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I have some existing code that uses a CImage which has an alpha channel, and I need to rotate it.
I have found the following suggestion which converts the CImage to a GDI+ Bitmap and then rotates it, and the rotated result ends up back in the CImage.
Bitmap* gdiPlusBitmap=Bitmap::FromHBITMAP(atlBitmap.Detach());
gdiPlusBitmap->RotateFlip(Rotate90FlipNone);
HBITMAP hbmp;
gdiPlusBitmap->GetHBITMAP(Color::White, &hbmp);
atlBitmap.Attach(hbmp);
Apparently it works without actually copying the bitmap bytes, which is great, but the problem is that if you create a Bitmap object from a HBITMAP it throws away the alpha channel.
Apparently to preserve the alpha channel you must instead create the Bitmap using the constructor
Bitmap(
[in] INT width,
[in] INT height,
[in] INT stride,
[in] PixelFormat format,
[in] BYTE *scan0
);
So I'm trying to adapt the above to use this constructor, but the interaction between CImage and Bitmap is a bit confusing. I think I need to create the Bitmap like this
Bitmap* gdiPlusBitmap = new Bitmap(
pCImage->GetWidth(),
pCImage->GetHeight(),
pCImage->GetPitch(),
PixelFormat32bppARGB,
(BYTE *)pCImage->GetBits());
nGDIStatus = gdiPlusBitmap->RotateFlip(Rotate90FlipNone);
but I'm not sure how to make the CImage pick up the changes (so that I end up with the original CImage rotated), or where to delete the Bitmap object.
Does anyone know the correct way to do this, preserving the alpha channel ?
Ideally I'd like to avoid copying the bitmap data, but it's not mandatory.
You can use Gdiplus::Graphics to draw bitmap on CImage.
Note, hard coding PixelFormat32bppARGB can cause problems if image doesn't support alpha channel. I added some basic error check.
CImage image;
if (S_OK != image.Load(L"c:\\test\\test.png"))
{
AfxMessageBox(L"can't open");
return 0;
}
int bpp = image.GetBPP();
//get pixel format:
HBITMAP hbmp = image.Detach();
Gdiplus::Bitmap* bmpTemp = Gdiplus::Bitmap::FromHBITMAP(hbmp, 0);
Gdiplus::PixelFormat pixel_format = bmpTemp->GetPixelFormat();
if (bpp == 32)
pixel_format = PixelFormat32bppARGB;
image.Attach(hbmp);
//rotate:
Gdiplus::Bitmap bmp(image.GetWidth(), image.GetHeight(), image.GetPitch(), pixel_format, static_cast<BYTE*>(image.GetBits()));
bmp.RotateFlip(Gdiplus::Rotate90FlipNone);
//convert back to image:
image.Destroy();
if (image.Create(bmp.GetWidth(), bmp.GetHeight(), 32, CImage::createAlphaChannel))
{
Gdiplus::Bitmap dst(image.GetWidth(), image.GetHeight(), image.GetPitch(), PixelFormat32bppARGB, static_cast<BYTE*>(image.GetBits()));
Gdiplus::Graphics graphics(&dst);
graphics.DrawImage(&bmp, 0, 0);
}
MFC doc/view architecture, GDI drawing/printing. I have a DIB backbuffer I need to display and print.
After the long and painful road I came to the conclusion than I need to use DIB created with CreateDIBSection (rather than DDB created with CreateCompatibleBitmap), and I have to blit it onto printer dc with StretchDIBits (rather than StretchBlt).
But i'm not able to get this thing to work.
