App: factor out the selection routine

app-proto/Cargo.toml

@@ -26,6 +26,7 @@ console_error_panic_hook = { version = "0.1.7", optional = true }
 [dependencies.web-sys]
 version = "0.3.69"
 features = [
+  'DomRect',
   'HtmlCanvasElement',
   'HtmlInputElement',
   'Performance',

app-proto/src/assembly.rs

@@ -1,4 +1,4 @@
-use nalgebra::{DMatrix, DVector};
+use nalgebra::{DMatrix, DVector, Vector3};
 use rustc_hash::FxHashMap;
 use slab::Slab;
 use std::{collections::BTreeSet, sync::atomic::{AtomicU64, Ordering}};
@@ -65,6 +65,49 @@ impl Element {
             column_index: 0
         }
     }
+    
+    // the smallest positive depth, represented as a multiple of `dir`, where
+    // the line generated by `dir` hits the element (which is assumed to be a
+    // sphere). returns `None` if the line misses the sphere. this function
+    // should be kept synchronized with `sphere_cast` in `inversive.frag`, which
+    // does essentially the same thing on the GPU side
+    pub fn cast(&self, dir: Vector3<f64>, assembly_to_world: &DMatrix<f64>) -> Option<f64> {
+        // if `a/b` is less than this threshold, we approximate
+        // `a*u^2 + b*u + c` by the linear function `b*u + c`
+        const DEG_THRESHOLD: f64 = 1e-9;
+        
+        let rep = self.representation.with_untracked(|rep| assembly_to_world * rep);
+        let a = -rep[3] * dir.norm_squared();
+        let b = rep.rows_range(..3).dot(&dir);
+        let c = -rep[4];
+        
+        let adjust = 4.0*a*c/(b*b);
+        if adjust < 1.0 {
+            // as long as `b` is non-zero, the linear approximation of
+            //
+            //   a*u^2 + b*u + c
+            //
+            // at `u = 0` will reach zero at a finite depth `u_lin`. the root of
+            // the quadratic adjacent to `u_lin` is stored in `lin_root`. if
+            // both roots have the same sign, `lin_root` will be the one closer
+            // to `u = 0`
+            let square_rect_ratio = 1.0 + (1.0 - adjust).sqrt();
+            let lin_root = -(2.0*c)/b / square_rect_ratio;
+            if a.abs() > DEG_THRESHOLD * b.abs() {
+                if lin_root > 0.0 {
+                    Some(lin_root)
+                } else {
+                    let other_root = -b/(2.*a) * square_rect_ratio;
+                    (other_root > 0.0).then_some(other_root)
+                }
+            } else {
+                (lin_root > 0.0).then_some(lin_root)
+            }
+        } else {
+            // the line through `dir` misses the sphere completely
+            None
+        }
+    }
 }
             
 

app-proto/src/display.rs

@@ -4,7 +4,9 @@ use sycamore::{prelude::*, motion::create_raf};
 use web_sys::{
     console,
     window,
+    Element,
     KeyboardEvent,
+    MouseEvent,
     WebGl2RenderingContext,
     WebGlProgram,
     WebGlShader,
@@ -12,7 +14,7 @@ use web_sys::{
     wasm_bindgen::{JsCast, JsValue}
 };
 
-use crate::AppState;
+use crate::{AppState, assembly::ElementKey};
 
 fn compile_shader(
     context: &WebGl2RenderingContext,
@@ -82,6 +84,24 @@ fn bind_vertex_attrib(
     );
 }
 
+// the direction in camera space that a mouse event is pointing along
+fn event_dir(event: &MouseEvent) -> Vector3<f64> {
+    let target: Element = event.target().unwrap().unchecked_into();
+    let rect = target.get_bounding_client_rect();
+    let width = rect.width();
+    let height = rect.height();
+    let shortdim = width.min(height);
+    
+    // this constant should be kept synchronized with `inversive.frag`
+    const FOCAL_SLOPE: f64 = 0.3;
+    
+    Vector3::new(
+        FOCAL_SLOPE * (2.0*(f64::from(event.client_x()) - rect.left()) - width) / shortdim,
+        FOCAL_SLOPE * (2.0*(rect.bottom() - f64::from(event.client_y())) - height) / shortdim,
+        -1.0
+    )
+}
+
 #[component]
 pub fn Display() -> View {
     let state = use_context::<AppState>();
@@ -89,6 +109,9 @@ pub fn Display() -> View {
     // canvas
     let display = create_node_ref();
     
