text: // dear imgui: Renderer Backend for modern OpenGL with shaders / programmatic pipeline
  // - Desktop GL: 2.x 3.x 4.x
  // - Embedded GL: ES 2.0 (WebGL 1.0), ES 3.0 (WebGL 2.0)
  // This needs to be used along with a Platform Backend (e.g. GLFW, SDL, Win32, custom..)
  
  // Implemented features:
  //  [X] Renderer: User texture binding. Use 'GLuint' OpenGL texture identifier as void*/ImTextureID. Read the FAQ about ImTextureID!
  //  [X] Renderer: Multi-viewport support. Enable with 'io.ConfigFlags |= ImGuiConfigFlags_ViewportsEnable'.
  //  [x] Renderer: Desktop GL only: Support for large meshes (64k+ vertices) with 16-bit indices.
  
  // You can use unmodified imgui_impl_* files in your project. See examples/ folder for examples of using this.
  // Prefer including the entire imgui/ repository into your project (either as a copy or as a submodule), and only build the backends you need.
  // If you are new to Dear ImGui, read documentation from the docs/ folder + read the top of imgui.cpp.
  // Read online: https://github.com/ocornut/imgui/tree/master/docs
  
  // CHANGELOG
  // (minor and older changes stripped away, please see git history for details)
  //  2021-XX-XX: Platform: Added support for multiple windows via the ImGuiPlatformIO interface.
  //  2021-12-15: OpenGL: Using buffer orphaning + glBufferSubData(), seems to fix leaks with multi-viewports with some Intel HD drivers.
  //  2021-08-23: OpenGL: Fixed ES 3.0 shader ("#version 300 es") use normal precision floats to avoid wobbly rendering at HD resolutions.
  //  2021-08-19: OpenGL: Embed and use our own minimal GL loader (imgui_impl_opengl3_loader.h), removing requirement and support for third-party loader.
  //  2021-06-29: Reorganized backend to pull data from a single structure to facilitate usage with multiple-contexts (all g_XXXX access changed to bd->XXXX).
  //  2021-06-25: OpenGL: Use OES_vertex_array extension on Emscripten + backup/restore current state.
  //  2021-06-21: OpenGL: Destroy individual vertex/fragment shader objects right after they are linked into the main shader.
  //  2021-05-24: OpenGL: Access GL_CLIP_ORIGIN when "GL_ARB_clip_control" extension is detected, inside of just OpenGL 4.5 version.
  //  2021-05-19: OpenGL: Replaced direct access to ImDrawCmd::TextureId with a call to ImDrawCmd::GetTexID(). (will become a requirement)
  //  2021-04-06: OpenGL: Don't try to read GL_CLIP_ORIGIN unless we're OpenGL 4.5 or greater.
  //  2021-02-18: OpenGL: Change blending equation to preserve alpha in output buffer.
  //  2021-01-03: OpenGL: Backup, setup and restore GL_STENCIL_TEST state.
  //  2020-10-23: OpenGL: Backup, setup and restore GL_PRIMITIVE_RESTART state.
  //  2020-10-15: OpenGL: Use glGetString(GL_VERSION) instead of glGetIntegerv(GL_MAJOR_VERSION, ...) when the later returns zero (e.g. Desktop GL 2.x)
  //  2020-09-17: OpenGL: Fix to avoid compiling/calling glBindSampler() on ES or pre 3.3 context which have the defines set by a loader.
  //  2020-07-10: OpenGL: Added support for glad2 OpenGL loader.
  //  2020-05-08: OpenGL: Made default GLSL version 150 (instead of 130) on OSX.
  //  2020-04-21: OpenGL: Fixed handling of glClipControl(GL_UPPER_LEFT) by inverting projection matrix.
  //  2020-04-12: OpenGL: Fixed context version check mistakenly testing for 4.0+ instead of 3.2+ to enable ImGuiBackendFlags_RendererHasVtxOffset.
  //  2020-03-24: OpenGL: Added support for glbinding 2.x OpenGL loader.
  //  2020-01-07: OpenGL: Added support for glbinding 3.x OpenGL loader.
  //  2019-10-25: OpenGL: Using a combination of GL define and runtime GL version to decide whether to use glDrawElementsBaseVertex(). Fix building with pre-3.2 GL loaders.
  //  2019-09-22: OpenGL: Detect default GL loader using __has_include compiler facility.
  //  2019-09-16: OpenGL: Tweak initialization code to allow application calling ImGui_ImplOpenGL3_CreateFontsTexture() before the first NewFrame() call.
  //  2019-05-29: OpenGL: Desktop GL only: Added support for large mesh (64K+ vertices), enable ImGuiBackendFlags_RendererHasVtxOffset flag.
  //  2019-04-30: OpenGL: Added support for special ImDrawCallback_ResetRenderState callback to reset render state.
  //  2019-03-29: OpenGL: Not calling glBindBuffer more than necessary in the render loop.
  //  2019-03-15: OpenGL: Added a 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.
  //  2019-02-01: OpenGL: Using GLSL 410 shaders for any version over 410 (e.g. 430, 450).
  //  2018-11-30: Misc: Setting up io.BackendRendererName so it can be displayed in the About Window.
  //  2018-11-13: OpenGL: Support for GL 4.5's glClipControl(GL_UPPER_LEFT) / GL_CLIP_ORIGIN.
  //  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.
  //  2018-06-08: Misc: Extracted imgui_impl_opengl3.cpp/.h away from the old combined GLFW/SDL+OpenGL3 examples.
  //  2018-06-08: OpenGL: Use draw_data->DisplayPos and draw_data->DisplaySize to setup projection matrix and clipping rectangle.
  //  2018-05-25: OpenGL: Removed unnecessary backup/restore of GL_ELEMENT_ARRAY_BUFFER_BINDING since this is part of the VAO state.
  //  2018-05-14: OpenGL: Making the call to glBindSampler() optional so 3.2 context won't fail if the function is a NULL pointer.
  //  2018-03-06: OpenGL: Added const char* glsl_version parameter to ImGui_ImplOpenGL3_Init() so user can override the GLSL version e.g. "#version 150".
  //  2018-02-23: OpenGL: Create the VAO in the render function so the setup can more easily be used with multiple shared GL context.
  //  2018-02-16: Misc: Obsoleted the io.RenderDrawListsFn callback and exposed ImGui_ImplSdlGL3_RenderDrawData() in the .h file so you can call it yourself.
  //  2018-01-07: OpenGL: Changed GLSL shader version from 330 to 150.
  //  2017-09-01: OpenGL: Save and restore current bound sampler. Save and restore current polygon mode.
  //  2017-05-01: OpenGL: Fixed save and restore of current blend func state.
  //  2017-05-01: OpenGL: Fixed save and restore of current GL_ACTIVE_TEXTURE.
  //  2016-09-05: OpenGL: Fixed save and restore of current scissor rectangle.
  //  2016-07-29: OpenGL: Explicitly setting GL_UNPACK_ROW_LENGTH to reduce issues because SDL changes it. (#752)
  