Here is what I do:
In my initialization routine, I setup the backbuffer, like this:
// Prepare device context:
CClientDC aDC(this);
OnPrepareDC(&aDC);
// Setup proper backbuffer:
_pMemDc = new CDC;
_pMemDc->CreateCompatibleDC(&aDC);
memset(&_bitmapInfo, 0, sizeof(BITMAPINFO));
_bitmapInfo.bmiHeader.biSize = sizeof(BITMAPINFOHEADER);
_bitmapInfo.bmiHeader.biWidth = _sizeBackBuffer.cx;
_bitmapInfo.bmiHeader.biHeight = -_sizeBackBuffer.cy; // top-down
_bitmapInfo.bmiHeader.biPlanes = 1;
_bitmapInfo.bmiHeader.biBitCount = 24; // Maybe 32?
_bitmapInfo.bmiHeader.biCompression = BI_RGB;
HANDLE hMemBitmap = CreateDIBSection(aDC.GetSafeHdc(), &_bitmapInfo, DIB_RGB_COLORS, (void**)&_pBitmapRawBits, 0, 0);
_hOldSelBitmap = (HBITMAP)_pMemDc->SelectObject(hMemBitmap);
Variables with underscores are (private) member variables, declared like this:
CDC *_pMemDc; // Backbuffer memory dc
HBITMAP _hOldSelBitmap;
BITMAPINFO _bitmapInfo; // Backbuffer DIB (header-only)
unsigned char *_pBitmapRawBits; // Pointer to pixel data of DIB
SIZE _sizeBackBuffer; // Size of backbuffer, i.e. size of that DIB
Now below is what I do in my OnDraw override:
Firstly I get the area to be drawn like this (simplified code):
CRect rectClipBoxPlayground;
if (pDC->IsPrinting())
{
rectClipBoxPlayground = _printingParams.pPrintInfo->m_rectDraw;
}
else
{
pDC->GetClipBox(&rectClipBoxPlayground);
}
Then I calculate the corresponding rect coordinates in my backbuffer, which is usually (much) larger than the DC. Details of this calculation are irrelevant here, I just say that
CRect rectClipBoxBackBuffer;
represents the corresponding rect of backbuffer (in pixel coordinates of backbuffer).
Then I draw onto my backbuffer, using the _pMemDc memory dc.
And finally comes the part where I have troubles: blitting my DIB onto target dc (screen or printer). Here is what I do:
// Copy back buffer to screen/printer dc:
pDC->SetStretchBltMode(HALFTONE);
SetBrushOrgEx(pDC->GetSafeHdc(), 0, 0, 0);
// BELOW COMMENTED CODE OF StretchBlt WORKS(!) INSTEAD OF StretchDIBits.
//
//BOOL bSuccess = pDC->StretchBlt(rectClipBoxPlayground.left, rectClipBoxPlayground.top,
// rectClipBoxPlayground.Width(), rectClipBoxPlayground.Height(),
// _pMemDc, rectClipBoxBackBuffer.left, rectClipBoxBackBuffer.top,
// rectClipBoxBackBuffer.Width(), rectClipBoxBackBuffer.Height(), SRCCOPY);
HBITMAP hMemBitmap = (HBITMAP)_pMemDc->SelectObject(_hOldSelBitmap);
DWORD dwLines = StretchDIBits(pDC->GetSafeHdc(),
rectClipBoxPlayground.left, rectClipBoxPlayground.top, rectClipBoxPlayground.Width(), rectClipBoxPlayground.Height(),
rectClipBoxBackBuffer.left, rectClipBoxBackBuffer.top, rectClipBoxBackBuffer.Width(), rectClipBoxBackBuffer.Height(),
_pBitmapRawBits, &_bitmapInfo, DIB_RGB_COLORS, SRCCOPY);
_pMemDc->SelectObject(hMemBitmap);
The problem is, the commented-out code of StretchBlt works flawlessly (except printing on some printers), but I can't use it because some printers have troubles with it. So I have to use StretchDIBits. Note that I firstly unselect the DIB from its memory dc temporarily, so that it is not associated with any dc. Then I use StretchDIBits but things just don't work! Output is messed up, like I give incorrect coordinates, areas are drawn off-set from where they should be drawn, and sometimes totally black. So I must be missing something (maybe something very trivial). Help! I tried changing signs of rectClipBoxBackBuffer.top and bitmapInfo.bmiHeader.biHeight, the results change, but nothing works like it should.
