[examples] shapes_collision_ellipses

examples/shapes/shapes_ellipse_collision.c

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+/*******************************************************************************************
+*
+*   raylib [shapes] example - ellipse collision
+*
+*   Example complexity rating: [★★☆☆] 2/4
+*
+*   Example originally created with raylib 5.5, last time updated with raylib 5.5
+*
+*   Example contributed by Ziya (@Monjaris)
+*
+*   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 Ziya (@Monjaris)
+*
+********************************************************************************************/
+
+#include "raylib.h"
+#include <math.h>
+
+// Check if point is inside ellipse
+static bool CheckCollisionPointEllipse(Vector2 point, Vector2 center, float rx, float ry)
+{
+    float dx = (point.x - center.x)/rx;
+    float dy = (point.y - center.y)/ry;
+    return (dx*dx + dy*dy) <= 1.0f;
+}
+
+// Check if two ellipses collide
+// Uses radial boundary distance in the direction between centers — scales correctly with radii
+static bool CheckCollisionEllipses(Vector2 c1, float rx1, float ry1, Vector2 c2, float rx2, float ry2)
+{
+    float dx = c2.x - c1.x;
+    float dy = c2.y - c1.y;
+    float dist = sqrtf(dx*dx + dy*dy);
+
+    // Ellipses are on top of each other
+    if (dist == 0.0f) return true;
+
+    float theta = atan2f(dy, dx);
+    float cosT = cosf(theta);
+    float sinT = sinf(theta);
+
+    // Radial distance from center to ellipse boundary in direction theta
+    // r(theta) = (rx * ry) / sqrt((ry*cos)^2 + (rx*sin)^2)
+    float r1 = (rx1*ry1)/sqrtf((ry1*cosT)*(ry1*cosT) + (rx1*sinT)*(rx1*sinT));
+    float r2 = (rx2*ry2)/sqrtf((ry2*cosT)*(ry2*cosT) + (rx2*sinT)*(rx2*sinT));
+
+    return dist <= (r1 + r2);
+}
+
+//------------------------------------------------------------------------------------
+// Program main entry point
+//------------------------------------------------------------------------------------
+int main(void)
+{
+    // Initialization
+    //--------------------------------------------------------------------------------------
+    const int screenWidth = 800;
+    const int screenHeight = 450;
+
+    InitWindow(screenWidth, screenHeight, "raylib [shapes] example - collision ellipses");
+    SetTargetFPS(60);
+
+    Vector2 ellipseACenter = { (float)screenWidth/4, (float)screenHeight/2 };
+    float ellipseARx = 120.0f;
+    float ellipseARy = 70.0f;
+
+    Vector2 ellipseBCenter = { (float)screenWidth*3/4, (float)screenHeight/2 };
+    float ellipseBRx = 90.0f;
+    float ellipseBRy = 140.0f;
+
+    // 0 = controlling A, 1 = controlling B
+    int controlled = 0;
+
+    //--------------------------------------------------------------------------------------
+
+    // Main game loop
+    while (!WindowShouldClose())    // Detect window close button or ESC key
+    {
+        // Update
+        //----------------------------------------------------------------------------------
+        if (IsKeyPressed(KEY_A)) controlled = 0;
+        if (IsKeyPressed(KEY_B)) controlled = 1;
+
+        if (controlled == 0) ellipseACenter = GetMousePosition();
+        else ellipseBCenter = GetMousePosition();
+
+        bool ellipsesCollide = CheckCollisionEllipses(
+            ellipseACenter, ellipseARx, ellipseARy,
+            ellipseBCenter, ellipseBRx, ellipseBRy
+        );
+
+        bool mouseInA = CheckCollisionPointEllipse(GetMousePosition(), ellipseACenter, ellipseARx, ellipseARy);
+        bool mouseInB = CheckCollisionPointEllipse(GetMousePosition(), ellipseBCenter, ellipseBRx, ellipseBRy);
+        //----------------------------------------------------------------------------------
+
+        // Draw
+        //----------------------------------------------------------------------------------
+        BeginDrawing();
+
+            ClearBackground(RAYWHITE);
+
+            DrawEllipse((int)ellipseACenter.x, (int)ellipseACenter.y, ellipseARx, ellipseARy, ellipsesCollide ? RED : BLUE);
+
+            DrawEllipse((int)ellipseBCenter.x, (int)ellipseBCenter.y, ellipseBRx, ellipseBRy, ellipsesCollide ? RED : GREEN);
+
+            DrawEllipseLines((int)ellipseACenter.x, (int)ellipseACenter.y, ellipseARx, ellipseARy, WHITE);
+
+            DrawEllipseLines((int)ellipseBCenter.x, (int)ellipseBCenter.y, ellipseBRx, ellipseBRy, WHITE);
+
+            DrawCircleV(ellipseACenter, 4, WHITE);
+            DrawCircleV(ellipseBCenter, 4, WHITE);
+
+            if (ellipsesCollide) DrawText("ELLIPSES COLLIDE", screenWidth/2 - 120, 40, 28, RED);
+            else DrawText("NO COLLISION", screenWidth/2 - 80, 40, 28, DARKGRAY);
+
+            DrawText(controlled == 0 ? "Controlling: A" : "Controlling: B", 20, screenHeight - 40, 20, YELLOW);
+
+            if (mouseInA && controlled != 0) DrawText("Mouse inside ellipse A", 20, screenHeight - 70, 20, BLUE);
+            if (mouseInB && controlled != 1) DrawText("Mouse inside ellipse B", 20, screenHeight - 70, 20, GREEN);
+
+            DrawText("Press [A] or [B] to switch control", 20, 20, 20, GRAY);
+
+        EndDrawing();
+        //----------------------------------------------------------------------------------
+    }
+
+    // De-Initialization
+    CloseWindow();
+
+    return 0;
+}