Examples: Add OpenGL ES 2.0 support to modern GL examples. (#2837, #3951)

docs/CHANGELOG.txt

@@ -56,6 +56,7 @@ Other Changes:
   workaround/fix state restoring issues. Unknown exactly why so, but bit of a cargo-cult fix. (#3857)
 - Backends: Vulkan: Fix mapped memory Vulkan validation error when buffer sizes are not multiple of
   VkPhysicalDeviceLimits::nonCoherentAtomSize. (#3957) [@AgentX1994]
+- Examples: Add OpenGL ES 2.0 support to modern GL examples. (#2837, #3951) [@lethal-guitar, @hinxx]
 - Examples: Vulkan: Rebuild swapchain on VK_SUBOPTIMAL_KHR. (#3881)
 - Docs: Improvements to minor mistakes in documentation comments (#3923) [@ANF-Studios]
 

examples/example_glfw_opengl3/Makefile

@@ -21,15 +21,19 @@ SOURCES += $(IMGUI_DIR)/imgui.cpp $(IMGUI_DIR)/imgui_demo.cpp $(IMGUI_DIR)/imgui
 SOURCES += $(IMGUI_DIR)/backends/imgui_impl_glfw.cpp $(IMGUI_DIR)/backends/imgui_impl_opengl3.cpp
 OBJS = $(addsuffix .o, $(basename $(notdir $(SOURCES))))
 UNAME_S := $(shell uname -s)
+LINUX_GL_LIBS = -lGL
 
 CXXFLAGS = -I$(IMGUI_DIR) -I$(IMGUI_DIR)/backends
 CXXFLAGS += -g -Wall -Wformat
 LIBS =
 
 ##---------------------------------------------------------------------
-## OPENGL LOADER
+## OPENGL LOADER / OPENGL ES
 ##---------------------------------------------------------------------
 
+## See below for OpenGL ES option (no loader required) - comment out
+## the following if you want to use OpenGL ES instead of Desktop GL.
+
 ## Using OpenGL loader: gl3w [default]
 SOURCES += ../libs/gl3w/GL/gl3w.c
 CXXFLAGS += -I../libs/gl3w -DIMGUI_IMPL_OPENGL_LOADER_GL3W
@@ -56,13 +60,18 @@ CXXFLAGS += -I../libs/gl3w -DIMGUI_IMPL_OPENGL_LOADER_GL3W
 # CXXFLAGS += -DIMGUI_IMPL_OPENGL_LOADER_GLBINDING2
 # LIBS += -lglbinding
 
+## Using OpenGL ES, no loader required
+## This assumes a GL ES library available in the system, e.g. libGLESv2.so
+# CXXFLAGS += -DIMGUI_IMPL_OPENGL_ES2
+# LINUX_GL_LIBS = -lGLESv2
+
 ##---------------------------------------------------------------------
 ## BUILD FLAGS PER PLATFORM
 ##---------------------------------------------------------------------
 
 ifeq ($(UNAME_S), Linux) #LINUX
 	ECHO_MESSAGE = "Linux"
-	LIBS += -lGL `pkg-config --static --libs glfw3`
+	LIBS += $(LINUX_GL_LIBS) `pkg-config --static --libs glfw3`
 
 	CXXFLAGS += `pkg-config --cflags glfw3`
 	CFLAGS = $(CXXFLAGS)

examples/example_glfw_opengl3/main.cpp

@@ -8,11 +8,13 @@
 #include "imgui_impl_opengl3.h"
 #include <stdio.h>
 
+#if defined(IMGUI_IMPL_OPENGL_ES2)
+#include <GLES2/gl2.h>
 // About Desktop OpenGL function loaders:
 //  Modern desktop OpenGL doesn't have a standard portable header file to load OpenGL function pointers.
 //  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)
+#elif 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()
@@ -57,7 +59,13 @@ int main(int, char**)
         return 1;
 