What am I doing wrong??
Dont't select the DIB into/out DC if you are going to use StretchDIBits.
DC can only contain DDB bitmap, if you supply a DIB, DC will convert it.
Microsoft's documentation about StretchDIBits is totally wrong. I found out that direction of Y axis has to be changed. Now following code works:
// Copy back buffer to screen dc:
pDC->SetStretchBltMode(HALFTONE);
SetBrushOrgEx(pDC->GetSafeHdc(), 0, 0, 0);
HBITMAP hMemBitmap = (HBITMAP)_pMemDc->SelectObject(_hOldSelBitmap);
DWORD dwLines = StretchDIBits(pDC->GetSafeHdc(),
rectClipBoxPlayground.left, rectClipBoxPlayground.top, rectClipBoxPlayground.Width(), rectClipBoxPlayground.Height(),
rectClipBoxBackBuffer.left, _sizeBackBuffer.cy - rectClipBoxBackBuffer.top - rectClipBoxBackBuffer.Height(), rectClipBoxBackBuffer.Width(), rectClipBoxBackBuffer.Height(),
_pBitmapRawBits, &_bitmapInfo, DIB_RGB_COLORS, SRCCOPY);
_pMemDc->SelectObject(hMemBitmap);
P.S.: Now it works for screen drawing and print preview, but fails for actual printing, which was my original problem discussed here: How to print DIB backbuffer on printer - GDI, MFC
I have an MFC control to which I pass a handle to a bitmap (HBITMAP). In the controls OnPaint method I am using BitBlt to render the bitmap. But the bitmap is being rendered upside down.
As a test I created a CBitmap object from this handle and write that out to a file and it created a bitmap that was right side up. So am I doing something wrong with my call to BitBlt?
I've posted my code from OnPaint below. I did try to change the mapping mode of my device context to MM_LOENGLISH and was able to get the bitmap to render right side up but it was very grainy. When I leave the mapping mode at MM_TEXT the quality of the image is perfect but as I said it is upside down. I haven't worked much with bitmaps, blitting etc...so I could be missing something easy. Any other suggestions would be appreciated. For some background I'm grabbing a BYTE* from a video camera driver and creating the HBITMAP to render the video.
How can I get this to render properly?? Many thanks
void BitmapControl::OnPaint()
{
EnterCriticalSection (&CriticalSection);
if (_handleBMP)
{
CPaintDC dc(this);
//dc.SetMapMode(MM_LOENGLISH);
CDC dcMem;
dcMem.CreateCompatibleDC(&dc);
CRect rect;
GetClientRect(&rect);
dc.DPtoLP(&rect);
CBitmap* pBmpOld = dcMem.SelectObject(CBitmap::FromHandle(_handleBMP));
BitBlt(dc,rect.left,rect.top,rect.Width(),rect.Height(),dcMem,rect.left,rect.top,SRCCOPY); //works with MM_TEXT but upsidedown
//BitBlt(dc,0,rect.bottom,rect.Width(),-rect.Height(),dcMem,0,0,SRCCOPY); //works with MM_LOENGLISH
dcMem.SelectObject(pBmpOld);
DeleteDC(dc);
DeleteDC(dcMem);
DeleteObject(_handleBMP);
DeleteObject(pBmpOld);
_handleBMP = NULL;
}
LeaveCriticalSection (&CriticalSection);
}
edit*
I was assuming because I could save the bitmap to disk in the correct orientation that the problem was with bitblt. Here is the code I use to generate the HBITMAP.
