Added First Collision Video - Balls #1
Javidx9
7 years ago
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/*
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OneLoneCoder.com - Programming Balls! #1 Circle Vs Circle Collisions
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"..it's just balls bangin' together init..." - @Javidx9 |
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Disclaimer |
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~~~~~~~~~~ |
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I don't care what you use this for. It's intended to be educational, and perhaps |
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to the oddly minded - a little bit of fun. Please hack this, change it and use it |
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in any way you see fit. BUT, you acknowledge that I am not responsible for anything |
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bad that happens as a result of your actions. However, if good stuff happens, I |
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would appreciate a shout out, or at least give the blog some publicity for me. |
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Cheers! |
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Background |
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~~~~~~~~~~ |
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Collision detection engines can get quite complicated. This program shows the interactions |
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between circular objects of different sizes and masses. Use Left mouse button to select |
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and drag a ball to examin static collisions, and use Right mouse button to apply velocity |
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to the balls as if using a pool/snooker/billiards cue. |
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Author |
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~~~~~~ |
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Twitter: @javidx9 |
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Blog: www.onelonecoder.com |
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Video: |
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~~~~~~ |
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Part #1 https://youtu.be/LPzyNOHY3A4
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Last Updated: 21/01/2017 |
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*/ |
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#include <iostream> |
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#include <string> |
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using namespace std; |
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#include "olcConsoleGameEngine.h" |
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struct sBall |
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{ |
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float px, py; |
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float vx, vy; |
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float ax, ay; |
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float radius; |
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float mass; |
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int id; |
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}; |
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class CirclePhysics : public olcConsoleGameEngine |
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{ |
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public: |
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CirclePhysics() |
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{ |
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m_sAppName = L"Circle Physics"; |
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} |
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private: |
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vector<pair<float, float>> modelCircle; |
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vector<sBall> vecBalls; |
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sBall *pSelectedBall = nullptr; |
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// Adds a ball to the vector
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void AddBall(float x, float y, float r = 5.0f) |
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{ |
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sBall b; |
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b.px = x; b.py = y; |
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b.vx = 0; b.vy = 0; |
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b.ax = 0; b.ay = 0; |
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b.radius = r; |
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b.mass = r * 10.0f; |
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b.id = vecBalls.size(); |
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vecBalls.emplace_back(b); |
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} |
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public: |
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bool OnUserCreate() |
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{ |
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// Define Circle Model
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modelCircle.push_back({ 0.0f, 0.0f }); |
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int nPoints = 20; |
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for (int i = 0; i < nPoints; i++) |
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modelCircle.push_back({ cosf(i / (float)(nPoints - 1) * 2.0f * 3.14159f) , sinf(i / (float)(nPoints - 1) * 2.0f * 3.14159f) }); |
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float fDefaultRad = 8.0f; |
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//AddBall(ScreenWidth() * 0.25f, ScreenHeight() * 0.5f, fDefaultRad);
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//AddBall(ScreenWidth() * 0.75f, ScreenHeight() * 0.5f, fDefaultRad);
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// Add 10 Random Balls
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for (int i = 0; i <10; i++) |
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AddBall(rand() % ScreenWidth(), rand() % ScreenHeight(), rand() % 16 + 2); |
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return true; |
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} |
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bool OnUserUpdate(float fElapsedTime) |
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{ |
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auto DoCirclesOverlap = [](float x1, float y1, float r1, float x2, float y2, float r2) |
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{ |
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return fabs((x1 - x2)*(x1 - x2) + (y1 - y2)*(y1 - y2)) <= (r1 + r2)*(r1 + r2); |
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}; |
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auto IsPointInCircle = [](float x1, float y1, float r1, float px, float py) |
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{ |
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return fabs((x1 - px)*(x1 - px) + (y1 - py)*(y1 - py)) < (r1 * r1); |
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}; |
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if (m_mouse[0].bPressed || m_mouse[1].bPressed) |
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{ |
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pSelectedBall = nullptr; |
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for (auto &ball : vecBalls) |
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{ |
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if (IsPointInCircle(ball.px, ball.py, ball.radius, m_mousePosX, m_mousePosY)) |
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{ |
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pSelectedBall = &ball; |
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break; |
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} |
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} |
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} |
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if (m_mouse[0].bHeld) |
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{ |
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if (pSelectedBall != nullptr) |
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{ |
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pSelectedBall->px = m_mousePosX; |
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pSelectedBall->py = m_mousePosY; |
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} |
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} |
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if (m_mouse[0].bReleased) |
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{ |
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pSelectedBall = nullptr; |
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} |
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if (m_mouse[1].bReleased) |
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{ |
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if (pSelectedBall != nullptr) |
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{ |
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// Apply velocity
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pSelectedBall->vx = 5.0f * ((pSelectedBall->px) - (float)m_mousePosX); |
