text: // ImGui GLFW binding with OpenGL3 + shaders
  // In this binding, ImTextureID is used to store an OpenGL 'GLuint' texture identifier. Read the FAQ about ImTextureID in imgui.cpp.
  
  // You can copy and use unmodified imgui_impl_* files in your project. See main.cpp for an example of using this.
  // If you use this binding you'll need to call 4 functions: ImGui_ImplXXXX_Init(), ImGui_ImplXXXX_NewFrame(), ImGui::Render() and ImGui_ImplXXXX_Shutdown().
  // If you are new to ImGui, see examples/README.txt and documentation at the top of imgui.cpp.
  // https://github.com/ocornut/imgui
  
  #include <imgui.h>
  #include "imgui_impl_glfw_gl3.h"
  
  // GL3W/GLFW
  #include <GL/glew.h>
  #include <GLFW/glfw3.h>
  #ifdef _WIN32
  #undef APIENTRY
  #define GLFW_EXPOSE_NATIVE_WIN32
  #define GLFW_EXPOSE_NATIVE_WGL
  #include <GLFW/glfw3native.h>
  #endif
  
  // Data
  static GLFWwindow*  g_Window = NULL;
  static double       g_Time = 0.0f;
  static bool         g_MousePressed[3] = { false, false, false };
  static float        g_MouseWheel = 0.0f;
  static GLuint       g_FontTexture = 0;
  static int          g_ShaderHandle = 0, g_VertHandle = 0, g_FragHandle = 0;
  static int          g_AttribLocationTex = 0, g_AttribLocationProjMtx = 0;
  static int          g_AttribLocationPosition = 0, g_AttribLocationUV = 0, g_AttribLocationColor = 0;
  static unsigned int g_VboHandle = 0, g_VaoHandle = 0, g_ElementsHandle = 0;
  
  // This is the main rendering function that you have to implement and provide to ImGui (via setting up 'RenderDrawListsFn' in the ImGuiIO structure)
  // If text or lines are blurry when integrating ImGui in your engine:
  // - in your Render function, try translating your projection matrix by (0.5f,0.5f) or (0.375f,0.375f)
  void ImGui_ImplGlfwGL3_RenderDrawLists(ImDrawData* draw_data)
  {
  	// Avoid rendering when minimized, scale coordinates for retina displays (screen coordinates != framebuffer coordinates)
  	ImGuiIO& io = ImGui::GetIO();
  	int fb_width = (int)(io.DisplaySize.x * io.DisplayFramebufferScale.x);
  	int fb_height = (int)(io.DisplaySize.y * io.DisplayFramebufferScale.y);
  	if (fb_width == 0 || fb_height == 0)
  		return;
  	draw_data->ScaleClipRects(io.DisplayFramebufferScale);
  
  	// Backup GL state
  	GLint last_program; glGetIntegerv(GL_CURRENT_PROGRAM, &last_program);
  	GLint last_texture; glGetIntegerv(GL_TEXTURE_BINDING_2D, &last_texture);
  	GLint last_active_texture; glGetIntegerv(GL_ACTIVE_TEXTURE, &last_active_texture);
  	GLint last_array_buffer; glGetIntegerv(GL_ARRAY_BUFFER_BINDING, &last_array_buffer);
  	GLint last_element_array_buffer; glGetIntegerv(GL_ELEMENT_ARRAY_BUFFER_BINDING, &last_element_array_buffer);
  	GLint last_vertex_array; glGetIntegerv(GL_VERTEX_ARRAY_BINDING, &last_vertex_array);
  	GLint last_blend_src; glGetIntegerv(GL_BLEND_SRC, &last_blend_src);
  	GLint last_blend_dst; glGetIntegerv(GL_BLEND_DST, &last_blend_dst);
  	GLint last_blend_equation_rgb; glGetIntegerv(GL_BLEND_EQUATION_RGB, &last_blend_equation_rgb);
  	GLint last_blend_equation_alpha; glGetIntegerv(GL_BLEND_EQUATION_ALPHA, &last_blend_equation_alpha);
  	GLint last_viewport[4]; glGetIntegerv(GL_VIEWPORT, last_viewport);
  	GLint last_scissor_box[4]; glGetIntegerv(GL_SCISSOR_BOX, last_scissor_box);
  	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_scissor_test = glIsEnabled(GL_SCISSOR_TEST);
  
