Make a win32 window transparent to messages (click, touch, keyboard)

Question

I created a semi transparent window using the source code from this discussion (posted by wilkie): How to make an OpenGL rendering context with transparent background?

It works, but I would like my window not to pick up mouse, touch and keyboard click messages. But above all, I would like these messages (click, touch, keyboard) to be received by the application located below my transparent window.

Example: My transparent window (TOP_MOST) is located on top of NotePad ++. If I click on my transparent window, I want this click to be received by NotePad++ and not by my transparent window.

I did not find valid answers on the Internet. I see two possibilities: _ Make my window transparent to all messages _ Or my transparent window must receive the messages, not react and redirect them by sending them to the window located below.

In both cases, I don't know how to do it :) Is it possible ?

Regards,

Edit with code:

#define _WIN32_WINNT 0x0500

#include <windows.h>
#include <windowsx.h>
#include <GL/gl.h>
#include <GL/glu.h>

#include <dwmapi.h>

#pragma comment (lib, "opengl32.lib")
#pragma comment (lib, "glu32.lib")

#pragma comment (lib, "dwmapi.lib")

#include <assert.h>
#include <tchar.h>

#ifdef  assert
#define verify(expr) if(!expr) assert(0)
#else verify(expr) expr
#endif

const TCHAR szAppName[] = _T("TransparentGL");
const TCHAR wcWndName[] = _T("TransparentGL");

HDC hDC;
HGLRC m_hrc;
int w = 240;
int h = 240;

BOOL initSC() {
    glEnable(GL_ALPHA_TEST);
    glEnable(GL_DEPTH_TEST);
    glEnable(GL_COLOR_MATERIAL);

    glEnable(GL_LIGHTING);
    glEnable(GL_LIGHT0);

    glEnable(GL_BLEND);
    glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
    glClearColor(0, 0, 0, 0);

    return 0;
}

void resizeSC(int width, int height) {
    glViewport(0, 0, width, height);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();

    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
}

BOOL renderSC() {
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    glPushMatrix();

    glColor3f(0, 1, 1);
    glBegin(GL_TRIANGLES);                              // Drawing Using Triangles
    glColor3f(1.0f, 0.0f, 0.0f);                      // Set The Color To Red
    glVertex3f(0.0f, 1.0f, 0.0f);                  // Top
    glColor3f(0.0f, 1.0f, 0.0f);                      // Set The Color To Green
    glVertex3f(-1.0f, -1.0f, 0.0f);                  // Bottom Left
    glColor3f(0.0f, 0.0f, 1.0f);                      // Set The Color To Blue
    glVertex3f(1.0f, -1.0f, 0.0f);                  // Bottom Right
    glEnd();

    glPopMatrix();
    glFlush();

    return 0;
}

BOOL CreateHGLRC(HWND hWnd) {
    PIXELFORMATDESCRIPTOR pfd = {
        sizeof(PIXELFORMATDESCRIPTOR),
        1,                                // Version Number
        PFD_DRAW_TO_WINDOW |         // Format Must Support Window
        PFD_SUPPORT_OPENGL |         // Format Must Support OpenGL
        PFD_SUPPORT_COMPOSITION |         // Format Must Support Composition
        PFD_DOUBLEBUFFER,                 // Must Support Double Buffering
        PFD_TYPE_RGBA,                    // Request An RGBA Format
        32,                               // Select Our Color Depth
        0, 0, 0, 0, 0, 0,                 // Color Bits Ignored
        8,                                // An Alpha Buffer
        0,                                // Shift Bit Ignored
        0,                                // No Accumulation Buffer
        0, 0, 0, 0,                       // Accumulation Bits Ignored
        24,                               // 16Bit Z-Buffer (Depth Buffer)
        8,                                // Some Stencil Buffer
        0,                                // No Auxiliary Buffer
        PFD_MAIN_PLANE,                   // Main Drawing Layer
        0,                                // Reserved
        0, 0, 0                           // Layer Masks Ignored
    };

    HDC hdc = GetDC(hWnd);
    int PixelFormat = ChoosePixelFormat(hdc, &pfd);
    if (PixelFormat == 0) {
        assert(0);
        return FALSE;
    }