  //----------------------------------------
  // OpenGL    GLSL      GLSL
  // version   version   string
  //----------------------------------------
  //  2.0       110       "#version 110"
  //  2.1       120       "#version 120"
  //  3.0       130       "#version 130"
  //  3.1       140       "#version 140"
  //  3.2       150       "#version 150"
  //  3.3       330       "#version 330 core"
  //  4.0       400       "#version 400 core"
  //  4.1       410       "#version 410 core"
  //  4.2       420       "#version 410 core"
  //  4.3       430       "#version 430 core"
  //  ES 2.0    100       "#version 100"      = WebGL 1.0
  //  ES 3.0    300       "#version 300 es"   = WebGL 2.0
  //----------------------------------------
  
  #if defined(_MSC_VER) && !defined(_CRT_SECURE_NO_WARNINGS)
  #define _CRT_SECURE_NO_WARNINGS
  #endif
  
  #include "imgui.h"
  #include "imgui_impl_opengl3.h"
  #include <stdio.h>
  #if defined(_MSC_VER) && _MSC_VER <= 1500 // MSVC 2008 or earlier
  #include <stddef.h>     // intptr_t
  #else
  #include <stdint.h>     // intptr_t
  #endif
  
  // GL includes
  #if defined(IMGUI_IMPL_OPENGL_ES2)
  #if (defined(__APPLE__) && (TARGET_OS_IOS || TARGET_OS_TV))
  #include <OpenGLES/ES2/gl.h>    // Use GL ES 2
  #else
  #include <GLES2/gl2.h>          // Use GL ES 2
  #endif
  #if defined(__EMSCRIPTEN__)
  #ifndef GL_GLEXT_PROTOTYPES
  #define GL_GLEXT_PROTOTYPES
  #endif
  #include <GLES2/gl2ext.h>
  #endif
  #elif defined(IMGUI_IMPL_OPENGL_ES3)
  #if defined(__APPLE__)
  #include <TargetConditionals.h>
  #endif
  #if (defined(__APPLE__) && (TARGET_OS_IOS || TARGET_OS_TV))
  #include <OpenGLES/ES3/gl.h>    // Use GL ES 3
  #else
  #include <GLES3/gl3.h>          // Use GL ES 3
  #endif
  #elif !defined(IMGUI_IMPL_OPENGL_LOADER_CUSTOM)
  // 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 using our own minimal custom loader based on gl3w.
  // In the rest of your app/engine, you can use another loader of your choice (gl3w, glew, glad, glbinding, glext, glLoadGen, etc.).
  // If you happen to be developing a new feature for this backend (imgui_impl_opengl3.cpp):
  // - You may need to regenerate imgui_impl_opengl3_loader.h to add new symbols. See https://github.com/dearimgui/gl3w_stripped
  // - You can temporarily use an unstripped version. See https://github.com/dearimgui/gl3w_stripped/releases
  // Changes to this backend using new APIs should be accompanied by a regenerated stripped loader version.
  #define IMGL3W_IMPL
  #include "imgui_impl_opengl3_loader.h"
  #endif
  
  // Vertex arrays are not supported on ES2/WebGL1 unless Emscripten which uses an extension
  #ifndef IMGUI_IMPL_OPENGL_ES2
  #define IMGUI_IMPL_OPENGL_USE_VERTEX_ARRAY
  #elif defined(__EMSCRIPTEN__)
  #define IMGUI_IMPL_OPENGL_USE_VERTEX_ARRAY
  #define glBindVertexArray       glBindVertexArrayOES
  #define glGenVertexArrays       glGenVertexArraysOES
  #define glDeleteVertexArrays    glDeleteVertexArraysOES
  #define GL_VERTEX_ARRAY_BINDING GL_VERTEX_ARRAY_BINDING_OES
  #endif
  
  // Desktop GL 2.0+ has glPolygonMode() which GL ES and WebGL don't have.
  #ifdef GL_POLYGON_MODE
  #define IMGUI_IMPL_HAS_POLYGON_MODE
  #endif
  
  // Desktop GL 3.2+ has glDrawElementsBaseVertex() which GL ES and WebGL don't have.
  #if !defined(IMGUI_IMPL_OPENGL_ES2) && !defined(IMGUI_IMPL_OPENGL_ES3) && defined(GL_VERSION_3_2)
  #define IMGUI_IMPL_OPENGL_MAY_HAVE_VTX_OFFSET
  #endif
  
  // Desktop GL 3.3+ has glBindSampler()
  #if !defined(IMGUI_IMPL_OPENGL_ES2) && !defined(IMGUI_IMPL_OPENGL_ES3) && defined(GL_VERSION_3_3)
  #define IMGUI_IMPL_OPENGL_MAY_HAVE_BIND_SAMPLER
  #endif
  
  // Desktop GL 3.1+ has GL_PRIMITIVE_RESTART state
  #if !defined(IMGUI_IMPL_OPENGL_ES2) && !defined(IMGUI_IMPL_OPENGL_ES3) && defined(GL_VERSION_3_1)
  #define IMGUI_IMPL_OPENGL_MAY_HAVE_PRIMITIVE_RESTART
  #endif
  
  // Desktop GL use extension detection
  #if !defined(IMGUI_IMPL_OPENGL_ES2) && !defined(IMGUI_IMPL_OPENGL_ES3)
  #define IMGUI_IMPL_OPENGL_MAY_HAVE_EXTENSIONS
  #endif
  
  // OpenGL Data
  struct ImGui_ImplOpenGL3_Data
  {
      GLuint          GlVersion;               // Extracted at runtime using GL_MAJOR_VERSION, GL_MINOR_VERSION queries (e.g. 320 for GL 3.2)
      char            GlslVersionString[32];   // Specified by user or detected based on compile time GL settings.
      GLuint          FontTextures[32] = { };
      GLuint          ShaderHandle;
      GLint           AttribLocationTex;       // Uniforms location
      GLint           AttribLocationProjMtx;
      GLuint          AttribLocationVtxPos;    // Vertex attributes location
      GLuint          AttribLocationVtxUV;
      GLuint          AttribLocationVtxColor;
      unsigned int    VboHandle, ElementsHandle;
      GLsizeiptr      VertexBufferSize;
      GLsizeiptr      IndexBufferSize;
      bool            HasClipOrigin;
  
      ImGui_ImplOpenGL3_Data() { memset(this, 0, sizeof(*this)); }
  };
  
