Remove linking against unused GLEW on GNU/Linux. (#420)

* Remove linking against unused GLEW on GNU/Linux.

* Use SDL OpenGL headers instead of GLEW headers.

* Try to fix Mac OS building.

* Try to fix MSVC building.

* Remove residual GLEW linking on Windows and Mac OS too.

* Revert "Remove residual GLEW linking on Windows and Mac OS too."

This reverts commit d3fcf48.

* Revert "Try to fix MSVC building."

This reverts commit 480b2d1.

* Revert "Try to fix Mac OS building."

This reverts commit 5f0de0b.

* Revert "Use SDL OpenGL headers instead of GLEW headers."

This reverts commit fdf95bd.

* Use proper SDL2 OpenGL header instead of GLEW headers GNU/Linux.

extern/CMakeLists.txt

@@ -118,12 +118,11 @@ elseif (CMAKE_SYSTEM_NAME STREQUAL "Darwin")
         XCODE_ATTRIBUTE_CLANG_ENABLE_OBJC_ARC YES 
     )
 elseif (CMAKE_SYSTEM_NAME STREQUAL "Linux")
-    find_package(GLEW REQUIRED)
     if (DEFINED USE_OPENGLES)
-        target_link_libraries(ImGui PUBLIC ${OPENGL_GLESv2_LIBRARY} GLEW::GLEW)
+        target_link_libraries(ImGui PUBLIC ${OPENGL_GLESv2_LIBRARY})
         add_compile_definitions(IMGUI_IMPL_OPENGL_ES3)
     else()
-        target_link_libraries(ImGui PUBLIC ${OPENGL_opengl_LIBRARY} GLEW::GLEW)
+        target_link_libraries(ImGui PUBLIC ${OPENGL_opengl_LIBRARY})
     endif()
 endif()
 

src/graphic/Fast3D/gfx_opengl.cpp

@@ -39,9 +39,8 @@
 #include <GLES3/gl3.h>
 #else
 #include <SDL2/SDL.h>
-#include <GL/glew.h>
 #define GL_GLEXT_PROTOTYPES 1
-// #include <SDL2/SDL_opengles2.h>
+#include <SDL2/SDL_opengl.h>
 #endif
 
 #include "gfx_cc.h"
@@ -847,7 +846,7 @@ static void gfx_opengl_draw_triangles(float buf_vbo[], size_t buf_vbo_len, size_
 }
 
 static void gfx_opengl_init(void) {
-#if !defined(__SWITCH__) && !defined(USE_OPENGLES)
+#if !defined(__SWITCH__) && !defined(__linux__)
     glewInit();
 #endif