Related
I'm trying to implement anti-aliasing in my MFC app, I'm using the technique described in this tutorial.
Create a bitmap (2x, 4x, 8x) the size of the original bitmap.
Draw on the resized bitmap (I'm only using simple figures (lines, circles and etc)).
Set StretchBlt Mode to HalfTone.
And Resize with StretchBlt to the original size.
Using this way, drawing in the resized bitmap it works, but I want to create a more generic function that receives a bitmap with the drawing already made and return with the anti-aliasing, I tried this:
static HBITMAP AntiAliasing(HBITMAP hBitmap)
{
int escala = 4;
HBITMAP bmp = __copia(hBitmap); // Copy the bitmap.
HDC hMemDC = CreateCompatibleDC(NULL);
HBITMAP bmpAntigo1 = (HBITMAP)::SelectObject(hMemDC, bmp);
BITMAP bitmap;
::GetObject(hBitmap, sizeof(BITMAP), &bitmap);
// Create a bitmap (2x, 4x, 8x) the size of the original bitmap.
HDC hDCDimensionado = ::CreateCompatibleDC(hMemDC);
HBITMAP bmpDimensionado = ::CreateCompatibleBitmap(hDCDimensionado,
bitmap.bmWidth * escala,
bitmap.bmHeight * escala);
HBITMAP hBmpVelho = (HBITMAP)::SelectObject(hDCDimensionado, bmpDimensionado);
// I also tried with {BLACKONWHITE, HALFTONE, WHITEONBLACK}
int oldStretchBltMode2 = ::SetStretchBltMode(hDCDimensionado, COLORONCOLOR);
// Resize the bitmap to the new size.
::StretchBlt(hDCDimensionado,
0, 0, bitmap.bmWidth * escala, bitmap.bmHeight * escala,
hMemDC,
0, 0, bitmap.bmWidth, bitmap.bmHeight,
SRCCOPY);
/*
* Here the bitmap has lost his colors and became black and white.
*/
::SetStretchBltMode(hDCDimensionado, oldStretchBltMode2);
// Set StretchBltMode to halfTone so can mimic the anti aliasing effect.
int oldStretchBltMode = ::SetStretchBltMode(hMemDC, HALFTONE);
// resize to the original size.
::StretchBlt(hMemDC,
0, 0, bitmap.bmWidth, bitmap.bmHeight,
hDCDimensionado,
0, 0, escala * bitmap.bmWidth, escala * bitmap.bmHeight,
SRCCOPY);
::SetStretchBltMode(hMemDC, oldStretchBltMode);
::SelectObject(hMemDC, bmpAntigo1);
::DeleteDC(hMemDC);
::SelectObject(hDCDimensionado, hBmpVelho);
DeleteDC(hDCDimensionado);
return bmp;
}
But this function doesn't work, the result loses its colors (all drawings became black) and there isn't anti aliasing.
Any help will be appreciated!
From documentation for CreateCompatibleBitmap:
Note: When a memory device context is created, it initially has a
1-by-1 monochrome bitmap selected into it. If this memory device
context is used in CreateCompatibleBitmap, the bitmap that is created
is a monochrome bitmap. To create a color bitmap, use the HDC that was
used to create the memory device context, as shown in the following
code:
Change the code and supply hdc for the desktop as show below:
HDC hdc = ::GetDC(0);
HBITMAP bmpDimensionado = ::CreateCompatibleBitmap(hdc, ...)
::ReleaseDC(0, hdc);
This will show the image, however this method will not produce the desired effect because it simply magnifies each pixel to larger size and reduces it back to the original pixel. There is no blending with neighboring pixels.
