Add logic to capture/restore existing GL context.

This fixes asserts in debug builds where Qt's GL context is set when
a ScopedGLContext is created. This can happen when we have a project
open and the user tries to open another project. When the event
callback is dispatched, the Qt GL context is still set. The fix
justs removes the assert and adds logic to save and restore any
existing GL context that is set.

Engine/OSGLContext_win.cpp

@@ -57,6 +57,18 @@ __declspec(dllexport) int AmdPowerXpressRequestHighPerformance = 1;
 
 NATRON_NAMESPACE_ENTER
 
+namespace {
+
+bool makeDCAndContextCurrent(HDC dc, HGLRC context)
+{
+    const OSGLContext_wgl_data* wglInfo = appPTR->getWGLData();
+
+    assert(wglInfo);
+    return wglInfo->MakeCurrent(dc, context);
+}
+
+}  // namespace
+
 bool
 OSGLContext_win::extensionSupported(const char* extension,
                                     OSGLContext_wgl_data* data)
@@ -96,6 +108,7 @@ OSGLContext_win::initWGLData(OSGLContext_wgl_data* wglInfo)
     wglInfo->CreateContext = (WGLCREATECONTEXT_T)GetProcAddress(wglInfo->instance, "wglCreateContext");
     wglInfo->DeleteContext = (WGLDELETECONTEXT_T)GetProcAddress(wglInfo->instance, "wglDeleteContext");
     wglInfo->GetCurrentContext = (WGLGETCURRENTCONTEXT_T)GetProcAddress(wglInfo->instance, "wglGetCurrentContext");
+    wglInfo->GetCurrentDC = (WGLGETCURRENTDC_T)GetProcAddress(wglInfo->instance, "wglGetCurrentDC");
     wglInfo->GetProcAddress = (WGLGETPROCADDRESS_T)GetProcAddress(wglInfo->instance, "wglGetProcAddress");
     wglInfo->MakeCurrent = (WGLMAKECURRENT_T)GetProcAddress(wglInfo->instance, "wglMakeCurrent");
     wglInfo->ShareLists = (WGLSHARELISTS_T)GetProcAddress(wglInfo->instance, "wglShareLists");
@@ -606,18 +619,16 @@ OSGLContext_win::~OSGLContext_win()
 bool
 OSGLContext_win::makeContextCurrent(const OSGLContext_win* context)
 {
-    const OSGLContext_wgl_data* wglInfo = appPTR->getWGLData();
-
-    assert(wglInfo);
     if (context) {
-        return wglInfo->MakeCurrent(context->_dc, context->_handle);
+        return makeDCAndContextCurrent(context->_dc, context->_handle);
     } else {
-        return wglInfo->MakeCurrent(0, 0);
+        return makeDCAndContextCurrent(0, 0);
     }
 }
 
 bool
-OSGLContext_win::threadHasACurrentContext() {
+OSGLContext_win::threadHasACurrentContext()
+{
     const OSGLContext_wgl_data* wglInfo = appPTR->getWGLData();
     assert(wglInfo);
     return wglInfo->GetCurrentContext() != nullptr;
@@ -722,7 +733,11 @@ namespace {
 class ScopedGLContext {
 public:
     ScopedGLContext(const GLRendererID& gid) {
-        assert(!OSGLContext_win::threadHasACurrentContext());
+        const OSGLContext_wgl_data* wglInfo = appPTR->getWGLData();
+        assert(wglInfo);
+        _oldDc = wglInfo->GetCurrentDC();
+        _oldContext = wglInfo->GetCurrentContext();
+
         try {
             _context = std::make_unique<OSGLContext_win>(FramebufferConfig(), GLVersion.major, GLVersion.minor, false, gid, nullptr);
         } catch (const std::exception& e) {
@@ -737,14 +752,16 @@ class ScopedGLContext {
 
     ~ScopedGLContext() {
         if (_context) {
-            OSGLContext_win::makeContextCurrent(nullptr);
+            makeDCAndContextCurrent(_oldDc, _oldContext);
         }
     }
 
     explicit operator bool() const { return (bool)_context; }
 
 private:
     std::unique_ptr<OSGLContext_win> _context;
+    HDC _oldDc = nullptr;
+    HGLRC _oldContext = nullptr;
 };
 } // namespace
 

Engine/OSGLContext_win.h

@@ -91,6 +91,7 @@ typedef PROC (WINAPI * WGLGETPROCADDRESS_T)(LPCSTR);
 typedef BOOL (WINAPI * WGLMAKECURRENT_T)(HDC, HGLRC);
 typedef BOOL (WINAPI * WGLSHARELISTS_T)(HGLRC, HGLRC);
 typedef HGLRC (WINAPI * WGLGETCURRENTCONTEXT_T)();
+typedef HDC (WINAPI * WGLGETCURRENTDC_T)();
 
 ////////// https://www.opengl.org/registry/specs/NV/gpu_affinity.txt
 
@@ -157,6 +158,7 @@ struct OSGLContext_wgl_data
     WGLCREATECONTEXT_T CreateContext;
     WGLDELETECONTEXT_T DeleteContext;
     WGLGETCURRENTCONTEXT_T GetCurrentContext;
+    WGLGETCURRENTDC_T GetCurrentDC;
     WGLGETPROCADDRESS_T GetProcAddress;
     WGLMAKECURRENT_T MakeCurrent;
     WGLSHARELISTS_T ShareLists;