+    // viewpoint
+    let assembly_to_world = create_signal(DMatrix::<f64>::identity(5, 5));
+    
     // navigation
     let pitch_up = create_signal(0.0);
     let pitch_down = create_signal(0.0);
@@ -296,7 +319,7 @@ pub fn Display() -> View {
                         0.0, 0.0,   0.0, 0.0, 1.0
                     ])
                 };
-                let assembly_to_world = &location * &orientation;
+                let asm_to_world = &location * &orientation;
                 
                 // get the assembly
                 let (
@@ -311,7 +334,7 @@ pub fn Display() -> View {
                         
                         // representation vectors in world coordinates
                         elts.iter().map(
-                            |(_, elt)| elt.representation.with(|rep| &assembly_to_world * rep)
+                            |(_, elt)| elt.representation.with(|rep| &asm_to_world * rep)
                         ).collect::<Vec<_>>(),
                         
                         // colors
@@ -370,6 +393,9 @@ pub fn Display() -> View {
                 // draw the scene
                 ctx.draw_arrays(WebGl2RenderingContext::TRIANGLES, 0, VERTEX_CNT as i32);
                 
+                // update the viewpoint
+                assembly_to_world.set(asm_to_world);
+                
                 // clear the scene change flag
                 scene_changed.set(
                     pitch_up_val != 0.0
@@ -458,6 +484,31 @@ pub fn Display() -> View {
                 yaw_left.set(0.0);
                 roll_ccw.set(0.0);
                 roll_cw.set(0.0);
+            },
+            on:click=move |event: MouseEvent| {
+                // find the nearest element along the pointer direction
+                let dir = event_dir(&event);
+                console::log_1(&JsValue::from(dir.to_string()));
+                let mut clicked: Option<(ElementKey, f64)> = None;
+                for (key, elt) in state.assembly.elements.get_clone_untracked() {
+                    match assembly_to_world.with(|asm_to_world| elt.cast(dir, asm_to_world)) {
+                        Some(depth) => match clicked {
+                            Some((_, best_depth)) => {
+                                if depth < best_depth {
+                                    clicked = Some((key, depth))
+                                }
+                            },
+                            None => clicked = Some((key, depth))
+                        }
+                        None => ()
+                    };
+                }
+                
+                // if we clicked something, select it
+                match clicked {
+                    Some((key, _)) => state.select(key, event.shift_key()),
+                    None => state.selection.update(|sel| sel.clear())
+                };
             }
         )
     }

app-proto/src/main.rs

@@ -25,6 +25,24 @@ impl AppState {
             selection: create_signal(FxHashSet::default())
         }
     }
+    
+    // in single-selection mode, select the element with the given key. in
+    // multiple-selection mode, toggle whether the element with the given key
+    // is selected
+    fn select(&self, key: ElementKey, multi: bool) {
+        if multi {
+            self.selection.update(|sel| {
+                if !sel.remove(&key) {
+                    sel.insert(key);
+                }
+            });
+        } else {
+            self.selection.update(|sel| {
+                sel.clear();
+                sel.insert(key);
+            });
+        }
+    }
 }
 
 fn main() {

app-proto/src/outline.rs

@@ -83,18 +83,7 @@ fn ElementOutlineItem(key: ElementKey, element: assembly::Element) -> View {
                         move |event: KeyboardEvent| {
                             match event.key().as_str() {
                                 "Enter" => {
-                                    if event.shift_key() {
-                                        state.selection.update(|sel| {
-                                            if !sel.remove(&key) {
-                                                sel.insert(key);
-                                            }
-                                        });
-                                    } else {
-                                        state.selection.update(|sel| {
-                                            sel.clear();
-                                            sel.insert(key);
-                                        });
-                                    }
+                                    state.select(key, event.shift_key());
                                     event.prevent_default();
                                 },
                                 "ArrowRight" if constrained.get() => {