Examples: OpenGL: Fix to be able to run on ES 2.0 / WebGL 1.0. [@rmitton, @gabrielcuvillier]

docs/CHANGELOG.txt

@@ -66,6 +66,7 @@ Other Changes:
   tree depth instead of a relative one.
 - Log/Capture: Fixed CollapsingHeader trailing ascii representation being "#" instead of "##".
 - Misc: Asserting in NewFrame() if style.WindowMinSize is zero or smaller than (1.0f,1.0f).
+- Examples: OpenGL: Fix to be able to run on ES 2.0 / WebGL 1.0. [@rmitton, @gabrielcuvillier]
 - Examples: OpenGL: Fix for OSX not supporting OpenGL 4.5, we don't try to read GL_CLIP_ORIGIN
   even if the OpenGL headers/loader happens to define the value. (#2366, #2186)
 - Examples: Allegro: Added support for touch events (emulating mouse). (#2219) [@dos1]

examples/imgui_impl_opengl3.cpp

@@ -12,6 +12,7 @@
 
 // CHANGELOG
 // (minor and older changes stripped away, please see git history for details)
+//  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.
 //  2019-02-01: OpenGL: Using GLSL 410 shaders for any version over 410 (e.g. 430, 450).
@@ -69,14 +70,18 @@
 #include "TargetConditionals.h"
 #endif
 
-// iOS, Android and Emscripten can use GL ES 3
-// Call ImGui_ImplOpenGL3_Init() with "#version 300 es"
-#if (defined(__APPLE__) && TARGET_OS_IOS) || (defined(__ANDROID__)) || (defined(__EMSCRIPTEN__))
-#define USE_GL_ES3
+// Auto-detect GL version
+#if !defined(IMGUI_IMPL_OPENGL_ES2) && !defined(IMGUI_IMPL_OPENGL_ES3)
+#if (defined(__APPLE__) && TARGET_OS_IOS) || (defined(__ANDROID__))
+#define IMGUI_IMPL_OPENGL_ES3       // iOS, Android  -> GL ES 3, "#version 300 es"
+#elif defined(__EMSCRIPTEN__)
+#define IMGUI_IMPL_OPENGL_ES2       // Emscripten    -> GL ES 2, "#version 100"
+#endif
 #endif
 
-#ifdef USE_GL_ES3
-// OpenGL ES 3
+#if defined(IMGUI_IMPL_OPENGL_ES2)
+#include <GLES2/gl2.h>
+#elif defined(IMGUI_IMPL_OPENGL_ES3)
 #include <GLES3/gl3.h>  // Use GL ES 3
 #else
 // About Desktop OpenGL function loaders:
@@ -109,7 +114,10 @@ bool    ImGui_ImplOpenGL3_Init(const char* glsl_version)
     io.BackendRendererName = "imgui_impl_opengl3";
 
     // Store GLSL version string so we can refer to it later in case we recreate shaders. Note: GLSL version is NOT the same as GL version. Leave this to NULL if unsure.
-#ifdef USE_GL_ES3
+#if defined(IMGUI_IMPL_OPENGL_ES2)
+    if (glsl_version == NULL)
+        glsl_version = "#version 100";
+#elif defined(IMGUI_IMPL_OPENGL_ES3)
     if (glsl_version == NULL)
         glsl_version = "#version 300 es";
 #else
@@ -154,7 +162,9 @@ void    ImGui_ImplOpenGL3_RenderDrawData(ImDrawData* draw_data)
     GLint last_sampler; glGetIntegerv(GL_SAMPLER_BINDING, &last_sampler);
 #endif
     GLint last_array_buffer; glGetIntegerv(GL_ARRAY_BUFFER_BINDING, &last_array_buffer);
+#ifndef IMGUI_IMPL_OPENGL_ES2
     GLint last_vertex_array; glGetIntegerv(GL_VERTEX_ARRAY_BINDING, &last_vertex_array);
+#endif
 #ifdef GL_POLYGON_MODE
     GLint last_polygon_mode[2]; glGetIntegerv(GL_POLYGON_MODE, last_polygon_mode);
 #endif
@@ -208,11 +218,14 @@ void    ImGui_ImplOpenGL3_RenderDrawData(ImDrawData* draw_data)
 #ifdef GL_SAMPLER_BINDING
     glBindSampler(0, 0); // We use combined texture/sampler state. Applications using GL 3.3 may set that otherwise.
 #endif
+
+#ifndef IMGUI_IMPL_OPENGL_ES2
     // Recreate the VAO every time
     // (This is to easily allow multiple GL contexts. VAO are not shared among GL contexts, and we don't track creation/deletion of windows so we don't have an obvious key to use to cache them.)
     GLuint vao_handle = 0;
     glGenVertexArrays(1, &vao_handle);
     glBindVertexArray(vao_handle);
+#endif
     glBindBuffer(GL_ARRAY_BUFFER, g_VboHandle);
     glEnableVertexAttribArray(g_AttribLocationPosition);
     glEnableVertexAttribArray(g_AttribLocationUV);
@@ -270,7 +283,9 @@ void    ImGui_ImplOpenGL3_RenderDrawData(ImDrawData* draw_data)
             idx_buffer_offset += pcmd->ElemCount * sizeof(ImDrawIdx);
         }
     }
+#ifndef IMGUI_IMPL_OPENGL_ES2
     glDeleteVertexArrays(1, &vao_handle);
+#endif
 
