C / C++ / MFC

29-Jun-05 17:39

After diving a lot in MS and other web waters, I must draw the following conclusion:
many ambiguities are kept alive about GDI, GDI+, DIB, DDB, ... and the GDI/GDI+ doc doesn't help much.
One of the best article I read about GDI+ is from Borland! ( http://bcbjournal.org/free_issue/vol8_num6.4.htm )

There are some abiguities I'd like to clear, please read the questions carefully and reply only if you know the answers for sure, thank you.

  1. GDI+ Bitmap class loads a file

- is the bitmap generated for sure a DIB? (ie not a DDB)
will the bitmap have the same PixelFormat as the one inside the file for sure?
(should be the case, but read so many various things on the web...)

  2. GDI+ Bitmap class and palettes

When a GDI+ Bitmap is read from a file in which a palette is embedded (e.g. a GIF) the superclass Image provides a GetPalette method, while the subclass Bitmap does not. So, what happens after a Bitmap::LockBits where the requested PixelFormat is Indexed?

- Does LockBits provides a color table (palette) somewhere? How to get it?

  3. GDI+ to HBITMAP etc...

After reading an image from a file, assuming the file format of Image is the one of the file, the corresponding old HBITMAP handle is necessary:

- will Bitmap::GetHBITMAP provide a "safe" handle (ie the Image object can be deleted?)

What about the Palette, if any:

- is a HPALETTE handle available somewhere, or the Image::GetPalette() call is necessary (after GetHBITMAP) and the re-construction of a HPALETTE object/handle is mandatory?

Thanks again
Regards

Christian Graus29-Jun-05 18:16

Christian Graus

29-Jun-05 18:16

EastMohican wrote:
is the bitmap generated for sure a DIB?

Yes, it always has the same pixel format as the image on disk

EastMohican wrote:
Does LockBits provides a color table (palette) somewhere? How to get it?

Lock bits provides the bits only, and may actually throw an exception if the image is 8 bit.

EastMohican wrote:
will Bitmap::GetHBITMAP provide a "safe" handle (ie the Image object can be deleted?)

I doubt it. An Image has to be a HBITMAP, no matter which way you look at it. So the easiest thing, and the least memory intensive thing, would be to pass the handle of what I assume is internally a DIBSection.

Christian Graus - Microsoft MVP - C++

EastMohican29-Jun-05 18:52

29-Jun-05 18:52

Thanks a lot Christian.

Maybe a last question about palettes:
after getting the HBITMAP from my GDI+ Bitmap::GetHBITMAP() method, in case the bitmaps is (for instance) Indexed 8 bits, where can I get the accompanying Palette information (if any) in order to make a HPALETTE (GDI)object?

Christian Graus29-Jun-05 19:22

Christian Graus

29-Jun-05 19:22

I'm sorry, I skipped that one as I have no idea. I only know about the exception thrown because people who have used my image processing code have reported it. I tried to stop my code loading GIF ( there was some talk that using GDI+ to load gif means that the third party needs to pay a Unisys licence, even if the code is free ), and I never use palettised images.

Christian Graus - Microsoft MVP - C++

Jim Crafton30-Jun-05 7:44

Jim Crafton

30-Jun-05 7:44

EastMohican wrote:
after getting the HBITMAP from my GDI+ Bitmap::GetHBITMAP() method, in case the bitmaps is (for instance) Indexed 8 bits, where can I get the accompanying Palette information (if any) in order to make a HPALETTE (GDI)object?

I think that, assuming the HBITMAP is a DIB, then calling GetDIBits and using DIB_PAL_COLORS will cause the BITMAPINFO's bmiColors array to be filled with the palette values.

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EastMohican2-Jul-05 15:35

2-Jul-05 15:35

Hi Jim,

thanks for your contribution.
Actually GetDIBits will take the bitmap handle and process the data in order to provide the requested format. E.g. DIB_PAL_COLORS for indexed colors, or DIB_RGB_COLORS for straight colors...

However, I don't need another processing! But rather retrieve the Palette information after GDI+ Bitmap::GetHBITMAP has been called... if the initial bitmap (handled HBITMAP) was actually Indexed, there should be the information somewhere in the Bitmap object!

regards

Andrew Kirillov29-Jun-05 21:06

Andrew Kirillov

29-Jun-05 21:06

Christian Graus wrote:
EastMohican wrote:
is the bitmap generated for sure a DIB?

Yes, it always has the same pixel format as the image on disk

Yes, but I was a little bit confused working with grayscale JPEGs. Working with such images using libjpeg, for example, you can determine that the image is grayscale. But GDI+ is loading such images using Format8bppIndexed. Sigh | :sigh:

So, how to check that the image is grayscale ? Only analyzing it's palette. Mad | :mad:

Christian Graus wrote:
Lock bits provides the bits only, and may actually throw an exception if the image is 8 bit.
Yes, it may. But why not to lock using the pixel format of the image ? So, you will not get exceptions. Besides, you will not get exception if you are locking for read only. It works for 8 bit images locking them as 24 bit.

