Examples: OpenGL: Added support for glew and glad OpenGL loaders out of the box. (#2001, #2002). Changelog, tweaks, applied changes to SDL+OpenGL3 example.

CHANGELOG.txt

@@ -104,6 +104,7 @@ Other Changes:
  - Examples: OpenGL3: Tweaked the imgui_impl_opengl3.cpp to work as-is with Emscripten + WebGL 2.0. (#1941). [@o-micron] 
  - Examples: OpenGL3: Made the example app default to GL 3.0 + GLSL 130 (instead of GL 3.2 + GLSL 150) unless on Mac.
  - Examples: OpenGL3: Added error output when shaders fail to compile/link.
+ - Examples: OpenGL3: Added support for glew and glad OpenGL loaders out of the box. (#2001, #2002) [@jdumas]
  - Examples: OpenGL2: Disabling/restoring GL_LIGHTING and GL_COLOR_MATERIAL to increase compatibility with legacy OpenGL applications. (#1996)
  - Examples: DirectX10, DirectX11: Fixed unreleased resources in Init and Shutdown functions. (#1944)
  - Examples: DirectX11: Querying for IDXGIFactory instead of IDXGIFactory1 to increase compatibility. (#1989) [@matt77hias]

examples/example_glfw_opengl3/Makefile

@@ -19,21 +19,28 @@ SOURCES = main.cpp
 SOURCES += ../imgui_impl_glfw.cpp ../imgui_impl_opengl3.cpp
 SOURCES += ../../imgui.cpp ../../imgui_demo.cpp ../../imgui_draw.cpp
 OBJS = $(addsuffix .o, $(basename $(notdir $(SOURCES))))
-
 UNAME_S := $(shell uname -s)
 
-# Default OpenGL loader: gl3w
+##---------------------------------------------------------------------
+## OPENGL LOADER
+##---------------------------------------------------------------------
+
+## Using OpenGL loader: gl3w [default]
 SOURCES += ../libs/gl3w/GL/gl3w.c
 CXXFLAGS = -I../libs/gl3w
 
-# You can switch to glad by changing the following compilation options,
+## Using OpenGL loader: glew
-# and changing the rule L73 of this Makefile
+## (This assumes a system-wide installation)
+# CXXFLAGS = -lGLEW -DIMGUI_IMPL_OPENGL_LOADER_GLEW
+
+## Using OpenGL loader: glad
+## (You'll also need to change the rule at line ~77 of this Makefile to compile/link glad.c/.o)
 # SOURCES += ../libs/glad/src/glad.c
 # CXXFLAGS = -I../libs/glad/include -DIMGUI_IMPL_OPENGL_LOADER_GLAD
 
-# You can also use glew are you OpenGL loader
+##---------------------------------------------------------------------
-# This assumes a system-wide installation
+## BUILD FLAGS PER PLATFORM
-# CXXFLAGS = -lGLEW -DIMGUI_IMPL_OPENGL_LOADER_GLEW
+##---------------------------------------------------------------------
 
 ifeq ($(UNAME_S), Linux) #LINUX
 	ECHO_MESSAGE = "Linux"
@@ -64,6 +71,9 @@ ifeq ($(findstring MINGW,$(UNAME_S)),MINGW)
    CFLAGS = $(CXXFLAGS)
 endif
 
+##---------------------------------------------------------------------
+## BUILD RULES
+##---------------------------------------------------------------------
 
 %.o:%.cpp
 	$(CXX) $(CXXFLAGS) -c -o $@ $<

examples/example_glfw_opengl3/main.cpp

@@ -1,22 +1,23 @@
 // ImGui - standalone example application for GLFW + OpenGL 3, using programmable pipeline
 // If you are new to ImGui, see examples/README.txt and documentation at the top of imgui.cpp.
 // (GLFW is a cross-platform general purpose library for handling windows, inputs, OpenGL/Vulkan graphics context creation, etc.)
-// (GL3W is a helper library to access OpenGL functions since there is no standard header to access modern OpenGL functions easily. Alternatives are GLEW, Glad, etc.)
 
