[examples] Added: directional billboard (#5351)

* Added models directional billboard example

* add killbot texture

* various fixes and formatting tweaks

* corrected stdlib

examples/models/models_directional_billboard.c

@@ -0,0 +1,116 @@
+/*******************************************************************************************
+*
+*   raylib [models] example - directional billboard
+*
+*   Example complexity rating: [★★☆☆] 2/4
+*
+*   Example originally created with raylib 5.6-dev, last time updated with raylib 5.6
+*
+*   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) 2025-2025 Robin (@RobinsAviary)
+*   Killbot art by patvanmackelberg https://opengameart.org/content/killbot-8-directional under CC0
+*
+********************************************************************************************/
+
+#include "raylib.h"
+#include "raymath.h"
+#include <stdlib.h>
+
+//------------------------------------------------------------------------------------
+// Program main entry point
+//------------------------------------------------------------------------------------
+int main(void)
+{
+    // Initialization
+    //--------------------------------------------------------------------------------------
+    const int screenWidth = 800;
+    const int screenHeight = 450;
+
+    InitWindow(screenWidth, screenHeight, "raylib [models] example - directional billboard");
+
+    // Set up the camera
+    Camera camera = { 0 };
+    camera.position = (Vector3){ 2.0f, 1.0f, 2.0f }; // Starting position
+    camera.target = (Vector3){ 0.0f, 0.5f, 0.0f };  // Target position
+    camera.up = (Vector3){ 0.0f, 1.0f, 0.0f }; // Up vector
+    camera.fovy = 45.0f; // FOV
+    camera.projection = CAMERA_PERSPECTIVE; // Projection type (Standard 3D perspective)
+
+    // Load billboard texture
+    Texture skillbot = LoadTexture("resources/skillbot.png");
+
+    // Timer to update animation
+    float anim_timer = 0.0f;
+    // Animation frame
+    unsigned int anim = 0;
+
+    SetTargetFPS(60);
+    //--------------------------------------------------------------------------------------
+
+    // Main game loop
+    while (!WindowShouldClose())    // Detect window close button or ESC key
+    {
+        // Update
+        //----------------------------------------------------------------------------------
+        UpdateCamera(&camera, CAMERA_ORBITAL);
+
+        // Update timer with delta time
+        anim_timer += GetFrameTime();
+
+        // Update frame index after a certain amount of time (half a second)
+        if (anim_timer > 0.5f) 
+        {
+            anim_timer = 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
+        float dir = (float)floor(((Vector2Angle((Vector2){ 2.0f, 0.0f }, (Vector2){ camera.position.x, camera.position.z })/PI)*4.0f) + 0.25f);
+
+        // Correct frame index if angle is negative
+        if (dir < 0.0f)
+        {
+            dir = 8.0f - (float)abs((int)dir);
+        }
+        //----------------------------------------------------------------------------------
+
+        // Draw
+        //----------------------------------------------------------------------------------
+        BeginDrawing();
+
+        ClearBackground(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, (Rectangle){ 0.0f + (anim*24.0f), 0.0f + (dir*24.0f), 24.0f, 24.0f }, Vector3Zero(), (Vector3){ 0.0f, 1.0f, 0.0f }, Vector2One(), (Vector2){ 0.5f, 0.0f }, 0, WHITE);
+
+        EndMode3D();
+
+        // Render various variables for reference
+        DrawText(TextFormat("animation: %d", anim), 10, 10, 20, DARKGRAY);
+        DrawText(TextFormat("direction frame: %.0f", dir), 10, 40, 20, DARKGRAY);
+
+        EndDrawing();
+        //----------------------------------------------------------------------------------
+    }
+
+    // De-Initialization
+    //--------------------------------------------------------------------------------------
+    // Unload billboard texture
+    UnloadTexture(skillbot);
+
+    CloseWindow();        // Close window and OpenGL context
+    //--------------------------------------------------------------------------------------
+
+    return 0;
+}