WIP: altitude foot point coords

html/images/space.svg

@@ -1,6 +1,6 @@
 <?xml version="1.0" encoding="UTF-8" standalone="no"?>
 <!-- <svg viewBox="-200 -150 400 300" version="1.1" xmlns="http://www.w3.org/2000/svg"> -->
-<svg viewBox="-10 -10 50 50" version="1.1" xmlns="http://www.w3.org/2000/svg">
+<svg viewBox="-10 -10 60 60" version="1.1" xmlns="http://www.w3.org/2000/svg">
   <style>
     foreignObject {
       font-size: 4pt;
@@ -63,6 +63,10 @@
       display: none;
     }
 
+    line {
+      stroke: red;
+    }
+
     .wall.inverse {
       fill: gray;
     }
@@ -81,7 +85,9 @@
     </g>
   </g>
 
-  <polygon class="wall" points="20,20 40,20 40,40 20,40" />
+  <!-- <polygon class="wall" points="20,20 30,20 40,40 20,40" /> -->
+  <polygon class="wall" points="20,20 30,20 40,40 10,40" />
+  <!-- <polygon class="wall" points="20,20 40,20 40,40 20,40" /> -->
   <!-- <polygon class="wall" points="10,10 20,10 20,20 10,20" /> -->
   <!-- <polygon class="wall" points="20,-50 -50,-50 -60,-70 -50,-100 80,-100 80,-90 -20,-90 -20,-60 40,-60 40,40 20,40" /> -->
   <!-- <polygon class="wall" points="-10,-30 -10,-40 30,-50 60,-30 80,0 150,0 150,10 60,50 -10,40 -20,20 20,20 20,-20" /> -->
@@ -418,6 +424,15 @@
       });
     }
 
+    function drawLine(xa, ya, xb, yb) {
+      const el = document.createElementNS(namespaceURIsvg, 'line');
+      el.setAttribute('x1', xa);
+      el.setAttribute('y1', ya);
+      el.setAttribute('x2', xb);
+      el.setAttribute('y2', yb);
+      svg.appendChild(el);
+    }
+
     function slope({ xa, ya, xb, yb }) {
       // const [[xa, ya], [xb, yb]] = edge.split(' ').map(n => n.split(',').map(n => +n));
       return (yb - ya) / (xb - xa);
@@ -428,17 +443,54 @@
       return Object.is(slope(edge), +0);
     }
 
-    // i need to know which edge
+    // i need to know the point of collision to position the ship adjacent to it
-    function detectEdgeCollision([xc, yc], edge, edgee) {
+    function detectEdgeCollision([xc, yc], edge, { xa, ya, xb, yb }) {
-      // console.log("edge", edge, "edgee", edgee);
       const shipRadius = 5;
-      const [[xa, ya], [xb, yb]] = edge.split(' ').map(n => n.split(',').map(n => +n));
+      // const [[xa, ya], [xb, yb]] = edge.split(' ').map(n => n.split(',').map(n => +n));
 
       const da = distance(xa, ya, xc, yc);
       const db = distance(xb, yb, xc, yc);
       // TODO: calculate this one ahead of time
       const dc = distance(xa, ya, xb, yb);
 
+      const baseSlope = slope({ xa, ya, xb, yb });
+
+      console.log("slope of base", baseSlope);
+
+      if (baseSlope === -Infinity) {
+        console.log("foot", xa + shipRadius, yc);
+      } else if (baseSlope === Infinity) {
+        console.log("foot", xa - shipRadius, yc);
+      } else if (Object.is(baseSlope, 0)) {
+        console.log("foot", xc, ya - shipRadius);
+      } else if (Object.is(baseSlope, -0)) {
+        console.log("foot", xc, ya + shipRadius);
+      } else {
+        console.log(xa, ya, xb, yb);
+        // 10, 40, 20, 20
+        // altitude slope (perpendicular of base)
+        const altitudeSlope = 1 / -baseSlope;
+        // point-slope formula
+        // y - ya = baseSlope * (x - xa)
+        // line equation of the base
+        // y = baseSlope * x - baseSlope * xa + ya
+        // y = -2x - (-2 * 10) + 40
+        // point-slope formula
+        // y - yc = altitudeSlope * (x - xc)
+        // line equation of the altitude
+        // y = altitudeSlope * x - altitudeSlope * xc + yc
+
+        // test point c 0, 20
+
+        // baseSlope * x - baseSlope * xa + ya = altitudeSlope * x - altitudeSlope * xc + yc
+        // baseSlope * x - altitudeSlope * x = -altitudeSlope * xc + yc + baseSlope * xa - ya
+        const isx = (-altitudeSlope * xc + yc + baseSlope * xa - ya) / (baseSlope - altitudeSlope);
+        const isy = altitudeSlope * isx - altitudeSlope * xc + yc;
+        // should be (35, 30)
+        console.log("foot coords", isx, isy);
+        drawLine(isx, isy, xc, yc);
+      }
+
       // 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);
@@ -529,7 +581,7 @@
       s.collision = detectCollisions(position, allWallCorners, findAllEdges(allEdgePts, position), getCollisionEdges(edgeszz, position));
 
       if (s.collision && !isLandable(s.collision.edge)) {
-        console.log("a");
+        console.log("a", "position", position, s.position);
         s.velocity = { x: 0, y: 0 };
       } else if (s.collision) {
         console.log("b", position, s.position);