Draft Scrollable widget (no clipping yet!)

wgpu/src/transformation.rs

@@ -1,30 +1,59 @@
-#[derive(Debug, Clone, Copy)]
-pub struct Transformation([f32; 16]);
+use nalgebra::Matrix3;
+use std::ops::Mul;
+
+/// A 2D transformation matrix.
+///
+/// It can be used to apply a transformation to a [`Target`].
+///
+/// [`Target`]: struct.Target.html
+#[derive(Debug, Clone, Copy, PartialEq)]
+pub struct Transformation(Matrix3<f32>);
 
 impl Transformation {
-    #[rustfmt::skip]
-    pub fn identity() -> Self {
-        Transformation([
-            1.0, 0.0, 0.0, 0.0,
-            0.0, 1.0, 0.0, 0.0,
-            0.0, 0.0, 1.0, 0.0,
-            0.0, 0.0, 0.0, 1.0,
-        ])
+    /// Get the identity transformation.
+    pub fn identity() -> Transformation {
+        Transformation(Matrix3::identity())
     }
 
+    /// Creates an orthographic projection.
+    ///
+    /// You should rarely need this. On creation, a [`Target`] is automatically
+    /// set up with the correct orthographic projection.
+    ///
+    /// [`Target`]: struct.Target.html
     #[rustfmt::skip]
-    pub fn orthographic(width: u16, height: u16) -> Self {
-        Transformation([
-            2.0 / width as f32, 0.0, 0.0, 0.0,
-            0.0, 2.0 / height as f32, 0.0, 0.0,
-            0.0, 0.0, 1.0, 0.0,
-            -1.0, -1.0, 0.0, 1.0,
-        ])
+    pub fn orthographic(width: u16, height: u16) -> Transformation {
+        Transformation(nalgebra::Matrix3::new(
+            2.0 / f32::from(width), 0.0, -1.0,
+            0.0, 2.0 / f32::from(height), -1.0,
+            0.0, 0.0, 1.0
+        ))
+    }
+
+    /// Creates a translate transformation.
+    ///
+    /// You can use this to pan your camera, for example.
+    pub fn translate(x: f32, y: f32) -> Transformation {
+        Transformation(Matrix3::new_translation(&nalgebra::Vector2::new(x, y)))
+    }
+}
+
+impl Mul for Transformation {
+    type Output = Self;
+
+    fn mul(self, rhs: Self) -> Self {
+        Transformation(self.0 * rhs.0)
     }
 }
 
 impl From<Transformation> for [f32; 16] {
-    fn from(transformation: Transformation) -> [f32; 16] {
-        transformation.0
+    #[rustfmt::skip]
+    fn from(t: Transformation) -> [f32; 16] {
+        [
+            t.0[0], t.0[1], 0.0, t.0[2],
+            t.0[3], t.0[4], 0.0, t.0[5],
+            0.0, 0.0, -1.0, 0.0,
+            t.0[6], t.0[7], 0.0, t.0[8]
+        ]
     }
 }