PlayerQuickItem: cleanup native display passthrough hack

This is used to pass a native display handle to mpv for the purpose of
hardware decoding. Currently it's used for Windows only, but it's going
to be needed on Linux as well to make use of the better Mesa 11
vaapi/OpenGL interop.

src/player/PlayerQuickItem.cpp

@@ -12,7 +12,7 @@
 #include "QsLog.h"
 #include "utils/Utils.h"
 
-#ifdef Q_OS_WIN32
+#if defined(Q_OS_WIN32)
 
 #include <windows.h>
 #include <d3d9.h>
@@ -73,7 +73,7 @@ void initD3DDevice(void)
 // Special libmpv-specific pseudo extension for better behavior with OpenGL
 // fullscreen modes. This is needed with some drivers which do not allow the
 // libmpv DXVA code to create a new D3D device.
-static void* __stdcall MPGetD3DInterface(const char* name)
+static void* __stdcall MPGetNativeDisplay(const char* name)
 {
   QLOG_INFO() << "Asking for " << qPrintable(QString::fromUtf8((name)));
   if (strcmp(name, "IDirect3DDevice9") == 0)
@@ -84,6 +84,13 @@ static void* __stdcall MPGetD3DInterface(const char* name)
   }
   return NULL;
 }
+// defined(Q_OS_WIN32)
+#else
+// Unsupported or not needed. Also, not using Windows-specific calling convention.
+static void* MPGetNativeDisplay(const char* name)
+{
+  return NULL;
+}
 #endif
 
 ///////////////////////////////////////////////////////////////////////////////////////////////////
@@ -96,11 +103,11 @@ static void* get_proc_address(void* ctx, const char* name)
     return NULL;
 
   void *res = (void *)glctx->getProcAddress(QByteArray(name));
-#ifdef Q_OS_WIN32
-  if (strcmp(name, "glMPGetD3DInterface") == 0)
+  if (strcmp(name, "glMPGetNativeDisplay") == 0)
   {
-    return (void *)&MPGetD3DInterface;
+    return (void *)&MPGetNativeDisplay;
   }
+#ifdef Q_OS_WIN32
   // wglGetProcAddress(), which is used by Qt, does not always resolve all
   // builtin functions with all drivers (only extensions). Qt compensates this
   // for a degree, but does this only for functions Qt happens to need. So
@@ -125,11 +132,8 @@ PlayerRenderer::PlayerRenderer(mpv::qt::Handle mpv, QQuickWindow* window)
 ///////////////////////////////////////////////////////////////////////////////////////////////////
 bool PlayerRenderer::init()
 {
-  const char *extensions = "";
-#ifdef Q_OS_WIN32
-  // For the custom IDirect3DDevice9 hack above.
-  extensions = "GL_MP_D3D_interfaces";
-#endif
+  // Signals presence of MPGetNativeDisplay().
+  const char *extensions = "GL_MP_MPGetNativeDisplay";
   return mpv_opengl_cb_init_gl(m_mpvGL, extensions, get_proc_address, NULL) >= 0;
 }