Use other methods such Direct2D with Gaussian blur effect, or use GDI+ instead with interpolation mode:
Gdiplus::GdiplusStartup...
void foo(HDC hdc)
{
Gdiplus::Bitmap bitmap(L"file.bmp");
if(bitmap.GetLastStatus() != 0)
return 0;
auto w = bitmap.GetWidth();
auto h = bitmap.GetHeight();
auto maxw = w * 2;
auto maxh = h * 2;
Gdiplus::Bitmap membmp(maxw, maxh);
Gdiplus::Graphics memgr(&membmp);
memgr.SetInterpolationMode(Gdiplus::InterpolationModeHighQualityBilinear);
memgr.DrawImage(&bitmap, 0, 0, maxw, maxh);
Gdiplus::Graphics gr(hdc);
gr.SetInterpolationMode(Gdiplus::InterpolationModeHighQualityBilinear);
gr.DrawImage(&membmp, 0, 0, w, h);
}
If target window is at least Vista, use GDI+ version 1.1 with blur effect. See also How to turn on GDI+ 1.1 in MFC project
#define GDIPVER 0x0110 //add this to precompiled header file
void blur(HDC hdc)
{
Gdiplus::Graphics graphics(hdc);
Gdiplus::Bitmap bitmap(L"file.bmp");
if(bitmap.GetLastStatus() != 0)
return;
Gdiplus::Blur blur;
Gdiplus::BlurParams blur_param;
blur_param.radius = 3; //change the radius for different result
blur_param.expandEdge = TRUE;
blur.SetParameters(&blur_param);
bitmap.ApplyEffect(&blur, NULL);
graphics.DrawImage(&bitmap, 0, 0);
}
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);
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);
So here's what I get:
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:
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.
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:
Any idea how to draw text so that the API could set those transparency bytes?
EDIT: 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);
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):
So clearly still an issue with transparency.
Taken from an old post by Microsoft MVP Mike D Sutton here.
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.
What you need to do is to create a Bitmap,
either DDB or DIBSection, and select that into your DC before drawing
to it.
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.
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;
}
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);
}
}
}
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.
This reply is coming almost 3 years after the question was posted, but people still consult these things long into the future. So I'll explain what's happening.
DrawText (and other GDI text functions) will work on a transparent bitmap. The text is not coming out black even though it displays that way. The alpha channel is set to 0 on all pixels the text draws to, overriding whatever alpha you had set previously. If you set an alpha value in SetTextColor the text will render all black. If you're feeling ambitious you can run through pixel by pixel and target anything not your fill color (which requires a single fill color) but the problem then becomes one of the nature of ClearType being overridden and all alphas are set to whatever you set them to. The text ends up looking very funky. If you use a constant alpha for your background fill you can simply do a blanket run across the entire bitmap's bits after the text is drawn and reset all the alpha values. Since you have to read a byte to determine if it's background or not, you might as well just set every pixel's alpha to whatever the standard alpha is for that image and bypass the slow compares. This works reasonably well and I've found it to be very acceptable. In this day and age, MS should have taken care of this long ago but it's not to be.
https://learn.microsoft.com/en-us/windows/win32/gdiplus/-gdiplus-antialiasing-with-text-use
Gdiplus::Bitmap bmp( your_Width, your_Height, PixelFormat64bppARGB);
//PixelFormat64bppARGB ARGB needed
FontFamily fontFamily(L"Arial");
Font font(&fontFamily, 29, FontStyleRegular, UnitPoint);
Gdiplus::RectF rectF(00.0f, 10.0f, your_Width, your_Height);
StringFormat stringFormat;
SolidBrush solidBrush(Color(63, 0, 0, 255));
stringFormat.SetAlignment(StringAlignmentCenter);
//solidBrush Color(63, 0, 0, 255) ARGB neede
graphics.SetTextRenderingHint(TextRenderingHintAntiAlias);
graphics.DrawString("your_text", -1, &font, rectF, &stringFormat, &solidBrush);
//TextRenderingHintAntiAlias this needed
I'm trying to use StretchBlt in order to copy pixels from a memory hdc to the window hdc.
The memory hdc gets the image from an invisible window which renders a stream using openGL.
Here's my code:
BITMAPINFOHEADER createBitmapHeader(int width, int height) {
BITMAPINFOHEADER header;
header.biSize = sizeof(BITMAPINFOHEADER);
header.biWidth = width;
header.biHeight = height;
header.biPlanes = 1;
header.biBitCount = 32;
header.biCompression = BI_RGB;
header.biSizeImage = 0;
header.biXPelsPerMeter = 0;
header.biYPelsPerMeter = 0;
header.biClrUsed = 0;
header.biClrImportant = 0;
return header;
}
...
