Keep focus point under cursor when moving model

This doesn't work perfectly yet, probably due to #18.

src/input/handler.rs

@@ -8,7 +8,7 @@ use winit::{
  },
 };
 
-use crate::{camera::Camera, math::Point};
+use crate::{camera::Camera, math::Point, window::Window};
 
 use super::{movement::Movement, rotation::Rotation, zoom::Zoom};
 
@@ -61,12 +61,13 @@ impl Handler {
  &mut self,
  cursor: PhysicalPosition<f64>,
  camera: &mut Camera,
+ window: &Window,
  ) {
  if let Some(previous) = self.cursor {
  let diff_x = cursor.x - previous.x;
  let diff_y = cursor.y - previous.y;
 
- self.movement.apply(diff_x, diff_y, camera);
+ self.movement.apply(self.cursor, camera, window);
  self.rotation.apply(diff_x, diff_y, camera);
  }
 
@@ -87,7 +88,7 @@ impl Handler {
  self.rotation.stop();
  }
  (MouseButton::Right, ElementState::Pressed) => {
- self.movement.start(focus_point);
+ self.movement.start(focus_point, self.cursor);
  }
  (MouseButton::Right, ElementState::Released) => {
  self.movement.stop();

src/input/movement.rs

@@ -1,51 +1,57 @@
-use nalgebra::Translation2;
+use nalgebra::{distance, Translation2};
+use winit::dpi::PhysicalPosition;
 
-use crate::{camera::Camera, math::Point};
+use crate::{camera::Camera, math::Point, window::Window};
 
 pub struct Movement {
  focus_point: Option<Point>,
+ cursor: Option<PhysicalPosition<f64>>,
 }
 
 impl Movement {
  pub fn new() -> Self {
- Self { focus_point: None }
+ Self {
+ focus_point: None,
+ cursor: None,
+ }
  }
 
- pub fn start(&mut self, focus_point: Option<Point>) {
+ pub fn start(
+ &mut self,
+ focus_point: Option<Point>,
+ cursor: Option<PhysicalPosition<f64>>,
+ ) {
  self.focus_point = focus_point;
+ self.cursor = cursor;
  }
 
  pub fn stop(&mut self) {
  self.focus_point = None;
  }
 
- pub fn apply(&mut self, diff_x: f64, diff_y: f64, camera: &mut Camera) {
- if let Some(_) = self.focus_point {
- // TASK: Moving feels good, if you're dragging the model exactly
- // where your mouse goes. It feels weird, if the mouse cursor
- // moves faster or slower than the model you're moving.
- //
- // The following factor achieves this good-feeling move for
- // relatively small models at the default distance between
- // camera and model origin. It breaks down when moving the
- // camera closer or away from the model, which is the far more
- // common case.
- //
- // It would be nicer to have a zoom factor that depends on the
- // distance between camera and model origin, or even the
- // distance between the camera and the part of the model the
- // mouse is currently pointing at (or more precisely, the
- // distance between the camera and a plane that touches the
- // surface of the model where the mouse is pointing, and whose
- // normal is parallel to the camera's viewing direction).
- let f = 0.2;
-
- let trans_x = diff_x * f;
- let trans_y = -diff_y * f;
-
- let translation = Translation2::new(trans_x, trans_y);
-
- camera.translation = translation * camera.translation;
+ pub fn apply(
+ &mut self,
+ cursor: Option<PhysicalPosition<f64>>,
+ camera: &mut Camera,
+ window: &Window,
+ ) {
+ if let (Some(previous), Some(cursor)) = (self.cursor, cursor) {
+ let previous = camera.cursor_to_model_space(previous, window);
+ let cursor = camera.cursor_to_model_space(cursor, window);
+
+ if let Some(focus_point) = self.focus_point {
+ let d1 = distance(&camera.position(), &cursor);
+ let d2 = distance(&camera.position(), &focus_point);
+
+ let f = d2 / d1;
+
+ let diff = (cursor - previous) * f;
+ let translation = Translation2::new(diff.x, diff.y);
+
+ camera.translation = translation * camera.translation;
+ }
  }
+
+ self.cursor = cursor;
  }
 }

src/main.rs

@@ -192,7 +192,11 @@ fn main() -> anyhow::Result<()> {
  event: WindowEvent::CursorMoved { position, .. },
  ..
  } => {
- input_handler.handle_cursor_moved(position, &mut camera);
+ input_handler.handle_cursor_moved(
+ position,
+ &mut camera,
+ &window,
+ );
  }
  Event::WindowEvent {
  event: WindowEvent::MouseInput { state, button, .. },