HBITMAP BitmapWriter::CreateBitmapFromFrame(BYTE* frame)
{
BITMAPFILEHEADER* bmfh;
bmfh = (BITMAPFILEHEADER*)frame;
BITMAPINFOHEADER* bmih = &_bmi;
BITMAPINFO* bmpInfo = (BITMAPINFO*)bmih;
HBITMAP hbmp = CreateDIBSection(_hdc,bmpInfo,DIB_RGB_COLORS,NULL,NULL,0);
SetBitmapBits(hbmp,_bmi.biSizeImage,frame);
return hbmp;
}
Oh, and I used the critical section because I pass the hbitmap to the control in a property and then access it in the OnPaint. If that's a potential problem I will have to rethink that. Thanks
Windows bitmaps are stored with the bottom line first. Most of the rest of the world works top line first, so I presume that's what you're getting from your camera.
You can use a negative height in the BITMAPINFOHEADER structure to reverse the normal order.
Just use a Negative value in the biHeight field of BITMAPINFOHEADER struct.
bi.biHeight = -height; //this is the line that makes it draw upside down or not
In MM_TEXT y-axis points down, while in the other mapping modes it points up. Try MM_ISOTROPIC mapping mode. For more precise control, you may need to set viewport and window offset and extents on CDC.
Bitmaps can be stored upside down, that is indicated by negative height in the BITMAPINFOHEADER structure, but this should not be a problem.
Ok, I seem to have this working. I ended up changing the mapping mode to MM_LOENGLISH. As I said before this gave me a grainy image but this was corrected by adding the following
dc.SetStretchBltMode(COLORONCOLOR);
I need to do a bit of reading to actually figure out why...but here is my rendering code now.
void BitmapControl::OnPaint()
{
EnterCriticalSection (&CriticalSection);
if (_handleBMP)
{
CPaintDC dc(this);
//dc.SetMapMode(MM_ISOTROPIC);
dc.SetMapMode(MM_LOENGLISH);
CDC dcMem;
dcMem.CreateCompatibleDC(&dc);
CRect rect;
GetClientRect(&rect);
dc.DPtoLP(&rect);
CBitmap* pBmpOld = dcMem.SelectObject(CBitmap::FromHandle(_handleBMP));
//tst
dc.SetStretchBltMode(COLORONCOLOR);
//BitBlt(dc,rect.left,-0,rect.Width(),rect.Height(),dcMem,rect.left,rect.top,SRCCOPY); //works with MM_TEXT but upsidedown
BitBlt(dc,0,rect.bottom,rect.Width(),-rect.Height(),dcMem,0,0,SRCCOPY); //works with MM_LOENGLISH
dcMem.SelectObject(pBmpOld);
DeleteDC(dc);
DeleteDC(dcMem);
DeleteObject(_handleBMP);
DeleteObject(pBmpOld);
_handleBMP = NULL;
}
LeaveCriticalSection (&CriticalSection);
}
(unmanaged C++)
I already succeeded drawing PNG files to a transparent layered window that I can drag around the desktop, but now my problem is drawing text on a transparent layered window
Here's my code and my attempt at drawing text in the middle, it's important to note that i'm using the screenDC instead of using the one in WM_PAINT messages
[edit]
updated code after the comments, now i'm just trying to write text on the bitmap before getting the HBITMAP version which i need to use
this time I'm using DrawString because textout() isn't GDI+, I hope DrawString really is GDI+ lol
still doesn't work though, wonder what i'm doing wrong
void Draw() // draws a frame on the layered window AND moves it based on x and y
{
HDC screenDC( NULL ); // grab screen
HDC sourceDC( CreateCompatibleDC(screenDC) );
POINT pos = {x,y}; // drawing location
POINT sourcePos = {0,0}; // top left of image
SIZE size = {100,100}; // 100x100 image
BLENDFUNCTION blendFunction = {0};
HBITMAP bufferBitmap = {0};
Bitmap* TheBitmap = crnimage; // crnimage was already loaded earlier
// ------------important part goes here, my attempt at drawing text ------------//
Gdiplus::Graphics Gx(TheBitmap);
// Font* myFont = new Font(sourceDC);
Font myFont(L"Arial", 16);
