feat: backporting existing raylib-cs examples and new official raylib examples to WASM, adopting raylib's original code style

Examples/Models/DirectionalBillboard.cs

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+/*******************************************************************************************
+*
+*   raylib [models] example - directional billboard
+*
+*   Example complexity rating: [★★☆☆] 2/4
+*
+*   Example originally created with raylib 6.0, last time updated with raylib 6.0
+*
+*   Example contributed by Robin (@RobinsAviary) 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 Robin (@RobinsAviary)
+*   Killbot art by patvanmackelberg https://opengameart.org/content/killbot-8-directional under CC0
+*
+********************************************************************************************/
+
+using System;
+using System.Numerics;
+using static Raylib_cs.Raylib;
+using static Raylib_cs.Raymath;
+
+namespace Examples.Models;
+
+public partial class DirectionalBillboard : IExample
+{
+    private const int screenWidth = 800;
+    private const int screenHeight = 450;
+
+    public string Name => "Models / Directional Billboard";
+
+    public string Title => "raylib [models] example - directional billboard";
+
+    private Camera3D camera;
+    private Texture2D skillbot;
+    private float animTimer;
+    private uint anim;
+
+    public void Init()
+    {
+        // Set up the camera
+        camera = new();
+        camera.Position = new Vector3(2.0f, 1.0f, 2.0f); // Starting position
+        camera.Target = new Vector3(0.0f, 0.5f, 0.0f);  // Target position
+        camera.Up = new Vector3(0.0f, 1.0f, 0.0f); // Up vector
+        camera.FovY = 45.0f; // FOV
+        camera.Projection = CameraProjection.Perspective; // Projection type (Standard 3D perspective)
+
+        // Load billboard texture
+        skillbot = LoadTexture("resources/skillbot.png");
+
+        // Timer to update animation
+        animTimer = 0.0f;
+        // Animation frame
+        anim = 0;
+    }
+
+    public void Update()
+    {
+        // Update
+        //----------------------------------------------------------------------------------
+        UpdateCamera(ref camera, CameraMode.Orbital);
+
+        // Update timer with delta time
+        animTimer += GetFrameTime();
+
+        // Update frame index after a certain amount of time (half a second)
+        if (animTimer > 0.5f)
+        {
+            animTimer = 0.0f;
+            anim += 1;
+        }
+
+        // Reset frame index to zero on overflow
+        if (anim >= 4)
+        {
+            anim = 0;
+        }
+
+        // Find the current direction frame based on the camera position to the billboard object
+        var dir = (float)Math.Floor(((Vector2Angle(new Vector2(2.0f, 0.0f), new Vector2(camera.Position.X, camera.Position.Z)) / MathF.PI) * 4.0f) + 0.25f);
+
+        // Correct frame index if angle is negative
+        if (dir < 0.0f)
+        {
+            dir = 8.0f - Math.Abs((int)dir);
+        }
+        //----------------------------------------------------------------------------------
+
+        // Draw
+        //----------------------------------------------------------------------------------
+        BeginDrawing();
+
+        ClearBackground(Color.RayWhite);
+
+        BeginMode3D(camera);
+
+        DrawGrid(10, 1.0f);
+
+        // Draw billboard pointing straight up to the sky, rotated relative to the camera and offset from the bottom
+        DrawBillboardPro(camera, skillbot, new Rectangle(0.0f + (anim * 24.0f), 0.0f + (dir * 24.0f), 24.0f, 24.0f),
+            Vector3.Zero, new Vector3(0.0f, 1.0f, 0.0f), Vector2.One, new Vector2(0.5f, 0.0f), 0, Color.White);
+
+        EndMode3D();
+
+        // Render various variables for reference
+        DrawText($"animation: {anim}", 10, 10, 20, Color.DarkGray);
+        DrawText($"direction frame: {dir:0}", 10, 40, 20, Color.DarkGray);
+
+        EndDrawing();
+        //----------------------------------------------------------------------------------
+    }
+
+    public void Unload()
+    {
+        // Unload billboard texture
+        UnloadTexture(skillbot);
+    }
+
+    public static int Main()
+    {
+        // Initialization
+        //--------------------------------------------------------------------------------------
+        InitWindow(screenWidth, screenHeight, "raylib [models] example - directional billboard");
+
+        SetTargetFPS(60);
+        //--------------------------------------------------------------------------------------
+
+        var game = new DirectionalBillboard();
+        game.Init();
+
+        // Main game loop
+        while (!WindowShouldClose())    // Detect window close button or ESC key
+        {
+            game.Update();
+        }
+
+        game.Unload();
+
+        // De-Initialization
+        //--------------------------------------------------------------------------------------
+        CloseWindow();        // Close window and OpenGL context
+        //--------------------------------------------------------------------------------------
+
+        return 0;
+    }
+}