  	// Setup render state: alpha-blending enabled, no face culling, no depth testing, scissor enabled
  	glEnable(GL_BLEND);
  	glBlendEquation(GL_FUNC_ADD);
  	glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
  	glDisable(GL_CULL_FACE);
  	glDisable(GL_DEPTH_TEST);
  	glEnable(GL_SCISSOR_TEST);
  	glActiveTexture(GL_TEXTURE0);
  
  	// Setup viewport, orthographic projection matrix
  	glViewport(0, 0, (GLsizei)fb_width, (GLsizei)fb_height);
  	const float ortho_projection[4][4] =
  	{
  		{ 2.0f / io.DisplaySize.x, 0.0f,                   0.0f, 0.0f },
  		{ 0.0f,                  2.0f / -io.DisplaySize.y, 0.0f, 0.0f },
  		{ 0.0f,                  0.0f,                  -1.0f, 0.0f },
  		{ -1.0f,                  1.0f,                   0.0f, 1.0f },
  	};
  	glUseProgram(g_ShaderHandle);
  	glUniform1i(g_AttribLocationTex, 0);
  	glUniformMatrix4fv(g_AttribLocationProjMtx, 1, GL_FALSE, &ortho_projection[0][0]);
  	glBindVertexArray(g_VaoHandle);
  
  	for (int n = 0; n < draw_data->CmdListsCount; n++)
  	{
  		const ImDrawList* cmd_list = draw_data->CmdLists[n];
  		const ImDrawIdx* idx_buffer_offset = 0;
  
  		glBindBuffer(GL_ARRAY_BUFFER, g_VboHandle);
  		glBufferData(GL_ARRAY_BUFFER, (GLsizeiptr)cmd_list->VtxBuffer.Size * sizeof(ImDrawVert), (GLvoid*)cmd_list->VtxBuffer.Data, GL_STREAM_DRAW);
  
  		glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, g_ElementsHandle);
  		glBufferData(GL_ELEMENT_ARRAY_BUFFER, (GLsizeiptr)cmd_list->IdxBuffer.Size * sizeof(ImDrawIdx), (GLvoid*)cmd_list->IdxBuffer.Data, GL_STREAM_DRAW);
  
  		for (int cmd_i = 0; cmd_i < cmd_list->CmdBuffer.Size; cmd_i++)
  		{
  			const ImDrawCmd* pcmd = &cmd_list->CmdBuffer[cmd_i];
  			if (pcmd->UserCallback)
  			{
  				pcmd->UserCallback(cmd_list, pcmd);
  			}
  			else
  			{
  				glBindTexture(GL_TEXTURE_2D, (GLuint)(intptr_t)pcmd->TextureId);
  				glScissor((int)pcmd->ClipRect.x, (int)(fb_height - pcmd->ClipRect.w), (int)(pcmd->ClipRect.z - pcmd->ClipRect.x), (int)(pcmd->ClipRect.w - pcmd->ClipRect.y));
  				glDrawElements(GL_TRIANGLES, (GLsizei)pcmd->ElemCount, sizeof(ImDrawIdx) == 2 ? GL_UNSIGNED_SHORT : GL_UNSIGNED_INT, idx_buffer_offset);
  			}
  			idx_buffer_offset += pcmd->ElemCount;
  		}
  	}
  
  	// Restore modified GL state
  	glUseProgram(last_program);
  	glActiveTexture(last_active_texture);
  	glBindTexture(GL_TEXTURE_2D, last_texture);
  	glBindVertexArray(last_vertex_array);
  	glBindBuffer(GL_ARRAY_BUFFER, last_array_buffer);
  	glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, last_element_array_buffer);
  	glBlendEquationSeparate(last_blend_equation_rgb, last_blend_equation_alpha);
  	glBlendFunc(last_blend_src, last_blend_dst);
  	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_scissor_test) glEnable(GL_SCISSOR_TEST); else glDisable(GL_SCISSOR_TEST);
  	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]);
  }
  
  static const char* ImGui_ImplGlfwGL3_GetClipboardText(void* user_data)
  {
  	return glfwGetClipboardString((GLFWwindow*)user_data);
  }
  
  static void ImGui_ImplGlfwGL3_SetClipboardText(void* user_data, const char* text)
  {
  	glfwSetClipboardString((GLFWwindow*)user_data, text);
  }
  