  // Backend data stored in io.BackendRendererUserData to allow support for multiple Dear ImGui contexts
  // It is STRONGLY preferred that you use docking branch with multi-viewports (== single Dear ImGui context + multiple windows) instead of multiple Dear ImGui contexts.
  static ImGui_ImplOpenGL3_Data* ImGui_ImplOpenGL3_GetBackendData()
  {
      return ImGui::GetCurrentContext() ? (ImGui_ImplOpenGL3_Data*)ImGui::GetIO().BackendRendererUserData : NULL;
  }
  
  // Forward Declarations
  static void ImGui_ImplOpenGL3_InitPlatformInterface();
  static void ImGui_ImplOpenGL3_ShutdownPlatformInterface();
  // OpenGL vertex attribute state
  #ifndef IMGUI_IMPL_OPENGL_USE_VERTEX_ARRAY
  struct ImGui_ImplOpenGL3_VtxAttribState
  {
      GLint   Enabled;
      GLint   Size;
      GLint   Type;
      GLint   Normalized;
      GLint   Stride;
      GLvoid* Ptr;
  };
  
  static void ImGui_ImplOpenGL3_BackupVertexAttribState(GLint index, ImGui_ImplOpenGL3_VtxAttribState* state)
  {
      glGetVertexAttribiv(index, GL_VERTEX_ATTRIB_ARRAY_ENABLED, &state->Enabled);
      glGetVertexAttribiv(index, GL_VERTEX_ATTRIB_ARRAY_SIZE, &state->Size);
      glGetVertexAttribiv(index, GL_VERTEX_ATTRIB_ARRAY_TYPE, &state->Type);
      glGetVertexAttribiv(index, GL_VERTEX_ATTRIB_ARRAY_NORMALIZED, &state->Normalized);
      glGetVertexAttribiv(index, GL_VERTEX_ATTRIB_ARRAY_STRIDE, &state->Stride);
      glGetVertexAttribPointerv(index, GL_VERTEX_ATTRIB_ARRAY_POINTER, &state->Ptr);
  }
  
  static void ImGui_ImplOpenGL3_RestoreVertexAttribState(GLint index, ImGui_ImplOpenGL3_VtxAttribState* state)
  {
      glVertexAttribPointer(index, state->Size, state->Type, state->Normalized, state->Stride, state->Ptr);
      if (state->Enabled) glEnableVertexAttribArray(index); else glDisableVertexAttribArray(index);
  }
  #endif
  
  // Functions
  bool    ImGui_ImplOpenGL3_Init(const char* glsl_version)
  {
      ImGuiIO& io = ImGui::GetIO();
      IM_ASSERT(io.BackendRendererUserData == NULL && "Already initialized a renderer backend!");
  
      // Initialize our loader
  #if !defined(IMGUI_IMPL_OPENGL_ES2) && !defined(IMGUI_IMPL_OPENGL_ES3) && !defined(IMGUI_IMPL_OPENGL_LOADER_CUSTOM)
      if (imgl3wInit() != 0)
      {
          fprintf(stderr, "Failed to initialize OpenGL loader!\n");
          return false;
      }
  #endif
  
      // Setup backend capabilities flags
      ImGui_ImplOpenGL3_Data* bd = IM_NEW(ImGui_ImplOpenGL3_Data)();
      io.BackendRendererUserData = (void*)bd;
      io.BackendRendererName = "imgui_impl_opengl3";
  
      // Query for GL version (e.g. 320 for GL 3.2)
  #if !defined(IMGUI_IMPL_OPENGL_ES2)
      GLint major = 0;
      GLint minor = 0;
      glGetIntegerv(GL_MAJOR_VERSION, &major);
      glGetIntegerv(GL_MINOR_VERSION, &minor);
      if (major == 0 && minor == 0)
      {
          // Query GL_VERSION in desktop GL 2.x, the string will start with "<major>.<minor>"
          const char* gl_version = (const char*)glGetString(GL_VERSION);
          sscanf(gl_version, "%d.%d", &major, &minor);
      }
      bd->GlVersion = (GLuint)(major * 100 + minor * 10);
  #else
      bd->GlVersion = 200; // GLES 2
  #endif
  
  #ifdef IMGUI_IMPL_OPENGL_MAY_HAVE_VTX_OFFSET
      if (bd->GlVersion >= 320)
          io.BackendFlags |= ImGuiBackendFlags_RendererHasVtxOffset;  // We can honor the ImDrawCmd::VtxOffset field, allowing for large meshes.
  #endif
      io.BackendFlags |= ImGuiBackendFlags_RendererHasViewports;  // We can create multi-viewports on the Renderer side (optional)
  
      // 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.
      if (glsl_version == NULL)
      {
  #if defined(IMGUI_IMPL_OPENGL_ES2)
          glsl_version = "#version 100";
  #elif defined(IMGUI_IMPL_OPENGL_ES3)
          glsl_version = "#version 300 es";
  #elif defined(__APPLE__)
          glsl_version = "#version 150";
  #else
          glsl_version = "#version 130";
  #endif
      }
      IM_ASSERT((int)strlen(glsl_version) + 2 < IM_ARRAYSIZE(bd->GlslVersionString));
      strcpy(bd->GlslVersionString, glsl_version);
      strcat(bd->GlslVersionString, "\n");
  
      // Make an arbitrary GL call (we don't actually need the result)
      // IF YOU GET A CRASH HERE: it probably means the OpenGL function loader didn't do its job. Let us know!
      GLint current_texture;
      glGetIntegerv(GL_TEXTURE_BINDING_2D, &current_texture);
  
      // Detect extensions we support
      bd->HasClipOrigin = (bd->GlVersion >= 450);
  #ifdef IMGUI_IMPL_OPENGL_MAY_HAVE_EXTENSIONS
      GLint num_extensions = 0;
      glGetIntegerv(GL_NUM_EXTENSIONS, &num_extensions);
      for (GLint i = 0; i < num_extensions; i++)
      {
          const char* extension = (const char*)glGetStringi(GL_EXTENSIONS, i);
          if (extension != NULL && strcmp(extension, "GL_ARB_clip_control") == 0)
              bd->HasClipOrigin = true;
      }
  #endif
  
      if (io.ConfigFlags & ImGuiConfigFlags_ViewportsEnable)
          ImGui_ImplOpenGL3_InitPlatformInterface();
  
      return true;
  }
  
  void    ImGui_ImplOpenGL3_Shutdown()
  {
      ImGui_ImplOpenGL3_Data* bd = ImGui_ImplOpenGL3_GetBackendData();
      IM_ASSERT(bd != NULL && "No renderer backend to shutdown, or already shutdown?");
      ImGuiIO& io = ImGui::GetIO();
  