RectF therect;
therect.Height = 20;
therect.Width = 180;
therect.X = 0;
therect.Y = 0;
StringFormat format;
format.SetAlignment(StringAlignmentCenter);
format.GenericDefault();
Gdiplus::SolidBrush GxTextBrush(Gdiplus::Color(255, 255, 0,255));
WCHAR thetext[] = L"Sample Text";
int stats = Gx.DrawString(thetext, -1, &myFont, therect, &format, &GxTextBrush);
if(stats) // DrawString returns nonzero if there is an error
msgbox(stats);
stats = Gx.DrawRectangle(&Pen(Color::Red, 3), therect);
// the rectangle and text both draw fine now
// ------------important part goes here, my attempt at drawing text ------------//
TheBitmap->GetHBITMAP(0, &bufferBitmap);
HBITMAP oldBmpSelInDC;
oldBmpSelInDC = (HBITMAP)SelectObject(sourceDC, bufferBitmap);
// some alpha blending
blendFunction.BlendOp = AC_SRC_OVER;
blendFunction.SourceConstantAlpha = wndalpha;
blendFunction.AlphaFormat = AC_SRC_ALPHA;
COLORREF colorKey( RGB(255,0,255) );
DWORD flags( ULW_ALPHA);
UpdateLayeredWindow(hWnd, screenDC, &pos, & size, sourceDC, &sourcePos,
colorKey, &blendFunction, flags);
// release buffered image from memory
SelectObject(sourceDC, oldBmpSelInDC);
DeleteDC(sourceDC);
DeleteObject(bufferBitmap);
// finally release the screen
ReleaseDC(0, screenDC);
}
I've been trying to write text on my layered window for two days now, but from those attempts I know there are several ways I can go about doing this
(unfortunately I have no idea how exactly)
The usual option I see is drawing text on a bitmap, then rendering the bitmap itself
Use Gdi+ to load a bitmap
Create a Graphics object from the bitmap
Use DrawString to write text to the bitmap
Dispose of the Graphics object
Use the bitmap Save method to save the result to a file
Apparently one can also make a graphics object from a DC, then draw text on the DC, but again i have no clue as to how to do this
The overall approach looks right, but I think you've got some problems with the DrawString call. Check out the documentation (especially the sample) on MSDN.
Gx.DrawString(thetext, 4, NULL, therect, NULL, NULL)
The third, fifth, and sixth parameters (font, format, and brush) probably need to be specified. The documentation doesn't say that they are optional. Passing NULL for these is probably causing GDI+ to treat the call as a no-op.
The second parameter should not include the terminating L'\0' in the string. It's probably safest to use -1 if your string is always terminated.
I have an image data in a buffer(type - long) from a scanner which is 32 bit.
For example, buffer[0]'s corresponding pixel value is 952 which is [184, 3, 0, 0] <-[R,G,B,A];
I want to display/Paint/draw on to the screen; I am confused when i tried to read about displying bitmaps. I looked at win32 functions, CBitmap class, windows forms (picture box) etc I am hard to understand the general idea/appraoch for displaying this buffer data on to a application window.
I have constructed the BITMAPFILEHEADER AND BITMAPINFOHEADER; Has the pixel data in a buffer, (unsigned char *)vInBuff whose size is vImageSz;
//construct the BMP file Header
vBmfh.bfType = 19778;
vBmfh.bfSize = 54+vImageSz;//size of the whole image
vBmfh.bfReserved2 = 0;
vBmfh.bfReserved1 = 0;
vBmfh.bfOffBits = 54;//offset from where the pixel data can be found
//Construct the BMP info header
vBmih.biSize = 40;//size of header from this point
vBmih.biWidth = 1004;
vBmih.biHeight = 1002;
vBmih.biPlanes = 1;
vBmih.biCompression = BI_RGB;
vBmih.biSizeImage = vBmih.biWidth*vBmih.biHeight*4;
vBmih.biBitCount = 32;
vBmih.biClrUsed = 0;
vBmih.biClrUsed = 0;
1.What is that i should be doing next to display this?
