OpenGL+Win32 Implementation Example

[rafaelkrause]

Hi,

Just to help users how Want to use Dear Imgui with Win32 + OpenGL.
Please keep free to move this to right place.

We use IMGUI version 1.63, with OpenGL and Win32 Implementation

Note: wglext.h is required

// =============================================================================
//                                  INCLUDES
// =============================================================================
#include <Windows.h>
#include <stdio.h>
#include "imgui.h"
#include "imgui_impl_win32.h"
#include "imgui_impl_opengl3.h"
#include "imgui_internal.h"
#include <GL/gl3w.h>  
#include <gl/GL.h>
#include "wglext.h"
#include <tchar.h>


// =============================================================================
//                                  DEFINES/MACROS
// =============================================================================

// =============================================================================
//                               GLOBAL VARIABLES
// =============================================================================
HGLRC   g_GLRenderContext;
HDC     g_HDCDeviceContext;
HWND    g_hwnd;
PFNWGLSWAPINTERVALEXTPROC       wglSwapIntervalEXT;
PFNWGLGETSWAPINTERVALEXTPROC    wglGetSwapIntervalEXT;
int     g_display_w = 800; 
int     g_display_h = 600;

// =============================================================================
//                             FOWARD DECLARATIONS
// =============================================================================
void CreateGlContext();
void SetCurrentContext();
bool SetSwapInterval(int interval); //0 - No Interval, 1 - Sync whit VSYNC, n - n times Sync with VSYNC
bool WGLExtensionSupported(const char *extension_name);
LRESULT WINAPI WndProc(HWND hWnd, UINT msg, WPARAM wParam, LPARAM lParam);


// =============================================================================
//                            CORE MAIN FUNCTIONS
// =============================================================================
//
// Aplication Entry
//------------------------------------------------------------------------------
 int WINAPI wWinMain(_In_ HINSTANCE hInstance, _In_opt_ HINSTANCE hPrevInstance, _In_ LPWSTR lpCmdLine, _In_ int nCmdShow){
	UNREFERENCED_PARAMETER(hPrevInstance);
	UNREFERENCED_PARAMETER(lpCmdLine);
	UNREFERENCED_PARAMETER(nCmdShow);

	WNDCLASS wc      = {0}; 
	wc.lpfnWndProc   = WndProc;
	wc.hInstance     = hInstance;
	wc.hbrBackground = (HBRUSH)(COLOR_BACKGROUND);
	wc.lpszClassName = "NCUI";
	wc.style = CS_OWNDC;
	if( !RegisterClass(&wc) )
		return 1;
	g_hwnd = CreateWindow(wc.lpszClassName,"teste",WS_OVERLAPPEDWINDOW|WS_VISIBLE,0,0,640,480,0,0,hInstance,0);

    // Show the window
    ShowWindow(g_hwnd, SW_SHOWDEFAULT);
    UpdateWindow(g_hwnd);

    //Prepare OpenGlContext
    CreateGlContext();
    SetSwapInterval(1);
    gl3wInit();

    // Setup Dear ImGui binding
    IMGUI_CHECKVERSION();
    ImGui::CreateContext();
    ImGuiIO& io = ImGui::GetIO(); (void)io;

    //Init Win32
    ImGui_ImplWin32_Init(g_hwnd);
            
    //Init OpenGL Imgui Implementation
    // GL 3.0 + GLSL 130
    const char* glsl_version = "#version 130";
    ImGui_ImplOpenGL3_Init(glsl_version);

    //Set Window bg color
	ImVec4 clear_color = ImVec4(1.000F, 1.000F, 1.000F, 1.0F);

    // Setup style
    ImGui::StyleColorsClassic();

    // Main loop
    MSG msg;
    ZeroMemory(&msg, sizeof(msg));
    while (msg.message != WM_QUIT)
    {
        // Poll and handle messages (inputs, window resize, etc.)
        // You can read the io.WantCaptureMouse, io.WantCaptureKeyboard flags to tell if dear imgui wants to use your inputs.
        // - When io.WantCaptureMouse is true, do not dispatch mouse input data to your main application.
        // - When io.WantCaptureKeyboard is true, do not dispatch keyboard input data to your main application.
        // Generally you may always pass all inputs to dear imgui, and hide them from your application based on those two flags.
        if (PeekMessage(&msg, NULL, 0U, 0U, PM_REMOVE))
        {
            TranslateMessage(&msg);
            DispatchMessage(&msg);
            continue;
        }

        // Start the Dear ImGui frame
        ImGui_ImplOpenGL3_NewFrame();
        ImGui_ImplWin32_NewFrame();
        ImGui::NewFrame();
        //show Main Window
        ImGui::ShowDemoWindow();
        // Rendering
        ImGui::Render();       
        wglMakeCurrent(g_HDCDeviceContext, g_GLRenderContext);
        glViewport(0, 0, g_display_w, g_display_h);                 //Display Size got from Resize Command
        glClearColor(clear_color.x, clear_color.y, clear_color.z, clear_color.w);
        glClear(GL_COLOR_BUFFER_BIT);
        ImGui_ImplOpenGL3_RenderDrawData(ImGui::GetDrawData());
        wglMakeCurrent(g_HDCDeviceContext, g_GLRenderContext);
        SwapBuffers(g_HDCDeviceContext);
         