      ImGui_ImplOpenGL3_ShutdownPlatformInterface();
      ImGui_ImplOpenGL3_DestroyDeviceObjects();
      io.BackendRendererName = NULL;
      io.BackendRendererUserData = NULL;
      IM_DELETE(bd);
  }
  
  void    ImGui_ImplOpenGL3_NewFrame()
  {
      ImGui_ImplOpenGL3_Data* bd = ImGui_ImplOpenGL3_GetBackendData();
      IM_ASSERT(bd != NULL && "Did you call ImGui_ImplOpenGL3_Init()?");
  
      if (!bd->ShaderHandle)
          ImGui_ImplOpenGL3_CreateDeviceObjects();
  }
  
  static void ImGui_ImplOpenGL3_SetupRenderState(ImDrawData* draw_data, int fb_width, int fb_height, GLuint vertex_array_object)
  {
      ImGui_ImplOpenGL3_Data* bd = ImGui_ImplOpenGL3_GetBackendData();
  
      // Setup render state: alpha-blending enabled, no face culling, no depth testing, scissor enabled, polygon fill
      glEnable(GL_BLEND);
      glBlendEquation(GL_FUNC_ADD);
      glBlendFuncSeparate(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA, GL_ONE, GL_ONE_MINUS_SRC_ALPHA);
      glDisable(GL_CULL_FACE);
      glDisable(GL_DEPTH_TEST);
      glDisable(GL_STENCIL_TEST);
      glEnable(GL_SCISSOR_TEST);
  #ifdef IMGUI_IMPL_OPENGL_MAY_HAVE_PRIMITIVE_RESTART
      if (bd->GlVersion >= 310)
          glDisable(GL_PRIMITIVE_RESTART);
  #endif
  #ifdef IMGUI_IMPL_HAS_POLYGON_MODE
      glPolygonMode(GL_FRONT_AND_BACK, GL_FILL);
  #endif
  
      // Support for GL 4.5 rarely used glClipControl(GL_UPPER_LEFT)
  #if defined(GL_CLIP_ORIGIN)
      bool clip_origin_lower_left = true;
      if (bd->HasClipOrigin)
      {
          GLenum current_clip_origin = 0; glGetIntegerv(GL_CLIP_ORIGIN, (GLint*)&current_clip_origin);
          if (current_clip_origin == GL_UPPER_LEFT)
              clip_origin_lower_left = false;
      }
  #endif
  
      // Setup viewport, orthographic projection matrix
      // Our visible imgui space lies from draw_data->DisplayPos (top left) to draw_data->DisplayPos+data_data->DisplaySize (bottom right). DisplayPos is (0,0) for single viewport apps.
      glViewport(0, 0, (GLsizei)fb_width, (GLsizei)fb_height);
      float L = draw_data->DisplayPos.x;
      float R = draw_data->DisplayPos.x + draw_data->DisplaySize.x;
      float T = draw_data->DisplayPos.y;
      float B = draw_data->DisplayPos.y + draw_data->DisplaySize.y;
  #if defined(GL_CLIP_ORIGIN)
      if (!clip_origin_lower_left) { float tmp = T; T = B; B = tmp; } // Swap top and bottom if origin is upper left
  #endif
      const float ortho_projection[4][4] =
      {
          { 2.0f/(R-L),   0.0f,         0.0f,   0.0f },
          { 0.0f,         2.0f/(T-B),   0.0f,   0.0f },
          { 0.0f,         0.0f,        -1.0f,   0.0f },
          { (R+L)/(L-R),  (T+B)/(B-T),  0.0f,   1.0f },
      };
      glUseProgram(bd->ShaderHandle);
      glUniform1i(bd->AttribLocationTex, 0);
      glUniformMatrix4fv(bd->AttribLocationProjMtx, 1, GL_FALSE, &ortho_projection[0][0]);
  
  #ifdef IMGUI_IMPL_OPENGL_MAY_HAVE_BIND_SAMPLER
      if (bd->GlVersion >= 330)
          glBindSampler(0, 0); // We use combined texture/sampler state. Applications using GL 3.3 may set that otherwise.
  #endif
  
      (void)vertex_array_object;
  #ifdef IMGUI_IMPL_OPENGL_USE_VERTEX_ARRAY
      glBindVertexArray(vertex_array_object);
  #endif
  
      // Bind vertex/index buffers and setup attributes for ImDrawVert
      glBindBuffer(GL_ARRAY_BUFFER, bd->VboHandle);
      glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, bd->ElementsHandle);
      glEnableVertexAttribArray(bd->AttribLocationVtxPos);
      glEnableVertexAttribArray(bd->AttribLocationVtxUV);
      glEnableVertexAttribArray(bd->AttribLocationVtxColor);
      glVertexAttribPointer(bd->AttribLocationVtxPos,   2, GL_FLOAT,         GL_FALSE, sizeof(ImDrawVert), (GLvoid*)IM_OFFSETOF(ImDrawVert, pos));
      glVertexAttribPointer(bd->AttribLocationVtxUV,    2, GL_FLOAT,         GL_FALSE, sizeof(ImDrawVert), (GLvoid*)IM_OFFSETOF(ImDrawVert, uv));
      glVertexAttribPointer(bd->AttribLocationVtxColor, 4, GL_UNSIGNED_BYTE, GL_TRUE,  sizeof(ImDrawVert), (GLvoid*)IM_OFFSETOF(ImDrawVert, col));
  }
  
  // OpenGL3 Render function.
  // Note that this implementation is little overcomplicated because we are saving/setting up/restoring every OpenGL state explicitly.
  // This is in order to be able to run within an OpenGL engine that doesn't do so.
  void    ImGui_ImplOpenGL3_RenderDrawData(ImDrawData* draw_data)
  {
      // Avoid rendering when minimized, scale coordinates for retina displays (screen coordinates != framebuffer coordinates)
      int fb_width = (int)(draw_data->DisplaySize.x * draw_data->FramebufferScale.x);
      int fb_height = (int)(draw_data->DisplaySize.y * draw_data->FramebufferScale.y);
      if (fb_width <= 0 || fb_height <= 0)
          return;
  
      ImGui_ImplOpenGL3_Data* bd = ImGui_ImplOpenGL3_GetBackendData();
  