2 What should i be using to display the 32bit bitmap? I see people using createwindows functions, windows forms, MFC etc;
3.I also understand that BitBlt,createDIBSection, OnPaint etc are being used? I am confused by these various functions and coding platforms? Please suggest me a simple approach.
4.How can i create a palette to display a 32 bit image?
Thanks
Raj
EDITED TRYING TO IMPLEMENT DAVE'S APPROACH, CAN SOMEBODY COMMENT ON MY IMPLEMTATION. I couldn't continue to the bitblt as i donot have two HDC, i donot know how to get this one? Any help please
DisplayDataToImageOnScreen(unsigned char* vInBuff, int vImageSz) // buffer with pixel data, Size of pixel data
{
unsigned char* vImageBuff = NULL;
HDC hdcMem=CreateCompatibleDC(NULL);
HBITMAP hBitmap = CreateDIBSection(hdcMem,
(BITMAPINFO*)&vBmih,
DIB_RGB_COLORS,
(void **)&vImageBuff,
NULL, 0);
GetDIBits(hdcMem,
hBitmap,
0,
1,
(void**)&vImageBuff,
(BITMAPINFO*)&vBmih,
DIB_RGB_COLORS);
memcpy(vImageBuff,vInBuff,vImageSz);
}
An alternative if you just want to plot it on screen is to use TinyPTC ( http://sourceforge.net/projects/tinyptc/files/ ). It's just 3 functions and very simple if you just want to plot some pixels.
EDIT: Seems like http://www.pixeltoaster.com is a continuation of TinyPTC, probably preffered.
If you have image's bytes already in a buffer you can use:
a CBitmap object (MFC) and the method CBitmap::CreateBitmapIndirect
or
win32 routine CreateBitmapIndirect.
Now you can use BitBlt to draw it on a DC. To get a window DC use GetDC.
There is no need to create a pallete for 32 bit images.
Here's a simplified approach you can try, broken down into steps:
BITMAPINFO bitmapinfo = { 0 };
bitmapinfo.bmiHeader.biSize = sizeof(BITMAPINFOHEADER);
bitmapinfo.bmiHeader.biWidth = 1004;
bitmapinfo.bmiHeader.biHeight = -1002;
bitmapinfo.bmiHeader.biPlanes = 1;
bitmapinfo.bmiHeader.biCompression = BI_RGB;
HBITMAP hBitmap = CreateDIBSection(NULL,
&bitmapinfo,
DIB_RGB_COLORS,
(void **)&vImageBuff,
NULL,
0);
Now party on vImageBuff and then cache hBitmap somewhere so that within your wndproc you can then in the WM_PAINT handler:
select hBitmap into temp compatible HDC
call BitBlt(..., SRCCOPY) from the compatible HDC to the window's HDC. the other parameters should be obvious. don't try to stretch or do anything fancy at first.
remember to select the original dummy bitmap into the temp HDC before destroying it.
If you aren't seeing results try looping through vImageBuff and just set every pixel to RGB(255, 0, 0), or something like that, just to sanity check the rest of the logic.
If nothing is drawing make sure that the alpha component for each pixel is 255.
If you're getting a garbled image then you need to double-check pixelformat, stride, etc.
Here's a strategy you might like:
Create a bitmap with the same size as your scanned data, and the same format (use CreateDIBSection).
Use GetDIBits to get the base address of the pixel data.
Copy your data (from the scanner) to the address GetDIBits returns.
Now render your bitmap! (use BitBlt, or somesuch).
Regarding palettes- a 32bit image does not, generally, have an explicit palette - you'd need 16.7million (assuming 8bits of alpha) values in the palette. Generally the palette is assumed to be 8bits red, 8bits green, 8bits blue, as you've described above.