  void ImGui_ImplGlfwGL3_MouseButtonCallback(GLFWwindow*, int button, int action, int /*mods*/)
  {
  	if (action == GLFW_PRESS && button >= 0 && button < 3)
  		g_MousePressed[button] = true;
  }
  
  void ImGui_ImplGlfwGL3_ScrollCallback(GLFWwindow*, double /*xoffset*/, double yoffset)
  {
  	g_MouseWheel += (float)yoffset; // Use fractional mouse wheel, 1.0 unit 5 lines.
  }
  
  void ImGui_ImplGlfwGL3_KeyCallback(GLFWwindow*, int key, int, int action, int mods)
  {
  	ImGuiIO& io = ImGui::GetIO();
  	if (action == GLFW_PRESS)
  		io.KeysDown[key] = true;
  	if (action == GLFW_RELEASE)
  		io.KeysDown[key] = false;
  
  	(void)mods; // Modifiers are not reliable across systems
  	io.KeyCtrl = io.KeysDown[GLFW_KEY_LEFT_CONTROL] || io.KeysDown[GLFW_KEY_RIGHT_CONTROL];
  	io.KeyShift = io.KeysDown[GLFW_KEY_LEFT_SHIFT] || io.KeysDown[GLFW_KEY_RIGHT_SHIFT];
  	io.KeyAlt = io.KeysDown[GLFW_KEY_LEFT_ALT] || io.KeysDown[GLFW_KEY_RIGHT_ALT];
  	io.KeySuper = io.KeysDown[GLFW_KEY_LEFT_SUPER] || io.KeysDown[GLFW_KEY_RIGHT_SUPER];
  }
  
  void ImGui_ImplGlfwGL3_CharCallback(GLFWwindow*, unsigned int c)
  {
  	ImGuiIO& io = ImGui::GetIO();
  	if (c > 0 && c < 0x10000)
  		io.AddInputCharacter((unsigned short)c);
  }
  
  bool ImGui_ImplGlfwGL3_CreateFontsTexture()
  {
  	// Build texture atlas
  	ImGuiIO& io = ImGui::GetIO();
  	unsigned char* pixels;
  	int width, height;
  	io.Fonts->GetTexDataAsRGBA32(&pixels, &width, &height);   // Load as RGBA 32-bits (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, &g_FontTexture);
  	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);
  	glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, pixels);
  
  	// Store our identifier
  	io.Fonts->TexID = (void *)(intptr_t)g_FontTexture;
  
  	// Restore state
  	glBindTexture(GL_TEXTURE_2D, last_texture);
  
  	return true;
  }
  
  bool ImGui_ImplGlfwGL3_CreateDeviceObjects()
  {
  	// Backup GL state
  	GLint last_texture, last_array_buffer, last_vertex_array;
  	glGetIntegerv(GL_TEXTURE_BINDING_2D, &last_texture);
  	glGetIntegerv(GL_ARRAY_BUFFER_BINDING, &last_array_buffer);
  	glGetIntegerv(GL_VERTEX_ARRAY_BINDING, &last_vertex_array);
  
  	const GLchar *vertex_shader =
  		"#version 330\n"
  		"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* fragment_shader =
  		"#version 330\n"
  		"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";
  
  	g_ShaderHandle = glCreateProgram();
  	g_VertHandle = glCreateShader(GL_VERTEX_SHADER);
  	g_FragHandle = glCreateShader(GL_FRAGMENT_SHADER);
  	glShaderSource(g_VertHandle, 1, &vertex_shader, 0);
  	glShaderSource(g_FragHandle, 1, &fragment_shader, 0);
  	glCompileShader(g_VertHandle);
  	glCompileShader(g_FragHandle);
  	glAttachShader(g_ShaderHandle, g_VertHandle);
  	glAttachShader(g_ShaderHandle, g_FragHandle);
  	glLinkProgram(g_ShaderHandle);
  
  	g_AttribLocationTex = glGetUniformLocation(g_ShaderHandle, "Texture");
  	g_AttribLocationProjMtx = glGetUniformLocation(g_ShaderHandle, "ProjMtx");
  	g_AttribLocationPosition = glGetAttribLocation(g_ShaderHandle, "Position");
  	g_AttribLocationUV = glGetAttribLocation(g_ShaderHandle, "UV");
  	g_AttribLocationColor = glGetAttribLocation(g_ShaderHandle, "Color");
  
  	glGenBuffers(1, &g_VboHandle);
  	glGenBuffers(1, &g_ElementsHandle);
  
  	glGenVertexArrays(1, &g_VaoHandle);
  	glBindVertexArray(g_VaoHandle);
  	glBindBuffer(GL_ARRAY_BUFFER, g_VboHandle);
  	glEnableVertexAttribArray(g_AttribLocationPosition);
  	glEnableVertexAttribArray(g_AttribLocationUV);
  	glEnableVertexAttribArray(g_AttribLocationColor);
  
