如何使用GDI绘制具有透明度的文本? [英] How to draw text with transparency using GDI?

问题描述

我的目标是(在运行时)将一些任意文本动态地放入HICON图像中.我正在使用以下代码:

My goal is to dynamically put some arbitrary text into an HICON image (at runtime.) I'm using the following code:

//Error checks are omitted for brevity

//First create font
LOGFONT lf = {0};
lf.lfHeight = -58;
lf.lfWeight = FW_NORMAL;
lf.lfOutPrecision = OUT_TT_PRECIS;  //Use TrueType fonts for anti-alliasing
lf.lfQuality = CLEARTYPE_QUALITY;
lstrcpy(lf.lfFaceName, L"Segoe UI");

HFONT hFont = ::CreateFontIndirect(&lf);


//HICON hIcon = original icon to use as a source
//I'm using a large 256x256 pixel icon
hIcon = (HICON)::LoadImage(theApp.m_hInstance, MAKEINTRESOURCE(IDI_ICON_GREEN_DIAMOND), IMAGE_ICON, 256, 256, LR_DEFAULTCOLOR);

ICONINFO ii = {0};
::GetIconInfo(hIcon, &ii);

BITMAP bm = {0};
::GetObject(ii.hbmColor, sizeof(bm), &bm);
SIZE szBmp = {bm.bmWidth, bm.bmHeight};

HDC hDc = ::GetDC(hWnd);
HDC hMemDC = ::CreateCompatibleDC(hDc);

HGDIOBJ hOldBmp = ::SelectObject(hMemDC, ii.hbmColor);
HGDIOBJ hOldFont = ::SelectObject(hMemDC, hFont);

::SetBkMode(hMemDC, TRANSPARENT);
::SetTextColor(hMemDC, RGB(255, 0, 0));     //Red text

//Draw text
//NOTE that DrawText API behaves in a similar way
::TextOut(hMemDC, 0, 0, L"Hello", 5);

::SelectObject(hMemDC, hOldFont);
::SelectObject(hMemDC, hOldBmp);


//We need a simple mask bitmap for the icon
HBITMAP hBmpMsk = ::CreateBitmap(szBmp.cx, szBmp.cy, 1, 1, NULL);

ICONINFO ii2 = {0};
ii2.fIcon = TRUE;
ii2.hbmColor = ii.hbmColor;
ii2.hbmMask = hBmpMsk;

//Create updated icon
HICON hIcon2 = ::CreateIconIndirect(&ii2);


//Cleanup
::DeleteObject(hBmpMsk);
::DeleteDC(hMemDC);
::ReleaseDC(hWnd, hDc);
::DeleteObject(ii.hbmColor);
::DeleteObject(ii.hbmMask);

::DeleteObject(hFont);

然后，我可以通过OnPaint()处理程序在窗口中显示图标(这样我就可以看到结果了)，如下所示:

and then I can display the icon in my window from OnPaint() handler (so that I can see how it turns out) as such:

::DrawIconEx(dc.GetSafeHdc(), 0, 0,
    hIcon2, 
    256, 256, NULL, 
    ::GetSysColorBrush(COLOR_BTNFACE),
    DI_NORMAL);

这就是我得到的:

要查看我的hIcon2中以像素为单位的情况，我打电话给

To see what's going on pixel-wise in my hIcon2 I called GetDIBits on its ii.hbmColor from the code above. The resulting pixel array where my word "Hello" was supposed to be shown looked like this:

在该内存转储中，像素被编码为BGRA，因此每个DWORD中的第4个字节代表透明度:0 =透明，FF =不透明.但是在这种情况下，TextOut不会填写透明度，或将其保留为0，这被解释为完全透明".取而代之的是，它似乎自己将它们预乘到了RGB颜色中.

The pixels are encoded as BGRA in that memory dump, so the 4th byte in each DWORD stands for transparency: 0=transparent, FF=opaque. But in this case TextOut doesn't fill out transparency, or leaves it as 0, which is interpreted as "fully transparent." Instead it seems to pre-multiply it into the RGB colors themselves.

请注意，如果我继续向下看同一位图(绿色菱形开始的地方)，则图像像素似乎已正确设置了透明字节:

Note that if I keep looking further down the same bitmap, where the green diamond begins, the image pixels seem to have transparency bytes set correctly:

有什么想法如何绘制文本，以便API可以设置这些透明字节?

