CImage and transparency
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I have a button that I want an image in, a basic colour swatch. I liked the idea of having a partially transparent shadow around it, so in GIMP, I created a 32 bit BMP with the desired alpha shadow, and a white, totally non-transparent square in the middle. The intention was to fill the white area in with the colour that the user chooses. Sounds simple enough. So, the basic code is such:
HDC hDC;
HANDLE hOldBmp;
HBRUSH hBrush;
LOGBRUSH zLogBrush;HBITMAP hColourShadowBmp_ = ::LoadBitmap( hInst, MAKEINTRESOURCE(IDB_COLOUR_SHADOW) );
zLogBrush.lbStyle = BS_SOLID;
zLogBrush.lbColor = RGB( m_Props.uiRed, m_Props.uiGreen, m_Props.uiBlue );
zLogBrush.lbHatch = NULL;hBrush = ::CreateBrushIndirect( &zLogBrush );
CImage zFinalImage;
CImage zSwatchImage;zFinalImage.Attach( hColourShadowBmp_ );
zSwatchImage.Create( 20, 20, 24 );hDC = zSwatchImage.GetDC();
::SelectObject( hDC, hBrush );
::Rectangle( hDC, 0, 0, 20, 20 );
zSwatchImage.ReleaseDC();hDC = zFinalImage.GetDC();
zSwatchImage.AlphaBlend( hDC, 2, 2, 255 );
zFinalImage.ReleaseDC();hOldBmp = (HANDLE)
::SendMessage( ::GetDlgItem( m_hWnd, IDC_COLOUR ),
BM_SETIMAGE,
(WPARAM)IMAGE_BITMAP,
(LPARAM)zFinalImage.Detach() );::DeleteObject( hBrush );
All I end up with is the source shadow image, with a lovely fully transparent square where the swatch should be. I know the swatch painting is working, as I can send that image and get the colour square I expect. Yet nothing I do seems to be able to make the colours get transferred. Crazily enough, the alpha is, if I set the alpha in the
AlphaBlend()call to 0, I get the original shadow image unchanged. So I know that it is modifying the alpha channel properly at least. The source is opaque, so no amount of pre-multiplying will help. FWIW, I also tried making thezSwatchImagea 32 bit with alpha, but it made no difference. The only solution I can see now is jumping into the bits for the shadow image and changing the RGB values to what I want. But surely I'm doing something wrong? It's hard to believe that a simply blend like this fails. Thanks, CraigL -
I have a button that I want an image in, a basic colour swatch. I liked the idea of having a partially transparent shadow around it, so in GIMP, I created a 32 bit BMP with the desired alpha shadow, and a white, totally non-transparent square in the middle. The intention was to fill the white area in with the colour that the user chooses. Sounds simple enough. So, the basic code is such:
HDC hDC;
HANDLE hOldBmp;
HBRUSH hBrush;
LOGBRUSH zLogBrush;HBITMAP hColourShadowBmp_ = ::LoadBitmap( hInst, MAKEINTRESOURCE(IDB_COLOUR_SHADOW) );
zLogBrush.lbStyle = BS_SOLID;
zLogBrush.lbColor = RGB( m_Props.uiRed, m_Props.uiGreen, m_Props.uiBlue );
zLogBrush.lbHatch = NULL;hBrush = ::CreateBrushIndirect( &zLogBrush );
CImage zFinalImage;
CImage zSwatchImage;zFinalImage.Attach( hColourShadowBmp_ );
zSwatchImage.Create( 20, 20, 24 );hDC = zSwatchImage.GetDC();
::SelectObject( hDC, hBrush );
::Rectangle( hDC, 0, 0, 20, 20 );
zSwatchImage.ReleaseDC();hDC = zFinalImage.GetDC();
zSwatchImage.AlphaBlend( hDC, 2, 2, 255 );
zFinalImage.ReleaseDC();hOldBmp = (HANDLE)
::SendMessage( ::GetDlgItem( m_hWnd, IDC_COLOUR ),
BM_SETIMAGE,
(WPARAM)IMAGE_BITMAP,
(LPARAM)zFinalImage.Detach() );::DeleteObject( hBrush );
All I end up with is the source shadow image, with a lovely fully transparent square where the swatch should be. I know the swatch painting is working, as I can send that image and get the colour square I expect. Yet nothing I do seems to be able to make the colours get transferred. Crazily enough, the alpha is, if I set the alpha in the
AlphaBlend()call to 0, I get the original shadow image unchanged. So I know that it is modifying the alpha channel properly at least. The source is opaque, so no amount of pre-multiplying will help. FWIW, I also tried making thezSwatchImagea 32 bit with alpha, but it made no difference. The only solution I can see now is jumping into the bits for the shadow image and changing the RGB values to what I want. But surely I'm doing something wrong? It's hard to believe that a simply blend like this fails. Thanks, CraigLDon't be surprised, GDI drawing methods zero out the aplha channel. When you call
Rectangleit "makes a hole" in your alpha channel. Use GDI+ or fill the pixels by writing memory directly.> The problem with computers is that they do what you tell them to do and not what you want them to do. < > Leela: Fry, you're wasting your life sitting in front of that TV. You need to get out and see the real world. Fry: But this is HDTV. It's got better resolution than the real world <
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Don't be surprised, GDI drawing methods zero out the aplha channel. When you call
Rectangleit "makes a hole" in your alpha channel. Use GDI+ or fill the pixels by writing memory directly.> The problem with computers is that they do what you tell them to do and not what you want them to do. < > Leela: Fry, you're wasting your life sitting in front of that TV. You need to get out and see the real world. Fry: But this is HDTV. It's got better resolution than the real world <
