dev-cpp-users

[Dev-C++] Painting transparent areas

[DXFX <vin...@ed...>]

I have been searching through the Win32 API reference and still have no answer. Currently, I don't have an internet connection and I'm using a free dial-up service to my Email only. I need help from you guys...

I've been testing values for the BitBlt function, and I haven't found any good solution. Ok now... here's the problem:

How do I do a bitmap so that when it draws, it wouldn't paint a specific color -- giving it a bitmap transparency. If you guys still don't get what I'm saying, I've attached a gif image with this email.

The one on the left is the original bitmap. It is basically a rectangle with curved corners, and a pink background(Max Red, Max Blue, 0 Green). The one on the right is what I want to accomplish when I'm going to paint it to another bitmap. that other bitmap will replace the pink background... Thus when I'm going to paint the original Bitmap, the pink areas/background would never be painted.

Currently, Im using BitBlt to do this... but all I can do with that function is paint the whole bitmap. Im unable to exclude the pink areas of the bitmap in drawing. Can anyone PLEASE POINT ME to the right DIRECTION.

Thanks to anyone

DXFX

Note: attached is "Sample1.gif", 1.24KB

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[Dev-C++] Painting transparent areas

[DXFX <vin...@ed...>]

Thanks,

Anyway:

> Windows 95/98: TransparentBlt contains a memory leak that can exhaust system resources. To draw a transparent bitmap using BitBlt, see Knowledge Base article Q79212.

Does this mean that the function does not free up resources after it uses it? Is there any other way? I have a Win98 machine(still finding considerations to upgrade to WinXP) and I am running low on resources(Which is why I haven't upgraded my OS). As much as possible, I want my programs(specially the ones that draw things on the desktop) use not so many resources. That would prove to be a challenge to me though...

Anyway... Im in the process of upgrading my compiler(and of course, I couldn't make the code to work... but Im looking forward to).

I've also been studying one solution that I think might do the trick, however, I'll have to sacrifice speed for that... I've been thinking to make a function that draws a bitmap, similar to BitBlt, but with an exception - It would scan the bitmap, byte-by-byte. If the byte isn't the color for transparency, it draws it do the screen... if it is, then it doesnt draw it(It also means I'll have to scan for an interval of three... scanning each R,G,B values. That is, if it is 24-bit color bitmap). However, that also means it will have to spend time scanning the bytes of the bitmap then draw them byte-by-byte on the screen.

I'll be looking on that Article(Knowledge Base article Q79212) to see if I could understand it. For now...

Anyone got any bright Ideas?

DXfX

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Re: [Dev-C++] Painting transparent areas

[Elias P. <eli...@ao...>]

> 
> How do I do a bitmap so that when it draws, it wouldn't paint a
> specific color -- giving it a bitmap transparency. If you guys
> still don't get what I'm saying, I've attached a gif image with
> this email.
>

An easy way to do what you want would be the TransparentBlt
function. It's not defined in the dev-c++ headers/libraries AFAIK,
but you can still use it (i'm using it myself):

The following would draw a 100x100 bitmap onto another, using
the color you mentioned as transparent:

TransparentBlt(hdc, 0, 0, 100, 100, bitmapdc, 0, 0, 100, 100,
RGB(255, 0, 255));

Because dev-c++ has no library for it, you have to add the DLL
containing the function to the linker options (I updated to the
current mingw version, so i'm not sure this works for you). For
me it is c:/windows/system/msimg32.dll.

I attached some example code which works for me, and the makefile
I'm using to compile it.

MSDN also says this about the above function:

Windows 95/98: TransparentBlt contains a memory leak that can exhaust system resources. To draw a transparent bitmap using BitBlt, see Knowledge Base article Q79212.

I looked at that article, but I don't understand it..

--
Elias Pschernig