Example for creating balls with simple physics simulation (#5372)

* Example for creating balls with simple physics simulation

The goal of this example is to create several colored balls whose movement is simulated and which respond to the action of being grabbed and dragged using the mouse.

* renaming example

renaming example from physics_bouncing_balls to shapes_ball_physics

Author: davidbuzatto

examples/shapes/shapes_ball_physics.c

@@ -0,0 +1,222 @@
+/*******************************************************************************************
+*
+*   raylib [shapes] example - physics bouncing balls
+*
+*   Example complexity rating: [★★☆☆] 2/4
+*
+*   Example originally created with raylib 5.5
+*
+*   Example contributed by David Buzatto (@davidbuzatto) and reviewed by Ramon Santamaria (@raysan5)
+*
+*   Example licensed under an unmodified zlib/libpng license, which is an OSI-certified,
+*   BSD-like license that allows static linking with closed source software
+*
+*   Copyright (c) 2025 David Buzatto (@davidbuzatto)
+*
+********************************************************************************************/
+
+#include <stdlib.h>
+#include <math.h>
+#include "raylib.h"
+
+#define MAX_BALLS 5000 // Maximum quantity of balls
+
+typedef struct Ball {
+    Vector2 pos;       // Position
+    Vector2 vel;       // Velocity
+    Vector2 ppos;      // Previous position
+    float radius;
+    float friction;   
+    float elasticity;
+    Color color;
+    bool grabbed;
+} Ball;
+
+//------------------------------------------------------------------------------------
+// Program main entry point
+//------------------------------------------------------------------------------------
+int main(void)
+{
+    // Initialization
+    //--------------------------------------------------------------------------------------
+    const int screenWidth = 800;
+    const int screenHeight = 450;
+
+    InitWindow(screenWidth, screenHeight, "raylib [shapes] example - physics bouncing balls");
+
+    Ball balls[MAX_BALLS] = {{
+        .pos = {GetScreenWidth()/2, GetScreenHeight()/2},
+        .vel = {200, 200},
+        .ppos = {0},
+        .radius = 40,
+        .friction = 0.99,
+        .elasticity = 0.9,
+        .color = BLUE,
+        .grabbed = false
+    }};
+    
+    int ballQuantity = 1;
+    Ball *grabbedBall = NULL;   // A pointer to the current ball that is grabbed
+    Vector2 pressOffset = {0};  // Mouse press offset relative to the ball that grabbedd
+
+    float gravity = 100;        // World gravity
+
+    SetTargetFPS(60);           // Set our game to run at 60 frames-per-second
+    //---------------------------------------------------------------------------------------
+
+    // Main game loop
+    while (!WindowShouldClose())    // Detect window close button or ESC key
+    {
+        // Update
+        //----------------------------------------------------------------------------------
+        float delta = GetFrameTime();
+        Vector2 mousePos = GetMousePosition();
+
+        // Checks if a ball was grabbed
+        if (IsMouseButtonPressed(MOUSE_BUTTON_LEFT))
+        {
+            for (int i = ballQuantity - 1; i >= 0; i--) {
+
+                Ball *ball = &balls[i];
+                pressOffset.x = mousePos.x - ball->pos.x;
+                pressOffset.y = mousePos.y - ball->pos.y;
+
+                // If the distance between the ball position and the mouse press position
+                // is less or equal the ball radius, the event occured inside the ball
+                if (hypot(pressOffset.x, pressOffset.y) <= ball->radius)
+                {
+                    ball->grabbed = true;
+                    grabbedBall = ball;
+                    break;
+                }
+
+            }
+        }
+
+        // Releases any ball the was grabbed
+        if (IsMouseButtonReleased(MOUSE_BUTTON_LEFT))
+        {
+            if (grabbedBall != NULL)
+            {
+                grabbedBall->grabbed = false;
+                grabbedBall = NULL;
+            }
+        }
+
+        // Creates a new ball
+        if (IsMouseButtonPressed(MOUSE_BUTTON_RIGHT) || (IsKeyDown(KEY_LEFT_CONTROL) && IsMouseButtonDown(MOUSE_BUTTON_RIGHT))) {
+            if (ballQuantity < MAX_BALLS) {
+                balls[ballQuantity++] = (Ball) {
+                    .pos = mousePos,
+                    .vel = {GetRandomValue(-300, 300), GetRandomValue(-300, 300)},
+                    .ppos = {0},
+                    .radius = 20 + GetRandomValue(0, 30),
