Win32 - Make part of window a translucent while another part opaque? - c

Question

I want one part of a window to display an image with a certain opacity while the other part to work as normal. Both parts shouldn't pass clicks through.
I have tried making the main window a certain colour then using SetLayeredWindowAttributes to make that colour transparent(so only the client area is transparent). Then having a child window over it with my translucent image. However the clicks pass through the window(even though I don't have WS_EX_TRANSPARENT). Alphablend doesn't seem to works since the bitmap isn't 32bmp. So now I am trying to use updatelayeredwindows but I am having trouble setting the region to update it.
case WM_CREATE:
hbmp = (HBITMAP)LoadImageA(NULL, "courtyard.bmp", IMAGE_BITMAP, 1920, 1080, LR_LOADFROMFILE);
HDC hdc = CreateCompatibleDC(NULL);
HBITMAP hbmp_old = (HBITMAP)SelectObject(hdc, hbmp);
POINT dcOffset = {0, 0};
SIZE size = {600, 395};
BLENDFUNCTION bf = {AC_SRC_OVER, 0, 100, 0};
RECT wrect;
GetClientRect(hwnd, &wrect);
wrect.top = wrect.top + 43;
UPDATELAYEREDWINDOWINFO info = {sizeof(info), GetDC(NULL), NULL, &size, hdc, &dcOffset, 0, &bf, ULW_ALPHA, &wrect};
UpdateLayeredWindowIndirect(hwnd, &info);
SelectObject(hdc, hbmp_old);
DeleteDC(hdc);
DeleteObject(hbmp);
HWND hbutton = CreateWindowExA(0,
"BUTTON",
"X",
WS_VISIBLE | WS_CHILD | BS_FLAT,
10,
10,
100,
100,
hwnd,
(HMENU)NULL,
NULL,
(LPVOID)NULL);
break;
The parts out of wrect are just a black translucent colour.
Here is my main window:
hwnd = CreateWindowExA(WS_EX_OVERLAPPEDWINDOW | WS_EX_LAYERED,
window_name,
window_title,
WS_OVERLAPPEDWINDOW,
(monitor_dimension.width - window_width) / 2,
(monitor_dimension.height - window_height) / 2 - 75,
window_width,
window_height,
(HWND)NULL,
(HMENU)NULL,
hInstance,
(LPVOID)NULL);