HDC memoryHdc = CreateCompatibleDC(windowHdc);
BITMAPINFO bitmapInfo;
bitmapInfo.bmiHeader = createBitmapHeader(targetDimensions.width, targetDimensions.height);
HBITMAP bitmap = CreateDIBitmap(windowHdc, &bitmapInfo.bmiHeader, CBM_INIT, offscreenBuffer, &bitmapInfo, DIB_RGB_COLORS);
SelectObject(memoryHdc, bitmap);
DeleteObject(bitmap);
SetStretchBltMode(windowHdc, COLORONCOLOR);
StretchBlt(windowHdc,
targetDimensions.x, targetDimensions.y,
targetDimensions.width, -targetDimensions.height,
memoryHdc,
sourceDimensions.x, sourceDimensions.y,
sourceDimensions.width, sourceDimensions.height,
SRCCOPY);
DeleteDC(memoryHdc);
Where windowHdc is the hdc of the window to which I want the StretchBlt to copy the pixels to, and offscreenBuffer is a void* to the pixels copied from the offscreen window in which the openGL is rendering.
This code works great, except that the image is upside down and I want it vertically flipped.
I know that this happens because:
If nHeightSrc and nHeightDest have different signs, the function
creates a mirror image of the bitmap along the y-axis
But when I remove the minus sign and both target and source heights are the same then I see no image in the window.
Just to check, I tried to put the minus on the sourceDimensions.height but that also results in no image, and the same if I try to negate the widths (both target and source).
Any idea why?
Thanks.
I have inherited an old-school MFC Windows CE program, and am having to make some modifications to it. As part of this I have to create a monochrome image with text on it, and both display it on a screen as well as send each row of the image to a printer one at a time.
I originally used a bitmap, and had success using DrawText() and getting a test string (Hello World) to display on the screen (this code is in Figure 1). However, I hit a wall at the stage where I am looking to extract the wrap data from the bitmap. What I am trying to get is an array with 1s or 0s representing black or white. I had first thought I would use GetBitmapBits() but unfortunately the code I am working with is so old that function is not supported yet. I thought I could get around this issue by using GetBitmap() and then accessing the bmBits parameter. However this appears to always be null which was confirmed when I found the following link: Why does GetObject return an BITMAP with null bmBits?.
My next attempt was to follow the advice in the link and use CreateDIBSection() instead of CreateCompatibleBitmap(). This seems like the right path, and I should have access to the data I want, but unfortunately I cannot get the DIB to display (code is in Figure 2). I suspect I am doing something wrong in creating the header of the DIB, but I cannot figure out what my mistake is.
If anyone has suggestions for a way to access the data in the bitmap, or can see what I am doing wrong with the DIB, I would greatly appreciate the help!
*** FIGURE 1: Code to create and display a bitmap
void CRunPage::OnPaint()
{
CPaintDC dc(this); // property page device context for painting
CBitmap mBmp; // CBitmap object for displaying built-in bitmaps
CDC mDCMem; // CDC object to handle built-in bitmap
int iWidth, iHeight; // dimension to draw on the screen
int icurLabel, // current label index of open print file
iLabelNum; // number of labels in open print file
LPBITMAPINFOHEADER pBMIH; // bitmap header object for current label
