Examples: OpenGL: Added a dummy GL call + comments in ImGui_ImplOpenGL3_Init() to detect uninitialized GL function loaders early, and help users understand what they are missing. (#2421)

docs/CHANGELOG.txt

@@ -36,6 +36,8 @@ HOW TO UPDATE?
 Breaking Changes:
 
 Other Changes:
+- Examples: OpenGL: Added a dummy GL call + comments in ImGui_ImplOpenGL3_Init() to detect uninitialized
+  GL function loaders early, and help users understand what they are missing. (#2421)
 
 
 -----------------------------------------------------------------------

examples/imgui_impl_opengl3.cpp

@@ -12,6 +12,7 @@
 
 // CHANGELOG
 // (minor and older changes stripped away, please see git history for details)
+//  2019-03-15: OpenGL: Added a dummy GL call + comments in ImGui_ImplOpenGL3_Init() to detect uninitialized GL function loaders early.
 //  2019-03-03: OpenGL: Fix support for ES 2.0 (WebGL 1.0).
 //  2019-02-20: OpenGL: Fix for OSX not supporting OpenGL 4.5, we don't try to read GL_CLIP_ORIGIN even if defined by the headers/loader.
 //  2019-02-11: OpenGL: Projecting clipping rectangles correctly using draw_data->FramebufferScale to allow multi-viewports for retina display.
@@ -89,11 +90,11 @@
 //  Helper libraries are often used for this purpose! Here we are supporting a few common ones (gl3w, glew, glad).
 //  You may use another loader/header of your choice (glext, glLoadGen, etc.), or chose to manually implement your own.
 #if defined(IMGUI_IMPL_OPENGL_LOADER_GL3W)
-#include <GL/gl3w.h>
+#include <GL/gl3w.h>    // Needs to be initialized with gl3wInit() in user's code
 #elif defined(IMGUI_IMPL_OPENGL_LOADER_GLEW)
-#include <GL/glew.h>
+#include <GL/glew.h>    // Needs to be initialized with glewInit() in user's code
 #elif defined(IMGUI_IMPL_OPENGL_LOADER_GLAD)
-#include <glad/glad.h>
+#include <glad/glad.h>  // Needs to be initialized with gladLoadGL() in user's code
 #else
 #include IMGUI_IMPL_OPENGL_LOADER_CUSTOM
 #endif
@@ -128,6 +129,12 @@ bool    ImGui_ImplOpenGL3_Init(const char* glsl_version)
     strcpy(g_GlslVersionString, glsl_version);
     strcat(g_GlslVersionString, "\n");
 
+    // Make a dummy GL call (we don't actually need the result)
+    // IF YOU GET A CRASH HERE: it probably means that you haven't initialized the OpenGL function loader used by this code.
+    // Desktop OpenGL 3/4 need a function loader. See the IMGUI_IMPL_OPENGL_LOADER_xxx explanation above.
+    GLint current_texture;
+    glGetIntegerv(GL_TEXTURE_BINDING_2D, &current_texture);
+
     return true;
 }
 

imgui_demo.cpp

@@ -2565,9 +2565,9 @@ static void ShowDemoWindowMisc()
             ImGui::Text("Mouse released:"); for (int i = 0; i < IM_ARRAYSIZE(io.MouseDown); i++) if (ImGui::IsMouseReleased(i))         { ImGui::SameLine(); ImGui::Text("b%d", i); }
             ImGui::Text("Mouse wheel: %.1f", io.MouseWheel);
 
-            ImGui::Text("Keys down:");      for (int i = 0; i < IM_ARRAYSIZE(io.KeysDown); i++) if (io.KeysDownDuration[i] >= 0.0f)     { ImGui::SameLine(); ImGui::Text("%d (%.02f secs)", i, io.KeysDownDuration[i]); }
-            ImGui::Text("Keys pressed:");   for (int i = 0; i < IM_ARRAYSIZE(io.KeysDown); i++) if (ImGui::IsKeyPressed(i))             { ImGui::SameLine(); ImGui::Text("%d", i); }
-            ImGui::Text("Keys release:");   for (int i = 0; i < IM_ARRAYSIZE(io.KeysDown); i++) if (ImGui::IsKeyReleased(i))            { ImGui::SameLine(); ImGui::Text("%d", i); }
+            ImGui::Text("Keys down:");      for (int i = 0; i < IM_ARRAYSIZE(io.KeysDown); i++) if (io.KeysDownDuration[i] >= 0.0f)     { ImGui::SameLine(); ImGui::Text("%d (0x%X) (%.02f secs)", i, i, io.KeysDownDuration[i]); }
+            ImGui::Text("Keys pressed:");   for (int i = 0; i < IM_ARRAYSIZE(io.KeysDown); i++) if (ImGui::IsKeyPressed(i))             { ImGui::SameLine(); ImGui::Text("%d (0x%X)", i, i); }
+            ImGui::Text("Keys release:");   for (int i = 0; i < IM_ARRAYSIZE(io.KeysDown); i++) if (ImGui::IsKeyReleased(i))            { ImGui::SameLine(); ImGui::Text("%d (0x%X)", i, i); }
             ImGui::Text("Keys mods: %s%s%s%s", io.KeyCtrl ? "CTRL " : "", io.KeyShift ? "SHIFT " : "", io.KeyAlt ? "ALT " : "", io.KeySuper ? "SUPER " : "");
 
             ImGui::Text("NavInputs down:"); for (int i = 0; i < IM_ARRAYSIZE(io.NavInputs); i++) if (io.NavInputs[i] > 0.0f)                    { ImGui::SameLine(); ImGui::Text("[%d] %.2f", i, io.NavInputs[i]); }