Move camera to standalone crate

Cargo.toml

@@ -5,6 +5,7 @@ members = [
     "demos/constraints",
     "demos/cli",
     "demos/viewer",
+    "demos/camera",
     "workspace-hack",
 ]
 exclude = ["demos/web-editor/crate"]

demos/camera/Cargo.toml

@@ -0,0 +1,8 @@
+[package]
+name = "camera"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
+nalgebra.workspace = true
+workspace-hack = { version = "0.1", path = "../../workspace-hack" }

demos/camera/src/lib.rs

@@ -0,0 +1,212 @@
+use nalgebra::Vector2;
+
+#[derive(Copy, Clone, Debug)]
+pub struct Camera2D {
+    /// Scale to translate between screen and world units
+    scale: f32,
+
+    /// Offset in world units
+    offset: Vector2<f32>,
+
+    /// Starting position for a drag, in world units
+    drag_start: Option<Vector2<f32>>,
+
+    /// Size of the viewport in screen units
+    viewport: Rect,
+}
+
+#[derive(Copy, Clone, Debug)]
+pub struct Rect {
+    pub min: Vector2<f32>,
+    pub max: Vector2<f32>,
+}
+
+impl Default for Camera2D {
+    fn default() -> Self {
+        Camera2D {
+            drag_start: None,
+            scale: 1.0,
+            offset: Vector2::zeros(),
+            viewport: Rect {
+                min: Vector2::new(f32::NAN, f32::NAN),
+                max: Vector2::new(f32::NAN, f32::NAN),
+            },
+        }
+    }
+}
+
+impl Camera2D {
+    /// Builds a new camera with an empty viewport
+    pub fn new() -> Self {
+        Self::default()
+    }
+
+    /// Returns the camera's current offset, in world units
+    pub fn offset(&self) -> Vector2<f32> {
+        self.offset
+    }
+
+    /// Returns the camera's current scale, mapping from screen to world units
+    pub fn scale(&self) -> f32 {
+        self.scale
+    }
+
+    /// Returns the current viewport, in screen units
+    pub fn viewport(&self) -> Rect {
+        self.viewport
+    }
+
+    /// Returns UV coordinates that cover the window
+    pub fn uv(&self) -> Rect {
+        let size = self.viewport.max - self.viewport.min;
+        if size.x > size.y {
+            let r = (1.0 - (size.y / size.x)) / 2.0;
+            Rect {
+                min: Vector2::new(0.0, r),
+                max: Vector2::new(1.0, 1.0 - r),
+            }
+        } else {
+            let r = (1.0 - (size.x / size.y)) / 2.0;
+            Rect {
+                min: Vector2::new(r, 0.0),
+                max: Vector2::new(1.0 - r, 1.0),
+            }
+        }
+    }
+
+    /// Updates the screen viewport size
+    pub fn set_viewport(&mut self, viewport: Rect) {
+        self.viewport = viewport;
+    }
+
+    /// Converts from mouse position to a UV position within the render window
+    fn screen_to_world(&self, p: Vector2<f32>) -> Vector2<f32> {
+        let size = self.viewport.max - self.viewport.min;
+        let out = (p - (self.viewport.min + self.viewport.max) / 2.0)
+            * self.scale
+            / size.x.max(size.y);
+        self.offset + out.component_mul(&Vector2::new(2.0, -2.0))
+    }
+
+    /// Updates the camera position when the mouse is held and dragged
+    ///
+    /// Returns `true` if the camera has changed
+    pub fn drag(&mut self, pos: Vector2<f32>) -> bool {
+        if let Some(start) = self.drag_start {
+            let prev_offset = self.offset;
+            self.offset = Vector2::zeros();
+            let pos = self.screen_to_world(pos);
+            let new_offset = start - pos;
+            let changed = prev_offset != new_offset;
+            self.offset = new_offset;
+            changed
+        } else {
+            let pos = self.screen_to_world(pos);
+            self.drag_start = Some(pos);
