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Created Getting Started (markdown)
Marcus Ottosson
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Getting-Started.md
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279
Getting-Started.md
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This article will guide you through getting up and running with as many assumptions about your system as possible.
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You are:
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- On Linux
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- Using C++11
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- Using OpenGL 3.3 or above, core profile
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- Using clang 3.4 or above
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- Using glfw 3.0 or above
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<br>
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<br>
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<br>
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### Layout
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This is the layout of your code.
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```
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| Directory | Description
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|---------------------|----------------------------------
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| myproject/ |
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| build/ | Output goes here
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| include/ | Any include files you may eventually have
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| src/ |
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| main.cpp | Your single source file
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| build.sh | Your build script
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```
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<br>
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<br>
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<br>
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### Build
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Here is how your code will be built.
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```bash
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$ cd myproject
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$ ./build.sh
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```
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**build.sh**
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```bash
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#!/usr/bin/env bash
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mkdir -p build && \
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pushd build && \
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clang++ \
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-o main \
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../ext/imgui/imgui.cpp \
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../ext/imgui/imgui_draw.cpp \
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../src/main.cpp \
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-Wall \
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-g `# Generate complete debug info` \
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-std=c++11 \
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-I ../include \
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-I ../ext/glfw/include \
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-I ../ext/imgui \
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-L ../lib \
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-lglfw3 \
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-lGL \
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-lGLU \
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-lX11 \
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-lXxf86vm \
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-lXrandr \
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-lpthread \
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-lXi \
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-lXinerama \
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-lXcursor && \
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popd || exit 1
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```
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<br>
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<br>
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<br>
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### Source
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Here is the source.
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**main.cpp**
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```cpp
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// dear imgui minimal example.
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#include <cstdlib>
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#include "GLFW/glfw3.h"
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#include "imgui.h"
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void setup(GLFWwindow* window);
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void renderer(ImDrawData* draw_data);
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int main(void)
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{
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if (!glfwInit())
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{
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exit(EXIT_FAILURE);
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}
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static GLFWwindow* window {
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glfwCreateWindow(320, 240, "Simple example", NULL, NULL)
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};
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if (!window)
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{
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glfwTerminate();
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exit(EXIT_FAILURE);
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}
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glfwMakeContextCurrent(window);
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// Close window on pressing ESC
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glfwSetKeyCallback(window, [](GLFWwindow* window, int key, int scancode, int action, int mods) {
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if (key == GLFW_KEY_ESCAPE && action == GLFW_PRESS)
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glfwSetWindowShouldClose(window, GL_TRUE);
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});
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setup(window);
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glClearColor(0.1f, 0.1f, 0.1f, 1.0f);
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while (!glfwWindowShouldClose(window))
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{
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glClear(GL_COLOR_BUFFER_BIT);
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glfwPollEvents();
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// Use ImGui functions between here and Render()
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ImGui::NewFrame();
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// This creates a window
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ImGui::Begin("Window Title Here");
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ImGui::Text("Hello, world!");
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ImGui::End();
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// ImGui functions end here
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ImGui::Render();
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glfwSwapBuffers(window);
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}
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glfwDestroyWindow(window);
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glfwTerminate();
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exit(EXIT_SUCCESS);
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}
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/*! /brief Initialise the ImGuiIO struct.
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*
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* The ImGuiIO struct is the main configuration and
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* I/O between your application and ImGui.
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*/
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void setup(GLFWwindow* window)
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{
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unsigned char* pixels;
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int width,
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height,
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display_width,
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display_height;
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GLuint g_FontTexture;
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ImGuiIO& io { ImGui::GetIO() };
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io.Fonts->GetTexDataAsAlpha8(&pixels, &width, &height);
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// Upload texture to graphics system
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GLint last_texture;
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glGetIntegerv(GL_TEXTURE_BINDING_2D, &last_texture);
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glGenTextures(1, &g_FontTexture);
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glBindTexture(GL_TEXTURE_2D, g_FontTexture);
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glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
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glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
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glTexImage2D(GL_TEXTURE_2D, 0, GL_ALPHA, width, height, 0, GL_ALPHA, GL_UNSIGNED_BYTE, pixels);
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// Get display size
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glfwGetWindowSize(window, &width, &height);
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glfwGetFramebufferSize(window, &display_width, &display_height);
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io.DisplaySize = ImVec2((float)width, (float)height);
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io.RenderDrawListsFn = renderer;
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io.Fonts->TexID = (void *)(intptr_t)g_FontTexture;
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// Restore state
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glBindTexture(GL_TEXTURE_2D, last_texture);
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}
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/*! /brief Boilerplate function for OpenGL 2.0 rendering.