     // Decide GL+GLSL versions
-#ifdef __APPLE__
+#if defined(IMGUI_IMPL_OPENGL_ES2)
+    // GL ES 2.0 + GLSL 100
+    const char* glsl_version = "#version 100";
+    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 2);
+    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 0);
+    glfwWindowHint(GLFW_CLIENT_API, GLFW_OPENGL_ES_API);
+#elif defined(__APPLE__)
     // GL 3.2 + GLSL 150
     const char* glsl_version = "#version 150";
     glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);

examples/example_sdl_opengl3/Makefile

@@ -21,15 +21,19 @@ SOURCES += $(IMGUI_DIR)/imgui.cpp $(IMGUI_DIR)/imgui_demo.cpp $(IMGUI_DIR)/imgui
 SOURCES += $(IMGUI_DIR)/backends/imgui_impl_sdl.cpp $(IMGUI_DIR)/backends/imgui_impl_opengl3.cpp
 OBJS = $(addsuffix .o, $(basename $(notdir $(SOURCES))))
 UNAME_S := $(shell uname -s)
+LINUX_GL_LIBS = -lGL
 
 CXXFLAGS = -I$(IMGUI_DIR) -I$(IMGUI_DIR)/backends
 CXXFLAGS += -g -Wall -Wformat
 LIBS =
 
 ##---------------------------------------------------------------------
-## OPENGL LOADER
+## OPENGL LOADER / OPENGL ES
 ##---------------------------------------------------------------------
 
+## See below for OpenGL ES option (no loader required) - comment out
+## the following if you want to use OpenGL ES instead of Desktop GL.
+
 ## Using OpenGL loader: gl3w [default]
 SOURCES += ../libs/gl3w/GL/gl3w.c
 CXXFLAGS += -I../libs/gl3w -DIMGUI_IMPL_OPENGL_LOADER_GL3W
@@ -56,13 +60,21 @@ CXXFLAGS += -I../libs/gl3w -DIMGUI_IMPL_OPENGL_LOADER_GL3W
 # CXXFLAGS += -DIMGUI_IMPL_OPENGL_LOADER_GLBINDING2
 # LIBS += -lglbinding
 
+## Using OpenGL ES, no loader required
+## This assumes a GL ES library available in the system, e.g. libGLESv2.so
+# CXXFLAGS += -DIMGUI_IMPL_OPENGL_ES2
+# LINUX_GL_LIBS = -lGLESv2
+## If you're on a Raspberry Pi and want to use the legacy drivers,
+## use the following instead:
+# LINUX_GL_LIBS = -L/opt/vc/lib -lbrcmGLESv2
+
 ##---------------------------------------------------------------------
 ## BUILD FLAGS PER PLATFORM
 ##---------------------------------------------------------------------
 
 ifeq ($(UNAME_S), Linux) #LINUX
 	ECHO_MESSAGE = "Linux"
-	LIBS += -lGL -ldl `sdl2-config --libs`
+	LIBS += $(LINUX_GL_LIBS) -ldl `sdl2-config --libs`
 
 	CXXFLAGS += `sdl2-config --cflags`
 	CFLAGS = $(CXXFLAGS)

examples/example_sdl_opengl3/main.cpp

@@ -10,11 +10,13 @@
 #include <stdio.h>
 #include <SDL.h>
 
+#if defined(IMGUI_IMPL_OPENGL_ES2)
+#include <GLES2/gl2.h>
 // About Desktop OpenGL function loaders:
 //  Modern desktop OpenGL doesn't have a standard portable header file to load OpenGL function pointers.
 //  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)
+#elif 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()
@@ -49,7 +51,14 @@ int main(int, char**)
     }
 
     // Decide GL+GLSL versions
-#ifdef __APPLE__
+#if defined(IMGUI_IMPL_OPENGL_ES2)
+    // GL ES 2.0 + GLSL 100
+    const char* glsl_version = "#version 100";
+    SDL_GL_SetAttribute(SDL_GL_CONTEXT_FLAGS, 0);
+    SDL_GL_SetAttribute(SDL_GL_CONTEXT_PROFILE_MASK, SDL_GL_CONTEXT_PROFILE_ES);
+    SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, 2);
+    SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, 0);
+#elif defined(__APPLE__)
     // GL 3.2 Core + GLSL 150
     const char* glsl_version = "#version 150";
     SDL_GL_SetAttribute(SDL_GL_CONTEXT_FLAGS, SDL_GL_CONTEXT_FORWARD_COMPATIBLE_FLAG); // Always required on Mac