+            false
+        }
+    }
+
+    /// Releases the drag
+    pub fn release(&mut self) {
+        self.drag_start = None
+    }
+
+    /// Updates the camera zoom when the mouse is scrolled
+    ///
+    /// If the mouse cursor position is provided (in screen units), then the
+    /// camera offset is updated to keep the same point under the cursor.
+    ///
+    /// Returns `true` if the camera has changed
+    pub fn scroll(&mut self, pos: Option<Vector2<f32>>, scroll: f32) -> bool {
+        if scroll != 0.0 {
+            let new_scale = self.scale / (scroll / 100.0).exp2();
+            match pos {
+                Some(p) => {
+                    let pos_before = self.screen_to_world(p);
+                    self.scale = new_scale;
+                    let pos_after = self.screen_to_world(p);
+                    self.offset += pos_before - pos_after;
+                }
+                None => {
+                    self.scale = new_scale;
+                }
+            }
+            true
+        } else {
+            false
+        }
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[test]
+    fn test_drag() {
+        let mut c = Camera2D::new();
+        c.set_viewport(Rect {
+            min: Vector2::new(0.0, 0.0),
+            max: Vector2::new(100.0, 100.0),
+        });
+        let p = c.screen_to_world(Vector2::new(0.0, 0.0));
+        assert_eq!(p, Vector2::new(-1.0, 1.0));
+        let p = c.screen_to_world(Vector2::new(100.0, 0.0));
+        assert_eq!(p, Vector2::new(1.0, 1.0));
+        let p = c.screen_to_world(Vector2::new(0.0, 100.0));
+        assert_eq!(p, Vector2::new(-1.0, -1.0));
+        let p = c.screen_to_world(Vector2::new(100.0, 100.0));
+        assert_eq!(p, Vector2::new(1.0, -1.0));
+
+        c.drag(Vector2::new(50.0, 50.0));
+        c.drag(Vector2::new(100.0, 50.0));
+        c.release();
+
+        let p = c.screen_to_world(Vector2::new(50.0, 50.0));
+        assert_eq!(p, Vector2::new(-1.0, 0.0));
+
+        c.drag(Vector2::new(50.0, 50.0));
+        c.drag(Vector2::new(50.0, 100.0));
+        c.release();
+
+        let p = c.screen_to_world(Vector2::new(50.0, 50.0));
+        assert_eq!(p, Vector2::new(-1.0, 1.0));
+    }
+
+    #[test]
+    fn test_zoom() {
+        let mut c = Camera2D::new();
+        c.set_viewport(Rect {
+            min: Vector2::new(0.0, 0.0),
+            max: Vector2::new(100.0, 100.0),
+        });
+
+        let points = [
+            (75.0, 75.0),
+            (75.0, 25.0),
+            (25.0, 75.0),
+            (25.0, 25.0),
+            (50.0, 50.0),
+        ]
+        .map(|(x, y)| Vector2::new(x, y));
+        for &p in &points {
+            let corner = Vector2::zeros();
+            let prev_p = c.screen_to_world(p);
+            let prev_corner = c.screen_to_world(corner);
+            c.scroll(Some(p), 100.0);
+            let next_p = c.screen_to_world(p);
+            let next_corner = c.screen_to_world(corner);
+
+            assert_eq!(prev_p, next_p);
+            assert_ne!(prev_corner, next_corner);
+        }
+
+        // Undo the zooming to put us back at the origin
+        assert_ne!(c.offset, Vector2::new(0.0, 0.0));
+        for &p in points.iter().rev() {
+            c.scroll(Some(p), -100.0);
+        }
+        assert_eq!(c.offset, Vector2::new(0.0, 0.0));
+    }
+}

demos/viewer/Cargo.toml

@@ -16,6 +16,7 @@ notify.workspace = true
 rhai.workspace = true
 
 fidget = { path = "../../fidget", default-features = false, features = ["render", "rhai"] }
+camera = { path = "../camera" }
 workspace-hack = { version = "0.1", path = "../../workspace-hack" }
 
 [features]