C / C++ / MFC

12-Nov-06 14:54

How do I get the white background from an imported bitmap to not show? (I am using Visual Studio .NET 2003, VC++.)

Mike_V12-Nov-06 15:05

Mike_V

12-Nov-06 15:05

When you draw it to the screen, try using the TransparentBlt function. But that will make every white area in the image transparent, which may or may not be what you want. And on Win9x (or maybe just 98) the function has a gdi leak. A workaround is present, though, in the function's msdn article.

An alternative is to use an imagelist - create two bitmaps: one is your normal bitmap, the other is black everywhere you want the background to show through, white everywhere else. This is your mask bitmap. When you add the image to the imagelist (via ImageList_AddMasked off the top of my head) you can specify both handles.

A pain, yes, I know.

Mike

BlitzPackage12-Nov-06 15:14

12-Nov-06 15:14

Thanks Mike,

I am trying to use it as an icon in an MDI application (i.e. for my tool bar and menu images). I import it using the Add Resource menu option. How do I set it to Transperent. To my knowledge, it is just resource ID.

Thanks,
BP

Mike_V12-Nov-06 15:27

Mike_V

12-Nov-06 15:27

In that case a lot of the hard work is already done for you.

To show it in the toolbar IIRC you have to put it into an imagelist. In that case you can specify a transparent color when you do that. If you don't do anything with imagelists, look for a toolbar control message to set the transparent color.

Of course, if you have white areas in your image that you want to keep, you can't use white as your transparent color. In that case, change the background color to something garish that you wouldn't use, such as bright magenta (RGB 255 0 255). Specify that as your background color.

Mike

Mark Salsbery12-Nov-06 15:07

12-Nov-06 15:07

What format are the source bitmaps? BMPs don't have a notion of transparency but a 32 bpp BMP
has an extra byte you could use as an alpha blending value. GDI+ can work with transparency.

BlitzPackage12-Nov-06 15:19

12-Nov-06 15:19

Thanks Mark.

The bitmaps were converted from PNGs or GIFs using Corel Draw. In Corel, the background is removed and doesn't show. Then when I choose to export it and use it in Visual Studio, it will show a white background when it is used in the software.

How do I do the things you mentioned?

BP

Christian Graus12-Nov-06 15:28

12-Nov-06 15:28

Although 32 bit bitmaps do contain an extra bit, there is nothing in GDI or GDI+ which uses this as a transparency mask. Your best bet is to pick a color to be transparent, set your border to this color, and use TransparentBlt. If you're using GDI+, you can set a transparency range, but you shouldn't need to do that.

BlitzPackage12-Nov-06 15:41

12-Nov-06 15:41

Thanks Christian,

Can you point me to an example of TransparentBlt in usage?

Thanks,
BP

Christian Graus12-Nov-06 15:45

12-Nov-06 15:45

Any of the hits I got when I typed 'transparentblt' into google would have done, but this one is on MSDN, which is where you should generally look for this sort of info:

Here

BlitzPackage12-Nov-06 15:53

12-Nov-06 15:53

Thanks Christian, I saw that but I don't know where to get all the values for that function's arguments, where to place it in the software (i.e. CMainFrm, CView), when to call it, etc... Do you know if there is a project here that uses it so that I can see how to use that function? Since I import it as a resource, I don't know how to get a hold of it or even adjust it's transparency setting.

Thanks,
BP

Christian Graus12-Nov-06 16:01

12-Nov-06 16:01

There is no transparency setting, you specify the color that is to be transparent. You can use LoadImage to load a bitmap from resources. You most probably want to paint it in your WM_PAINT event handler.

Where you call it depends entirely on where the code is that is drawing the icon, which depends on where the icon is being displayed.

BlitzPackage12-Nov-06 16:04

12-Nov-06 16:04

Last question, when I do that, how do I specify the color that is to be transparent?

Christian Graus12-Nov-06 16:30

12-Nov-06 16:30

I would tend to use the last parameter of TransparentBlt to do that:

UINT crTransparent  // color to make transparent

You can specify a color in hex, 0xFFCC00 is FF red, CC green, 00 blue.

Mark Salsbery13-Nov-06 6:00

13-Nov-06 6:00

Instead of converting to bitmaps (where you lose transparency) you can load them as GDI+
Bitmap objects and GDI+ will handle the alpha blending right for transparency.

As a starting point, try something like this in OnPaint or OnEraseBkgnd...wherever you're painting
a window...

HICON hIcon = ::LoadIcon(AfxGetInstanceHandle(), CResId(IDR_MAINFRAME));
Bitmap bitmap(hIcon);
Graphics graphics(*pDC);
graphics.DrawImage(&bitmap, 0, 0);

Of course, in real life you wouldn't want to reload an icon resource (or worse, bitmap from a
file) every time you paint so you'd load it once (in the window class constructor or OnCreate)
and use the same object to draw every time.