  #define OFFSETOF(TYPE, ELEMENT) ((size_t)&(((TYPE *)0)->ELEMENT))
  	glVertexAttribPointer(g_AttribLocationPosition, 2, GL_FLOAT, GL_FALSE, sizeof(ImDrawVert), (GLvoid*)OFFSETOF(ImDrawVert, pos));
  	glVertexAttribPointer(g_AttribLocationUV, 2, GL_FLOAT, GL_FALSE, sizeof(ImDrawVert), (GLvoid*)OFFSETOF(ImDrawVert, uv));
  	glVertexAttribPointer(g_AttribLocationColor, 4, GL_UNSIGNED_BYTE, GL_TRUE, sizeof(ImDrawVert), (GLvoid*)OFFSETOF(ImDrawVert, col));
  #undef OFFSETOF
  
  	ImGui_ImplGlfwGL3_CreateFontsTexture();
  
  	// Restore modified GL state
  	glBindTexture(GL_TEXTURE_2D, last_texture);
  	glBindBuffer(GL_ARRAY_BUFFER, last_array_buffer);
  	glBindVertexArray(last_vertex_array);
  
  	return true;
  }
  
  void    ImGui_ImplGlfwGL3_InvalidateDeviceObjects()
  {
  	if (g_VaoHandle) glDeleteVertexArrays(1, &g_VaoHandle);
  	if (g_VboHandle) glDeleteBuffers(1, &g_VboHandle);
  	if (g_ElementsHandle) glDeleteBuffers(1, &g_ElementsHandle);
  	g_VaoHandle = g_VboHandle = g_ElementsHandle = 0;
  
  	if (g_ShaderHandle && g_VertHandle) glDetachShader(g_ShaderHandle, g_VertHandle);
  	if (g_VertHandle) glDeleteShader(g_VertHandle);
  	g_VertHandle = 0;
  
  	if (g_ShaderHandle && g_FragHandle) glDetachShader(g_ShaderHandle, g_FragHandle);
  	if (g_FragHandle) glDeleteShader(g_FragHandle);
  	g_FragHandle = 0;
  
  	if (g_ShaderHandle) glDeleteProgram(g_ShaderHandle);
  	g_ShaderHandle = 0;
  
  	if (g_FontTexture)
  	{
  		glDeleteTextures(1, &g_FontTexture);
  		ImGui::GetIO().Fonts->TexID = 0;
  		g_FontTexture = 0;
  	}
  }
  
  bool    ImGui_ImplGlfwGL3_Init(GLFWwindow* window, bool install_callbacks)
  {
  	g_Window = window;
  
  	ImGuiIO& io = ImGui::GetIO();
  	io.KeyMap[ImGuiKey_Tab] = GLFW_KEY_TAB;                         // Keyboard mapping. ImGui will use those indices to peek into the io.KeyDown[] array.
  	io.KeyMap[ImGuiKey_LeftArrow] = GLFW_KEY_LEFT;
  	io.KeyMap[ImGuiKey_RightArrow] = GLFW_KEY_RIGHT;
  	io.KeyMap[ImGuiKey_UpArrow] = GLFW_KEY_UP;
  	io.KeyMap[ImGuiKey_DownArrow] = GLFW_KEY_DOWN;
  	io.KeyMap[ImGuiKey_PageUp] = GLFW_KEY_PAGE_UP;
  	io.KeyMap[ImGuiKey_PageDown] = GLFW_KEY_PAGE_DOWN;
  	io.KeyMap[ImGuiKey_Home] = GLFW_KEY_HOME;
  	io.KeyMap[ImGuiKey_End] = GLFW_KEY_END;
  	io.KeyMap[ImGuiKey_Delete] = GLFW_KEY_DELETE;
  	io.KeyMap[ImGuiKey_Backspace] = GLFW_KEY_BACKSPACE;
  	io.KeyMap[ImGuiKey_Enter] = GLFW_KEY_ENTER;
  	io.KeyMap[ImGuiKey_Escape] = GLFW_KEY_ESCAPE;
  	io.KeyMap[ImGuiKey_A] = GLFW_KEY_A;
  	io.KeyMap[ImGuiKey_C] = GLFW_KEY_C;
  	io.KeyMap[ImGuiKey_V] = GLFW_KEY_V;
  	io.KeyMap[ImGuiKey_X] = GLFW_KEY_X;
  	io.KeyMap[ImGuiKey_Y] = GLFW_KEY_Y;
  	io.KeyMap[ImGuiKey_Z] = GLFW_KEY_Z;
  