      // Backup GL state
      GLenum last_active_texture; glGetIntegerv(GL_ACTIVE_TEXTURE, (GLint*)&last_active_texture);
      glActiveTexture(GL_TEXTURE0);
      GLuint last_program; glGetIntegerv(GL_CURRENT_PROGRAM, (GLint*)&last_program);
      GLuint last_texture; glGetIntegerv(GL_TEXTURE_BINDING_2D, (GLint*)&last_texture);
  #ifdef IMGUI_IMPL_OPENGL_MAY_HAVE_BIND_SAMPLER
      GLuint last_sampler; if (bd->GlVersion >= 330) { glGetIntegerv(GL_SAMPLER_BINDING, (GLint*)&last_sampler); } else { last_sampler = 0; }
  #endif
      GLuint last_array_buffer; glGetIntegerv(GL_ARRAY_BUFFER_BINDING, (GLint*)&last_array_buffer);
  
      // This is part of VAO on OpenGL 3.0+ and OpenGL ES 3.0+.
  #ifndef IMGUI_IMPL_OPENGL_USE_VERTEX_ARRAY
      GLint last_element_array_buffer; glGetIntegerv(GL_ELEMENT_ARRAY_BUFFER_BINDING, &last_element_array_buffer);
      ImGui_ImplOpenGL3_VtxAttribState last_vtx_attrib_state_pos, last_vtx_attrib_state_uv, last_vtx_attrib_state_color;
      ImGui_ImplOpenGL3_BackupVertexAttribState(bd->AttribLocationVtxPos, &last_vtx_attrib_state_pos);
      ImGui_ImplOpenGL3_BackupVertexAttribState(bd->AttribLocationVtxUV, &last_vtx_attrib_state_uv);
      ImGui_ImplOpenGL3_BackupVertexAttribState(bd->AttribLocationVtxColor, &last_vtx_attrib_state_color);
  #endif
  #ifdef IMGUI_IMPL_OPENGL_USE_VERTEX_ARRAY
      GLuint last_vertex_array_object; glGetIntegerv(GL_VERTEX_ARRAY_BINDING, (GLint*)&last_vertex_array_object);
  #endif
  #ifdef IMGUI_IMPL_HAS_POLYGON_MODE
      GLint last_polygon_mode[2]; glGetIntegerv(GL_POLYGON_MODE, last_polygon_mode);
  #endif
      GLint last_viewport[4]; glGetIntegerv(GL_VIEWPORT, last_viewport);
      GLint last_scissor_box[4]; glGetIntegerv(GL_SCISSOR_BOX, last_scissor_box);
      GLenum last_blend_src_rgb; glGetIntegerv(GL_BLEND_SRC_RGB, (GLint*)&last_blend_src_rgb);
      GLenum last_blend_dst_rgb; glGetIntegerv(GL_BLEND_DST_RGB, (GLint*)&last_blend_dst_rgb);
      GLenum last_blend_src_alpha; glGetIntegerv(GL_BLEND_SRC_ALPHA, (GLint*)&last_blend_src_alpha);
      GLenum last_blend_dst_alpha; glGetIntegerv(GL_BLEND_DST_ALPHA, (GLint*)&last_blend_dst_alpha);
      GLenum last_blend_equation_rgb; glGetIntegerv(GL_BLEND_EQUATION_RGB, (GLint*)&last_blend_equation_rgb);
      GLenum last_blend_equation_alpha; glGetIntegerv(GL_BLEND_EQUATION_ALPHA, (GLint*)&last_blend_equation_alpha);
      GLboolean last_enable_blend = glIsEnabled(GL_BLEND);
      GLboolean last_enable_cull_face = glIsEnabled(GL_CULL_FACE);
      GLboolean last_enable_depth_test = glIsEnabled(GL_DEPTH_TEST);
      GLboolean last_enable_stencil_test = glIsEnabled(GL_STENCIL_TEST);
      GLboolean last_enable_scissor_test = glIsEnabled(GL_SCISSOR_TEST);
  #ifdef IMGUI_IMPL_OPENGL_MAY_HAVE_PRIMITIVE_RESTART
      GLboolean last_enable_primitive_restart = (bd->GlVersion >= 310) ? glIsEnabled(GL_PRIMITIVE_RESTART) : GL_FALSE;
  #endif
  
      // Setup desired GL state
      // Recreate the VAO every time (this is to easily allow multiple GL contexts to be rendered to. VAO are not shared among GL contexts)
      // The renderer would actually work without any VAO bound, but then our VertexAttrib calls would overwrite the default one currently bound.
      GLuint vertex_array_object = 0;
  #ifdef IMGUI_IMPL_OPENGL_USE_VERTEX_ARRAY
      glGenVertexArrays(1, &vertex_array_object);
  #endif
      ImGui_ImplOpenGL3_SetupRenderState(draw_data, fb_width, fb_height, vertex_array_object);
  
      // Will project scissor/clipping rectangles into framebuffer space
      ImVec2 clip_off = draw_data->DisplayPos;         // (0,0) unless using multi-viewports
      ImVec2 clip_scale = draw_data->FramebufferScale; // (1,1) unless using retina display which are often (2,2)
  
      // Render command lists
      for (int n = 0; n < draw_data->CmdListsCount; n++)
      {
          const ImDrawList* cmd_list = draw_data->CmdLists[n];
  
          // Upload vertex/index buffers
          GLsizeiptr vtx_buffer_size = (GLsizeiptr)cmd_list->VtxBuffer.Size * (int)sizeof(ImDrawVert);
          GLsizeiptr idx_buffer_size = (GLsizeiptr)cmd_list->IdxBuffer.Size * (int)sizeof(ImDrawIdx);
          if (bd->VertexBufferSize < vtx_buffer_size)
          {
              bd->VertexBufferSize = vtx_buffer_size;
              glBufferData(GL_ARRAY_BUFFER, bd->VertexBufferSize, NULL, GL_STREAM_DRAW);
          }
          if (bd->IndexBufferSize < idx_buffer_size)
          {
              bd->IndexBufferSize = idx_buffer_size;
              glBufferData(GL_ELEMENT_ARRAY_BUFFER, bd->IndexBufferSize, NULL, GL_STREAM_DRAW);
          }
          glBufferSubData(GL_ARRAY_BUFFER, 0, vtx_buffer_size, (const GLvoid*)cmd_list->VtxBuffer.Data);
          glBufferSubData(GL_ELEMENT_ARRAY_BUFFER, 0, idx_buffer_size, (const GLvoid*)cmd_list->IdxBuffer.Data);
  
          for (int cmd_i = 0; cmd_i < cmd_list->CmdBuffer.Size; cmd_i++)
          {
              const ImDrawCmd* pcmd = &cmd_list->CmdBuffer[cmd_i];
              if (pcmd->UserCallback != NULL)
              {
                  // User callback, registered via ImDrawList::AddCallback()
                  // (ImDrawCallback_ResetRenderState is a special callback value used by the user to request the renderer to reset render state.)
                  if (pcmd->UserCallback == ImDrawCallback_ResetRenderState)
                      ImGui_ImplOpenGL3_SetupRenderState(draw_data, fb_width, fb_height, vertex_array_object);
                  else
                      pcmd->UserCallback(cmd_list, pcmd);
              }
              else
              {
                  // Project scissor/clipping rectangles into framebuffer space
                  ImVec2 clip_min((pcmd->ClipRect.x - clip_off.x) * clip_scale.x, (pcmd->ClipRect.y - clip_off.y) * clip_scale.y);
                  ImVec2 clip_max((pcmd->ClipRect.z - clip_off.x) * clip_scale.x, (pcmd->ClipRect.w - clip_off.y) * clip_scale.y);
                  if (clip_max.x <= clip_min.x || clip_max.y <= clip_min.y)
                      continue;
  