Answer 1

I get the result using SetLayeredWindowAttributes(hWnd, RGB(255, 0, 0), 0, LWA_COLORKEY); without manifest and the clicks don't pass through.
The following code adapted from SetLayeredWindowAttributes() causes mouse clicks to go through after minimizing window | WinAPI.
// WindowsProject2.cpp : Defines the entry point for the application.
//
#include "framework.h"
#include "WindowsProject2.h"
#define MAX_LOADSTRING 100
// Global Variables:
HINSTANCE hInst; // current instance
WCHAR szTitle[MAX_LOADSTRING]; // The title bar text
WCHAR szWindowClass[MAX_LOADSTRING]; // the main window class name
// Forward declarations of functions included in this code module:
ATOM MyRegisterClass(HINSTANCE hInstance);
BOOL InitInstance(HINSTANCE, int);
LRESULT CALLBACK WndProc(HWND, UINT, WPARAM, LPARAM);
INT_PTR CALLBACK About(HWND, UINT, WPARAM, LPARAM);
int APIENTRY wWinMain(_In_ HINSTANCE hInstance,
_In_opt_ HINSTANCE hPrevInstance,
_In_ LPWSTR lpCmdLine,
_In_ int nCmdShow)
{
UNREFERENCED_PARAMETER(hPrevInstance);
UNREFERENCED_PARAMETER(lpCmdLine);
// TODO: Place code here.
// Initialize global strings
LoadStringW(hInstance, IDS_APP_TITLE, szTitle, MAX_LOADSTRING);
LoadStringW(hInstance, IDC_WINDOWSPROJECT2, szWindowClass, MAX_LOADSTRING);
MyRegisterClass(hInstance);
// Perform application initialization:
if (!InitInstance (hInstance, nCmdShow))
{
return FALSE;
}
HACCEL hAccelTable = LoadAccelerators(hInstance, MAKEINTRESOURCE(IDC_WINDOWSPROJECT2));
MSG msg;
// Main message loop:
while (GetMessage(&msg, nullptr, 0, 0))
{
if (!TranslateAccelerator(msg.hwnd, hAccelTable, &msg))
{
TranslateMessage(&msg);
DispatchMessage(&msg);
}
}
return (int) msg.wParam;
}
//
// FUNCTION: MyRegisterClass()
//
// PURPOSE: Registers the window class.
//
ATOM MyRegisterClass(HINSTANCE hInstance)
{
WNDCLASSEXW wcex;
wcex.cbSize = sizeof(WNDCLASSEX);
wcex.style = CS_HREDRAW | CS_VREDRAW;
wcex.lpfnWndProc = WndProc;
wcex.cbClsExtra = 0;
wcex.cbWndExtra = 0;
wcex.hInstance = hInstance;
wcex.hIcon = LoadIcon(hInstance, MAKEINTRESOURCE(IDI_WINDOWSPROJECT2));
wcex.hCursor = LoadCursor(nullptr, IDC_ARROW);
wcex.hbrBackground = (HBRUSH)CreateSolidBrush(RGB(255, 0, 0));
wcex.lpszMenuName = MAKEINTRESOURCEW(IDC_WINDOWSPROJECT2);
wcex.lpszClassName = szWindowClass;
wcex.hIconSm = LoadIcon(wcex.hInstance, MAKEINTRESOURCE(IDI_SMALL));
return RegisterClassExW(&wcex);
}
//
// FUNCTION: InitInstance(HINSTANCE, int)
//
// PURPOSE: Saves instance handle and creates main window
//
// COMMENTS:
//
// In this function, we save the instance handle in a global variable and
// create and display the main program window.
//
BOOL InitInstance(HINSTANCE hInstance, int nCmdShow)
{
hInst = hInstance; // Store instance handle in our global variable
HWND hWnd = CreateWindowW(szWindowClass, szTitle, WS_OVERLAPPEDWINDOW,
CW_USEDEFAULT, 0, CW_USEDEFAULT, 0, nullptr, nullptr, hInstance, nullptr);
if (!hWnd)
{
return FALSE;
}
ShowWindow(hWnd, nCmdShow);
UpdateWindow(hWnd);
return TRUE;
}
//
// FUNCTION: WndProc(HWND, UINT, WPARAM, LPARAM)
//
// PURPOSE: Processes messages for the main window.
//
// WM_COMMAND - process the application menu
// WM_PAINT - Paint the main window
// WM_DESTROY - post a quit message and return
//
//
LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
{
switch (message)
{
case WM_CREATE:
{
SetWindowLong(hWnd, GWL_EXSTYLE, GetWindowLong(hWnd, GWL_EXSTYLE) | WS_EX_LAYERED);
SetLayeredWindowAttributes(hWnd, RGB(255, 0, 0), 0 /*doesn't matter*/, LWA_COLORKEY);
HWND hbutton = CreateWindowExA(0,
"BUTTON",
"X",
WS_VISIBLE | WS_CHILD | BS_FLAT,
10,
10,
100,
100,
hWnd,
(HMENU)NULL,
NULL,
(LPVOID)NULL);
/*HWND hbackground = CreateWindowEx(0,
L"STATIC",
NULL,
WS_CHILD | WS_VISIBLE | SS_BITMAP,
0,
0,
600,
400,
hWnd,
NULL,
NULL,
(LPVOID)NULL);
setImage(hbackground, L"test.bmp", 600, 400);*/
//SetWindowLong(hbackground, GWL_EXSTYLE, GetWindowLong(hbackground, GWL_EXSTYLE) | WS_EX_LAYERED);
//SetLayeredWindowAttributes(hbackground, 0, (255 * 50) / 100, LWA_ALPHA);
}
break;
case WM_COMMAND:
{
int wmId = LOWORD(wParam);
// Parse the menu selections:
switch (wmId)
{
case IDM_ABOUT:
DialogBox(hInst, MAKEINTRESOURCE(IDD_ABOUTBOX), hWnd, About);
break;
case IDM_EXIT:
DestroyWindow(hWnd);
break;
default:
return DefWindowProc(hWnd, message, wParam, lParam);
}
}
break;
case WM_PAINT:
{
PAINTSTRUCT ps;
HDC hdc = BeginPaint(hWnd, &ps);
// TODO: Add any drawing code that uses hdc here...
EndPaint(hWnd, &ps);
}
break;
case WM_DESTROY:
PostQuitMessage(0);
break;
default:
return DefWindowProc(hWnd, message, wParam, lParam);
}
return 0;
}
// Message handler for about box.
INT_PTR CALLBACK About(HWND hDlg, UINT message, WPARAM wParam, LPARAM lParam)
{
UNREFERENCED_PARAMETER(lParam);
switch (message)
{
case WM_INITDIALOG:
return (INT_PTR)TRUE;
case WM_COMMAND:
if (LOWORD(wParam) == IDOK || LOWORD(wParam) == IDCANCEL)
{
EndDialog(hDlg, LOWORD(wParam));
return (INT_PTR)TRUE;
}
break;
}
return (INT_PTR)FALSE;
}