  	io.RenderDrawListsFn = ImGui_ImplGlfwGL3_RenderDrawLists;       // Alternatively you can set this to NULL and call ImGui::GetDrawData() after ImGui::Render() to get the same ImDrawData pointer.
  	io.SetClipboardTextFn = ImGui_ImplGlfwGL3_SetClipboardText;
  	io.GetClipboardTextFn = ImGui_ImplGlfwGL3_GetClipboardText;
  	io.ClipboardUserData = g_Window;
  #ifdef _WIN32
  	io.ImeWindowHandle = glfwGetWin32Window(g_Window);
  #endif
  
  	if (install_callbacks)
  	{
  		glfwSetMouseButtonCallback(window, ImGui_ImplGlfwGL3_MouseButtonCallback);
  		glfwSetScrollCallback(window, ImGui_ImplGlfwGL3_ScrollCallback);
  		glfwSetKeyCallback(window, ImGui_ImplGlfwGL3_KeyCallback);
  		glfwSetCharCallback(window, ImGui_ImplGlfwGL3_CharCallback);
  	}
  
  	return true;
  }
  
  void ImGui_ImplGlfwGL3_Shutdown()
  {
  	ImGui_ImplGlfwGL3_InvalidateDeviceObjects();
  	ImGui::Shutdown();
  }
  
  void ImGui_ImplGlfwGL3_NewFrame()
  {
  	if (!g_FontTexture)
  		ImGui_ImplGlfwGL3_CreateDeviceObjects();
  
  	ImGuiIO& io = ImGui::GetIO();
  
  	// Setup display size (every frame to accommodate for window resizing)
  	int w, h;
  	int display_w, display_h;
  	glfwGetWindowSize(g_Window, &w, &h);
  	glfwGetFramebufferSize(g_Window, &display_w, &display_h);
  	io.DisplaySize = ImVec2((float)w, (float)h);
  	io.DisplayFramebufferScale = ImVec2(w > 0 ? ((float)display_w / w) : 0, h > 0 ? ((float)display_h / h) : 0);
  
  	// Setup time step
  	double current_time = glfwGetTime();
  	io.DeltaTime = g_Time > 0.0 ? (float)(current_time - g_Time) : (float)(1.0f / 60.0f);
  	g_Time = current_time;
  
  	// Setup inputs
  	// (we already got mouse wheel, keyboard keys & characters from glfw callbacks polled in glfwPollEvents())
  	if (glfwGetWindowAttrib(g_Window, GLFW_FOCUSED))
  	{
  		double mouse_x, mouse_y;
  		glfwGetCursorPos(g_Window, &mouse_x, &mouse_y);
  		io.MousePos = ImVec2((float)mouse_x, (float)mouse_y);   // Mouse position in screen coordinates (set to -1,-1 if no mouse / on another screen, etc.)
  	}
  	else
  	{
  		io.MousePos = ImVec2(-1, -1);
  	}
  
  	for (int i = 0; i < 3; i++)
  	{
  		io.MouseDown[i] = g_MousePressed[i] || glfwGetMouseButton(g_Window, i) != 0;    // If a mouse press event came, always pass it as "mouse held this frame", so we don't miss click-release events that are shorter than 1 frame.
  		g_MousePressed[i] = false;
  	}
  
  	io.MouseWheel = g_MouseWheel;
  	g_MouseWheel = 0.0f;
  
  	// Hide OS mouse cursor if ImGui is drawing it
  	glfwSetInputMode(g_Window, GLFW_CURSOR, io.MouseDrawCursor ? GLFW_CURSOR_HIDDEN : GLFW_CURSOR_NORMAL);
  
  	// Start the frame
  	ImGui::NewFrame();
  }