    }

    // Cleanup
    ImGui_ImplOpenGL3_Shutdown();
    wglDeleteContext(g_GLRenderContext);
    ImGui::DestroyContext();
    ImGui_ImplWin32_Shutdown();

    DestroyWindow(g_hwnd);
    UnregisterClass(_T("NCUI"), wc.hInstance);

	return 0;
}

extern LRESULT ImGui_ImplWin32_WndProcHandler(HWND hWnd, UINT msg, WPARAM wParam, LPARAM lParam);
LRESULT WINAPI WndProc(HWND hWnd, UINT msg, WPARAM wParam, LPARAM lParam){
    if (ImGui_ImplWin32_WndProcHandler(hWnd, msg, wParam, lParam))
        return true;

    switch (msg)
    {
    case WM_SIZE:
        if (wParam != SIZE_MINIMIZED)
        {
            g_display_w = (UINT)LOWORD(lParam);
            g_display_h = (UINT)HIWORD(lParam);
        }
       return 0;
    case WM_SYSCOMMAND:
        if ((wParam & 0xfff0) == SC_KEYMENU) // Disable ALT application menu
            return 0;
        break;
    case WM_DESTROY:
        PostQuitMessage(0);
        return 0;
    }
    return DefWindowProc(hWnd, msg, wParam, lParam);
}

void CreateGlContext(){

	PIXELFORMATDESCRIPTOR pfd =
	{
		sizeof(PIXELFORMATDESCRIPTOR),
		1,
		PFD_DRAW_TO_WINDOW | PFD_SUPPORT_OPENGL | PFD_DOUBLEBUFFER,    //Flags
		PFD_TYPE_RGBA,        // The kind of framebuffer. RGBA or palette.
		32,                   // Colordepth of the framebuffer.
		0, 0, 0, 0, 0, 0,
		0,
		0,
		0,
		0, 0, 0, 0,
		24,                   // Number of bits for the depthbuffer
		8,                    // Number of bits for the stencilbuffer
		0,                    // Number of Aux buffers in the framebuffer.
		PFD_MAIN_PLANE,
		0,
		0, 0, 0
	};

	g_HDCDeviceContext = GetDC(g_hwnd);   

    int pixelFormal = ChoosePixelFormat(g_HDCDeviceContext, &pfd); 
    SetPixelFormat(g_HDCDeviceContext,pixelFormal, &pfd);
    g_GLRenderContext = wglCreateContext(g_HDCDeviceContext);
    wglMakeCurrent(g_HDCDeviceContext, g_GLRenderContext);       
}

bool SetSwapInterval(int interval){	
    if (WGLExtensionSupported("WGL_EXT_swap_control"))
    {
        // Extension is supported, init pointers.
        wglSwapIntervalEXT = (PFNWGLSWAPINTERVALEXTPROC) wglGetProcAddress("wglSwapIntervalEXT");

        // this is another function from WGL_EXT_swap_control extension
        wglGetSwapIntervalEXT = (PFNWGLGETSWAPINTERVALEXTPROC) wglGetProcAddress("wglGetSwapIntervalEXT");

        wglSwapIntervalEXT(interval);
        return true;
    }
    
    return false;

}

//Got from https://stackoverflow.com/questions/589064/how-to-enable-vertical-sync-in-opengl/589232
bool WGLExtensionSupported(const char *extension_name){
    // this is pointer to function which returns pointer to string with list of all wgl extensions
    PFNWGLGETEXTENSIONSSTRINGEXTPROC _wglGetExtensionsStringEXT = NULL;

    // determine pointer to wglGetExtensionsStringEXT function
    _wglGetExtensionsStringEXT = (PFNWGLGETEXTENSIONSSTRINGEXTPROC) wglGetProcAddress("wglGetExtensionsStringEXT");

    if (strstr(_wglGetExtensionsStringEXT(), extension_name) == NULL)
    {
        // string was not found
        return false;
    }

    // extension is supported
    return true;
}

[ice1000]

Could you please share your color style?

[ocornut]

Thank you @rafaelkrause. Will try at some point to provide a raw Win32 example and this will be useful. Also linking to #1553.

[rafaelkrause]

@ice1000

Could you please share your color style?

This is the Default Imgui Color with a White Background Window.

See code

// Setup style
ImGui::StyleColorsClassic();

[ocornut]

Your pixel format has Red and Blue inverted, hence the unexpected colors.

[rafaelkrause]

I see, do you know Where I can fix it?

[eXtreames]

I use this method, everything is drawn perfectly, but Geforce Experience captures this window and records it. How to fix this behavior?

[OPstriker]

Something I realized is that you haven't set up the DPI for High DPI screens.
Can be Done with:

SetProcessDpiAwarenessContext(DPI_AWARENESS_CONTEXT_PER_MONITOR_AWARE_V2);

And Oh Yeah, It works well...

[OPstriker]

I use this method, everything is drawn perfectly, but Geforce Experience captures this window and records it. How to fix this behavior?

Seems like a issue you need to fix with Geforce Experience, I maybe wrong.....

[ocornut]

Closed/solved, see #3218 (comment)