I am trying to write a program with a graphical user interface using ImGui and draw 3-D figures with modern OpenGL methods in this program. I want to use GLFW and openGL3 to make this interface so I use the backends: imgui_impl_opengl3_loader.h, imgui_impl_opengl3.cpp, imgui_impl_opengl3.h with all ImGui basic files: ImGui_....
I use GLFW with the static library libglfw3.a file (build for Mac OS) and header glfw3.h.
As ImGui library loads gl functions using imgui_impl_opengl3_loader.h and it "is custom-generated, based on gl3w but automatically filtered to only include enums/functions that we use in our imgui_impl_opengl3.cpp source file in order to be small", I use GLAD to load gl functions with glad.c, glad.h and khrplatform.h.
A simplified version of my code is shown below:
#include <iostream>
#include "imgui.h"
#include "glad.h"
#include "imgui_impl_glfw.h"
#include "imgui_impl_opengl3.h"
#define GL_SILENCE_DEPRECATION
#if defined(IMGUI_IMPL_OPENGL_ES2)
#include <GLES2/gl2.h>
#endif
#include "glfw3.h"
// Vertex shader source
const char *vertexShaderSource = "#version 330 core\n"
"layout (location = 0) in vec3 aPos;\n"
"void main()\n"
"{\n"
" gl_Position = vec4(aPos.x, aPos.y, aPos.z, 1.0);\n"
"}\0";
// Fragment shader source
const char *fragmentShaderSource = "#version 330 core\n"
"out vec4 FragColor;\n"
"void main()\n"
"{\n"
" FragColor = vec4(1.0f, 0.5f, 0.2f, 1.0f);\n"
"}\0";
// Fragment shader
int main()
{
// Initiate GLFW
glfwInit();
// Decide GL+GLSL versions
#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);
glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 2);
glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE); // 3.2+ only
glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE); // Required on Mac
#else
// GL 3.0 + GLSL 130
const char *glsl_version = "#version 130";
glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 0);
// glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE); // 3.2+ only
// glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE); // 3.0+ only
#endif
// demonstrate a new window
GLFWwindow *window = glfwCreateWindow(1280, 720, "TestWindow1", NULL, NULL);
if (window == NULL)
{
std::cout << "ERROR" << std::endl;
return -1;
}
glfwMakeContextCurrent(window);
glfwSwapInterval(1);
// Setup GLAD
if (!gladLoadGLLoader((GLADloadproc)glfwGetProcAddress))
{
std::cout << "Failed to initialize GLAD" << std::endl;
return -1;
}
// Setup Dear ImGui context
IMGUI_CHECKVERSION();
ImGui::CreateContext();
ImGuiIO &io = ImGui::GetIO();
(void)io;
io.ConfigFlags |= ImGuiConfigFlags_NavEnableKeyboard; // Enable Keyboard Controls
io.ConfigFlags |= ImGuiConfigFlags_NavEnableGamepad; // Enable Gamepad Controls
// Setup Dear ImGui style
ImGui::StyleColorsLight();
// Setup Platform/Renderer backends
ImGui_ImplGlfw_InitForOpenGL(window, true);
ImGui_ImplOpenGL3_Init(glsl_version);
ImVec4 clear_color = ImVec4(0.45f, 0.55f, 0.60f, 1.00f);
// a bool value to control the show figure window
bool showFigure = false;
// Compile and link shaders
unsigned int vertexShader = glCreateShader(GL_VERTEX_SHADER);
glShaderSource(vertexShader, 1, &vertexShaderSource, NULL);
glCompileShader(vertexShader);
int success;
char infoLog[512];
glGetShaderiv(vertexShader, GL_COMPILE_STATUS, &success);
if (!success)
{
glGetShaderInfoLog(vertexShader, 512, NULL, infoLog);
std::cout << "ERROR::SHADER::VERTEX::COMPILATION_FAILED\n"
<< infoLog << std::endl;
}
unsigned int fragmentShader;
fragmentShader = glCreateShader(GL_FRAGMENT_SHADER);
glShaderSource(fragmentShader, 1, &fragmentShaderSource, NULL);
glCompileShader(fragmentShader);
glGetShaderiv(fragmentShader, GL_COMPILE_STATUS, &success);
if (!success)
{
glGetShaderInfoLog(vertexShader, 512, NULL, infoLog);
