// Gaussian elimination: back substitution
+		let mut solutions = [0.; 4];
+		for col in (0..4).rev() {
+			assert!(augmented_matrix[col][col].abs() > f32::EPSILON);
+
+			solutions[col] = augmented_matrix[col][4] / augmented_matrix[col][col];
+
+			for row in (0..col).rev() {
+				augmented_matrix[row][4] -= augmented_matrix[row][col] * solutions[col];
+				augmented_matrix[row][col] = 0.;
+			}
+		}
+
+		solutions
+	}
+
+	pub fn interpolate(&self, input: f32, solutions: &[f32]) -> f32 {
+		if input <= self.x[0] {
+			return self.y[0];
+		}
+		if input >= self.x[self.x.len() - 1] {
+			return self.y[self.x.len() - 1];
+		}
+
+		// Find the segment that the input falls between
+		let mut segment = 1;
+		while self.x[segment] < input {
+			segment += 1;
+		}
+		let segment_start = segment - 1;
+		let segment_end = segment;
+
+		// Calculate the output value using quadratic interpolation
+		let input_value = self.x[segment_start];
+		let input_value_prev = self.x[segment_end];
+		let output_value = self.y[segment_start];
+		let output_value_prev = self.y[segment_end];
+		let solutions_value = solutions[segment_start];
+		let solutions_value_prev = solutions[segment_end];
+
+		let output_delta = solutions_value_prev * (input_value - input_value_prev) - (output_value - output_value_prev);
+		let solution_delta = (output_value - output_value_prev) - solutions_value * (input_value - input_value_prev);
+
+		let input_ratio = (input - input_value_prev) / (input_value - input_value_prev);
+		let prev_output_ratio = (1. - input_ratio) * output_value_prev;
+		let output_ratio = input_ratio * output_value;
+		let quadratic_ratio = input_ratio * (1. - input_ratio) * (output_delta * (1. - input_ratio) + solution_delta * input_ratio);
+
+		let result = prev_output_ratio + output_ratio + quadratic_ratio;
+		result.clamp(0., 1.)
+	}
+}