[emath] RectTransform: transforms Pos2 from one Rect to another

Very useful for transforming coordinate systems, e.g. for painting

emath/src/rect_transform.rs

@@ -0,0 +1,73 @@
+use crate::*;
+
+/// Linearly transforms positions from one [`Rect`] to another.
+///
+/// `RectTransform` stores the rectangles, and therefore supports clamping and culling.
+#[derive(Clone, Copy, Debug, PartialEq)]
+pub struct RectTransform {
+    from: Rect,
+    to: Rect,
+}
+
+impl RectTransform {
+    pub fn identity(from_and_to: Rect) -> Self {
+        Self::from_to(from_and_to, from_and_to)
+    }
+
+    pub fn from_to(from: Rect, to: Rect) -> Self {
+        Self { from, to }
+    }
+
+    pub fn from(&self) -> &Rect {
+        &self.from
+    }
+
+    pub fn to(&self) -> &Rect {
+        &self.to
+    }
+
+    pub fn inverse(&self) -> RectTransform {
+        Self::from_to(self.to, self.from)
+    }
+
+    /// Transforms the given coordinate in the `from` space to the `to` space.
+    pub fn transform_pos(&self, pos: Pos2) -> Pos2 {
+        pos2(
+            remap(pos.x, self.from.x_range(), self.to.x_range()),
+            remap(pos.y, self.from.y_range(), self.to.y_range()),
+        )
+    }
+
+    /// Transforms the given rectangle in the `in`-space to a rectangle in the `out`-space.
+    pub fn transform_rect(&self, rect: Rect) -> Rect {
+        Rect {
+            min: self.transform_pos(rect.min),
+            max: self.transform_pos(rect.max),
+        }
+    }
+
+    /// Transforms the given coordinate in the `from` space to the `to` space,
+    /// clamping if necessary.
+    pub fn transform_pos_clamped(&self, pos: Pos2) -> Pos2 {
+        pos2(
+            remap_clamp(pos.x, self.from.x_range(), self.to.x_range()),
+            remap_clamp(pos.y, self.from.y_range(), self.to.y_range()),
+        )
+    }
+}
+
+/// Transforms the position.
+impl std::ops::Mul<Pos2> for RectTransform {
+    type Output = Pos2;
+    fn mul(self, pos: Pos2) -> Pos2 {
+        self.transform_pos(pos)
+    }
+}
+
+/// Transforms the position.
+impl std::ops::Mul<Pos2> for &RectTransform {
+    type Output = Pos2;
+    fn mul(self, pos: Pos2) -> Pos2 {
+        self.transform_pos(pos)
+    }
+}