+                    .friction = 0.99,
+                    .elasticity = 0.9,
+                    .color = {GetRandomValue(0, 255), GetRandomValue(0, 255), GetRandomValue(0, 255), 255},
+                    .grabbed = false
+                };
+            }
+        }
+
+        // Shake balls
+        if (IsMouseButtonPressed(MOUSE_BUTTON_MIDDLE)) {
+            for (int i = 0; i < ballQuantity; i++) {
+                Ball *ball = &balls[i];
+                if (!ball->grabbed) {
+                    ball->vel = (Vector2) {GetRandomValue(-2000, 2000), GetRandomValue(-2000, 2000)};
+                }
+            }
+        }
+
+        // Changes gravity
+        gravity += GetMouseWheelMove() * 5;
+
+        // Updates each ball state
+        for (int i = 0; i < ballQuantity; i++) {
+
+            Ball *ball = &balls[i];
+
+            // The ball is not grabbed
+            if (!ball->grabbed) 
+            {
+                // Ball repositioning using the velocity
+                ball->pos.x += ball->vel.x * delta;
+                ball->pos.y += ball->vel.y * delta;
+
+                // Does the ball hit the screen right boundary?
+                if (ball->pos.x + ball->radius >= screenWidth) 
+                {
+                    ball->pos.x = screenWidth - ball->radius; // Ball repositioning
+                    ball->vel.x = -ball->vel.x * ball->elasticity;  // Elasticity makes the ball lose 10% of its velocity on hit
+                } 
+                // Does the ball hit the screen left boundary?
+                else if (ball->pos.x - ball->radius <= 0)
+                { 
+                    ball->pos.x = ball->radius;
+                    ball->vel.x = -ball->vel.x * ball->elasticity;
+                }
+
+                // The same for y axis
+                if (ball->pos.y + ball->radius >= screenHeight) 
+                {
+                    ball->pos.y = screenHeight - ball->radius;
+                    ball->vel.y = -ball->vel.y * ball->elasticity;
+                } 
+                else if (ball->pos.y - ball->radius <= 0) 
+                { 
+                    ball->pos.y = ball->radius;
+                    ball->vel.y = -ball->vel.y * ball->elasticity;
+                }
+
+                // Friction makes the ball lose 1% of its velocity each frame
+                ball->vel.x = ball->vel.x * ball->friction;
+                // Gravity affects only the y axis
+                ball->vel.y = ball->vel.y * ball->friction + gravity;
+
+            }
+            else
+            {
+                // Ball repositioning using the mouse position
+                ball->pos.x = mousePos.x - pressOffset.x;
+                ball->pos.y = mousePos.y - pressOffset.y;
+                // While the ball is grabbed, recalculates its velocity
+                ball->vel.x = (ball->pos.x - ball->ppos.x) / delta;
+                ball->vel.y = (ball->pos.y - ball->ppos.y) / delta;
+                ball->ppos = ball->pos;
+            }
+        }
+        
+        //----------------------------------------------------------------------------------
+
+        // Draw
+        //----------------------------------------------------------------------------------
+        BeginDrawing();
+
+            ClearBackground(RAYWHITE);
+
+            for (int i = 0; i < ballQuantity; i++)
+            {
+                Ball *ball = &balls[i];
+                DrawCircleV(ball->pos, ball->radius, ball->color);
+                DrawCircleLinesV(ball->pos, ball->radius, BLACK);
+            }
+
+            DrawText("grab a ball by pressing with the mouse and throw it by releasing", 10, 10, 20, DARKGRAY);
+            DrawText("right click to create new balls (keep left control pressed to create a lot)", 10, 30, 20, DARKGRAY);
+            DrawText("use mouse wheel to change gravity", 10, 50, 20, DARKGRAY);
+            DrawText("middle click to shake", 10, 70, 20, DARKGRAY);
+            DrawText(TextFormat("ball quantity: %d", ballQuantity), 10, GetScreenHeight() - 55, 20, BLACK);
+            DrawText(TextFormat("gravity: %.2f", gravity), 10, GetScreenHeight() - 35, 20, BLACK);
+
+        EndDrawing();
+        //----------------------------------------------------------------------------------
+    }
+
+    // De-Initialization
+    //--------------------------------------------------------------------------------------
+    CloseWindow();        // Close window and OpenGL context
+    //--------------------------------------------------------------------------------------
+
+    return 0;
+}