examples/opengl_example/main.cpp

#define GLEW_STATIC
#include <GL/glew.h>
#include <GLFW/glfw3.h>
#define STB_IMAGE_IMPLEMENTATION
#include "stb_image.h"					// for .png loading
#include "../../imgui.h"
#ifdef _MSC_VER
#pragma warning (disable: 4996)			// 'This function or variable may be unsafe': strcpy, strdup, sprintf, vsnprintf, sscanf, fopen
#endif

static GLFWwindow* window;
static GLuint fontTex;

// This is the main rendering function that you have to implement and provide to ImGui (via setting up 'RenderDrawListsFn' in the ImGuiIO structuer)
// We are using the fixed pipeline. 
// A faster way would be to collate all vertices from all cmd_lists into a single vertex buffer
static void ImImpl_RenderDrawLists(ImDrawList** const cmd_lists, int cmd_lists_count)
{
	if (cmd_lists_count == 0)
		return;

	// Setup render state: alpha-blending enabled, no face culling, no depth testing
	glEnable(GL_BLEND);
	glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
	glDisable(GL_CULL_FACE);
	glDisable(GL_DEPTH_TEST);
	//glEnable(GL_SCISSOR_TEST);
	glEnableClientState(GL_VERTEX_ARRAY);
	glEnableClientState(GL_TEXTURE_COORD_ARRAY);
	glEnableClientState(GL_COLOR_ARRAY);

	// Bind texture
	glBindTexture(GL_TEXTURE_2D, fontTex);
	glEnable(GL_TEXTURE_2D);

	// Setup matrices
	glMatrixMode(GL_PROJECTION);
	glLoadIdentity();
	glOrtho(0.0f, ImGui::GetIO().DisplaySize.x, ImGui::GetIO().DisplaySize.y, 0.0f, -1.0f, +1.0f);
	glMatrixMode(GL_MODELVIEW);
	glLoadIdentity();

	// Render command lists
	for (int n = 0; n < cmd_lists_count; n++)
	{
		const ImDrawList* cmd_list = cmd_lists[n];
		const unsigned char* vtx_buffer = (const unsigned char*)cmd_list->vtx_buffer.begin();
		glVertexPointer(2, GL_FLOAT, sizeof(ImDrawVert), (void*)(vtx_buffer));
		glTexCoordPointer(2, GL_FLOAT, sizeof(ImDrawVert), (void*)(vtx_buffer+8));
		glColorPointer(4, GL_UNSIGNED_BYTE, sizeof(ImDrawVert), (void*)(vtx_buffer+16));

		int vtx_offset = 0;
		const ImDrawCmd* pcmd_end = cmd_list->commands.end();
		for (const ImDrawCmd* pcmd = cmd_list->commands.begin(); pcmd != pcmd_end; pcmd++)
		{
			glScissor((int)pcmd->clip_rect.x, (int)pcmd->clip_rect.y, (int)(pcmd->clip_rect.z - pcmd->clip_rect.x), (int)(pcmd->clip_rect.w - pcmd->clip_rect.y));
			glDrawArrays(GL_TRIANGLES, vtx_offset, pcmd->vtx_count);
			vtx_offset += pcmd->vtx_count;
		}
	}
	glDisable(GL_SCISSOR_TEST);
}

static const char* ImImpl_GetClipboardTextFn()
{
	return glfwGetClipboardString(window);
}

static void ImImpl_SetClipboardTextFn(const char* text, const char* text_end)
{
	if (!text_end)
		text_end = text + strlen(text);

	// Add a zero-terminator because glfw function doesn't take a size
	char* buf = (char*)malloc(text_end - text + 1);
	memcpy(buf, text, text_end-text);
	buf[text_end-text] = '\0';
	glfwSetClipboardString(window, buf);
	free(buf);
}

// GLFW callbacks to get events
static void glfw_error_callback(int error, const char* description)
{
	fputs(description, stderr);
}

static float mouse_wheel = 0.0f;
static void glfw_scroll_callback(GLFWwindow* window, double xoffset, double yoffset)
{
	mouse_wheel = (float)yoffset;
}

static void glfw_key_callback(GLFWwindow* window, int key, int scancode, int action, int mods)
{
	ImGuiIO& io = ImGui::GetIO();
	if (action == GLFW_PRESS)
		io.KeysDown[key] = true;
	if (action == GLFW_RELEASE)
		io.KeysDown[key] = false;
	io.KeyCtrl = (mods & GLFW_MOD_CONTROL) != 0;
	io.KeyShift = (mods & GLFW_MOD_SHIFT) != 0;
}

static void glfw_char_callback(GLFWwindow* window, unsigned int c)
{
	if (c > 0 && c <= 255)
		ImGui::GetIO().AddInputCharacter((char)c);
}

