From: Elijah Cohen <eli@eli173.com>
Date: Thu, 2 May 2019 06:56:31 +0000 (-0500)
Subject: some collision logic, getting started
X-Git-Url: https://git.eli173.com/?a=commitdiff_plain;h=483c71fcc5ca47a4bfafc30d189cace3ffe9fd29;p=pong_br

some collision logic, getting started
---

diff --git a/.gitignore b/.gitignore
index 40198b0..2a43901 100644
--- a/.gitignore
+++ b/.gitignore
@@ -35,3 +35,4 @@ server/node_modules/*
 /web/draw.js~
 /web/main.js~
 /web/play.html~
+/server/collisions.js~
diff --git a/server/collisions.js b/server/collisions.js
new file mode 100644
index 0000000..62aab48
--- /dev/null
+++ b/server/collisions.js
@@ -0,0 +1,88 @@
+
+const Coord = require('./coord.js');
+
+const Endpoints = require('./endpoints.js'); // i guess slightly useful here
+
+/*
+ * okay, game plan:
+ * we look at line segments: the segments from the endpoints,
+ * and segments defined by the balls' current and future positions
+ * 
+ * once that is done, I still need to fix the bounce issue.
+ * dunno if that part is good or not. i suspect it's okay
+*/
+
+function nearest_point_on_line(c, ep) {
+    // finds the point on the line defined by ep closest to center c
+    if(ep.f.x == ep.s.x) {
+	// vertical line, undef slope
+	return new Coord(ep.f.x, c.y);
+    }
+    if(ep.f.y == ep.s.y) {
+	// horizontal line, zero slope
+	return new Coord(c.x, ep.f.y);
+    }
+    var sl = (ep.f.y-ep.s.y)/(ep.f.x-ep.s.x);
+    var sr = 1/sl;
+    var x_int = (sl*ep.f.x - sr*c.x + c.y - ep.f.y)/(sl-sr);
+    var y_int = sr*(x_int-c.x) + c.y;
+    return new Coord(x_int, y_int);
+}
+
+
+var segments_intersect = function(e1, e2) {
+    // takes 2 sets of endpoints for the segments
+    // start with simple checks to rule things out
+    // don't need to do these actually, math not intensive plus crucial checks done afterwards
+    // if(Math.max(e1.f.x,e1.s.x) < Math.min(e2.f.x, e2.s.x))
+    // 	return false;
+    // if(Math.max(e1.f.y,e1.s.y) < Math.min(e2.f.y, e2.s.y))
+    // 	return false;
+    // if(Math.max(e2.f.x,e2.s.x) < Math.min(e1.f.x, e1.s.x))
+    // 	return false;
+    // if(Math.max(e2.f.y,e2.s.y) < Math.min(e1.f.y, e1.s.y))
+    // 	return false;
+    // now bounding rectangles at least overlap
+    // get the intersection of the /lines/, then check both rectangles for that point
+    var x1 = e1.f.x;
+    var y1 = e1.f.y;
+    var x2 = e1.s.x;
+    var y2 = e1.s.y;
+    var x3 = e2.f.x;
+    var y3 = e2.f.y;
+    var x4 = e2.s.x;
+    var y4 = e2.s.y;
+    // first check if parallel, with nice algebra to avoid verticality issues
+    if((x3-x4)*(y1-y2) == (x1-x2)*(y3-y4))
+	return false;
+    // stolen from wikipedia
+    var x_val = ((x1*y2-y1*x2)*(x3-x4)-(x1-x2)*(x3*y4-y3*x4))/((x1-x2)*(y3-y4)-(y1-y2)*(x3-x4));
+    var y_val = ((x1*y2-y1*x2)*(y3-y4)-(y1-y2)*(x3*y4-y3*x4))/((x1-x2)*(y3-y4)-(y1-y2)*(x3-x4));
+    if(Math.min(e1.x, e2.x) < x_val && x_val < Math.max(e1.x, e2.x))
+	return false;
+    if(Math.min(e1.y, e2.y) < y_val && y_val < Math.max(e1.y, e2.y))
+	return false;
+    if(Math.min(e2.x, e1.x) < x_val && x_val < Math.max(e2.x, e1.x))
+	return false;
+    if(Math.min(e2.y, e1.y) < y_val && y_val < Math.max(e2.y, e1.y))
+	return false;
+    return true;
+}
+
+var handleWalls = function(ball, walls) {
+    // returns true if there's a collision
+    for(var wall of walls) {
+	var nearest = nearest_point_on_line(ball.coord, wall);
+	if(ball.coord.dist2(nearest) < (ball.radius)**2) { // there's a collision
+	    // so the midpoint of the wall gives a nice normal vector
+	    var norm = ball.coord;
+	}
+    }
+
+}
+
+var handlePaddles = function() {
+
+}
+
+module.exports = {handleWalls: handleWalls, handlePaddles, handlePaddles};