Improved billboards example, highlighting rotation and draw order (#2779)

* Improved billboards example, highlighting rotation and draw order

* changes to conform to the raylib conventions

* NOW it conforms

Co-authored-by: nobytesgiven <nobytesgiven@users.noreply.github.com>

examples/models/models_billboard.c

@@ -12,6 +12,7 @@
 ********************************************************************************************/
 
 #include "raylib.h"
+#include "raymath.h"
 
 //------------------------------------------------------------------------------------
 // Program main entry point
@@ -33,11 +34,28 @@ int main(void)
     camera.fovy = 45.0f;
     camera.projection = CAMERA_PERSPECTIVE;
 
-    Texture2D bill = LoadTexture("resources/billboard.png");     // Our texture billboard
+    Texture2D bill = LoadTexture("resources/billboard.png");     // Our billboard texture
-    Vector3 billPosition = { 0.0f, 2.0f, 0.0f };                 // Position where draw billboard
+    Vector3 billPositionStatic = { 0.0f, 2.0f, 0.0f };                 // Position of billboard
+    Vector3 billPositionRotating = { 1.0f, 2.0f, 1.0f };
 
+    // Entire billboard texture, source is used to take a segment from a larger texture.
+    Rectangle source = { 0.0f, 0.0f, (float)bill.width, (float)bill.height };
+
+    // NOTE: Billboard locked on axis-Y
+    Vector3 billUp = { 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 = { 0.0f };
     SetCameraMode(camera, CAMERA_ORBITAL);  // Set an orbital camera mode
 
+    // 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;
+    float distanceRotating;
+
+    float rotation = 0.0f;
     SetTargetFPS(60);                       // Set our game to run at 60 frames-per-second
     //--------------------------------------------------------------------------------------
 
@@ -47,6 +65,9 @@ int main(void)
         // Update
         //----------------------------------------------------------------------------------
         UpdateCamera(&camera);
+        rotation += 0.4f;
+        distanceStatic = Vector3Distance(camera.position, billPositionStatic);
+        distanceRotating = Vector3Distance(camera.position, billPositionRotating);
         //----------------------------------------------------------------------------------
 
         // Draw
@@ -59,8 +80,18 @@ int main(void)
 
                 DrawGrid(10, 1.0f);        // Draw a grid
 
-                DrawBillboard(camera, bill, billPosition, 2.0f, WHITE);
+                // Draw order matters!
-
+                if (distanceStatic > distanceRotating) 
+                {
+                    DrawBillboard(camera, bill, billPositionStatic, 2.0f, WHITE);
+                    DrawBillboardPro(camera, bill, source, billPositionRotating, billUp, (Vector2) {1.0f, 1.0f}, rotateOrigin, rotation, WHITE);
+                } 
+                else
+                {
+                    DrawBillboardPro(camera, bill, source, billPositionRotating, billUp, (Vector2) {1.0f, 1.0f}, rotateOrigin, rotation, WHITE);
+                    DrawBillboard(camera, bill, billPositionStatic, 2.0f, WHITE);
+                }
+                
             EndMode3D();
 
             DrawFPS(10, 10);