Texture video source is flipped correctly (#284)

Author: MaxHeimbrock

Runtime/Scripts/TextureVideoSource.cs

@@ -10,6 +10,7 @@ namespace LiveKit
     public class TextureVideoSource : RtcVideoSource
     {
         TextureFormat _textureFormat;
+        private RenderTexture _flippedRT;
 
         public Texture Texture { get; }
 
@@ -39,6 +40,17 @@ public TextureVideoSource(Texture texture, VideoBufferType bufferType = VideoBuf
             Dispose(false);
         }
 
+        protected override void Dispose(bool disposing)
+        {
+            if (disposing && _flippedRT != null)
+            {
+                _flippedRT.Release();
+                UnityEngine.Object.Destroy(_flippedRT);
+                _flippedRT = null;
+            }
+            base.Dispose(disposing);
+        }
+
         // Read the texture data into a native array asynchronously
         protected override bool ReadBuffer()
         {
@@ -53,10 +65,20 @@ protected override bool ReadBuffer()
                 _bufferType = GetVideoBufferType(_textureFormat);
                 _captureBuffer = new NativeArray<byte>(GetWidth() * GetHeight() * GetStrideForBuffer(_bufferType), Allocator.Persistent);
                 _previewTexture = new Texture2D(GetWidth(), GetHeight(), _textureFormat, false);
+                if (_flippedRT != null)
+                {
+                    _flippedRT.Release();
+                    UnityEngine.Object.Destroy(_flippedRT);
+                }
+                _flippedRT = new RenderTexture(GetWidth(), GetHeight(), 0, compatibleFormat);
                 textureChanged = true;
             }
-            Graphics.CopyTexture(Texture, _previewTexture);
-            AsyncGPUReadback.RequestIntoNativeArray(ref _captureBuffer, _previewTexture, 0, _textureFormat, OnReadback);
+            // Vertically flip into an intermediate RT so the bytes AsyncGPUReadback produces are
+            // top-down (WebRTC expects top-down; Unity render textures are bottom-up on macOS/Metal
+            // and other GL-origin platforms).
+            Graphics.Blit(Texture, _flippedRT, new Vector2(1f, -1f), new Vector2(0f, 1f));
+            Graphics.CopyTexture(_flippedRT, _previewTexture);
+            AsyncGPUReadback.RequestIntoNativeArray(ref _captureBuffer, _flippedRT, 0, _textureFormat, OnReadback);
             return textureChanged;
         }
     }