     // Restore modified GL state
     glUseProgram(last_program);
@@ -279,7 +294,9 @@ void    ImGui_ImplOpenGL3_RenderDrawData(ImDrawData* draw_data)
     glBindSampler(0, last_sampler);
 #endif
     glActiveTexture(last_active_texture);
+#ifndef IMGUI_IMPL_OPENGL_ES2
     glBindVertexArray(last_vertex_array);
+#endif
     glBindBuffer(GL_ARRAY_BUFFER, last_array_buffer);
     glBlendEquationSeparate(last_blend_equation_rgb, last_blend_equation_alpha);
     glBlendFuncSeparate(last_blend_src_rgb, last_blend_dst_rgb, last_blend_src_alpha, last_blend_dst_alpha);
@@ -309,7 +326,9 @@ bool ImGui_ImplOpenGL3_CreateFontsTexture()
     glBindTexture(GL_TEXTURE_2D, g_FontTexture);
     glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
     glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
+#ifdef GL_UNPACK_ROW_LENGTH
     glPixelStorei(GL_UNPACK_ROW_LENGTH, 0);
+#endif
     glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, pixels);
 
     // Store our identifier
@@ -371,10 +390,13 @@ static bool CheckProgram(GLuint handle, const char* desc)
 bool    ImGui_ImplOpenGL3_CreateDeviceObjects()
 {
     // Backup GL state
-    GLint last_texture, last_array_buffer, last_vertex_array;
+    GLint last_texture, last_array_buffer;
     glGetIntegerv(GL_TEXTURE_BINDING_2D, &last_texture);
     glGetIntegerv(GL_ARRAY_BUFFER_BINDING, &last_array_buffer);
+#ifndef IMGUI_IMPL_OPENGL_ES2
+    GLint last_vertex_array;
     glGetIntegerv(GL_VERTEX_ARRAY_BINDING, &last_vertex_array);
+#endif
 
     // Parse GLSL version string
     int glsl_version = 130;
@@ -538,7 +560,9 @@ bool    ImGui_ImplOpenGL3_CreateDeviceObjects()
     // Restore modified GL state
     glBindTexture(GL_TEXTURE_2D, last_texture);
     glBindBuffer(GL_ARRAY_BUFFER, last_array_buffer);
+#ifndef IMGUI_IMPL_OPENGL_ES2
     glBindVertexArray(last_vertex_array);
+#endif
 
     return true;
 }

examples/imgui_impl_opengl3.h

@@ -22,6 +22,10 @@
 
 #pragma once
 
+// Specific OpenGL versions
+//#define IMGUI_IMPL_OPENGL_ES2     // Auto-detected on Emscripten
+//#define IMGUI_IMPL_OPENGL_ES3     // Auto-detected on iOS/Android
+
 // Set default OpenGL3 loader to be gl3w
 #if !defined(IMGUI_IMPL_OPENGL_LOADER_GL3W)     \
  && !defined(IMGUI_IMPL_OPENGL_LOADER_GLEW)     \