                  // Apply scissor/clipping rectangle (Y is inverted in OpenGL)
                  glScissor((int)clip_min.x, (int)(fb_height - clip_max.y), (int)(clip_max.x - clip_min.x), (int)(clip_max.y - clip_min.y));
  
                  // Bind texture, Draw
                  glBindTexture(GL_TEXTURE_2D, (GLuint)(intptr_t)pcmd->GetTexID());
  #ifdef IMGUI_IMPL_OPENGL_MAY_HAVE_VTX_OFFSET
                  if (bd->GlVersion >= 320)
                      glDrawElementsBaseVertex(GL_TRIANGLES, (GLsizei)pcmd->ElemCount, sizeof(ImDrawIdx) == 2 ? GL_UNSIGNED_SHORT : GL_UNSIGNED_INT, (void*)(intptr_t)(pcmd->IdxOffset * sizeof(ImDrawIdx)), (GLint)pcmd->VtxOffset);
                  else
  #endif
                  glDrawElements(GL_TRIANGLES, (GLsizei)pcmd->ElemCount, sizeof(ImDrawIdx) == 2 ? GL_UNSIGNED_SHORT : GL_UNSIGNED_INT, (void*)(intptr_t)(pcmd->IdxOffset * sizeof(ImDrawIdx)));
              }
          }
      }
  
      // Destroy the temporary VAO
  #ifdef IMGUI_IMPL_OPENGL_USE_VERTEX_ARRAY
      glDeleteVertexArrays(1, &vertex_array_object);
  #endif
  
      // Restore modified GL state
      glUseProgram(last_program);
      glBindTexture(GL_TEXTURE_2D, last_texture);
  #ifdef IMGUI_IMPL_OPENGL_MAY_HAVE_BIND_SAMPLER
      if (bd->GlVersion >= 330)
          glBindSampler(0, last_sampler);
  #endif
      glActiveTexture(last_active_texture);
  #ifdef IMGUI_IMPL_OPENGL_USE_VERTEX_ARRAY
      glBindVertexArray(last_vertex_array_object);
  #endif
      glBindBuffer(GL_ARRAY_BUFFER, last_array_buffer);
  #ifndef IMGUI_IMPL_OPENGL_USE_VERTEX_ARRAY
      glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, last_element_array_buffer);
      ImGui_ImplOpenGL3_RestoreVertexAttribState(bd->AttribLocationVtxPos, &last_vtx_attrib_state_pos);
      ImGui_ImplOpenGL3_RestoreVertexAttribState(bd->AttribLocationVtxUV, &last_vtx_attrib_state_uv);
      ImGui_ImplOpenGL3_RestoreVertexAttribState(bd->AttribLocationVtxColor, &last_vtx_attrib_state_color);
  #endif
      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);
      if (last_enable_blend) glEnable(GL_BLEND); else glDisable(GL_BLEND);
      if (last_enable_cull_face) glEnable(GL_CULL_FACE); else glDisable(GL_CULL_FACE);
      if (last_enable_depth_test) glEnable(GL_DEPTH_TEST); else glDisable(GL_DEPTH_TEST);
      if (last_enable_stencil_test) glEnable(GL_STENCIL_TEST); else glDisable(GL_STENCIL_TEST);
      if (last_enable_scissor_test) glEnable(GL_SCISSOR_TEST); else glDisable(GL_SCISSOR_TEST);
  #ifdef IMGUI_IMPL_OPENGL_MAY_HAVE_PRIMITIVE_RESTART
      if (bd->GlVersion >= 310) { if (last_enable_primitive_restart) glEnable(GL_PRIMITIVE_RESTART); else glDisable(GL_PRIMITIVE_RESTART); }
  #endif
  
  #ifdef IMGUI_IMPL_HAS_POLYGON_MODE
      glPolygonMode(GL_FRONT_AND_BACK, (GLenum)last_polygon_mode[0]);
  #endif
      glViewport(last_viewport[0], last_viewport[1], (GLsizei)last_viewport[2], (GLsizei)last_viewport[3]);
      glScissor(last_scissor_box[0], last_scissor_box[1], (GLsizei)last_scissor_box[2], (GLsizei)last_scissor_box[3]);
      (void)bd; // Not all compilation paths use this
  }
  
  ImTextureID ImGui_ImplOpenGL3_CreateFontsTexture(ImFontAtlas* fonts)
  {
      ImGuiIO& io = ImGui::GetIO();
      ImGui_ImplOpenGL3_Data* bd = ImGui_ImplOpenGL3_GetBackendData();
  
      // Build texture atlas
      unsigned char* pixels;
      int width, height;
      GLuint font_texture = 0;
      fonts->GetTexDataAsRGBA32(&pixels, &width, &height);   // Load as RGBA 32-bit (75% of the memory is wasted, but default font is so small) because it is more likely to be compatible with user's existing shaders. If your ImTextureId represent a higher-level concept than just a GL texture id, consider calling GetTexDataAsAlpha8() instead to save on GPU memory.
  