I can see that being a problem if I had an alpha channel in the
zSwatchImage. And at one point I did, so I guess I'd expect the behaviour I saw. But it's absurd to me that an "alpha blend" function can't take a 24bit image and "do the right thing" by copying it will the alpha channel opaque. Especially when you TELL it what the alpha value to copy with should be. If it isn't there, you'd think it would use the alpha provided as the source alpha, not just the blend alpha. But to take a 24bit image and assume the alpha is zero? And, I had thought thatCImagedid use GDI+, so the 24 -> 32 bpp copy would make sense. I guess I just expect too much fromCImage. Course, now I'm having fun trying to get the bits directly from a BMP loaded via::LoadBitmap... I guess graphics never really was a win32 strong point. Thanks for the reply. Normally, I totally exclude win32 APIs wrt image handling, just needed the BMP to use the easy way one can put it on a button. This exercise has just cinched that opinion even more =) -
I can see that being a problem if I had an alpha channel in the
zSwatchImage. And at one point I did, so I guess I'd expect the behaviour I saw. But it's absurd to me that an "alpha blend" function can't take a 24bit image and "do the right thing" by copying it will the alpha channel opaque. Especially when you TELL it what the alpha value to copy with should be. If it isn't there, you'd think it would use the alpha provided as the source alpha, not just the blend alpha. But to take a 24bit image and assume the alpha is zero? And, I had thought thatCImagedid use GDI+, so the 24 -> 32 bpp copy would make sense. I guess I just expect too much fromCImage. Course, now I'm having fun trying to get the bits directly from a BMP loaded via::LoadBitmap... I guess graphics never really was a win32 strong point. Thanks for the reply. Normally, I totally exclude win32 APIs wrt image handling, just needed the BMP to use the easy way one can put it on a button. This exercise has just cinched that opinion even more =)OK, I stumbled upon the
::LoadImage()after thinking there must be a function more up-to-date that::LoadBitmap(), and it lets me load a DIB from a resource, and then::GetObject()gives me the bits. Thanks, CraigL -
I can see that being a problem if I had an alpha channel in the
zSwatchImage. And at one point I did, so I guess I'd expect the behaviour I saw. But it's absurd to me that an "alpha blend" function can't take a 24bit image and "do the right thing" by copying it will the alpha channel opaque. Especially when you TELL it what the alpha value to copy with should be. If it isn't there, you'd think it would use the alpha provided as the source alpha, not just the blend alpha. But to take a 24bit image and assume the alpha is zero? And, I had thought thatCImagedid use GDI+, so the 24 -> 32 bpp copy would make sense. I guess I just expect too much fromCImage. Course, now I'm having fun trying to get the bits directly from a BMP loaded via::LoadBitmap... I guess graphics never really was a win32 strong point. Thanks for the reply. Normally, I totally exclude win32 APIs wrt image handling, just needed the BMP to use the easy way one can put it on a button. This exercise has just cinched that opinion even more =)Hi Craig,
Craig Longman wrote:
Course, now I'm having fun trying to get the bits directly from a BMP loaded via ::LoadBitmap
From LoadBitmap[^] LoadBitmap creates a compatible bitmap of the display. Use LoadImage()[^] with
LR_CREATEDIBSECTIONto use the xxxBlend GDI functions. As was already answered GDI+ (not MFCCImagewhich uses it only for file exchanges) handles that correctly. cheers, ARWhen the wise (person) points at the moon the fool looks at the finger (Chinese proverb)
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OK, I stumbled upon the
::LoadImage()after thinking there must be a function more up-to-date that::LoadBitmap(), and it lets me load a DIB from a resource, and then::GetObject()gives me the bits. Thanks, CraigLCool :thumbsup: :)
> The problem with computers is that they do what you tell them to do and not what you want them to do. < > Leela: Fry, you're wasting your life sitting in front of that TV. You need to get out and see the real world. Fry: But this is HDTV. It's got better resolution than the real world <
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Don't be surprised, GDI drawing methods zero out the aplha channel. When you call
Rectangleit "makes a hole" in your alpha channel. Use GDI+ or fill the pixels by writing memory directly.> The problem with computers is that they do what you tell them to do and not what you want them to do. < > Leela: Fry, you're wasting your life sitting in front of that TV. You need to get out and see the real world. Fry: But this is HDTV. It's got better resolution than the real world <
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transoft wrote:
GDI+ is not working properly under windows 7
Can you give an example... do you mean performance problems with alpha blending on Windows 7?