    BOOL bResult = SetPixelFormat(hdc, PixelFormat, &pfd);
    if (bResult == FALSE) {
        assert(0);
        return FALSE;
    }

    m_hrc = wglCreateContext(hdc);
    if (!m_hrc) {
        assert(0);
        return FALSE;
    }

    ReleaseDC(hWnd, hdc);

    return TRUE;
}

LRESULT CALLBACK WindowFunc(HWND hWnd, UINT msg, WPARAM wParam, LPARAM lParam) {


    switch (msg) {
    case WM_CREATE:
        break;

    case WM_DESTROY:
        if (m_hrc) {
            wglMakeCurrent(NULL, NULL);
            wglDeleteContext(m_hrc);
        }
        PostQuitMessage(0);
        break;

    default:
        return DefWindowProc(hWnd, msg, wParam, lParam);
    }

    return 0;
}

int WINAPI WinMain(HINSTANCE hThisInst, HINSTANCE hPrevInst, LPSTR str, int nWinMode) {
    WNDCLASSEX wc;
    memset(&wc, 0, sizeof(wc));
    wc.cbSize = sizeof(WNDCLASSEX);
    wc.hIconSm = LoadIcon(NULL, IDI_APPLICATION);
    wc.style = CS_HREDRAW | CS_VREDRAW;
    wc.lpfnWndProc = (WNDPROC)WindowFunc;
    wc.cbClsExtra = 0;
    wc.cbWndExtra = 0;
    wc.hInstance = hThisInst;
    wc.hIcon = LoadIcon(NULL, IDI_APPLICATION);
    wc.hCursor = LoadCursor(NULL, IDC_ARROW);
    wc.hbrBackground = (HBRUSH)CreateSolidBrush(0x00000000);
    wc.lpszClassName = szAppName;

    if (!RegisterClassEx(&wc)) {
        MessageBox(NULL, _T("RegisterClassEx - failed"), _T("Error"), MB_OK | MB_ICONERROR);
        return FALSE;
    }

    HWND hWnd = CreateWindowEx(WS_EX_APPWINDOW | WS_EX_TOPMOST | WS_EX_TRANSPARENT, szAppName, wcWndName,
        WS_VISIBLE | WS_POPUP, 200, 150, w, h,
        NULL, NULL, hThisInst, NULL);

    if (!hWnd) {
        MessageBox(NULL, _T("CreateWindowEx - failed"), _T("Error"), MB_OK | MB_ICONERROR);
        return FALSE;
    }

    DWM_BLURBEHIND bb = { 0 };
    HRGN hRgn = CreateRectRgn(0, 0, -1, -1);
    bb.dwFlags = DWM_BB_ENABLE | DWM_BB_BLURREGION;
    bb.hRgnBlur = hRgn;
    bb.fEnable = TRUE;
    DwmEnableBlurBehindWindow(hWnd, &bb);

    CreateHGLRC(hWnd);

    HDC hdc = GetDC(hWnd);
    wglMakeCurrent(hdc, m_hrc);
    initSC();
    resizeSC(w, h);
    ReleaseDC(hWnd, hdc);

    MSG msg;
    while (1) {
        if (PeekMessage(&msg, NULL, 0, 0, PM_REMOVE)) {
            TranslateMessage(&msg);
            DispatchMessage(&msg);
        }
        else {
            HDC hdc = GetDC(hWnd);
            wglMakeCurrent(hdc, m_hrc);

            renderSC();

            SwapBuffers(hdc);
            ReleaseDC(hWnd, hdc);
        }
    }

    return (FALSE);
}

Answer 1

Thanks to Zhu Song - MSFT and David Heffernan, this is the full source code of the modified sample originaly posted in this post: How to make an OpenGL rendering context with transparent background?