LPBYTE pImage; // bitmap data for current label
CSize size; // size of label
int PreviewLeft,PreviewTop,PreviewWidth,PreviewHeight;
CRect Rect;
BITMAP bm;
LPVOID bmBits=NULL;
// Calculate the preview area
PreviewLeft=5;
PreviewTop=5;
GetDlgItem(IDC_RUN_NEXT)->GetWindowRect(&Rect);
ScreenToClient(&Rect);
PreviewWidth=Rect.left-PreviewLeft*2;
GetDlgItem(IDC_RUN_WRAPTEXT)->GetWindowRect(&Rect);
ScreenToClient(&Rect);
PreviewHeight=Rect.top-PreviewTop*2;
CRect textRect;
CString testText(_T("Hello World"));
CBitmap * pOldBitmap;
CBrush whiteBrush, *pOldBrush;
CPen blackPen, *pOldPen;
mDCMem.CreateCompatibleDC(&dc);
mBmp.CreateCompatibleBitmap(&dc, PreviewWidth+PreviewLeft*2, PreviewHeight+PreviewTop*2);
//mBmp.CreateCompatibleBitmap(&dc, PreviewWidth, PreviewHeight);
pOldBitmap = mDCMem.SelectObject(&mBmp);
blackPen.CreatePen(PS_SOLID, 2, RGB(0, 0, 0));
whiteBrush.CreateSolidBrush(RGB(255,255,255));
textRect.SetRect(0,0,PreviewWidth, PreviewHeight);
// this means behind the text will be a white box w/ a black boarder
pOldBrush = mDCMem.SelectObject(&whiteBrush);
pOldPen = mDCMem.SelectObject(&blackPen);
//these commands draw on the memory-only context (mDCMem)
mDCMem.Rectangle(&textRect);
mDCMem.DrawText((LPCTSTR)testText, 11, &textRect, DT_CENTER|DT_VCENTER);
mDCMem.SelectObject(pOldBrush);
mDCMem.SelectObject(pOldPen);
dc.StretchBlt(PreviewLeft,PreviewTop, PreviewWidth, PreviewHeight, & mDCMem, 0, 0, PreviewWidth, PreviewHeight, SRCCOPY);
mDCMem.SelectObject(pOldBitmap);
}
*** FIGURE 2: Trying to use a DIB instead of a bitmap
void CRunPage::OnPaint()
{
CPaintDC dc(this); // property page device context for painting
CBitmap mBmp; // CBitmap object for displaying built-in bitmaps
CDC mDCMem; // CDC object to handle built-in bitmap
int iWidth, iHeight; // dimension to draw on the screen
int icurLabel, // current label index of open print file
iLabelNum; // number of labels in open print file
LPBITMAPINFOHEADER pBMIH; // bitmap header object for current label
LPBYTE pImage; // bitmap data for current label
CSize size; // size of label
int PreviewLeft,PreviewTop,PreviewWidth,PreviewHeight;
CRect Rect;
BITMAP bm;
// Calculate the preview area
PreviewLeft=5;
PreviewTop=5;
GetDlgItem(IDC_RUN_NEXT)->GetWindowRect(&Rect);
ScreenToClient(&Rect);
PreviewWidth=Rect.left-PreviewLeft*2;
GetDlgItem(IDC_RUN_WRAPTEXT)->GetWindowRect(&Rect);
ScreenToClient(&Rect);
PreviewHeight=Rect.top-PreviewTop*2;
CRect textRect;
CString testText(_T("Hello World"));
CBitmap * pOldBitmap;
CBrush whiteBrush, *pOldBrush;
CPen blackPen, *pOldPen;
LPBYTE pFWandImageMem=NULL, pImageMem=NULL, pTemp=NULL;
int i=0,j=0, buffSize=0, numBytesPerRow=0, bitmapWidthPix,bitmapHeightPix;
char *numBytesPerRowString;
char temp;
void ** ppvBits;
BITMAPINFOHEADER bmif;
BITMAPINFO bmi;
HBITMAP myDIB, myOldDIB;
mDCMem.CreateCompatibleDC(&dc);
//this rect is the area in which I can draw (its x,y location is set by BitBlt or StretchBlt
//mBmp.CreateCompatibleBitmap(&dc, PreviewWidth+PreviewLeft*2, PreviewHeight+PreviewTop*2);
bmif.biSize = sizeof(BITMAPINFOHEADER);
bmif.biWidth = PreviewWidth+PreviewLeft*2;
bmif.biHeight = -(PreviewHeight+PreviewTop*2);//- means top down (I think? I tried both ways and neither worked)
bmif.biPlanes = 1;
bmif.biBitCount = 1;
bmif.biCompression = BI_RGB; // no compression
bmif.biSizeImage = 0; // Size (bytes) if image - this can be set to 0 for uncompressed images
