Added First Collision Video - Balls #1

OneLoneCoder_Balls1.cpp

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