      // Upload texture to graphics system
      GLint last_texture;
      glGetIntegerv(GL_TEXTURE_BINDING_2D, &last_texture);
      glGenTextures(1, &font_texture);
      glBindTexture(GL_TEXTURE_2D, font_texture);
      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 // Not on WebGL/ES
      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
      fonts->SetTexID((ImTextureID)(intptr_t)font_texture);
  
      // Restore state
      glBindTexture(GL_TEXTURE_2D, last_texture);
  
      return fonts->TexID;
  }
  
  bool ImGui_ImplOpenGL3_CreateFontsTexture(ImGui_ImplOpenGL3_Data* bd)
  {
      ImGuiIO& io = ImGui::GetIO();
      if (io.ConfigFlags & ImGuiConfigFlags_DpiEnableScaleFonts)
      {
          IM_ASSERT(!io.AllFonts.empty() && "All font atlases participating in DPI font scaling should be in io.AllFonts");
          IM_ASSERT(io.AllFonts.Size < IM_ARRAYSIZE(bd->FontTextures));
          for (int i = 0; i < io.AllFonts.Size; i++)
          {
              bd->FontTextures[i] = (GLuint)(intptr_t)ImGui_ImplOpenGL3_CreateFontsTexture(io.AllFonts[i]);
              if (!bd->FontTextures[i])
                  return false;
          }
      }
      else
      {
          bd->FontTextures[0] = (GLuint)(intptr_t)ImGui_ImplOpenGL3_CreateFontsTexture(io.Fonts);
          if (!bd->FontTextures[0])
              return false;
      }
      return true;
  }
  
  void ImGui_ImplOpenGL3_DestroyFontsTexture()
  {
      ImGuiIO& io = ImGui::GetIO();
      ImGui_ImplOpenGL3_Data* bd = ImGui_ImplOpenGL3_GetBackendData();
      for (int i = 0; i < IM_ARRAYSIZE(bd->FontTextures); i++)
      {
          if (bd->FontTextures[i])
          {
              glDeleteTextures(1, &bd->FontTextures[i]);
              io.Fonts->SetTexID(0);
              bd->FontTextures[i] = 0;
          }
      }
  }
  
  // If you get an error please report on github. You may try different GL context version or GLSL version. See GL<>GLSL version table at the top of this file.
  static bool CheckShader(GLuint handle, const char* desc)
  {
      ImGui_ImplOpenGL3_Data* bd = ImGui_ImplOpenGL3_GetBackendData();
      GLint status = 0, log_length = 0;
      glGetShaderiv(handle, GL_COMPILE_STATUS, &status);
      glGetShaderiv(handle, GL_INFO_LOG_LENGTH, &log_length);
      if ((GLboolean)status == GL_FALSE)
          fprintf(stderr, "ERROR: ImGui_ImplOpenGL3_CreateDeviceObjects: failed to compile %s! With GLSL: %s\n", desc, bd->GlslVersionString);
      if (log_length > 1)
      {
          ImVector<char> buf;
          buf.resize((int)(log_length + 1));
          glGetShaderInfoLog(handle, log_length, NULL, (GLchar*)buf.begin());
          fprintf(stderr, "%s\n", buf.begin());
      }
      return (GLboolean)status == GL_TRUE;
  }
  
  // If you get an error please report on GitHub. You may try different GL context version or GLSL version.
  static bool CheckProgram(GLuint handle, const char* desc)
  {
      ImGui_ImplOpenGL3_Data* bd = ImGui_ImplOpenGL3_GetBackendData();
      GLint status = 0, log_length = 0;
      glGetProgramiv(handle, GL_LINK_STATUS, &status);
      glGetProgramiv(handle, GL_INFO_LOG_LENGTH, &log_length);
      if ((GLboolean)status == GL_FALSE)
          fprintf(stderr, "ERROR: ImGui_ImplOpenGL3_CreateDeviceObjects: failed to link %s! With GLSL %s\n", desc, bd->GlslVersionString);
      if (log_length > 1)
      {
          ImVector<char> buf;
          buf.resize((int)(log_length + 1));
          glGetProgramInfoLog(handle, log_length, NULL, (GLchar*)buf.begin());
          fprintf(stderr, "%s\n", buf.begin());
      }
      return (GLboolean)status == GL_TRUE;
  }
  
  bool    ImGui_ImplOpenGL3_CreateDeviceObjects()
  {
      ImGui_ImplOpenGL3_Data* bd = ImGui_ImplOpenGL3_GetBackendData();
  
      // Backup GL state
      GLint last_texture, last_array_buffer;
      glGetIntegerv(GL_TEXTURE_BINDING_2D, &last_texture);
      glGetIntegerv(GL_ARRAY_BUFFER_BINDING, &last_array_buffer);
  #ifdef IMGUI_IMPL_OPENGL_USE_VERTEX_ARRAY
      GLint last_vertex_array;
      glGetIntegerv(GL_VERTEX_ARRAY_BINDING, &last_vertex_array);
  #endif
  
      // Parse GLSL version string
      int glsl_version = 130;
      sscanf(bd->GlslVersionString, "#version %d", &glsl_version);
  
      const GLchar* vertex_shader_glsl_120 =
          "uniform mat4 ProjMtx;\n"
          "attribute vec2 Position;\n"
          "attribute vec2 UV;\n"
          "attribute vec4 Color;\n"
          "varying vec2 Frag_UV;\n"
          "varying vec4 Frag_Color;\n"
          "void main()\n"
          "{\n"
          "    Frag_UV = UV;\n"
          "    Frag_Color = Color;\n"
          "    gl_Position = ProjMtx * vec4(Position.xy,0,1);\n"
          "}\n";
  
      const GLchar* vertex_shader_glsl_130 =
          "uniform mat4 ProjMtx;\n"
          "in vec2 Position;\n"
          "in vec2 UV;\n"
          "in vec4 Color;\n"
          "out vec2 Frag_UV;\n"
          "out vec4 Frag_Color;\n"
          "void main()\n"
          "{\n"
          "    Frag_UV = UV;\n"
          "    Frag_Color = Color;\n"
          "    gl_Position = ProjMtx * vec4(Position.xy,0,1);\n"
          "}\n";
  
      const GLchar* vertex_shader_glsl_300_es =
          "precision highp float;\n"
          "layout (location = 0) in vec2 Position;\n"
          "layout (location = 1) in vec2 UV;\n"
          "layout (location = 2) in vec4 Color;\n"
          "uniform mat4 ProjMtx;\n"
          "out vec2 Frag_UV;\n"
          "out vec4 Frag_Color;\n"
          "void main()\n"
          "{\n"
          "    Frag_UV = UV;\n"
          "    Frag_Color = Color;\n"
          "    gl_Position = ProjMtx * vec4(Position.xy,0,1);\n"
          "}\n";
  
      const GLchar* vertex_shader_glsl_410_core =
          "layout (location = 0) in vec2 Position;\n"
          "layout (location = 1) in vec2 UV;\n"
          "layout (location = 2) in vec4 Color;\n"
          "uniform mat4 ProjMtx;\n"
          "out vec2 Frag_UV;\n"
          "out vec4 Frag_Color;\n"
          "void main()\n"
          "{\n"
          "    Frag_UV = UV;\n"
          "    Frag_Color = Color;\n"
          "    gl_Position = ProjMtx * vec4(Position.xy,0,1);\n"
          "}\n";
  
      const GLchar* fragment_shader_glsl_120 =
          "#ifdef GL_ES\n"
          "    precision mediump float;\n"
          "#endif\n"
          "uniform sampler2D Texture;\n"
          "varying vec2 Frag_UV;\n"
          "varying vec4 Frag_Color;\n"
          "void main()\n"
          "{\n"
          "    gl_FragColor = Frag_Color * texture2D(Texture, Frag_UV.st);\n"
          "}\n";
  