bmif.biXPelsPerMeter = 0;
bmif.biYPelsPerMeter = 0;
bmif.biClrUsed =0;
bmif.biClrImportant = 0;
bmi.bmiColors[0].rgbBlue=0;
bmi.bmiColors[0].rgbGreen=0;
bmi.bmiColors[0].rgbRed=0;
bmi.bmiColors[0].rgbReserved=0;
bmi.bmiColors[1].rgbBlue=255;
bmi.bmiColors[1].rgbGreen=255;
bmi.bmiColors[1].rgbRed=255;
bmi.bmiColors[1].rgbReserved=0;
bmi.bmiHeader=bmif;
myDIB = CreateDIBSection(dc.GetSafeHdc(), &bmi, DIB_RGB_COLORS, ppvBits, NULL, 0);
myOldDIB = (HBITMAP)mDCMem.SelectObject(myDIB);//SelectObject(mDCMem, myDIB);
blackPen.CreatePen(PS_SOLID, 2, RGB(0, 0, 0));
whiteBrush.CreateSolidBrush(RGB(255,255,255));
textRect.SetRect(0,0,PreviewWidth, PreviewHeight);
// this means behind the text will be a white box w/ a black boarder
pOldBrush = mDCMem.SelectObject(&whiteBrush);
pOldPen = mDCMem.SelectObject(&blackPen);
//these commands draw on the memory-only context (mDCMem)
mDCMem.Rectangle(&textRect);
mDCMem.DrawText((LPCTSTR)testText, 11, &textRect, DT_CENTER|DT_VCENTER);
mDCMem.SelectObject(pOldBrush);
mDCMem.SelectObject(pOldPen);
dc.StretchBlt(PreviewLeft,PreviewTop, PreviewWidth, PreviewHeight, & mDCMem, 0, 0, PreviewWidth, PreviewHeight, SRCCOPY);
mDCMem.SelectObject(myOldDIB);
}
So I made two minor changes to the DIB code, and it is displaying the image correctly now.
First, I changed the way I passed in my pointer to the CreateDIBSection():
void ** ppvBits;
to
LPBYTE pBits;
And then I had to change how I passed that into CreateDIBSection. I also explicitly casted the return of CreateDIBSection() to an HBITMAP:
myDIB = CreateDIBSection(dc.GetSafeHdc(), &bmi, DIB_RGB_COLORS, (void**)&pBits, NULL, 0);
to
myDIB = (HBITMAP) CreateDIBSection(dc.GetSafeHdc(), &bmi, DIB_RGB_COLORS, ppvBits, NULL, 0);
I have not had a chance to see if I can access the image data, but I am past the initial issues now. Thanks to anyone who looked at this, and if people know how to do the first (device dependent bitmap) method I would be interested to know.
Does anyone know how I can create a Completely transparent image or given am image (HBITMAP) how can I wipe it Completely so that all pixels in it are 100% transparent?
Thank you.
The bitmap needs to be 32-bit so it has an alpha channel that you can set opacity values with. If your image is not 32-bit, you will have to create a new 32-bit bitmap and copy the original pixels into it.
I also found the solution without the use of GDI+.
BITMAPV5HEADER bi = {sizeof(BITMAPV5HEADER), 320, 240, 1, 32, BI_BITFIELDS, 0, 0, 0, 0, 0, 0x00FF0000, 0x0000FF00, 0x000000FF, 0xFF000000};
HDC hDc = ::CreateCompatibleDC(0);
if(NULL != hDc)
{
RGBQUAD* pArgb;
HBITMAP tBmp = ::CreateDIBSection(hDc, (BITMAPINFO*)&bi, DIB_RGB_COLORS, (void**)&pArgb, NULL, 0);
if(NULL != tBmp)
{
int x, y;
DWORD pBits;
pBits = (DWORD*)pArgb;
for(y = 0; y < bi.bV5Height; y++)
{
for(x = 0; x < bi.bV5Width; x++)
{
*pBits = 0;
pBits++;
}
}
}
::DeleteObject(hDc);
}
tBmp will be a 320 x 240 bitmap that is completely transparent
You can use a monochrome bitmap as a mask to create transparent images from colour ones. This is quite complex. See this example (in VB but uses Win32 APIs directly)
Alternatively, the TransparentBlt function might make what you're trying to do unnecessary.
I found the answer in GDI+. The best way to do this is to attach the device context of the image that you are working with with GDI+ graphic object and then call its clear method.