From 50a20982a4d9c0e4c8016b1eeb81667f07d2c23d Mon Sep 17 00:00:00 2001
From: Catalin Constantin Mititiuc <webdevcat@proton.me>
Date: Sat, 20 Dec 2025 08:40:41 -0800
Subject: [PATCH] Move collision detection code into its own function

---
 html/images/space.svg | 97 ++++++++++++++++++-------------------------
 1 file changed, 41 insertions(+), 56 deletions(-)

diff --git a/html/images/space.svg b/html/images/space.svg
index 0071be3..c1f2192 100644
--- a/html/images/space.svg
+++ b/html/images/space.svg
@@ -314,6 +314,44 @@
       });
     }
 
+    function detectCollision(points, visibleTriangles) {
+      const cornerCollision = points.some(([x, y]) => {
+        cornerPt.x = x - positionX;
+        cornerPt.y = y - positionY;
+
+        return shipBody.isPointInFill(cornerPt);
+      });
+
+      const shipRadius = 5;
+      const sideCollision = [...visibleTriangles].reduce((acc, t) => {
+        const [[ax, ay], [bx, by], [shipx, shipy]] =
+          t.getAttribute('points').split(' ').map(n => n.split(',').map(n => +n));
+
+        const da = distance(ax, ay, shipx, shipy);
+        const db = distance(bx, by, shipx, shipy);
+        // TODO: calculate this one ahead of time
+        const dc = distance(ax, ay, bx, by);
+
+        // https://en.wikipedia.org/wiki/Altitude_(triangle)#Altitude_in_terms_of_the_sides
+        // Find altitude of side c (the base)
+        const s = (1 / 2) * (da + db + dc);
+        const hc = (2 / dc) * Math.sqrt(s * (s - da) * (s - db) * (s - dc));
+
+        // https://en.wikipedia.org/wiki/Law_of_cosines
+        // Solve for angles alpha and beta with inverse cosine (arccosine) function
+        const alpha = Math.acos((db**2 + dc**2 - da**2) / (2 * db * dc));
+        const beta = Math.acos((da**2 + dc**2 - db**2) / (2 * da * dc));
+
+        // Is acute if both angles are < 90 degrees
+        // TODO: what about right triangles?
+        const isAcute = alpha < halfPi && beta < halfPi;
+
+        return isAcute ? [...acc, hc] : acc;
+      }, []).some(h => h <= shipRadius);
+
+      return cornerCollision || sideCollision;
+    }
+
     requestAnimationFrame(firstFrame);
 
     let start;
@@ -408,65 +446,12 @@
         drawEdges(trianglePts);
       }
 
-      // info.innerText = [...visibleTriangles].map(t => {
-      //   const [[ax, ay], [bx, by], [shipx, shipy]] =
-      //     t.getAttribute('points').split(' ').map(n => n.split(',').map(n => +n));
-      //
-      //   const da = distance(ax, ay, shipx, shipy);
-      //   const db = distance(bx, by, shipx, shipy);
-      //   const dc = distance(ax, ay, bx, by);
-      //   const s = (1 / 2) * (da + db + dc);
-      //   const hc = (2 / dc) * Math.sqrt(s * (s - da) * (s - db) * (s - dc));
-      //
-      //   const alpha = Math.acos((db**2 + dc**2 - da**2) / (2 * db * dc));
-      //   const beta = Math.acos((da**2 + dc**2 - db**2) / (2 * da * dc));
-      //
-      //   const PI = Math.PI / 2;
-      //   const acute = alpha < PI && beta < PI;
-      //
-      //   return `${da.toFixed(2)} ${db.toFixed(2)} ${dc.toFixed(2)} ${hc.toFixed(2)} ${alpha.toFixed(2)} ${beta.toFixed(2)}`;
-      // }).join('\n');
+      const collision = detectCollision(points, visibleTriangles);
 
-      // can do this after side collision detection
-      // const ts = updateTriangles(position);
-      // const corners = ts.reduce((acc, t) => {
-      //   const [a, b,] = t.getAttribute('points').split(' ');
-      //   // return p.map(t => t.split(','));
-      //   // acc.push(a);
-      //   // acc.push(b);
-      //   return [a, b, ...acc];
-      // }, []);
-      //
-      // const uniqueCorners = [...new Set(corners)].map(n => n.split(',').map(n => +n));
-
-      const cornerCollision = points.some(([x, y]) => {
-        cornerPt.x = x - positionX;
-        cornerPt.y = y - positionY;
-
-        return shipBody.isPointInFill(cornerPt);
-      });
-
-      const shipRadius = 5;
-      const sideCollision = [...visibleTriangles].reduce((acc, t) => {
-        const [[ax, ay], [bx, by], [shipx, shipy]] =
-          t.getAttribute('points').split(' ').map(n => n.split(',').map(n => +n));
-
-        const da = distance(ax, ay, shipx, shipy);
-        const db = distance(bx, by, shipx, shipy);
-        const dc = distance(ax, ay, bx, by);
-        const s = (1 / 2) * (da + db + dc);
-        const hc = (2 / dc) * Math.sqrt(s * (s - da) * (s - db) * (s - dc));
-        const alpha = Math.acos((db**2 + dc**2 - da**2) / (2 * db * dc));
-        const beta = Math.acos((da**2 + dc**2 - db**2) / (2 * da * dc));
-        const acute = alpha < halfPi && beta < halfPi;
-
-        return acute ? [...acc, hc] : acc;
-      }, []).some(h => h <= shipRadius);
-
-      wall.setAttribute('fill', cornerCollision || sideCollision ? 'red' : 'black');
+      wall.setAttribute('fill', collision ? 'red' : 'black');
       hitbox.style.transform = `translate(${positionX}px, ${positionY}px)`;
 
-      if (cornerCollision || sideCollision) {
+      if (collision) {
         // restart game
         zeroForTimer = timestamp;
         restart = true;