From ba49dcea293a2506379cceafd38621feefe0103d Mon Sep 17 00:00:00 2001
From: Aaron Colwell <300262+acolwell@users.noreply.github.com>
Date: Sat, 29 Jun 2024 13:54:32 -0700
Subject: [PATCH] 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 | 33 +++++++++++++++++++++++++--------
 Engine/OSGLContext_win.h   |  2 ++
 2 files changed, 27 insertions(+), 8 deletions(-)

diff --git a/Engine/OSGLContext_win.cpp b/Engine/OSGLContext_win.cpp
index b9b78ff28..2e994c3eb 100644
--- a/Engine/OSGLContext_win.cpp
+++ b/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) {
@@ -737,7 +752,7 @@ class ScopedGLContext {
 
     ~ScopedGLContext() {
         if (_context) {
-            OSGLContext_win::makeContextCurrent(nullptr);
+            makeDCAndContextCurrent(_oldDc, _oldContext);
         }
     }
 
@@ -745,6 +760,8 @@ class ScopedGLContext {
 
 private:
     std::unique_ptr<OSGLContext_win> _context;
+    HDC _oldDc = nullptr;
+    HGLRC _oldContext = nullptr;
 };
 } // namespace
 
diff --git a/Engine/OSGLContext_win.h b/Engine/OSGLContext_win.h
index 862f8f65d..85906aa57 100644
--- a/Engine/OSGLContext_win.h
+++ b/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;