Transformations

1 files changed, 73 insertions, 0 deletions

diff --git a/src/geom/transform.rs b/src/geom/transform.rs
new file mode 100644
index 00000000..ca44667b
--- /dev/null
+++ b/src/geom/transform.rs
@@ -0,0 +1,73 @@
+use super::*;
+
+/// A scale-skew-translate transformation.
+#[derive(Debug, Copy, Clone, Eq, PartialEq, Hash, Serialize, Deserialize)]
+pub struct Transform {
+    pub sx: Relative,
+    pub ky: Relative,
+    pub kx: Relative,
+    pub sy: Relative,
+    pub tx: Length,
+    pub ty: Length,
+}
+
+impl Transform {
+    /// The identity transformation.
+    pub const fn identity() -> Self {
+        Self {
+            sx: Relative::one(),
+            ky: Relative::zero(),
+            kx: Relative::zero(),
+            sy: Relative::one(),
+            tx: Length::zero(),
+            ty: Length::zero(),
+        }
+    }
+
+    /// A translation transform.
+    pub const fn translation(tx: Length, ty: Length) -> Self {
+        Self { tx, ty, ..Self::identity() }
+    }
+
+    /// A scaling transform.
+    pub const fn scaling(sx: Relative, sy: Relative) -> Self {
+        Self { sx, sy, ..Self::identity() }
+    }
+
+    /// A rotation transform.
+    pub fn rotation(angle: Angle) -> Self {
+        let v = angle.to_rad();
+        let cos = Relative::new(v.cos());
+        let sin = Relative::new(v.sin());
+        Self {
+            sx: cos,
+            ky: sin,
+            kx: -sin,
+            sy: cos,
+            ..Self::default()
+        }
+    }
+
+    /// Whether this is the identity transformation.
+    pub fn is_identity(&self) -> bool {
+        *self == Self::identity()
+    }
+
+    /// Pre-concatenate another transformation.
+    pub fn pre_concat(&self, prev: Self) -> Self {
+        Transform {
+            sx: self.sx * prev.sx + self.kx * prev.ky,
+            ky: self.ky * prev.sx + self.sy * prev.ky,
+            kx: self.sx * prev.kx + self.kx * prev.sy,
+            sy: self.ky * prev.kx + self.sy * prev.sy,
+            tx: self.sx.resolve(prev.tx) + self.kx.resolve(prev.ty) + self.tx,
+            ty: self.ky.resolve(prev.tx) + self.sy.resolve(prev.ty) + self.ty,
+        }
+    }
+}
+
+impl Default for Transform {
+    fn default() -> Self {
+        Self::identity()
+    }
+}