Any idea how to draw text so that the API could set those transparency bytes?

如以下建议，我尝试了以下GDI +方法:

As was suggested below I tried the following GDI+ method:

HGDIOBJ hOldBmp = ::SelectObject(hMemDC, ii.hbmColor);

Graphics grpx(hMemDC);

RectF rcfTxt(0.0f, 0.0f, (REAL)szBmp.cx, (REAL)szBmp.cy);
Font gdiFont(L"Segoe UI", 58.0f, FontStyleRegular, UnitPixel);

SolidBrush gdiBrush(Color(255, 0, 0));

StringFormat gdiSF;
gdiSF.SetAlignment(StringAlignmentNear);
gdiSF.SetFormatFlags(StringFormatFlagsNoWrap);
gdiSF.SetHotkeyPrefix(HotkeyPrefixNone);

//The reason I was using GDI was because I was setting
//spacing between letters using SetTextCharacterExtra()
//Unfortunately with GDI+ this does not work!
HDC hTmpDC = grpx.GetHDC();
::SetTextCharacterExtra(hTmpDC, -4);  //This doesn't do anything!
grpx.ReleaseHDC(hTmpDC);

grpx.DrawString(L"Hello", 5, &gdiFont, rcfTxt, &gdiSF, &gdiBrush);

::SelectObject(hMemDC, hOldBmp);

除了无法设置字符间距(我可以使用SetTextCharacterExtra使用GDI设置字符间距)之外，这也是我得到的(为可视性略有扩大):

and besides not being able to set character spacing (which I could with GDI using SetTextCharacterExtra) here's what I got (slightly enlarged for visibility):

显然，透明度仍然是一个问题.

So clearly still an issue with transparency.

推荐答案

来自Microsoft MVP Mike D Sutton的旧帖子

Taken from an old post by Microsoft MVP Mike D Sutton here.

创建DC时，最初选择了默认的库存"对象 包括股票1 * 1 * 1位图.由于有位图 当您调用DrawText()时已经选择到DC中的它将仍然 尝试渲染它，尽管几乎所有内容(除了 一个像素)将被裁剪.

When you create a DC it initially has default 'stock' objects selected into it, including the stock 1*1*1 Bitmap. Since there is a Bitmap already selected into the DC when you call DrawText() it will still try and render to it even though pretty much everything (apart from one pixel) will be clipped.

您需要做的是创建一个位图， DDB或DIBSection，然后在绘制之前将其选择到DC中

What you need to do is to create a Bitmap, either DDB or DIBSection, and select that into your DC before drawing to it.

首先，尽管自从您需要找到位图的大小 希望它足够大以显示您的文本，因此您可以使用 DrawText()在初始DC上再次调用，但包含DT_CALCRECT 旗帜.这是在做什么，而不是简单地绘制任何内容 测量文本的大小并将其转储到您通过的RECT中 电话.从这里开始，您可以使用来创建DIBSection 这些尺寸，然后将其选择到您的DC中.最后执行你的 现有的DrawText()调用(您可能还想使用SetBkMode/Color()) 这会将文本呈现到DIBSection，您可以从中获取 数据.

First though you need to find the size of your Bitmap since you want it large enough to display your text in, so for that you use the DrawText() call again on the initial DC but include the DT_CALCRECT flag. What this does is rather than drawing anything it simply measures how large the text is and dumps that into the RECT you pass the call. From here you can go ahead and create your DIBSection using those dimensions and select it into your DC. Finally perform your existing DrawText ()call (you may also want to use SetBkMode/Color()) which will render the text to the DIBSection from which you can get at the data.