 #include "imgui.h"
 #include "imgui_impl_glfw.h"
 #include "imgui_impl_opengl3.h"
 #include <stdio.h>
 
-// This example is using gl3w to access OpenGL functions. You may use another OpenGL loader/header such as: glew, glext, glad, glLoadGen, etc.
+// About OpenGL function loaders: modern OpenGL doesn't have a standard header file and requires individual function pointers to be loaded manually. 
+// 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>    // Initialize with gl3wInit()
 #elif defined(IMGUI_IMPL_OPENGL_LOADER_GLEW)
-#include <GL/glew.h>
+#include <GL/glew.h>    // Initialize with glewInit()
 #elif defined(IMGUI_IMPL_OPENGL_LOADER_GLAD)
-#include <glad/glad.h>
+#include <glad/glad.h>  // Initialize with gladLoadGL()
 #else
-#pragma error("Cannot use custom loader for example application.")
+#include IMGUI_IMPL_OPENGL_LOADER_CUSTOM
 #endif
 
 #include <GLFW/glfw3.h> // Include glfw3.h after our OpenGL definitions
@@ -56,17 +57,18 @@ int main(int, char**)
         return 1;
     glfwMakeContextCurrent(window);
     glfwSwapInterval(1); // Enable vsync
+
+    // Initialize OpenGL loader
 #if defined(IMGUI_IMPL_OPENGL_LOADER_GL3W)
-    GLenum err = gl3wInit();
+    bool err = gl3wInit() != 0;
-    if (!err) {
 #elif defined(IMGUI_IMPL_OPENGL_LOADER_GLEW)
-    GLenum err = glewInit();
+    bool err = glewInit() != GLEW_OK;
-    if (GLEW_OK != err) {
 #elif defined(IMGUI_IMPL_OPENGL_LOADER_GLAD)
-    GLenum err = gladLoadGL();
+    bool err = gladLoadGL() != 0;
-    if (!err) {
 #endif
-        fprintf(stderr, "Failed to initialize OpenGL\n");
+    if (err)
+    {
+        fprintf(stderr, "Failed to initialize OpenGL loader!\n");
         return 1;
     }
 

examples/example_sdl_opengl3/Makefile

@@ -18,11 +18,29 @@ EXE = example_sdl_opengl3
 SOURCES = main.cpp
 SOURCES += ../imgui_impl_sdl.cpp ../imgui_impl_opengl3.cpp
 SOURCES += ../../imgui.cpp ../../imgui_demo.cpp ../../imgui_draw.cpp
-SOURCES += ../libs/gl3w/GL/gl3w.c
 OBJS = $(addsuffix .o, $(basename $(notdir $(SOURCES))))
-
 UNAME_S := $(shell uname -s)
 
+##---------------------------------------------------------------------
+## OPENGL LOADER
+##---------------------------------------------------------------------
+
+## Using OpenGL loader: gl3w [default]
+SOURCES += ../libs/gl3w/GL/gl3w.c
+CXXFLAGS = -I../libs/gl3w
+
+## Using OpenGL loader: glew
+## (This assumes a system-wide installation)
+# CXXFLAGS = -lGLEW -DIMGUI_IMPL_OPENGL_LOADER_GLEW
+
+## Using OpenGL loader: glad
+## (You'll also need to change the rule at line ~77 of this Makefile to compile/link glad.c/.o)
+# SOURCES += ../libs/glad/src/glad.c
+# CXXFLAGS = -I../libs/glad/include -DIMGUI_IMPL_OPENGL_LOADER_GLAD
+
+##---------------------------------------------------------------------
+## BUILD FLAGS PER PLATFORM
+##---------------------------------------------------------------------
 
 ifeq ($(UNAME_S), Linux) #LINUX
 	ECHO_MESSAGE = "Linux"
@@ -51,6 +69,9 @@ ifeq ($(findstring MINGW,$(UNAME_S)),MINGW)
    CFLAGS = $(CXXFLAGS)
 endif
 
+##---------------------------------------------------------------------
+## BUILD RULES
+##---------------------------------------------------------------------
 
 %.o:%.cpp
 	$(CXX) $(CXXFLAGS) -c -o $@ $<

examples/example_sdl_opengl3/main.cpp

@@ -9,10 +9,18 @@
 #include <stdio.h>
 #include <SDL.h>
 
-#include <GL/gl3w.h>    // This example is using gl3w to access OpenGL functions. You may use another OpenGL loader/header such as: glew, glext, glad, glLoadGen, etc.
+// About OpenGL function loaders: modern OpenGL doesn't have a standard header file and requires individual function pointers to be loaded manually. 
-//#include <glew.h>
+// Helper libraries are often used for this purpose! Here we are supporting a few common ones: gl3w, glew, glad.
-//#include <glext.h>
+// You may use another loader/header of your choice (glext, glLoadGen, etc.), or chose to manually implement your own.
-//#include <glad/glad.h>
+#if defined(IMGUI_IMPL_OPENGL_LOADER_GL3W)
+#include <GL/gl3w.h>    // Initialize with gl3wInit()
+#elif defined(IMGUI_IMPL_OPENGL_LOADER_GLEW)
+#include <GL/glew.h>    // Initialize with glewInit()
+#elif defined(IMGUI_IMPL_OPENGL_LOADER_GLAD)
+#include <glad/glad.h>  // Initialize with gladLoadGL()
+#else
+#include IMGUI_IMPL_OPENGL_LOADER_CUSTOM
+#endif
 