This just makes a simple test example...try it Smile | :)

To try it on PNGs and GIFs replace these lines

HICON hIcon = ::LoadIcon(AfxGetInstanceHandle(), CResId(IDR_MAINFRAME));
Bitmap bitmap(hIcon);

with

Bitmap bitmap(L"path\MyPNGFile.png", TRUE);

BlitzPackage13-Nov-06 8:14

13-Nov-06 8:14

Thanks Mark.

Do you also know how to use the CImage::SetTransparentColor(...) function?

Thanks,
BP

Mark Salsbery13-Nov-06 8:29

13-Nov-06 8:29

BlitzPackage wrote:
Do you also know how to use the CImage::SetTransparentColor(...) function?

I've never used the CImage class...sorry.

Mark Salsbery13-Nov-06 8:33

13-Nov-06 8:33

I took a glance at CImage - It looks like it uses GDI+ as well so I would assume that if
you load the original icons/gifs/pngs (not the ones converted to bitmaps) they should draw
properly like the code sample I posted.

BlitzPackage13-Nov-06 8:45

13-Nov-06 8:45

Thanks Mark.

If I do that, how do I get them to their proper place on the toolbars, buttons, menus, etc...?

BP

Mark Salsbery13-Nov-06 9:10

13-Nov-06 9:10

Ohhhh you are using them as bitmaps on conrols? I thought you were just rendering them to the
screen in a window Smile | :)

In that case I would put them in a bitmap and use image lists in the code.

Example 18 pixel wide bitmap(s) using bright green as transparent color in the bitmaps:
CImageList MyImageList;
...
MyImageList.Create(IDB_BITMAP, 18, 18, RGB(0x00,0xFF,0x00));

This will get you an image list. Check out the controls you're using and look for SetImageList()
method in the classes (CToolBar, CButton, etc.)

I could post some sample code but I'm not sure what exactly you are trying to do with the bitmaps.

Mark

BlitzPackage13-Nov-06 9:22

13-Nov-06 9:22

Thanks Mark,

If you could post some sample code that would be great. I am just trying to use them as menu icons, button icons, tool bar icons, etc...

Any help you can provide would be great.

Thanks again.

BP

Mark Salsbery13-Nov-06 10:54

13-Nov-06 10:54

Here's an example of a Windows toolbar common control with two buttons...

Add these to your window class:

CToolBarCtrl ToolBar;
CImageList MyImageList;

Add this to your window class' .cpp file

static TBBUTTON ToolBarButtonDescs[] =
{
	{0, ID_BUTTON1, TBSTATE_ENABLED, TBSTYLE_BUTTON, {0,0}, 0, 0} ,
	{1, ID_BUTTON2, TBSTATE_ENABLED, TBSTYLE_BUTTON, {0,0}, 0, 0} //,
};

Add this to the window class constructor

MyImageList.Create(IDB_BITMAP, 18, 18, RGB(0x00,0xFF,0x00));

Add this to the window class' OnCreate() (WM_CREATE handler)

ToolBar.Create(WS_CHILD | WS_VISIBLE, CRect(0,0,100,20), this, ID_TOOLBAR);
ToolBar.SetImageList(&MyImageList);
ToolBar.AddButtons(sizeof(ToolBarButtonDescs) / sizeof(TBBUTTON), ToolBarButtonDescs);

The trick is creating the image list bitmap. In this case I have two buttons, 18 pixels wide so
add a bitmap resource 36x18. I've set the bitmap index for button 1 to index 0 and button 2 to
index 1 in the image list. So the rect (0,0,17,17) in the bitmap needs to be the image you want
on the first button and the rect (18,0,35,17) will be the image for the second button. I've
specified RGB(0x00,0xFF,0x00) (bright green) as the transparent color so draw any areas you want
to be transparent in that color. The image list bitmap is the images for all the buttons side-by-
side. I've used 18 pixel wide bitmap (per button) as an example but you can use whatever width
you want. The height will be calculated automagically based on the image width you specify in
this call:
MyImageList.Create(IDB_BITMAP, 18, 18, RGB(0x00,0xFF,0x00));
where the first 18 is the per-image width in the list and the second 18 is the grow-by value
when programatically adding bitmaps to the list.
You can use a different transparency color too.
Make sense?

BlitzPackage13-Nov-06 14:48

13-Nov-06 14:48

Thanks Mark,

That is very understandable. I will apply what you have provided. For buttons, I guess I will use the SetImageList function...right?

Thanks again,
BP

Mark Salsbery13-Nov-06 15:31