c - 从位图和透明度颜色创建蒙版-Windows GDI

Question

这是我过去两天尝试调试的代码:

#include <windows.h>

HBITMAP createImageMask(HBITMAP bitmapHandle, const COLORREF transparencyColor) {
    // For getting information about the bitmap's height and width in this context
    BITMAP bitmap;

    // Create the device contexts for the bitmap and its mask
    HDC bitmapGraphicsDeviceContext = CreateCompatibleDC(NULL);
    HDC bitmapMaskGraphicsDeviceContext = CreateCompatibleDC(NULL);

    // For the device contexts to re-select the initial object they initialized with
    // and de-select the bitmap and mask
    HGDIOBJ bitmapDummyObject;
    HGDIOBJ bitmapMaskDummyObject;

    // The actual mask
    HBITMAP bitmapMaskHandle;

    // 1. Generate the mask.
    GetObject(bitmapHandle, sizeof(BITMAP), &bitmap);
    bitmapMaskHandle = CreateBitmap(bitmap.bmWidth, bitmap.bmHeight, 1, 1, NULL);

    // 2. Setup the device context for the mask (and the bitmap)
    //    — also get the initial selected objects in the device contexts.
    bitmapDummyObject = SelectObject(bitmapGraphicsDeviceContext, (HGDIOBJ) (HBITMAP) bitmapHandle);
    bitmapMaskDummyObject = SelectObject(bitmapMaskGraphicsDeviceContext, (HGDIOBJ) (HBITMAP) bitmapMaskHandle);

    // 3. Set the background color of the mask.
    SetBkColor(bitmapGraphicsDeviceContext, transparencyColor);

    // 4. Copy the bitmap to the mask and invert it so it blends with the background color.
    BitBlt(bitmapMaskGraphicsDeviceContext, 0, 0, bitmap.bmWidth, bitmap.bmHeight, bitmapGraphicsDeviceContext, 0, 0, SRCCOPY);
    BitBlt(bitmapGraphicsDeviceContext, 0, 0, bitmap.bmWidth, bitmap.bmHeight, bitmapMaskGraphicsDeviceContext, 0, 0, SRCINVERT);

    // 5. Select the bitmaps out before deleting the device contexts to avoid any issues.
    SelectObject(bitmapGraphicsDeviceContext, bitmapDummyObject);
    SelectObject(bitmapMaskGraphicsDeviceContext, bitmapMaskDummyObject);

    // Clean-up
    DeleteDC(bitmapGraphicsDeviceContext);
    DeleteDC(bitmapMaskGraphicsDeviceContext);

    // Voila!
    return bitmapMaskHandle;
}

它创建一个位图句柄( HBITMAP)，并且不会产生任何错误(来自 GetLastError函数)。

问题:它不会生成我应用于它的位图的单色版本，
而是只创建一个仅填充黑色的位图。

那么代码是怎么回事，我在做什么错呢？
或者如何正确创建位图蒙版？

(如果可能，我尝试在没有GDI +或其他库的情况下执行此操作)

这是透明度颜色为红色( RGB(255, 0, 0))的图像:

这是图像 mask (分别是预期结果和实际结果(从左到右)):



此处引用: theForger’s Win32 API Programming Tutorial - Transparent Bitmaps

Answer 1

该代码可以正常工作，尽管它并没有完全按照您的想象做。如果没有看到任何输出，则说明此功能的外部原因是什么。

该代码的作用是设置两个位图，以供一种旧的Win32技术使用，以绘制一个 Sprite ，其中您使用不同的光栅操作代码对BitBlt进行两次调用，一个调用一个蒙版，另一个绘制该 Sprite ，以使 Sprite 的背景将不会被绘制。请注意，它既在创建掩码，也在更改源位图。 (“const HBITMAP bitmapHandle”中的“const”实际上并没有做任何事情。位图句柄就像资源ID一样，指的是Windows所管理的位图，而C++对此一无所知。如果您查看代码，最终的BitBlit将变为源位图，而不是掩码。该调用的作用是使源位图中的键色变黑，这是使用rop代码和两次blit绘制sprite所必需的。

顺便说一句，这项技术是一种非常古老的实现方法，在将MaskBlt引入API之前，该方法将在一次调用中完成您想做的事情。但更进一步，MaskBlt在这一点上已经过时了。您可能想为游戏或类似游戏的游戏绘制 Sprite 。几乎可以肯定，您真正想要的是使用每个像素的Alpha加载PNG，并使用Alpha合成对其进行绘制。您可以使用GDI+或开放源代码图形库(例如FreeImage)来执行此操作。