It display an OpenGL Triangle in transparente Window and support Click-Through:

#define _WIN32_WINNT 0x0500

#include <windows.h>
#include <windowsx.h>
#include <GL/gl.h>
#include <GL/glu.h>

#include <dwmapi.h>

#pragma comment (lib, "opengl32.lib")
#pragma comment (lib, "glu32.lib")

#pragma comment (lib, "dwmapi.lib")

#include <assert.h>
#include <tchar.h>

#ifdef  assert
#define verify(expr) if(!expr) assert(0)
#else verify(expr) expr
#endif

const TCHAR szAppName[] = _T("TransparentGL");
const TCHAR wcWndName[] = _T("TransparentGL");

HDC hDC;
HGLRC m_hrc;
int w = 240;
int h = 240;

BOOL initSC() {
    glEnable(GL_ALPHA_TEST);
    glEnable(GL_DEPTH_TEST);
    glEnable(GL_COLOR_MATERIAL);

    glEnable(GL_LIGHTING);
    glEnable(GL_LIGHT0);

    glEnable(GL_BLEND);
    glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
    glClearColor(0, 0, 0, 0);

    return 0;
}

void resizeSC(int width, int height) {
    glViewport(0, 0, width, height);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();

    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
}

BOOL renderSC() {
    static float angle = 0.0f;
    angle = (angle < 360.0f ) ? angle + 0.01f : 0.0f;

    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    glPushMatrix();

    glRotatef(angle, 0.0f, 0.0f, 1.0f);

    glColor3f(0, 1, 1);
    glBegin(GL_TRIANGLES);                              // Drawing Using Triangles
    glColor4f(1.0f, 0.0f, 0.0f,0.5f);                      // Set The Color To Red
    glVertex3f(0.0f, 1.0f, 0.0f);                  // Top
    glColor4f(0.0f, 1.0f, 0.0f, 0.5f);                      // Set The Color To Green
    glVertex3f(-1.0f, -1.0f, 0.0f);                  // Bottom Left
    glColor4f(0.0f, 0.0f, 1.0f, 0.5f);                      // Set The Color To Blue
    glVertex3f(1.0f, -1.0f, 0.0f);                  // Bottom Right
    glEnd();

    glPopMatrix();
    glFlush();

    return 0;
}

BOOL CreateHGLRC(HWND hWnd) {
    PIXELFORMATDESCRIPTOR pfd = {
        sizeof(PIXELFORMATDESCRIPTOR),
        1,                                // Version Number
        PFD_DRAW_TO_WINDOW |         // Format Must Support Window
        PFD_SUPPORT_OPENGL |         // Format Must Support OpenGL
        PFD_SUPPORT_COMPOSITION |         // Format Must Support Composition
        PFD_DOUBLEBUFFER,                 // Must Support Double Buffering
        PFD_TYPE_RGBA,                    // Request An RGBA Format
        32,                               // Select Our Color Depth
        0, 0, 0, 0, 0, 0,                 // Color Bits Ignored
        8,                                // An Alpha Buffer
        0,                                // Shift Bit Ignored
        0,                                // No Accumulation Buffer
        0, 0, 0, 0,                       // Accumulation Bits Ignored
        24,                               // 16Bit Z-Buffer (Depth Buffer)
        8,                                // Some Stencil Buffer
        0,                                // No Auxiliary Buffer
        PFD_MAIN_PLANE,                   // Main Drawing Layer
        0,                                // Reserved
        0, 0, 0                           // Layer Masks Ignored
    };

    HDC hdc = GetDC(hWnd);
    int PixelFormat = ChoosePixelFormat(hdc, &pfd);
    if (PixelFormat == 0) {
        assert(0);
        return FALSE;
    }

    BOOL bResult = SetPixelFormat(hdc, PixelFormat, &pfd);
    if (bResult == FALSE) {
        assert(0);
        return FALSE;
    }

    m_hrc = wglCreateContext(hdc);
    if (!m_hrc) {
        assert(0);
        return FALSE;
    }

    ReleaseDC(hWnd, hdc);

    return TRUE;
}

LRESULT CALLBACK WindowFunc(HWND hWnd, UINT msg, WPARAM wParam, LPARAM lParam) {
    PAINTSTRUCT ps;

    switch (msg) {

    case WM_CREATE:
        break;

    case WM_DESTROY:
        if (m_hrc) {
            wglMakeCurrent(NULL, NULL);
            wglDeleteContext(m_hrc);
        }
        PostQuitMessage(0);
        break;

