【发布时间】：2020-04-20 18:03:15
【问题描述】：
我有一个子类按钮，我希望它显示一个具有透明背景的位图。在搜索互联网后，我发现你必须使用 AlphaBlend 函数来完成（我试过这个，但也没有用）。我也看到了这个bitmap transparency in Visual Studio 2013 C++ 线程，我尝试了这些步骤，但我做不到。只要我能获得带有透明背景图像的按钮，我就可以使用 GDI 或 GDI+。 示例：
这是我的代码——我知道它很乱，但请放心，因为我尝试了很多东西来让它工作（有很多复制和粘贴）
更新：这里又是代码，但修剪后没有所有的脂肪，是的，我确实在两个窗口上都尝试了 WS_EX_LAYERED。
// CustomButton2.cpp : Defines the entry point for the application.
//
#include "framework.h"
#include "CustomButton2.h"
#include <commctrl.h>
#include <gdiplus.h>
#include <system_error>
#include "SkinClass/skin.h"
#define MAX_LOADSTRING 100
#define CRAPPY 567
#pragma comment(linker,"/manifestdependency:\"type='win32' name='Microsoft.Windows.Common-Controls' " "version='6.0.0.0' processorArchitecture='*' publicKeyToken='6595b64144ccf1df' language='*'\"")
// Global Variables:
HINSTANCE hInst; // current instance
WCHAR szTitle[MAX_LOADSTRING]; // The title bar text
WCHAR szWindowClass[MAX_LOADSTRING]; // the main window class name
const char g_szClassName[] = "MyClassName";
// Forward declarations of functions included in this code module:
ATOM MyRegisterClass(HINSTANCE hInstance);
void RegisterClass1(HINSTANCE);
LRESULT CALLBACK WndProc(HWND, UINT, WPARAM, LPARAM);
/// Turn given window into a layered window and load a bitmap from given resource ID
/// into it.
/// The window will be resized to fit the bitmap.
/// Bitmap must be 32bpp, top-down row order, premultiplied alpha.
///
/// \note For child windows, this requires Win 8 or newer OS
/// (and "supportedOS" element for Win 8 in application manifest)
///
/// \exception Throws std::system_error in case of any error.
void SetLayeredWindowFromBitmapResource(
HWND hwnd, UINT bitmapResourceId, HINSTANCE hInstance = nullptr)
{
// Enable "layered" mode for the child window. This enables full alpha channel
// transparency.
// GetWindowLong() won't reset the last error in case of success.
// As we can't judge from the return value of GetWindowLong() alone if
// the function was successful (0 may be returned even in case of
// success), we must reset the last error to reliably detect errors.
::SetLastError(0);
DWORD exStyle = ::GetWindowLong(hwnd, GWL_EXSTYLE);
if (!exStyle)
{
// NOTE: Call GetLastError() IMMEDIATELY when a function's return value
// indicates failure and it is documented that said function supports
// GetLastError().
// ANY other code (be it your own or library code) before the next line
// must be avoided as it may invalidate the last error value.
if (DWORD err = ::GetLastError())
throw std::system_error(static_cast<int>(err),
std::system_category(),
"SetLayeredWindowFromBitmapResource: Could not get extended window style");
}
// SetWindowLong() won't reset the last error in case of success.
// As we can't judge from the return value of GetWindowLong() alone if
// the function was successful (0 may be returned even in case of
// success), we must reset the last error to reliably detect errors.
::SetLastError(0);
if (!::SetWindowLong(hwnd, GWL_EXSTYLE, exStyle | WS_EX_LAYERED))
{
if (DWORD err = ::GetLastError())
throw std::system_error(static_cast<int>(err),
std::system_category(),
"SetLayeredWindowFromBitmapResource: Could not set extended window style");
}
// Use RAII ( https://en.wikipedia.org/wiki/Resource_acquisition_is_initialization )
// to cleanup resources even in case of exceptions.
// This greatly simplifies the code because now we don't have to manually cleanup the
// resources at every location in the code where we throw an exception.
struct Resources {
HBITMAP hImage = nullptr;
HGDIOBJ hOldImage = nullptr;
HDC hMemDC = nullptr;
// This destructor will be automatically called before the function
// SetLayeredWindowFromBitmapResource() returns aswell as any locations
// in the code where the "throw" keyword is used to throw an exception.
~Resources()
{
if (hMemDC)
{
if (hOldImage)
::SelectObject(hMemDC, hOldImage);
::DeleteDC(hMemDC);
}
if (hImage)
::DeleteObject(hImage);
}
} res;
// Make it possible to use nullptr as an argument for the hInstance parameter of
// this function. This means we will load the resources from the current executable
// (instead of another DLL).
if (!hInstance)
hInstance = ::GetModuleHandle(nullptr);
// Load bitmap with alpha channel from resource.
// Flag LR_CREATEDIBSECTION is required to create a device-independent bitmap that
// preserves the alpha channel.
res.hImage = reinterpret_cast<HBITMAP>(::LoadImage(
hInstance, MAKEINTRESOURCE(bitmapResourceId), IMAGE_BITMAP,
0, 0, LR_CREATEDIBSECTION));
if (!res.hImage)
{
DWORD err = ::GetLastError();
throw std::system_error(static_cast<int>(err),
std::system_category(),
"SetLayeredWindowFromBitmapResource: Could not load bitmap resource");
}
// Get bitmap information (width, height, etc.)
BITMAP imgInfo{ 0 };
if (!::GetObject(res.hImage, sizeof(imgInfo), &imgInfo))
{
DWORD err = ::GetLastError();
throw std::system_error(static_cast<int>(err),
std::system_category(),
"SetLayeredWindowFromBitmapResource: Could not get bitmap information");
}
if (imgInfo.bmBitsPixel != 32 || imgInfo.bmPlanes != 1)
{
// Use a constant error value here because this is our own error condition.