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pSelectedBall->vy = 5.0f * ((pSelectedBall->py) - (float)m_mousePosY); |
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} |
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pSelectedBall = nullptr; |
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} |
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vector<pair<sBall*, sBall*>> vecCollidingPairs; |
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// Update Ball Positions
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for (auto &ball : vecBalls) |
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{ |
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// Add Drag to emulate rolling friction
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ball.ax = -ball.vx * 0.8f;
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ball.ay = -ball.vy * 0.8f; |
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// Update ball physics
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ball.vx += ball.ax * fElapsedTime; |
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ball.vy += ball.ay * fElapsedTime; |
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ball.px += ball.vx * fElapsedTime; |
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ball.py += ball.vy * fElapsedTime; |
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// Wrap the balls around screen
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if (ball.px < 0) ball.px += (float)ScreenWidth(); |
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if (ball.px >= ScreenWidth()) ball.px -= (float)ScreenWidth(); |
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if (ball.py < 0) ball.py += (float)ScreenHeight(); |
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if (ball.py >= ScreenHeight()) ball.py -= (float)ScreenHeight(); |
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// Clamp velocity near zero
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if (fabs(ball.vx*ball.vx + ball.vy*ball.vy) < 0.01f) |
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{ |
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ball.vx = 0; |
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ball.vy = 0; |
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} |
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} |
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// Static collisions, i.e. overlap
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for (auto &ball : vecBalls) |
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{ |
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for (auto &target : vecBalls) |
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{ |
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if (ball.id != target.id) |
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{ |
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if (DoCirclesOverlap(ball.px, ball.py, ball.radius, target.px, target.py, target.radius)) |
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{ |
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// Collision has occured
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vecCollidingPairs.push_back({ &ball, &target }); |
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// Distance between ball centers
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float fDistance = sqrtf((ball.px - target.px)*(ball.px - target.px) + (ball.py - target.py)*(ball.py - target.py)); |
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// Calculate displacement required
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float fOverlap = 0.5f * (fDistance - ball.radius - target.radius); |
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// Displace Current Ball away from collision
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ball.px -= fOverlap * (ball.px - target.px) / fDistance; |
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ball.py -= fOverlap * (ball.py - target.py) / fDistance; |
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// Displace Target Ball away from collision
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target.px += fOverlap * (ball.px - target.px) / fDistance; |
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target.py += fOverlap * (ball.py - target.py) / fDistance; |
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} |
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} |
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} |
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} |
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// Now work out dynamic collisions
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for (auto c : vecCollidingPairs) |
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{ |
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sBall *b1 = c.first; |
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sBall *b2 = c.second; |
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// Distance between balls
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float fDistance = sqrtf((b1->px - b2->px)*(b1->px - b2->px) + (b1->py - b2->py)*(b1->py - b2->py)); |
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// Normal
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float nx = (b2->px - b1->px) / fDistance; |
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float ny = (b2->py - b1->py) / fDistance; |
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// Tangent
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float tx = -ny; |
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float ty = nx; |
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// Dot Product Tangent
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float dpTan1 = b1->vx * tx + b1->vy * ty; |
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float dpTan2 = b2->vx * tx + b2->vy * ty; |
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// Dot Product Normal
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float dpNorm1 = b1->vx * nx + b1->vy * ny; |
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float dpNorm2 = b2->vx * nx + b2->vy * ny; |
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// Conservation of momentum in 1D
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float m1 = (dpNorm1 * (b1->mass - b2->mass) + 2.0f * b2->mass * dpNorm2) / (b1->mass + b2->mass); |
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float m2 = (dpNorm2 * (b2->mass - b1->mass) + 2.0f * b1->mass * dpNorm1) / (b1->mass + b2->mass); |
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// Update ball velocities
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b1->vx = tx * dpTan1 + nx * m1; |
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b1->vy = ty * dpTan1 + ny * m1; |
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b2->vx = tx * dpTan2 + nx * m2; |
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b2->vy = ty * dpTan2 + ny * m2; |
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// Wikipedia Version - Maths is smarter but same
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//float kx = (b1->vx - b2->vx);
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//float ky = (b1->vy - b2->vy);
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//float p = 2.0 * (nx * kx + ny * ky) / (b1->mass + b2->mass);
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//b1->vx = b1->vx - p * b2->mass * nx;
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//b1->vy = b1->vy - p * b2->mass * ny;
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//b2->vx = b2->vx + p * b1->mass * nx;
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//b2->vy = b2->vy + p * b1->mass * ny;
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} |
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// Clear Screen
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Fill(0, 0, ScreenWidth(), ScreenHeight(), ' '); |
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// Draw Balls
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for (auto ball : vecBalls) |
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DrawWireFrameModel(modelCircle, ball.px, ball.py, atan2f(ball.vy, ball.vx), ball.radius, FG_WHITE); |
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// Draw static collisions
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for (auto c : vecCollidingPairs) |
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DrawLine(c.first->px, c.first->py, c.second->px, c.second->py, PIXEL_SOLID, FG_RED); |
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// Draw Cue
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if (pSelectedBall != nullptr) |
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DrawLine(pSelectedBall->px, pSelectedBall->py, m_mousePosX, m_mousePosY, PIXEL_SOLID, FG_BLUE); |
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return true; |
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} |
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}; |
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int main() |
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{ |
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CirclePhysics game; |
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if (game.ConstructConsole(160, 120, 8, 8)) |
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game.Start(); |
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else |
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wcout << L"Could not construct console" << endl; |
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return 0; |
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}; |
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