      const GLchar* fragment_shader_glsl_130 =
          "uniform sampler2D Texture;\n"
          "in vec2 Frag_UV;\n"
          "in vec4 Frag_Color;\n"
          "out vec4 Out_Color;\n"
          "void main()\n"
          "{\n"
          "    Out_Color = Frag_Color * texture(Texture, Frag_UV.st);\n"
          "}\n";
  
      const GLchar* fragment_shader_glsl_300_es =
          "precision mediump float;\n"
          "uniform sampler2D Texture;\n"
          "in vec2 Frag_UV;\n"
          "in vec4 Frag_Color;\n"
          "layout (location = 0) out vec4 Out_Color;\n"
          "void main()\n"
          "{\n"
          "    Out_Color = Frag_Color * texture(Texture, Frag_UV.st);\n"
          "}\n";
  
      const GLchar* fragment_shader_glsl_410_core =
          "in vec2 Frag_UV;\n"
          "in vec4 Frag_Color;\n"
          "uniform sampler2D Texture;\n"
          "layout (location = 0) out vec4 Out_Color;\n"
          "void main()\n"
          "{\n"
          "    Out_Color = Frag_Color * texture(Texture, Frag_UV.st);\n"
          "}\n";
  
      // Select shaders matching our GLSL versions
      const GLchar* vertex_shader = NULL;
      const GLchar* fragment_shader = NULL;
      if (glsl_version < 130)
      {
          vertex_shader = vertex_shader_glsl_120;
          fragment_shader = fragment_shader_glsl_120;
      }
      else if (glsl_version >= 410)
      {
          vertex_shader = vertex_shader_glsl_410_core;
          fragment_shader = fragment_shader_glsl_410_core;
      }
      else if (glsl_version == 300)
      {
          vertex_shader = vertex_shader_glsl_300_es;
          fragment_shader = fragment_shader_glsl_300_es;
      }
      else
      {
          vertex_shader = vertex_shader_glsl_130;
          fragment_shader = fragment_shader_glsl_130;
      }
  
      // Create shaders
      const GLchar* vertex_shader_with_version[2] = { bd->GlslVersionString, vertex_shader };
      GLuint vert_handle = glCreateShader(GL_VERTEX_SHADER);
      glShaderSource(vert_handle, 2, vertex_shader_with_version, NULL);
      glCompileShader(vert_handle);
      CheckShader(vert_handle, "vertex shader");
  
      const GLchar* fragment_shader_with_version[2] = { bd->GlslVersionString, fragment_shader };
      GLuint frag_handle = glCreateShader(GL_FRAGMENT_SHADER);
      glShaderSource(frag_handle, 2, fragment_shader_with_version, NULL);
      glCompileShader(frag_handle);
      CheckShader(frag_handle, "fragment shader");
  
      // Link
      bd->ShaderHandle = glCreateProgram();
      glAttachShader(bd->ShaderHandle, vert_handle);
      glAttachShader(bd->ShaderHandle, frag_handle);
      glLinkProgram(bd->ShaderHandle);
      CheckProgram(bd->ShaderHandle, "shader program");
  
      glDetachShader(bd->ShaderHandle, vert_handle);
      glDetachShader(bd->ShaderHandle, frag_handle);
      glDeleteShader(vert_handle);
      glDeleteShader(frag_handle);
  
      bd->AttribLocationTex = glGetUniformLocation(bd->ShaderHandle, "Texture");
      bd->AttribLocationProjMtx = glGetUniformLocation(bd->ShaderHandle, "ProjMtx");
      bd->AttribLocationVtxPos = (GLuint)glGetAttribLocation(bd->ShaderHandle, "Position");
      bd->AttribLocationVtxUV = (GLuint)glGetAttribLocation(bd->ShaderHandle, "UV");
      bd->AttribLocationVtxColor = (GLuint)glGetAttribLocation(bd->ShaderHandle, "Color");
  
      // Create buffers
      glGenBuffers(1, &bd->VboHandle);
      glGenBuffers(1, &bd->ElementsHandle);
  
      ImGui_ImplOpenGL3_CreateFontsTexture(bd);
  
      // Restore modified GL state
      glBindTexture(GL_TEXTURE_2D, last_texture);
      glBindBuffer(GL_ARRAY_BUFFER, last_array_buffer);
  #ifdef IMGUI_IMPL_OPENGL_USE_VERTEX_ARRAY
      glBindVertexArray(last_vertex_array);
  #endif
  
      return true;
  }
  
  void    ImGui_ImplOpenGL3_DestroyDeviceObjects()
  {
      ImGui_ImplOpenGL3_Data* bd = ImGui_ImplOpenGL3_GetBackendData();
      if (bd->VboHandle)      { glDeleteBuffers(1, &bd->VboHandle); bd->VboHandle = 0; }
      if (bd->ElementsHandle) { glDeleteBuffers(1, &bd->ElementsHandle); bd->ElementsHandle = 0; }
      if (bd->ShaderHandle)   { glDeleteProgram(bd->ShaderHandle); bd->ShaderHandle = 0; }
      ImGui_ImplOpenGL3_DestroyFontsTexture();
  }
  
  //--------------------------------------------------------------------------------------------------------
  // MULTI-VIEWPORT / PLATFORM INTERFACE SUPPORT
  // This is an _advanced_ and _optional_ feature, allowing the backend to create and handle multiple viewports simultaneously.
  // If you are new to dear imgui or creating a new binding for dear imgui, it is recommended that you completely ignore this section first..
  //--------------------------------------------------------------------------------------------------------
  
  static void ImGui_ImplOpenGL3_RenderWindow(ImGuiViewport* viewport, void*)
  {
      if (!(viewport->Flags & ImGuiViewportFlags_NoRendererClear))
      {
          ImVec4 clear_color = ImVec4(0.0f, 0.0f, 0.0f, 1.0f);
          glClearColor(clear_color.x, clear_color.y, clear_color.z, clear_color.w);
          glClear(GL_COLOR_BUFFER_BIT);
      }
      ImGui_ImplOpenGL3_RenderDrawData(viewport->DrawData);
  }
  
  static void ImGui_ImplOpenGL3_InitPlatformInterface()
  {
      ImGuiPlatformIO& platform_io = ImGui::GetPlatformIO();
      platform_io.Renderer_RenderWindow = ImGui_ImplOpenGL3_RenderWindow;
  }
  
  static void ImGui_ImplOpenGL3_ShutdownPlatformInterface()
  {
      ImGui::DestroyPlatformWindows();
  }
  