Fix EGL/GLX mismatch causing blank 3D preview on Linux (#12308)

- Add configurable GLEW_USE_EGL option (default OFF) to match wxWidgets
- Explicitly set wxUSE_GLCANVAS_EGL=OFF for vendored wxWidgets build
- Add compile-time check to detect EGL/GLX backend mismatch between
  GLEW and wxWidgets, preventing silent rendering failures

The bug occurred when GLEW was compiled with EGL support (using
eglGetProcAddress) but wxWidgets created GLX contexts. This mismatch
caused OpenGL function pointers to fail loading, resulting in blank
3D model preview.

Co-authored-by: SoftFever <softfeverever@gmail.com>

deps/GLEW/GLEW.cmake

@@ -5,6 +5,8 @@ find_package(OpenGL QUIET REQUIRED)
 orcaslicer_add_cmake_project(
   GLEW
   SOURCE_DIR  ${CMAKE_CURRENT_LIST_DIR}/glew
+  CMAKE_ARGS
+    -DGLEW_USE_EGL=OFF
 )
 
 if (MSVC)

deps/GLEW/glew/CMakeLists.txt

@@ -3,9 +3,17 @@ project(GLEW)
 
 find_package(OpenGL REQUIRED)
 
-if(OpenGL_EGL_FOUND)
-    message(STATUS "building GLEW for EGL (hope that wxWidgets agrees, otherwise you won't have any output!)")
+# Allow parent project to control EGL usage.
+# Default to OFF since OrcaSlicer forces GDK_BACKEND=x11 (using GLX contexts).
+# GLEW must use glXGetProcAddressARB (GLX) to match wxWidgets GL canvas.
+# Using EGL function loading with GLX contexts causes rendering failures.
+option(GLEW_USE_EGL "Use EGL instead of GLX for OpenGL function loading" OFF)
+
+if(GLEW_USE_EGL)
+    message(STATUS "Building GLEW with EGL support")
     set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -DGLEW_EGL")
+else()
+    message(STATUS "Building GLEW with GLX support")
 endif()
 
 add_library(GLEW src/glew.c)

deps/wxWidgets/wxWidgets.cmake

@@ -51,6 +51,7 @@ orcaslicer_add_cmake_project(
         -DwxUSE_UNICODE=ON
         -DwxUSE_PRIVATE_FONTS=ON
         -DwxUSE_OPENGL=ON
+        -DwxUSE_GLCANVAS_EGL=OFF
         -DwxUSE_WEBREQUEST=ON
         -DwxUSE_WEBVIEW=ON
         ${_wx_edge}

src/slic3r/GUI/OpenGLManager.cpp

@@ -25,6 +25,18 @@
 #include "../Utils/MacDarkMode.hpp"
 #endif // __APPLE__
 
+// Verify GLEW and wxWidgets use the same OpenGL backend (EGL vs GLX).
+// A mismatch causes rendering failures: GLEW's function loading must match
+// the context type created by wxWidgets.
+#if defined(__linux__)
+    #if defined(GLEW_EGL) && (!defined(wxUSE_GLCANVAS_EGL) || !wxUSE_GLCANVAS_EGL)
+        #error "OpenGL backend mismatch: GLEW has EGL support enabled but wxWidgets does not. Ensure GLEW_USE_EGL and wxUSE_GLCANVAS_EGL are both ON or both OFF."
+    #endif
+    #if !defined(GLEW_EGL) && defined(wxUSE_GLCANVAS_EGL) && wxUSE_GLCANVAS_EGL
+        #error "OpenGL backend mismatch: wxWidgets has EGL support enabled but GLEW does not. Ensure GLEW_USE_EGL and wxUSE_GLCANVAS_EGL are both ON or both OFF."
+    #endif
+#endif
+
 namespace Slic3r {
 namespace GUI {