// OpenGL code based on http://open.gl tutorials
void InitGL()
{
	glfwSetErrorCallback(glfw_error_callback);

	if (!glfwInit())
		exit(1);

	glfwWindowHint(GLFW_RESIZABLE, GL_FALSE);
	window = glfwCreateWindow(1280, 720, "ImGui OpenGL example", NULL, NULL);
	glfwMakeContextCurrent(window);
	glfwSetKeyCallback(window, glfw_key_callback);
	glfwSetScrollCallback(window, glfw_scroll_callback);
	glfwSetCharCallback(window, glfw_char_callback);

	glewInit();
}

void InitImGui()
{
	int w, h;
	glfwGetWindowSize(window, &w, &h);

	ImGuiIO& io = ImGui::GetIO();
	io.DisplaySize = ImVec2((float)w, (float)h);            // Display size, in pixels. For clamping windows positions.
	io.DeltaTime = 1.0f/60.0f;                                // Time elapsed since last frame, in seconds (in this sample app we'll override this every frame because our timestep is variable)
	io.PixelCenterOffset = 0.5f;                            // Align OpenGL texels
	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_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 = ImImpl_RenderDrawLists;
	io.SetClipboardTextFn = ImImpl_SetClipboardTextFn;
	io.GetClipboardTextFn = ImImpl_GetClipboardTextFn;

	// Load font texture
	glGenTextures(1, &fontTex);
	glBindTexture(GL_TEXTURE_2D, fontTex);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
	const void* png_data;
	unsigned int png_size;
	ImGui::GetDefaultFontData(NULL, NULL, &png_data, &png_size);
	int tex_x, tex_y, tex_comp;
	void* tex_data = stbi_load_from_memory((const unsigned char*)png_data, (int)png_size, &tex_x, &tex_y, &tex_comp, 0);
	glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, tex_x, tex_y, 0, GL_RGBA, GL_UNSIGNED_BYTE, tex_data);
	stbi_image_free(tex_data);
}

void Shutdown()
{
	ImGui::Shutdown();
	glfwTerminate();
}

int main(int argc, char** argv)
{
	InitGL();
	InitImGui();

	double time = glfwGetTime();
	while (!glfwWindowShouldClose(window))
	{
		ImGuiIO& io = ImGui::GetIO();
		glfwPollEvents();

		// 1) ImGui start frame, setup time delta & inputs
		const double current_time =  glfwGetTime();
		io.DeltaTime = (float)(current_time - time);
		time = current_time;
		double mouse_x, mouse_y;
		glfwGetCursorPos(window, &mouse_x, &mouse_y);
		io.MousePos = ImVec2((float)mouse_x, (float)mouse_y);                            // Mouse position, in pixels (set to -1,-1 if no mouse / on another screen, etc.)
		io.MouseDown[0] = glfwGetMouseButton(window, GLFW_MOUSE_BUTTON_LEFT) != 0;
		io.MouseDown[1] = glfwGetMouseButton(window, GLFW_MOUSE_BUTTON_RIGHT) != 0;
		io.MouseWheel = (mouse_wheel != 0) ? mouse_wheel > 0.0f ? 1 : - 1 : 0;            // Mouse wheel: -1,0,+1
		mouse_wheel = 0.0f;
		ImGui::NewFrame();

		// 2) ImGui usage
		static bool show_test_window = true;
		static bool show_another_window = false;
		static float f;
		ImGui::Text("Hello, world!");
		ImGui::SliderFloat("float", &f, 0.0f, 1.0f);
		show_test_window ^= ImGui::Button("Test Window");
		show_another_window ^= ImGui::Button("Another Window");

		// Calculate and show framerate
		static float ms_per_frame[120] = { 0 };
		static int ms_per_frame_idx = 0;
		static float ms_per_frame_accum = 0.0f;
		ms_per_frame_accum -= ms_per_frame[ms_per_frame_idx];
		ms_per_frame[ms_per_frame_idx] = io.DeltaTime * 1000.0f;
		ms_per_frame_accum += ms_per_frame[ms_per_frame_idx];
		ms_per_frame_idx = (ms_per_frame_idx + 1) % 120;
		const float ms_per_frame_avg = ms_per_frame_accum / 120;
		ImGui::Text("Application average %.3f ms/frame (%.1f FPS)", ms_per_frame_avg, 1000.0f / ms_per_frame_avg);

		if (show_test_window)
		{
			// More example code in ShowTestWindow()
			ImGui::SetNewWindowDefaultPos(ImVec2(650, 20));        // Normally user code doesn't need/want to call it because positions are saved in .ini file anyway. Here we just want to make the demo initial state a bit more friendly!
			ImGui::ShowTestWindow(&show_test_window);
		}

		if (show_another_window)
		{
			ImGui::Begin("Another Window", &show_another_window, ImVec2(200,100));
			ImGui::Text("Hello");
			ImGui::End();
		}

		// 3) Rendering
		glViewport(0, 0, (int)io.DisplaySize.x, (int)io.DisplaySize.y);
		glClearColor(0.8f, 0.6f, 0.6f, 1.0f);
		glClear(GL_COLOR_BUFFER_BIT);
		ImGui::Render();

		glfwSwapBuffers(window);
	}

	Shutdown();
	return 0;
}