Andrew

EastMohican29-Jun-05 21:34

29-Jun-05 21:34

Thanks Andrew. Any idea about the Palette if I want to convert a GIF to HBITMAP for instance (without forcing the pix format as > 8 bits) ?
<< after getting the HBITMAP from my GDI+ Bitmap::GetHBITMAP() method, in case the bitmaps is (for instance) Indexed 8 bits, where can I get the accompanying Palette information (if any) in order to make a HPALETTE (GDI)object? >>

Andrew Kirillov29-Jun-05 21:44

Andrew Kirillov

29-Jun-05 21:44

Sorry, but I have no ideas. I remember, that I had some problems with palette of HBITMAP. But it was not so important for me that time. I am working mostly with image processing, so it's not preferable for me to work with 8 bpp images (only if they are grayscale).

Andrew

EastMohican29-Jun-05 22:03

29-Jun-05 22:03

Thanks anyway.

Amazing the tremendous confusion dominating the Web and newsgroup regarding GDI/GDI+.
Even the posts apparently signed from Microsoft staff are often vague or ambiguous and sometimes wrong. Sounds like nobody is working on it...

Regarding the help, it's like a supermarket where apples are between the shoes and the fridges! Important linked concepts are rarely connected, it's worse than hell to solve the puzzle(s).

Is there a pilot in the plane?

Andrew Kirillov29-Jun-05 22:08

Andrew Kirillov

29-Jun-05 22:08

EastMohican wrote:
Is there a pilot in the plane?

He is jumped out Big Grin | :-D

MS forgot about Video for Windows after DirectShow was appeared. So will be with GDI too, because there is GDI+ now. They are too busy with their new technologies.

Andrew

Breakpoint on a bunch of functions

Christian Graus30-Jun-05 13:11

Christian Graus

30-Jun-05 13:11

Andrew Kirillov wrote:
But why not to lock using the pixel format of the image ?

I said 'may' because all I know for sure is that it does in my image processing articles ( which I never tested against 8 bit, IMO 8 bit is crap ).

Christian Graus - Microsoft MVP - C++

Anonymous29-Jun-05 13:19

Anonymous

29-Jun-05 13:19

Hi,
Any easy way to set breakpoints on a bunch of functions? Eg all methods in a class or functions matching a string?
Thanks.

Re: Breakpoint on a bunch of functions

Nilesh K.29-Jun-05 16:40

Nilesh K.

29-Jun-05 16:40

Writing a macro for that might just help.

<bold>- Nilesh
<italics>"Reading made Don Quixote a gentleman. Believing what he read made him mad" -George Bernard Shaw

CSlider Control Problems.

jerry1211a29-Jun-05 12:48

jerry1211a

29-Jun-05 12:48

Hi!

I create an object of class A in my code. An object of dialogWnd, dlg, is created. See dialogWnd below. When I attempt m_Slide.SetRange(1, 300), in OnInitDialog(), my program crashes every time. Can anyone give me some idea what is going on? Also, how do you distinguish between CSlider controls if you have more than one is a dialog resource?

class A : public CMDIChildWnd
{
public:
dialogWnd dlg;
};

BOOL dialogWnd::OnInitDialog()
{
CDialog::OnInitDialog();
m_Slide.SetRange(1, 300);

return TRUE;
}

class dialogWnd : public CDialog
{
public:
dialogWnd(CWnd* pParent = NULL);
virtual ~dialogWnd();
//Dialog Data
//{{AFX_DATA(dialogWnd)
enum {IDD = IDD_DIALOGWND};
CSliderCtrl m_Slide;
//}}AFX_DATA

Thanks.
Jerry
Smile | :)

PJ Arends29-Jun-05 15:33

PJ Arends

29-Jun-05 15:33

jerry1211a wrote:
my program crashes every time.

Kind of vague on your description aren't you? Usually when a program crashes (especially in DEBUG mode) there will be some kind of error message. If you would enlighten those of us without mind reading abilities as to what the actual error message is we may be able to help you.

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Nilesh K.29-Jun-05 16:50

Nilesh K.

29-Jun-05 16:50

jerry1211a wrote:
how do you distinguish between CSlider controls

Check with GetDlgCtrlID.

<bold>- Nilesh
<italics>"Reading made Don Quixote a gentleman. Believing what he read made him mad" -George Bernard Shaw

David Crow29-Jun-05 16:51

David Crow

29-Jun-05 16:51

What does the dialog's DoDataExchange() method look like? Put a breakpoint on the SetRange() method and single-step from there. Where does it "crash?"

"Ideas are a dime a dozen. People who put them into action are priceless." - Unknown

jerry1211a30-Jun-05 1:53

jerry1211a

30-Jun-05 1:53

Hey there!

Sorry about my confusing explanation, I had been coding all day as was burned out. Anyway, what I am looking for is a simple example of a project just using a slider control, showing DoDataExchange, etc. I assume I need a separate slider class to init the control through a construtor?? I can't seem to find an example.

Thanks again, you have helped me before
Smile | :)

Jerry

David Crow30-Jun-05 2:36

David Crow

30-Jun-05 2:36

jerry1211a wrote:
Anyway, what I am looking for is a simple example of a project just using a slider control, showing DoDataExchange, etc...I can't seem to find an example.

There are several examples here.

jerry1211a wrote:
I assume I need a separate slider class to init the control through a construtor??

For each slider control on the dialog, a CSliderCtrl member control variable will be needed.

"Ideas are a dime a dozen. People who put them into action are priceless." - Unknown