    default:
        return DefWindowProc(hWnd, msg, wParam, lParam);
    }

    return 0;
}

int WINAPI WinMain(HINSTANCE hThisInst, HINSTANCE hPrevInst, LPSTR str, int nWinMode) {
    WNDCLASSEX wc;
    memset(&wc, 0, sizeof(wc));
    wc.cbSize = sizeof(WNDCLASSEX);
    wc.hIconSm = LoadIcon(NULL, IDI_APPLICATION);
    wc.style = CS_HREDRAW | CS_VREDRAW;
    wc.lpfnWndProc = (WNDPROC)WindowFunc;
    wc.cbClsExtra = 0;
    wc.cbWndExtra = 0;
    wc.hInstance = hThisInst;
    wc.hIcon = LoadIcon(NULL, IDI_APPLICATION);
    wc.hCursor = LoadCursor(NULL, IDC_ARROW);
    wc.hbrBackground = (HBRUSH)CreateSolidBrush(0x00000000);
    wc.lpszClassName = szAppName;

    if (!RegisterClassEx(&wc)) {
        MessageBox(NULL, _T("RegisterClassEx - failed"), _T("Error"), MB_OK | MB_ICONERROR);
        return FALSE;
    }

    HWND hWnd = CreateWindowEx(WS_EX_LAYERED | WS_EX_APPWINDOW | WS_EX_TOPMOST | WS_EX_TRANSPARENT, szAppName, wcWndName,
        WS_VISIBLE | WS_POPUP, 200, 150, w, h,
        NULL, NULL, hThisInst, NULL);
    if (!hWnd) {
        MessageBox(NULL, _T("CreateWindowEx - failed"), _T("Error"), MB_OK | MB_ICONERROR);
        return FALSE;
    }
    SetLayeredWindowAttributes(hWnd, 0, 255, LWA_ALPHA);

    DWM_BLURBEHIND bb = { 0 };
    HRGN hRgn = CreateRectRgn(0, 0, -1, -1);
    bb.dwFlags = DWM_BB_ENABLE | DWM_BB_BLURREGION;
    bb.hRgnBlur = hRgn;
    bb.fEnable = TRUE;
    DwmEnableBlurBehindWindow(hWnd, &bb);

    CreateHGLRC(hWnd);

    HDC hdc = GetDC(hWnd);
    wglMakeCurrent(hdc, m_hrc);
    initSC();
    resizeSC(w, h);
    ReleaseDC(hWnd, hdc);

    MSG msg;
    while (1) {
        if (PeekMessage(&msg, NULL, 0, 0, PM_REMOVE)) {
            TranslateMessage(&msg);
            DispatchMessage(&msg);
        }
        else {
            HDC hdc = GetDC(hWnd);
            wglMakeCurrent(hdc, m_hrc);

            renderSC();

            SwapBuffers(hdc);
            ReleaseDC(hWnd, hdc);
        }
    }

    return (FALSE);
}

If it can help other peoples, if you want to do the same thing with QT:

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);

    _glWidget = new MyOpenGLWidget(this); // derived from: public QOpenGLWidget, protected QOpenGLFunctions_3_3_Core

   setAttribute(Qt::WA_InputMethodTransparent);
   setAttribute(Qt::WA_TranslucentBackground, true);
   setAttribute(Qt::WA_TransparentForMouseEvents);
   SetForegroundWindow((HWND)winId());
   setWindowFlags(Qt::Window | Qt::FramelessWindowHint |Qt::WindowStaysOnTopHint);

    ui->verticalLayout->addWidget(_glWidget);                      
}

Answer 2

You can add the WS_EX_LAYERED style when creating the form, and set the opacity of the window through the SetLayeredWindowAttributes function.

HWND hWnd = CreateWindowEx(WS_EX_LAYERED |  WS_EX_APPWINDOW | WS_EX_TOPMOST | WS_EX_TRANSPARENT, szAppName, wcWndName,
WS_VISIBLE | WS_POPUP, 200, 150, w, h,
NULL, NULL, hThisInst, NULL);
if (!hWnd) {
    MessageBox(NULL, _T("CreateWindowEx - failed"), _T("Error"), MB_OK | MB_ICONERROR);
    return FALSE;
}
SetLayeredWindowAttributes(hWnd, 0, 255, LWA_ALPHA);

Then it works for me: