add following eyes example

examples/shapes/following_eyes.zig

@@ -0,0 +1,85 @@
+const std = @import("std");
+const math = std.math;
+const rl = @import("raylib");
+
+pub fn main() anyerror!void {
+    // Initialization
+    //--------------------------------------------------------------------------------------
+    const screenWidth = 800;
+    const screenHeight = 450;
+
+    rl.initWindow(screenWidth, screenHeight, "raylib-zig [shapes] example - following eyes");
+    defer rl.closeWindow(); // Close window and OpenGL context
+
+    const scleraLeftPosition = rl.Vector2{ .x = @as(f32, @floatFromInt(rl.getScreenWidth())) / 2.0 - 100.0, .y = @as(f32, @floatFromInt(rl.getScreenHeight())) / 2.0 };
+    const scleraRightPosition = rl.Vector2{ .x = @as(f32, @floatFromInt(rl.getScreenWidth())) / 2.0 + 100.0, .y = @as(f32, @floatFromInt(rl.getScreenHeight())) / 2.0 };
+    const scleraRadius: i32 = 80;
+
+    var irisLeftPosition = rl.Vector2{ .x = @as(f32, @floatFromInt(rl.getScreenWidth())) / 2.0 - 100.0, .y = @as(f32, @floatFromInt(rl.getScreenHeight())) / 2.0 };
+    var irisRightPosition = rl.Vector2{ .x = @as(f32, @floatFromInt(rl.getScreenWidth())) / 2.0 + 100.0, .y = @as(f32, @floatFromInt(rl.getScreenHeight())) / 2.0 };
+    const irisRadius: i32 = 24;
+
+    var angle: f32 = 0.0;
+    var dx: f32 = 0.0;
+    var dy: f32 = 0.0;
+    var dxx: f32 = 0.0;
+    var dyy: f32 = 0.0;
+
+    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
+        //----------------------------------------------------------------------------------
+        irisLeftPosition = rl.getMousePosition();
+        irisRightPosition = rl.getMousePosition();
+
+        // Check not inside the left eye sclera
+        if (!rl.checkCollisionPointCircle(irisLeftPosition, scleraLeftPosition, scleraRadius - irisRadius)) {
+            dx = irisLeftPosition.x - scleraLeftPosition.x;
+            dy = irisLeftPosition.y - scleraLeftPosition.y;
+
+            angle = math.atan2(dy, dx);
+
+            dxx = (scleraRadius - irisRadius) * math.cos(angle);
+            dyy = (scleraRadius - irisRadius) * math.sin(angle);
+
+            irisLeftPosition.x = scleraLeftPosition.x + dxx;
+            irisLeftPosition.y = scleraLeftPosition.y + dyy;
+        }
+
+        // Check not inside the right eye sclera
+        if (!rl.checkCollisionPointCircle(irisRightPosition, scleraRightPosition, scleraRadius - irisRadius)) {
+            dx = irisRightPosition.x - scleraRightPosition.x;
+            dy = irisRightPosition.y - scleraRightPosition.y;
+
+            angle = math.atan2(dy, dx);
+
+            dxx = (scleraRadius - irisRadius) * math.cos(angle);
+            dyy = (scleraRadius - irisRadius) * math.sin(angle);
+
+            irisRightPosition.x = scleraRightPosition.x + dxx;
+            irisRightPosition.y = scleraRightPosition.y + dyy;
+        }
+        //----------------------------------------------------------------------------------
+
+        // Draw
+        //----------------------------------------------------------------------------------
+        rl.beginDrawing();
+        defer rl.endDrawing();
+
+        rl.drawCircleV(scleraLeftPosition, scleraRadius, rl.Color.light_gray);
+        rl.drawCircleV(irisLeftPosition, irisRadius, rl.Color.brown);
+        rl.drawCircleV(irisLeftPosition, 10, rl.Color.black);
+
+        rl.drawCircleV(scleraRightPosition, scleraRadius, rl.Color.light_gray);
+        rl.drawCircleV(irisRightPosition, irisRadius, rl.Color.dark_green);
+        rl.drawCircleV(irisRightPosition, 10, rl.Color.black);
+
+        rl.drawFPS(10, 10);
+
+        rl.clearBackground(rl.Color.ray_white);
+        //----------------------------------------------------------------------------------
+    }
+}