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  • Mass Ball-to-Ball Collision Handling (as in, lots of balls)

    - by BlueThen
    Update: Found out that I was using the radius as the diameter, which was why the mtd was overcompensating. Hi, StackOverflow. I've written a Processing program awhile back simulating ball physics. Basically, I have a large number of balls (1000), with gravity turned on. Detection works great, but my issue is that they start acting weird when they're bouncing against other balls in all directions. I'm pretty confident this involves the handling. For the most part, I'm using Jay Conrod's code. One part that's different is if (distance > 1.0) return; which I've changed to if (distance < 1.0) return; because the collision wasn't even being performed with the first bit of code, I'm guessing that's a typo. The balls overlap when I use his code, which isn't what I was looking for. My attempt to fix it was to move the balls to the edge of each other: float angle = atan2(y - collider.y, x - collider.x); float distance = dist(x,y, balls[ID2].x,balls[ID2].y); x = collider.x + radius * cos(angle); y = collider.y + radius * sin(angle); This isn't correct, I'm pretty sure of that. I tried the correction algorithm in the previous ball-to-ball topic: // get the mtd Vector2d delta = (position.subtract(ball.position)); float d = delta.getLength(); // minimum translation distance to push balls apart after intersecting Vector2d mtd = delta.multiply(((getRadius() + ball.getRadius())-d)/d); // resolve intersection -- // inverse mass quantities float im1 = 1 / getMass(); float im2 = 1 / ball.getMass(); // push-pull them apart based off their mass position = position.add(mtd.multiply(im1 / (im1 + im2))); ball.position = ball.position.subtract(mtd.multiply(im2 / (im1 + im2))); except my version doesn't use vectors, and every ball's weight is 1. The resulting code I get is this: PVector delta = new PVector(collider.x - x, collider.y - y); float d = delta.mag(); PVector mtd = new PVector(delta.x * ((radius + collider.radius - d) / d), delta.y * ((radius + collider.radius - d) / d)); // push-pull apart based on mass x -= mtd.x * 0.5; y -= mtd.y * 0.5; collider.x += mtd.x * 0.5; collider.y += mtd.y * 0.5; This code seems to over-correct collisions. Which doesn't make sense to me because in no other way do I modify the x and y values of each ball, other than this. Some other part of my code could be wrong, but I don't know. Here's the snippet of the entire ball-to-ball collision handling I'm using: if (alreadyCollided.contains(new Integer(ID2))) // if the ball has already collided with this, then we don't need to reperform the collision algorithm return; Ball collider = (Ball) objects.get(ID2); PVector collision = new PVector(x - collider.x, y - collider.y); float distance = collision.mag(); if (distance == 0) { collision = new PVector(1,0); distance = 1; } if (distance < 1) return; PVector velocity = new PVector(vx,vy); PVector velocity2 = new PVector(collider.vx, collider.vy); collision.div(distance); // normalize the distance float aci = velocity.dot(collision); float bci = velocity2.dot(collision); float acf = bci; float bcf = aci; vx += (acf - aci) * collision.x; vy += (acf - aci) * collision.y; collider.vx += (bcf - bci) * collision.x; collider.vy += (bcf - bci) * collision.y; alreadyCollided.add(new Integer(ID2)); collider.alreadyCollided.add(new Integer(ID)); PVector delta = new PVector(collider.x - x, collider.y - y); float d = delta.mag(); PVector mtd = new PVector(delta.x * ((radius + collider.radius - d) / d), delta.y * ((radius + collider.radius - d) / d)); // push-pull apart based on mass x -= mtd.x * 0.2; y -= mtd.y * 0.2; collider.x += mtd.x * 0.2; collider.y += mtd.y * 0.2; Thanks. (Apologies for lack of sources, stackoverflow thinks I'm a spammer)

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  • C++ Linked List - Reading data from a file with a sentinel

    - by Nick
    So I've done quite a bit of research on this and can't get my output to work correctly. I need to read in data from a file and have it stored into a Linked List. The while loop used should stop once it hits the $$$$$ sentinel. Then I am to display the data (by searching by ID Number[user input]) I am not that far yet I just want to properly display the data and get it read in for right now. My problem is when it displays the data is isn't stopping at the $$$$$ (even if I do "inFile.peek() != EOF and omit the $$$$$) I am still getting an extra garbage record. I know it has something to do with my while loop and how I am creating a new Node but I can't get it to work any other way. Any help would be appreciated. students.txt Nick J Cooley 324123 60 70 80 90 Jay M Hill 412254 70 80 90 100 $$$$$ assign6.h file #pragma once #include <iostream> #include <string> using namespace std; class assign6 { public: assign6(); // constructor void displayStudents(); private: struct Node { string firstName; string midIni; string lastName; int idNum; int sco1; //Test score 1 int sco2; //Test score 2 int sco3; //Test score 3 int sco4; //Test score 4 Node *next; }; Node *head; Node *headPtr; }; assign6Imp.cpp // Implementation File #include "assign6.h" #include <fstream> #include <iostream> #include <string> using namespace std; assign6::assign6() //constructor { ifstream inFile; inFile.open("students.txt"); head = NULL; head = new Node; headPtr = head; while (inFile.peek() != EOF) //reading in from file and storing in linked list { inFile >> head->firstName >> head->midIni >> head->lastName; inFile >> head->idNum; inFile >> head->sco1; inFile >> head->sco2; inFile >> head->sco3; inFile >> head->sco4; if (inFile != "$$$$$") { head->next = NULL; head->next = new Node; head = head->next; } } head->next = NULL; inFile.close(); } void assign6::displayStudents() { int average = 0; for (Node *cur = headPtr; cur != NULL; cur = cur->next) { cout << cur->firstName << " " << cur->midIni << " " << cur->lastName << endl; cout << cur->idNum << endl; average = (cur->sco1 + cur->sco2 + cur->sco3 + cur->sco4)/4; cout << cur->sco1 << " " << cur->sco2 << " " << cur->sco3 << " " << cur->sco4 << " " << "average: " << average << endl; } }

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