这似乎在这里效果很好:

This seems to work pretty well here:

HBITMAP CreateAlphaTextBitmap(LPCSTR inText, HFONT inFont, COLORREF inColour) {
    int TextLength = (int)strlen(inText);
    if (TextLength <= 0) return NULL;

    // Create DC and select font into it
    HDC hTextDC = CreateCompatibleDC(NULL);
    HFONT hOldFont = (HFONT)SelectObject(hTextDC, inFont);
    HBITMAP hMyDIB = NULL;

    // Get text area
    RECT TextArea = {0, 0, 0, 0};
    DrawText(hTextDC, inText, TextLength, &TextArea, DT_CALCRECT);

    if ((TextArea.right > TextArea.left) && (TextArea.bottom > TextArea.top)) {
        BITMAPINFOHEADER BMIH;
        memset(&BMIH, 0x0, sizeof(BITMAPINFOHEADER));

        void *pvBits = NULL;

        // Specify DIB setup
        BMIH.biSize = sizeof(BMIH);
        BMIH.biWidth = TextArea.right - TextArea.left;
        BMIH.biHeight = TextArea.bottom - TextArea.top;
        BMIH.biPlanes = 1;
        BMIH.biBitCount = 32;
        BMIH.biCompression = BI_RGB;

        // Create and select DIB into DC
        hMyDIB = CreateDIBSection(hTextDC, (LPBITMAPINFO)&BMIH, 0, (LPVOID*)&pvBits, NULL, 0);
        HBITMAP hOldBMP = (HBITMAP)SelectObject(hTextDC, hMyDIB);

        if (hOldBMP != NULL) {
            // Set up DC properties
            SetTextColor(hTextDC, 0x00FFFFFF);
            SetBkColor(hTextDC, 0x00000000);
            SetBkMode(hTextDC, OPAQUE);

            // Draw text to buffer
            DrawText(hTextDC, inText, TextLength, &TextArea, DT_NOCLIP);

            BYTE* DataPtr = (BYTE*)pvBits;
            BYTE FillR = GetRValue(inColour);
            BYTE FillG = GetGValue(inColour);
            BYTE FillB = GetBValue(inColour);
            BYTE ThisA;

            for (int LoopY = 0; LoopY < BMIH.biHeight; LoopY++) {
                for (int LoopX = 0; LoopX < BMIH.biWidth; LoopX++) {
                    ThisA = *DataPtr; // Move alpha and pre-multiply with RGB
                    *DataPtr++ = (FillB * ThisA) >> 8;
                    *DataPtr++ = (FillG * ThisA) >> 8;
                    *DataPtr++ = (FillR * ThisA) >> 8;
                    *DataPtr++ = ThisA; // Set Alpha
                }
            }

            // De-select bitmap
            SelectObject(hTextDC, hOldBMP);
        }
    }

    // De-select font and destroy temp DC
    SelectObject(hTextDC, hOldFont);
    DeleteDC(hTextDC);

    // Return DIBSection
    return hMyDIB;
}

如果您需要有关如何调用它的示例，请尝试这样的操作 (inDC是要渲染的DC):

If you need an example of how to call it then try something like this (inDC is the DC to render to):

void TestAlphaText(HDC inDC, int inX, int inY) {
    const char *DemoText = "Hello World!\0";

    RECT TextArea = {0, 0, 0, 0};
    HFONT TempFont = CreateFont(50, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, "Arial\0");
    HBITMAP MyBMP = CreateAlphaTextBitmap(DemoText, TempFont, 0xFF);
    DeleteObject(TempFont);

    if (MyBMP) { // Create temporary DC and select new Bitmap into it
        HDC hTempDC = CreateCompatibleDC(inDC);
        HBITMAP hOldBMP = (HBITMAP)SelectObject(hTempDC, MyBMP);

        if (hOldBMP) {
            BITMAP BMInf; // Get Bitmap image size
            GetObject(MyBMP, sizeof(BITMAP), &BMInf);

            // Fill blend function and blend new text to window
            BLENDFUNCTION bf;
            bf.BlendOp = AC_SRC_OVER;
            bf.BlendFlags = 0;
            bf.SourceConstantAlpha = 0x80;
            bf.AlphaFormat = AC_SRC_ALPHA;
            AlphaBlend(inDC, inX, inY, BMInf.bmWidth, BMInf.bmHeight,
                hTempDC, 0, 0, BMInf.bmWidth, BMInf.bmHeight, bf);

            // Clean up
            SelectObject(hTempDC, hOldBMP);
            DeleteObject(MyBMP);
            DeleteDC(hTempDC);
        }
    }
}

所有的答案和代码功劳都归于该论坛的原始张贴者，我只是将其重新发布，这样，如果链接消失，该答案将是有效的.

All credit to answer and code go to original posters on that forum, I've simply reposted it so that this answer will be valid if the links die.

这篇关于如何使用GDI绘制具有透明度的文本?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！