win32: migrate to imgui's opengl loader [p=2656531]

glbindings has a fatal bug when initializing and releasing multiple contexts (cginternals/glbinding#343)
+ it adds an excessive 1.4MB to the size of release builds

src/CMakeLists.txt

@@ -37,10 +37,7 @@ if(WIN32)
     win32_window.cpp
   )
 
-  target_link_libraries(src Dwmapi Imm32)
-
-  find_package(glbinding REQUIRED)
-  target_link_libraries(src glbinding::glbinding Opengl32)
+  target_link_libraries(src Dwmapi Imm32 Opengl32)
 
   set(D3D_SHADERS
     "d3d10_pixel.hlsl\;ps_4_0"

src/opengl_renderer.cpp

@@ -23,8 +23,10 @@
 #ifdef __APPLE__
 #  include <OpenGL/gl3.h>
 #elif _WIN32
-#  include <glbinding/gl32/gl.h>
-using namespace gl32;
+#  include <imgui/backends/imgui_impl_opengl3_loader.h>
+constexpr int GL_TEXTURE_WRAP_S { 0x2802 },
+              GL_TEXTURE_WRAP_T { 0x2803 },
+              GL_REPEAT         { 0x2901 };
 #else
 #  include <epoxy/gl.h>
 #endif

src/win32_opengl.cpp

@@ -20,8 +20,9 @@
 #include "error.hpp"
 #include "window.hpp"
 
-#include <glbinding/glbinding.h>
+#define IMGL3W_IMPL
 #include <imgui/imgui.h>
+#include <imgui/backends/imgui_impl_opengl3_loader.h>
 
 // https://registry.khronos.org/OpenGL/api/GL/wglext.h
 constexpr int WGL_CONTEXT_MAJOR_VERSION_ARB    { 0x2091 },
@@ -31,11 +32,6 @@ constexpr int WGL_CONTEXT_MAJOR_VERSION_ARB    { 0x2091 },
 typedef HGLRC (WINAPI *PFNWGLCREATECONTEXTATTRIBSARBPROC)
   (HDC hDC, HGLRC hShareContext, const int *attribList);
 
-static glbinding::ProcAddress getProcAddress(const char *funcName)
-{
-  return reinterpret_cast<glbinding::ProcAddress>(wglGetProcAddress(funcName));
-}
-
 class Win32OpenGL : public OpenGLRenderer {
 public:
   Win32OpenGL(RendererFactory *, Window *);
@@ -59,7 +55,6 @@ class MakeCurrent {
     : m_gl { gl }
   {
     wglMakeCurrent(dc, m_gl);
-    glbinding::useContext(reinterpret_cast<glbinding::ContextHandle>(m_gl));
   }
 
   ~MakeCurrent()
@@ -74,7 +69,6 @@ class MakeCurrent {
 struct GLDeleter {
   void operator()(HGLRC gl)
   {
-    glbinding::releaseContext(reinterpret_cast<glbinding::ContextHandle>(gl));
     wglDeleteContext(gl);
   }
 };
@@ -135,31 +129,30 @@ void Win32OpenGL::setPixelFormat()
 void Win32OpenGL::createContext()
 {
   HGLRC dummyGl { wglCreateContext(m_dc) }; // creates a legacy (< 2.1) context
-  wglMakeCurrent(m_dc, dummyGl);
+  wglMakeCurrent(m_dc, m_gl = dummyGl);
 
   PFNWGLCREATECONTEXTATTRIBSARBPROC wglCreateContextAttribsARB
     { reinterpret_cast<PFNWGLCREATECONTEXTATTRIBSARBPROC>
       (wglGetProcAddress("wglCreateContextAttribsARB")) };
 
-  if(!wglCreateContextAttribsARB)
-    throw backend_error { "OpenGL 3 is not available on this system" };
-
-  // https://www.khronos.org/registry/OpenGL/extensions/ARB/WGL_ARB_create_context.txt
-  constexpr int attrs[] {
-    WGL_CONTEXT_MAJOR_VERSION_ARB, 3, WGL_CONTEXT_MINOR_VERSION_ARB, 2,
-    WGL_CONTEXT_PROFILE_MASK_ARB, WGL_CONTEXT_CORE_PROFILE_BIT_ARB,
-    0
-  };
-
-  m_gl = wglCreateContextAttribsARB(m_dc, nullptr, attrs);
-  wglMakeCurrent(m_dc, m_gl);
-  wglDeleteContext(dummyGl);
-
-  if(!m_gl)
-    throw backend_error { "failed to initialize OpenGL 3.2 core context" };
+  if(wglCreateContextAttribsARB) {
+    // https://www.khronos.org/registry/OpenGL/extensions/ARB/WGL_ARB_create_context.txt
+    constexpr int attrs[] {
+      WGL_CONTEXT_MAJOR_VERSION_ARB, 3, WGL_CONTEXT_MINOR_VERSION_ARB, 2,
+      WGL_CONTEXT_PROFILE_MASK_ARB, WGL_CONTEXT_CORE_PROFILE_BIT_ARB,
+      0
+    };
+
+    if(HGLRC coreGl { wglCreateContextAttribsARB(m_dc, nullptr, attrs) }) {
+      wglMakeCurrent(m_dc, m_gl = coreGl);
+      wglDeleteContext(dummyGl);
+    }
+  }
 
-  glbinding::useContext(reinterpret_cast<glbinding::ContextHandle>(m_gl));
-  glbinding::initialize(getProcAddress, false);
+  if(imgl3wInit()) {
+    wglDeleteContext(m_gl);
+    throw backend_error { "OpenGL 3.2 is not available on this system" };
+  }
 }
 
 void Win32OpenGL::render(void *)

vcpkg.json

@@ -9,7 +9,6 @@
     { "name": "boost-variant2", "platform": "!windows" },
     { "name": "freetype", "default-features": false,
       "features": ["png", "zlib"], "platform": "!linux" },
-    { "name": "glbinding", "platform": "windows" },
     { "name": "libjpeg-turbo" },
     { "name": "libpng", "platform": "!linux" },
     "cmark",