在下面的任何情况下，最少的代码都会演示此掩码代码的实际工作原理。只需更改以下来源，即可使“D:\test\hex_badge.bmp”成为您在问题中具有该六角形位图的位置的路径。

#include <windows.h>

LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam);

HBITMAP g_bmp;
HBITMAP g_bmpMask;

HBITMAP createImageMask( HBITMAP bitmapHandle, const COLORREF transparencyColor) {
    // For getting information about the bitmap's height and width in this context
    BITMAP bitmap;

    // Create the device contexts for the bitmap and its mask
    HDC bitmapGraphicsDeviceContext = CreateCompatibleDC(NULL);
    HDC bitmapMaskGraphicsDeviceContext = CreateCompatibleDC(NULL);

    // The actual mask
    HBITMAP bitmapMaskHandle;

    // 1. Generate the mask.
    GetObject(bitmapHandle, sizeof(BITMAP), &bitmap);
    bitmapMaskHandle = CreateBitmap(bitmap.bmWidth, bitmap.bmHeight, 1, 1, NULL);

    // 2. Setup the device context for the mask (and the bitmap).
    SelectObject(bitmapGraphicsDeviceContext, bitmapHandle);
    SelectObject(bitmapMaskGraphicsDeviceContext, bitmapMaskHandle);

    // 3. Set the background color of the mask.
    SetBkColor(bitmapGraphicsDeviceContext, transparencyColor);

    // 4. Copy the bitmap to the mask and invert it so it blends with the background color.
    BitBlt(bitmapMaskGraphicsDeviceContext, 0, 0, bitmap.bmWidth, bitmap.bmHeight, bitmapGraphicsDeviceContext, 0, 0, SRCCOPY);
    BitBlt(bitmapGraphicsDeviceContext, 0, 0, bitmap.bmWidth, bitmap.bmHeight, bitmapMaskGraphicsDeviceContext, 0, 0, SRCINVERT);

    // Clean-up
    DeleteDC(bitmapGraphicsDeviceContext);
    DeleteDC(bitmapMaskGraphicsDeviceContext);

    // Voila!
    return bitmapMaskHandle;
}

int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nCmdShow)
{

    MSG msg = { 0 };
    WNDCLASS wc = { 0 };
    wc.lpfnWndProc = WndProc;
    wc.hInstance = hInstance;
    wc.hbrBackground = (HBRUSH)(COLOR_BACKGROUND);
    wc.lpszClassName = L"minwindowsapp";

    g_bmp = (HBITMAP)LoadImage(hInstance, L"D:\\test\\hex_badge.bmp", IMAGE_BITMAP, 0, 0, LR_LOADFROMFILE);
    g_bmpMask = createImageMask(g_bmp, RGB(255, 0, 0));

    if (!RegisterClass(&wc))
        return 1;

    if (!CreateWindow(wc.lpszClassName,
        L"Minimal Windows Application",
        WS_OVERLAPPEDWINDOW | WS_VISIBLE,
        0, 0, 640, 480, 0, 0, hInstance, NULL))
        return 2;

    while (GetMessage(&msg, NULL, 0, 0) > 0) {
        TranslateMessage(&msg);
        DispatchMessage(&msg);
    }
    return 0;
}

LRESULT HandleWmPaint(HWND hWnd, WPARAM wParam, LPARAM lParam)
{
    PAINTSTRUCT ps;

    HDC hdcScr = GetDC(NULL);
    HDC hdcBmp = CreateCompatibleDC(hdcScr);
    HBITMAP hbmOld = (HBITMAP)SelectObject(hdcBmp, g_bmp);

    HDC hdcMask = CreateCompatibleDC(hdcScr);
    HBITMAP hbmOldMask = (HBITMAP) SelectObject(hdcMask, g_bmpMask );

    HDC hdc = BeginPaint(hWnd, &ps);
    BitBlt(hdc, 0, 0, 184, 184, hdcMask, 0, 0, SRCCOPY);
    BitBlt(hdc, 184, 0, 184, 184, hdcBmp, 0, 0, SRCCOPY);
    EndPaint(hWnd, &ps);

    SelectObject(hdcMask, hbmOldMask);
    DeleteDC(hdcMask);

    SelectObject(hdcBmp, hbmOld);
    DeleteDC(hdcBmp);
    ReleaseDC(NULL, hdcScr);

    return 0;
}

LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
{

    switch (message)
    {
    case WM_CLOSE:
        PostQuitMessage(0);
        break;

    case WM_PAINT:
         return HandleWmPaint(hWnd, wParam, lParam);

    default:
        return DefWindowProc(hWnd, message, wParam, lParam);
    }
    return 0;

输出如下:



我不确定为什么您没有得到输出，但是很可能您要么没有成功加载位图，要么没有成功绘制到屏幕上。