Refactor transform decomposition API with skew support, add 'Decompose Skew' node, and fix stroke transform interpolation (#3973)

* Refactor transform decomposition API with skew support, add Decompose Skew node, and fix stroke transform interpolation

* Fix bug in master with skew changing Area node calculated value

* Code review simplification

* More code review fixes

* Rename cases where "shear" terminology was used in place of "skew"

node-graph/nodes/gstd/src/pixel_preview.rs

@@ -22,7 +22,7 @@ pub async fn pixel_preview<'a: 'n>(
 	let physical_scale = render_params.scale;
 
 	let footprint = *ctx.footprint();
-	let viewport_zoom = footprint.decompose_scale().x * physical_scale;
+	let viewport_zoom = footprint.scale_magnitudes().x * physical_scale;
 
 	if render_params.render_mode != RenderMode::PixelPreview || !matches!(render_params.render_output_type, RenderOutputTypeRequest::Vello) || viewport_zoom <= 1. {
 		let context = OwnedContextImpl::from(ctx).into_context();

node-graph/nodes/gstd/src/render_cache.rs

@@ -393,7 +393,7 @@ pub async fn render_output_cache<'a: 'n>(
 	}
 
 	let device_scale = render_params.scale;
-	let zoom = footprint.decompose_scale().x;
+	let zoom = footprint.scale_magnitudes().x;
 	let rotation = footprint.decompose_rotation();
 
 	let viewport_origin_offset = footprint.transform.translation;

node-graph/nodes/gstd/src/render_node.rs

@@ -108,7 +108,7 @@ async fn create_context<'a: 'n>(
 		render_output_type,
 		footprint: Footprint::default(),
 		scale: render_config.scale,
-		viewport_zoom: footprint.decompose_scale().x,
+		viewport_zoom: footprint.scale_magnitudes().x,
 		..Default::default()
 	};
 

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

@@ -203,7 +203,7 @@ pub fn mask(
 		.into_iter()
 		.filter_map(|mut row| {
 			let image_size = DVec2::new(row.element.width as f64, row.element.height as f64);
-			let mask_size = stencil.transform.decompose_scale();
+			let mask_size = stencil.transform.scale_magnitudes();
 
 			if mask_size == DVec2::ZERO {
 				return None;

node-graph/nodes/transform/src/transform_nodes.rs

@@ -1,7 +1,7 @@
 use core::f64;
 use core_types::color::Color;
 use core_types::table::Table;
-use core_types::transform::{ApplyTransform, Transform};
+use core_types::transform::{ApplyTransform, ScaleType, Transform};
 use core_types::{CloneVarArgs, Context, Ctx, ExtractAll, InjectFootprint, ModifyFootprint, OwnedContextImpl};
 use glam::{DAffine2, DMat2, DVec2};
 use graphic_types::Graphic;
@@ -77,7 +77,7 @@ fn reset_transform<T>(
 				row.transform.matrix2 = DMat2::IDENTITY;
 			}
 			(true, false) => {
-				let scale = row.transform.decompose_scale();
+				let scale = row.transform.scale_magnitudes();
 				row.transform.matrix2 = DMat2::from_diagonal(scale);
 			}
 			(false, true) => {
@@ -143,15 +143,24 @@ fn decompose_translation(_: impl Ctx, transform: DAffine2) -> DVec2 {
 }
 
 /// Extracts the rotation component (in degrees) from the input transform.
-/// This, together with the "Decompose Scale" node, also may jointly represent any shear component in the original transform.
 #[node_macro::node(category("Math: Transform"))]
 fn decompose_rotation(_: impl Ctx, transform: DAffine2) -> f64 {
 	transform.decompose_rotation().to_degrees()
 }
 
 /// Extracts the scale component from the input transform.
-/// This, together with the "Decompose Rotation" node, also may jointly represent any shear component in the original transform.
+/// **Magnitude** returns the visual length of each axis (always positive, includes any skew contribution).
+/// **Pure** returns the isolated scale factors with rotation and skew stripped away (can be negative for flipped axes).
 #[node_macro::node(category("Math: Transform"))]
-fn decompose_scale(_: impl Ctx, transform: DAffine2) -> DVec2 {
-	transform.decompose_scale()
+fn decompose_scale(_: impl Ctx, transform: DAffine2, scale_type: ScaleType) -> DVec2 {
+	match scale_type {
+		ScaleType::Magnitude => transform.scale_magnitudes(),
+		ScaleType::Pure => transform.decompose_scale(),
+	}
+}
+
+/// Extracts the skew angle (in degrees) from the input transform.
+#[node_macro::node(category("Math: Transform"))]
+fn decompose_skew(_: impl Ctx, transform: DAffine2) -> f64 {
+	transform.decompose_skew().atan().to_degrees()
 }

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

@@ -4,7 +4,7 @@ use core::hash::{Hash, Hasher};
 use core_types::bounds::{BoundingBox, RenderBoundingBox};
 use core_types::registry::types::{Angle, Length, Multiplier, Percentage, PixelLength, Progression, SeedValue};
 use core_types::table::{Table, TableRow, TableRowMut};
-use core_types::transform::{Footprint, Transform};
+use core_types::transform::Footprint;
 use core_types::{CloneVarArgs, Color, Context, Ctx, ExtractAll, OwnedContextImpl};
 use glam::{DAffine2, DVec2};
 use graphic_types::Vector;
@@ -2534,8 +2534,8 @@ async fn area(ctx: impl Ctx + CloneVarArgs + ExtractAll, content: impl Node<Cont
 	vector
 		.iter()
 		.map(|row| {
-			let scale = row.transform.decompose_scale();
-			row.element.stroke_bezpath_iter().map(|subpath| subpath.area() * scale.x * scale.y).sum::<f64>()
+			let area_scale = row.transform.matrix2.determinant().abs();
+			row.element.stroke_bezpath_iter().map(|subpath| subpath.area() * area_scale).sum::<f64>()
 		})
 		.sum()
 }