std::cout << "ERROR::SHADER::FRAGMENT::COMPILATION_FAILED\n"
<< infoLog << std::endl;
}
unsigned int shaderProgram;
shaderProgram = glCreateProgram();
glAttachShader(shaderProgram, vertexShader);
glAttachShader(shaderProgram, fragmentShader);
glLinkProgram(shaderProgram);
glGetProgramiv(shaderProgram, GL_LINK_STATUS, &success);
if (!success)
{
glGetProgramInfoLog(shaderProgram, 512, NULL, infoLog);
std::cout << "ERROR::SHADER_PROGRAM::LINKING_FAILED\n"
<< infoLog << std::endl;
}
unsigned int VAO;
glGenVertexArrays(1, &VAO);
glBindVertexArray(VAO);
float vertices[] = {
-0.5f, -0.5f, 0.0f,
0.5f, -0.5f, 0.0f,
0.0f, 0.5f, 0.0f};
unsigned int vertexBuffer0;
glGenBuffers(1, &vertexBuffer0);
glBindBuffer(GL_ARRAY_BUFFER, vertexBuffer0);
glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(float), (void *)0);
glEnableVertexAttribArray(0);
while (!glfwWindowShouldClose(window))
{
// check and call events and swap the buffers
glfwPollEvents();
// Start the Dear ImGui frame
ImGui_ImplOpenGL3_NewFrame();
ImGui_ImplGlfw_NewFrame();
ImGui::NewFrame();
// Main Window
ImVec2 mainWindowSize = ImVec2(1000, 600);
ImGui::SetNextWindowSize(mainWindowSize);
ImGui::Begin("TestGui");
// This button is used to set the showFigure bool value from false to true
if (ImGui::Button("Show Figure"))
{
showFigure = true;
}
// Show Figure in a new GLFW window
if (showFigure == true)
{
showFigure = false;
GLFWwindow *figureWindow = glfwCreateWindow(500, 500, "Figure", NULL, NULL);
glfwMakeContextCurrent(figureWindow);
glfwSwapInterval(1);
while (!glfwWindowShouldClose(figureWindow))
{
// Background color
glClearColor(0.2, 0.3, 0.3, 1.0);
glClear(GL_COLOR_BUFFER_BIT);
glUseProgram(shaderProgram);
glBindVertexArray(VAO);
glDrawArrays(GL_TRIANGLES, 0, 3);
glfwSwapBuffers(figureWindow);
glfwPollEvents();
}
glfwDestroyWindow(figureWindow);
glfwMakeContextCurrent(window);
}
ImGui::End();
// Render Main Window
ImGui::Render();
int display_w, display_h;
glfwGetFramebufferSize(window, &display_w, &display_h);
glViewport(0, 0, display_w, display_h);
glClearColor(clear_color.x * clear_color.w, clear_color.y * clear_color.w, clear_color.z * clear_color.w, clear_color.w);
glClear(GL_COLOR_BUFFER_BIT);
ImGui_ImplOpenGL3_RenderDrawData(ImGui::GetDrawData());
glfwSwapBuffers(window);
}
// Cleanup
glDeleteVertexArrays(1, &VAO);
glDeleteBuffers(1, &vertexBuffer0);
glDeleteProgram(shaderProgram);
ImGui_ImplOpenGL3_Shutdown();
ImGui_ImplGlfw_Shutdown();
ImGui::DestroyContext();
glfwDestroyWindow(window);
glfwTerminate();
return 0;
}
I use gcc to compile and link all the files:
gcc -std=c++17 -I/INCLUDE...PATH/ -c Test.cpp imgui.cpp imgui_widgets.cpp imgui_tables.cpp imgui_impl_opengl3.cpp imgui_impl_glfw.cpp imgui_draw.cpp imgui_demo.cpp
gcc -c glad.c
gcc -L/LIBRARY...PATH/ -lglfw3 -std=c++17 -lstdc++ -framework Carbon -framework Cocoa -framework OpenGL -framework IOKit -o aTest.out Test.o imgui.o imgui_widgets.o
imgui_tables.o imgui_impl_opengl3.o imgui_impl_glfw.o imgui_draw.o imgui_demo.o glad.o
The result is as follows: ./aTest.out
When I clicked the button, it failed to demonstrate the triangle as I expected. Click the "Show Figure" buttom
However, this "drawing" code works just fine without ImGui, I'm wondering is there anything wrong/confilicts with the ImGui rendering process and GL rendering process?
Any advice?
The GLFW Window to show the figure should be created using:
GLFWwindow *figureWindow = glfwCreateWindow(500, 500, "Figure", NULL, window);
instead of
GLFWwindow *figureWindow = glfwCreateWindow(500, 500, "Figure", NULL, NULL);
The new window should share the context of the main window because the shader programs are defined in the main window's context.