Update/merge examples back into main repo (#192)

Examples/Models/BillboardDemo.cs

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+/*******************************************************************************************
+*
+*   raylib [models] example - Drawing billboards
+*
+*   This example has been created using raylib 1.3 (www.raylib.com)
+*   raylib is licensed under an unmodified zlib/libpng license (View raylib.h for details)
+*
+*   Copyright (c) 2015 Ramon Santamaria (@raysan5)
+*
+********************************************************************************************/
+
+using System.Numerics;
+using static Raylib_cs.Raylib;
+
+namespace Examples.Models;
+
+public class BillboardDemo
+{
+    public static int Main()
+    {
+        // Initialization
+        //--------------------------------------------------------------------------------------
+        const int screenWidth = 800;
+        const int screenHeight = 450;
+
+        InitWindow(screenWidth, screenHeight, "raylib [models] example - drawing billboards");
+
+        // Define the camera to look into our 3d world
+        Camera3D camera = new();
+        camera.Position = new Vector3(5.0f, 4.0f, 5.0f);
+        camera.Target = new Vector3(0.0f, 2.0f, 0.0f);
+        camera.Up = new Vector3(0.0f, 1.0f, 0.0f);
+        camera.FovY = 45.0f;
+        camera.Projection = CameraProjection.CAMERA_PERSPECTIVE;
+
+        // Our texture billboard
+        Texture2D bill = LoadTexture("resources/billboard.png");
+
+        // Position of billboard billboard
+        Vector3 billPositionStatic = new(0.0f, 2.0f, 0.0f);
+        Vector3 billPositionRotating = new(1.0f, 2.0f, 1.0f);
+
+        // Entire billboard texture, source is used to take a segment from a larger texture.
+        Rectangle source = new(0.0f, 0.0f, (float)bill.Width, (float)bill.Height);
+
+        // NOTE: Billboard locked on axis-Y
+        Vector3 billUp = new(0.0f, 1.0f, 0.0f);
+
+        // Rotate around origin
+        // Here we choose to rotate around the image center
+        // NOTE: (-1, 1) is the range where origin.X, origin.Y is inside the texture
+        Vector2 rotateOrigin = Vector2.Zero;
+
+        // Distance is needed for the correct billboard draw order
+        // Larger distance (further away from the camera) should be drawn prior to smaller distance.
+        float distanceStatic = 0.0f;
+        float distanceRotating = 0.0f;
+
+        float rotation = 0.0f;
+
+        SetTargetFPS(60);
+        //--------------------------------------------------------------------------------------
+
+        // Main game loop
+        while (!WindowShouldClose())
+        {
+            // Update
+            //----------------------------------------------------------------------------------
+            UpdateCamera(ref camera, CameraMode.CAMERA_ORBITAL);
+            rotation += 0.4f;
+            distanceStatic = Vector3.Distance(camera.Position, billPositionStatic);
+            distanceRotating = Vector3.Distance(camera.Position, billPositionRotating);
+            //----------------------------------------------------------------------------------
+
+            // Draw
+            //----------------------------------------------------------------------------------
+            BeginDrawing();
+            ClearBackground(Color.RAYWHITE);
+
+            BeginMode3D(camera);
+
+            DrawGrid(10, 1.0f);
+
+            // Draw order matters!
+            if (distanceStatic > distanceRotating)
+            {
+                DrawBillboard(camera, bill, billPositionStatic, 2.0f, Color.WHITE);
+                DrawBillboardPro(
+                    camera,
+                    bill,
+                    source,
+                    billPositionRotating,
+                    billUp,
+                    new Vector2(1.0f, 1.0f),
+                    rotateOrigin,
+                    rotation,
+                    Color.WHITE
+                );
+            }
+            else
+            {
+                DrawBillboardPro(
+                    camera,
+                    bill,
+                    source,
+                    billPositionRotating,
+                    billUp,
+                    new Vector2(1.0f, 1.0f),
+                    rotateOrigin,
+                    rotation,
+                    Color.WHITE
+                );
+                DrawBillboard(camera, bill, billPositionStatic, 2.0f, Color.WHITE);
+            }
+
+            EndMode3D();
+
+            DrawFPS(10, 10);
+
+            EndDrawing();
+            //----------------------------------------------------------------------------------
+        }
+
+        // De-Initialization
+        //--------------------------------------------------------------------------------------
+        UnloadTexture(bill);
+
+        CloseWindow();
+        //--------------------------------------------------------------------------------------
+
+        return 0;
+    }
+}
+