 int main(int, char**)
 {
@@ -49,7 +57,20 @@ int main(int, char**)
     SDL_Window* window = SDL_CreateWindow("Dear ImGui SDL2+OpenGL3 example", SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED, 1280, 720, SDL_WINDOW_OPENGL|SDL_WINDOW_RESIZABLE);
     SDL_GLContext gl_context = SDL_GL_CreateContext(window);
     SDL_GL_SetSwapInterval(1); // Enable vsync
-    gl3wInit();
+
+    // Initialize OpenGL loader
+#if defined(IMGUI_IMPL_OPENGL_LOADER_GL3W)
+    bool err = gl3wInit() != 0;
+#elif defined(IMGUI_IMPL_OPENGL_LOADER_GLEW)
+    bool err = glewInit() != GLEW_OK;
+#elif defined(IMGUI_IMPL_OPENGL_LOADER_GLAD)
+    bool err = gladLoadGL() != 0;
+#endif
+    if (err)
+    {
+        fprintf(stderr, "Failed to initialize OpenGL loader!\n");
+        return 1;
+    }
 
     // Setup Dear ImGui binding
     IMGUI_CHECKVERSION();

examples/imgui_impl_opengl3.cpp

@@ -11,6 +11,7 @@
 
 // CHANGELOG
 // (minor and older changes stripped away, please see git history for details)
+//  2018-08-29: OpenGL: Added support for more OpenGL loaders: glew and glad, with comments indicative that any loader can be used.
 //  2018-08-09: OpenGL: Default to OpenGL ES 3 on iOS and Android. GLSL version default to "#version 300 ES".
 //  2018-07-30: OpenGL: Support for GLSL 300 ES and 410 core. Fixes for Emscripten compilation.
 //  2018-07-10: OpenGL: Support for more GLSL versions (based on the GLSL version string). Added error output when shaders fail to compile/link.
@@ -72,18 +73,16 @@
 // OpenGL ES 3
 #include <GLES3/gl3.h>  // Use GL ES 3
 #else
-// OpenGL Regular
+// Regular OpenGL
-// (About OpenGL function loaders: modern OpenGL doesn't have a standard header file and requires individual functions to be loaded manually. 
+// About OpenGL function loaders: modern OpenGL doesn't have a standard header file and requires individual function pointers to be loaded manually. 
-//  Helper libraries are often used for this purpose! Here we are using gl3w.h, which requires a call to gl3wInit(). 
+// Helper libraries are often used for this purpose! Here we are supporting a few common ones: gl3w, glew, glad.
-//  You may use another any other loader/header of your choice, such as glew, glext, glad, glLoadGen, etc.)
+// 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>
 #elif defined(IMGUI_IMPL_OPENGL_LOADER_GLEW)
 #include <GL/glew.h>
 #elif defined(IMGUI_IMPL_OPENGL_LOADER_GLAD)
 #include <glad/glad.h>
-#elif defined(IMGUI_IMPL_OPENGL_LOADER_GLEXT)
-#include <glext.h>
 #else
 #include IMGUI_IMPL_OPENGL_LOADER_CUSTOM
 #endif

examples/imgui_impl_opengl3.h

@@ -10,9 +10,9 @@
 // https://github.com/ocornut/imgui
 
 // About OpenGL function loaders: 
-// Modern OpenGL requires individual functions to be loaded manually. Helper libraries are often used for this purpose.
+// About OpenGL function loaders: modern OpenGL doesn't have a standard header file and requires individual function pointers to be loaded manually. 
-// Here we are using gl3w.h, which requires a call to gl3wInit().
+// Helper libraries are often used for this purpose! Here we are supporting a few common ones: gl3w, glew, glad. 
-// You may use another any other loader/header of your choice, such as glew, glext, glad, glLoadGen, etc.
+// You may use another loader/header of your choice (glext, glLoadGen, etc.), or chose to manually implement your own.
 
 // About GLSL version:
 // The 'glsl_version' initialization parameter should be NULL (default) or a "#version XXX" string.