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*
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* This function isn't written by us, but is mandatory
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* boilerplate from the library. It can be copy/pasted
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* into your projects, but should really be part of the
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* library itself?
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*/
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void renderer(ImDrawData* draw_data)
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{
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ImGuiIO& io { ImGui::GetIO() };
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int fb_width { (int)(io.DisplaySize.x * io.DisplayFramebufferScale.x) };
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int fb_height { (int)(io.DisplaySize.y * io.DisplayFramebufferScale.y) };
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draw_data->ScaleClipRects(io.DisplayFramebufferScale);
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GLint last_texture; glGetIntegerv(GL_TEXTURE_BINDING_2D, &last_texture);
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GLint last_viewport[4]; glGetIntegerv(GL_VIEWPORT, last_viewport);
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glPushAttrib(GL_ENABLE_BIT | GL_COLOR_BUFFER_BIT | GL_TRANSFORM_BIT);
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glEnable(GL_BLEND);
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glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
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glDisable(GL_CULL_FACE);
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glDisable(GL_DEPTH_TEST);
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glEnable(GL_SCISSOR_TEST);
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glEnableClientState(GL_VERTEX_ARRAY);
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glEnableClientState(GL_TEXTURE_COORD_ARRAY);
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glEnableClientState(GL_COLOR_ARRAY);
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glEnable(GL_TEXTURE_2D);
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// Setup viewport, orthographic projection matrix
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glViewport(0, 0, (GLsizei)fb_width, (GLsizei)fb_height);
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glMatrixMode(GL_PROJECTION);
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glPushMatrix();
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glLoadIdentity();
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glOrtho(0.0f, io.DisplaySize.x, io.DisplaySize.y, 0.0f, -1.0f, +1.0f);
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glMatrixMode(GL_MODELVIEW);
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glPushMatrix();
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glLoadIdentity();
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// Render command lists
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#define OFFSETOF(TYPE, ELEMENT) ((size_t)&(((TYPE *)0)->ELEMENT))
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for (int n = 0; n < draw_data->CmdListsCount; n++)
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{
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const ImDrawList* cmd_list = draw_data->CmdLists[n];
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const unsigned char* vtx_buffer = (const unsigned char*)&cmd_list->VtxBuffer.front();
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const ImDrawIdx* idx_buffer = &cmd_list->IdxBuffer.front();
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glVertexPointer(2, GL_FLOAT, sizeof(ImDrawVert), (void*)(vtx_buffer + OFFSETOF(ImDrawVert, pos)));
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glTexCoordPointer(2, GL_FLOAT, sizeof(ImDrawVert), (void*)(vtx_buffer + OFFSETOF(ImDrawVert, uv)));
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glColorPointer(4, GL_UNSIGNED_BYTE, sizeof(ImDrawVert), (void*)(vtx_buffer + OFFSETOF(ImDrawVert, col)));
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for (int cmd_i = 0; cmd_i < cmd_list->CmdBuffer.size(); cmd_i++)
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{
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const ImDrawCmd* pcmd = &cmd_list->CmdBuffer[cmd_i];
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if (pcmd->UserCallback)
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{
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pcmd->UserCallback(cmd_list, pcmd);
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}
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else
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{
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glBindTexture(GL_TEXTURE_2D, (GLuint)(intptr_t)pcmd->TextureId);
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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));
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glDrawElements(GL_TRIANGLES, (GLsizei)pcmd->ElemCount, sizeof(ImDrawIdx) == 2 ? GL_UNSIGNED_SHORT : GL_UNSIGNED_INT, idx_buffer);
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}
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idx_buffer += pcmd->ElemCount;
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}
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}
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#undef OFFSETOF
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// Restore modified state
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glDisableClientState(GL_COLOR_ARRAY);
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glDisableClientState(GL_TEXTURE_COORD_ARRAY);
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glDisableClientState(GL_VERTEX_ARRAY);
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glBindTexture(GL_TEXTURE_2D, last_texture);
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glMatrixMode(GL_MODELVIEW);
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glPopMatrix();
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glMatrixMode(GL_PROJECTION);
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glPopMatrix();
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glPopAttrib();
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glViewport(last_viewport[0], last_viewport[1], (GLsizei)last_viewport[2], (GLsizei)last_viewport[3]);
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}
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```
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<br>
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<br>
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<br>
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#### TODO
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Here are some ideas for how to shorten this example substantially.
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- Remove lines that aren't absolutely critical
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- Remove `renderer()` - Seems unnecessary and better included with ImGui?
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- Remove need to manually upload texture to GPU in `setup()`, can/should be included in ImGui?
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