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following eyes

★★☆☆by Ramon Santamaria (@raysan5)

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//! raylib [shapes] example - following eyes
//!
//! Zig-API translation of examples/shapes/shapes_following_eyes.c (raylib 6.2).
//! Example licensed under an unmodified zlib/libpng license.
//! Copyright (c) 2013-2025 Ramon Santamaria (@raysan5)

const std = @import("std");
const rl = @import("raylib");

/// Keep the iris inside the sclera: if it would leave, clamp it to the rim
/// along the direction from the sclera center.
fn clampIris(iris: rl.Vector2, sclera: rl.Vector2, max_distance: f32) rl.Vector2 {
    if (rl.checkCollisionPointCircle(iris, sclera, max_distance)) return iris;

    const angle = std.math.atan2(iris.y - sclera.y, iris.x - sclera.x);
    return .{
        .x = sclera.x + max_distance * @cos(angle),
        .y = sclera.y + max_distance * @sin(angle),
    };
}

pub fn main() void {
    // Initialization
    const screen_width = 800;
    const screen_height = 450;

    rl.initWindow(screen_width, screen_height, "raylib [shapes] example - following eyes");
    defer rl.closeWindow(); // Close window and OpenGL context

    const half_width = @as(f32, @floatFromInt(rl.getScreenWidth())) / 2.0;
    const half_height = @as(f32, @floatFromInt(rl.getScreenHeight())) / 2.0;

    const sclera_left_position: rl.Vector2 = .{ .x = half_width - 100.0, .y = half_height };
    const sclera_right_position: rl.Vector2 = .{ .x = half_width + 100.0, .y = half_height };
    const sclera_radius: f32 = 80;
    const iris_radius: f32 = 24;

    rl.setTargetFPS(60); // Set our game to run at 60 frames-per-second

    // Main game loop
    while (!rl.windowShouldClose()) { // Detect window close button or ESC key
        // Update
        const iris_left_position = clampIris(rl.getMousePosition(), sclera_left_position, sclera_radius - iris_radius);
        const iris_right_position = clampIris(rl.getMousePosition(), sclera_right_position, sclera_radius - iris_radius);

        // Draw
        rl.beginDrawing();
        defer rl.endDrawing();

        rl.clearBackground(.ray_white);

        rl.drawCircleV(sclera_left_position, sclera_radius, .light_gray);
        rl.drawCircleV(iris_left_position, iris_radius, .brown);
        rl.drawCircleV(iris_left_position, 10, .black);

        rl.drawCircleV(sclera_right_position, sclera_radius, .light_gray);
        rl.drawCircleV(iris_right_position, iris_radius, .dark_green);
        rl.drawCircleV(iris_right_position, 10, .black);

        rl.drawFPS(10, 10);
    }
}
/*******************************************************************************************
*
*   raylib [shapes] example - following eyes
*
*   Example complexity rating: [★★☆☆] 2/4
*
*   Example originally created with raylib 2.5, last time updated with raylib 2.5
*
*   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) 2013-2025 Ramon Santamaria (@raysan5)
*
********************************************************************************************/

#include "raylib.h"

#include <math.h>       // Required for: atan2f()

//------------------------------------------------------------------------------------
// Program main entry point
//------------------------------------------------------------------------------------
int main(void)
{
    // Initialization
    //--------------------------------------------------------------------------------------
    const int screenWidth = 800;
    const int screenHeight = 450;

    InitWindow(screenWidth, screenHeight, "raylib [shapes] example - following eyes");

    Vector2 scleraLeftPosition = { GetScreenWidth()/2.0f - 100.0f, GetScreenHeight()/2.0f };
    Vector2 scleraRightPosition = { GetScreenWidth()/2.0f + 100.0f, GetScreenHeight()/2.0f };
    float scleraRadius = 80;

    Vector2 irisLeftPosition = { GetScreenWidth()/2.0f - 100.0f, GetScreenHeight()/2.0f };
    Vector2 irisRightPosition = { GetScreenWidth()/2.0f + 100.0f, GetScreenHeight()/2.0f };
    float irisRadius = 24;

    float angle = 0.0f;
    float dx = 0.0f, dy = 0.0f, dxx = 0.0f, dyy = 0.0f;

    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
        //----------------------------------------------------------------------------------
        irisLeftPosition = GetMousePosition();
        irisRightPosition = GetMousePosition();

        // Check not inside the left eye sclera
        if (!CheckCollisionPointCircle(irisLeftPosition, scleraLeftPosition, scleraRadius - irisRadius))
        {
            dx = irisLeftPosition.x - scleraLeftPosition.x;
            dy = irisLeftPosition.y - scleraLeftPosition.y;

            angle = atan2f(dy, dx);

            dxx = (scleraRadius - irisRadius)*cosf(angle);
            dyy = (scleraRadius - irisRadius)*sinf(angle);

            irisLeftPosition.x = scleraLeftPosition.x + dxx;
            irisLeftPosition.y = scleraLeftPosition.y + dyy;
        }

        // Check not inside the right eye sclera
        if (!CheckCollisionPointCircle(irisRightPosition, scleraRightPosition, scleraRadius - irisRadius))
        {
            dx = irisRightPosition.x - scleraRightPosition.x;
            dy = irisRightPosition.y - scleraRightPosition.y;

            angle = atan2f(dy, dx);

            dxx = (scleraRadius - irisRadius)*cosf(angle);
            dyy = (scleraRadius - irisRadius)*sinf(angle);

            irisRightPosition.x = scleraRightPosition.x + dxx;
            irisRightPosition.y = scleraRightPosition.y + dyy;
        }
        //----------------------------------------------------------------------------------

        // Draw
        //----------------------------------------------------------------------------------
        BeginDrawing();

            ClearBackground(RAYWHITE);

            DrawCircleV(scleraLeftPosition, scleraRadius, LIGHTGRAY);
            DrawCircleV(irisLeftPosition, irisRadius, BROWN);
            DrawCircleV(irisLeftPosition, 10, BLACK);

            DrawCircleV(scleraRightPosition, scleraRadius, LIGHTGRAY);
            DrawCircleV(irisRightPosition, irisRadius, DARKGREEN);
            DrawCircleV(irisRightPosition, 10, BLACK);

            DrawFPS(10, 10);

        EndDrawing();
        //----------------------------------------------------------------------------------
    }

    // De-Initialization
    //--------------------------------------------------------------------------------------
    CloseWindow();        // Close window and OpenGL context
    //--------------------------------------------------------------------------------------

    return 0;
}

From raylib 6.2. The original on GitHub.