ensure texture is not copied in one thread while it's read in another

This seems to cause issues in the rendering pipeline, so this commit never lets
a texture copy and read occur at the same time.

app/render/backend/opengl/openglbackend.cpp

@@ -159,6 +159,8 @@ void OpenGLBackend::EmitCachedFrameReady(const QList<rational> &times, const QVa
 
 OpenGLTexturePtr OpenGLBackend::CopyTexture(OpenGLTexturePtr input)
 {
+  input->Lock();
+
   QOpenGLContext* ctx = QOpenGLContext::currentContext();
 
   OpenGLTexturePtr copy = std::make_shared<OpenGLTexture>();
@@ -176,5 +178,7 @@ OpenGLTexturePtr OpenGLBackend::CopyTexture(OpenGLTexturePtr input)
   copy_buffer_.Release();
   copy_buffer_.Detach();
 
+  input->Unlock();
+
   return copy;
 }

app/render/backend/opengl/opengltexture.cpp

@@ -156,6 +156,16 @@ void OpenGLTexture::Upload(const void *data)
   Release();
 }
 
+void OpenGLTexture::Lock()
+{
+  mutex_.lock();
+}
+
+void OpenGLTexture::Unlock()
+{
+  mutex_.unlock();
+}
+
 void OpenGLTexture::CreateInternal(QOpenGLContext* create_ctx, GLuint* tex, const void *data)
 {
   QOpenGLFunctions* f = create_ctx->functions();

app/render/backend/opengl/opengltexture.h

@@ -22,6 +22,7 @@
 #define OPENGLTEXTURE_H
 
 #include <memory>
+#include <QMutex>
 #include <QOpenGLFunctions>
 
 #include "codec/frame.h"
@@ -59,6 +60,10 @@ public:
 
   void Upload(const void *data);
 
+  void Lock();
+
+  void Unlock();
+
 public slots:
   void Destroy();
 
@@ -75,6 +80,8 @@ private:
 
   PixelFormat::Format format_;
 
+  QMutex mutex_;
+
 };
 
 using OpenGLTexturePtr = std::shared_ptr<OpenGLTexture>;

app/render/backend/opengl/openglworker.cpp

@@ -355,6 +355,8 @@ void OpenGLWorker::TextureToBuffer(const QVariant &tex_in, QByteArray &buffer)
 
   PixelFormat::Info format_info = PixelService::GetPixelFormatInfo(video_params().format());
 
+  texture->texture()->Lock();
+
   QOpenGLFunctions* f = QOpenGLContext::currentContext()->functions();
   buffer_.Attach(texture->texture());
   buffer_.Bind();
@@ -369,6 +371,8 @@ void OpenGLWorker::TextureToBuffer(const QVariant &tex_in, QByteArray &buffer)
 
   buffer_.Release();
   buffer_.Detach();
+
+  texture->texture()->Unlock();
 }
 
 void OpenGLWorker::FinishInit()