// Of course GetLastError() wouldn't return anything useful in this case.
DWORD err = ERROR_INVALID_DATA;
throw std::system_error(err, std::system_category(),
"SetLayeredWindowFromBitmapResource: bitmap must be 32 bpp, single plane");
}
// Create a memory DC that will be associated with the image.
// UpdateLayeredWindow() can't use image directly, it must be in a memory DC.
res.hMemDC = ::CreateCompatibleDC(nullptr);
if (!res.hMemDC)
{
DWORD err = ::GetLastError();
throw std::system_error(static_cast<int>(err),
std::system_category(),
"SetLayeredWindowFromBitmapResource: Could not create memory DC");
}
res.hOldImage = ::SelectObject(res.hMemDC, res.hImage);
if (!res.hOldImage)
{
DWORD err = ::GetLastError();
throw std::system_error(static_cast<int>(err),
std::system_category(),
"SetLayeredWindowFromBitmapResource: Could not select bitmap into memory DC");
}
// Assign the image to the child window, making it transparent.
SIZE size{ imgInfo.bmWidth, imgInfo.bmHeight };
POINT ptSrc{ 0, 0 };
BLENDFUNCTION blend{ AC_SRC_OVER, 0, 255, AC_SRC_ALPHA };
if (!::UpdateLayeredWindow(hwnd, nullptr, nullptr, &size, res.hMemDC, &ptSrc,
0, &blend, ULW_ALPHA))
{
DWORD err = ::GetLastError();
throw std::system_error(static_cast<int>(err),
std::system_category(),
"SetLayeredWindowFromBitmapResource: Could not update layered window");
}
// Destructor of res object will cleanup resources here!
}
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.
RegisterClass1(hInstance);
HWND hWnd = CreateWindowExA(WS_EX_LAYERED, g_szClassName, "Scenes", WS_OVERLAPPEDWINDOW | WS_EX_LAYERED, CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT, NULL, NULL,
hInstance, NULL);
HWND hButton = CreateWindow(TEXT("BUTTON"), TEXT("START EDITING!"), WS_CHILD | WS_VISIBLE | BS_OWNERDRAW | WS_EX_LAYERED, 1, 1,228, 228,
hWnd, (HMENU)CRAPPY, NULL, NULL);
//SetLayeredWindowFromBitmapResource(hButton, ID_THECIRCLE, hInstance);
SetLayeredWindowAttributes(hWnd, 0, 249, LWA_ALPHA);
ShowWindow(hWnd, nCmdShow);
UpdateWindow(hWnd);
SetLayeredWindowFromBitmapResource(hButton, ID_THECIRCLE);
MSG msg;
// Main message loop:
while (GetMessage(&msg, nullptr, 0, 0))
{
TranslateMessage(&msg);
DispatchMessage(&msg);
}
return (int) msg.wParam;
}
//
// FUNCTION: RegisterClass1()
//
// PURPOSE: Registers the class
//
// COMMENTS:
//
//
//
//
void RegisterClass1(HINSTANCE hInstance) {
WNDCLASSEXA wc;
wc.cbSize = sizeof(WNDCLASSEX);
wc.cbClsExtra = 0;
wc.cbWndExtra = 0;
//wc.hbrBackground = (HBRUSH)(COLOR_WINDOW + 1);
wc.hbrBackground = CreateSolidBrush(RGB(255, 0, 0));
wc.hCursor = LoadCursor(NULL, IDC_ARROW);
wc.hIcon = LoadIcon(NULL, IDI_APPLICATION);
wc.hIconSm = LoadIcon(NULL, IDI_APPLICATION);
wc.hInstance = hInstance;
wc.lpfnWndProc = WndProc;
wc.lpszClassName = g_szClassName;
wc.lpszMenuName = "MENU";
wc.style = CS_HREDRAW | CS_VREDRAW;
if (!RegisterClassEx(&wc))
{
MessageBox(NULL, "Window Registration Failed!", "Error!",
MB_ICONEXCLAMATION | MB_OK);
}
}
//
// 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_COMMAND:
{
int wmId = LOWORD(wParam);
// Parse the menu selections:
switch (wmId)
{
case IDM_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;
}
【问题讨论】：
-
要使用
UpdateLayeredWindow，窗口需要设置WS_EX_LAYERED扩展样式，这可能就是您尝试在按钮上使用SetLayeredWindowFromBitmapResource失败的原因。如果您查看找到的代码，您会看到一条关于需要使用LR_CREATEDIBSECTION的评论，这就是您尝试使用LoadBitmap失败的原因——alpha 通道没有被保留。我建议如果您在这里需要帮助，请尝试创建一个minimal reproducible example，以便人们更轻松地编译和尝试您的代码。 -
我可能有一些代码可以做到这一点。涉及加载 PNG，iirc 但我不记得它有那么复杂。
-
你谈论乔纳森波特的那部分是那个用户的代码，它通过我调用他们的函数来工作。在前面的代码中，我确实使用了带有该标志的 loadImage，但它仍然不起作用。无论如何，这里的代码又是什么，没有它所拥有的所有不必要的垃圾。即使使用 WS_EX_LAYERED，代码也不起作用。我通过调试器检查并在函数 SetLayeredWindowFromBitmapResource 的末尾抛出异常
-
@selbie 我不介意我是否必须使用 png，只要它完成就可以了。
-
我正在查看我的古老代码。它只是所有者绘制并使用 Gdi+ 将 alpha 混合项目渲染到所有者绘制的按钮上。它可能适用于您的场景，也可能不适用于您的场景。让我看看今晚晚些时候我能不能把它变成一个工作样本。
标签： c++ winapi bitmap transparency