wxQuantize problem

[Randajad]

Hello for all! I trying to create gif image from images so i use wxQuantize, but have a problem. Simple code:

Code: Select all

wxImage my_image;
...

wxImage image;
wxQuantize::Quantize(my_image, image, 256);

image.SaveFile("res.png"); /// image have no transparent, but it was!

What i'm doing wrong?

[doublemax]

As i see no mentioning of "alpha" or "transparency" in quantize.cpp, i would guess it's just not implemented.

[Manolo]

Mmmm....
Get the alpha channel with wxImage::GetAlpha()
Do quantization
Set the stored alpha with wxImage::SetAlpha()

[Randajad]

Okay, it works and now i can save png after quatize. But wxGIFHandler::SaveAnimation doesn't uses alpha channel, so, i think, it's need to be transparent color in pallette. Or i goes in wrong way?
I'm need to create gif image from others images.

[Manolo]

GIF images does not use alpha. They use a 256 colours palette.
One of the colours in the palette can be told be transparent. This is not the same as setting for each pixel a different level of transparency.
Each image of the animation has it own palette and trasnparent index.

So, it's not just a matter of adding an alpha channel to a GIF.

Have you read this?
http://docs.wxwidgets.org/trunk/classwx_image.html

Saving GIFs requires images of maximum 8 bpp (see wxQuantize), and the alpha channel converted to a mask (see wxImage::ConvertAlphaToMask). Saving an animated GIF requires images of the same size (see wxGIFHandler::SaveAnimation)

[Randajad]

Tkanks!
Okay, i try to do this after quantize. It works, i see. But i have another problem. It seems, that frame doesn't clears after drawing.



It seems bug in wx. When i don't use alpha, all is ok.

[Randajad]

Bump. Should i post this to bug trac?

[doublemax]

It seems, that frame doesn't clears after drawing.

This is hardly a useful error description. If you draw with tranparency, the background must be in a "defined" state, e.g. usually it has to be cleared first. So you if had a blank erase background handler before to avoid flickering, you'll probably get redraw problems now.

But without seeing code what you're actually doing, it's only guessing.

[Randajad]

Okay. I don't draw anything. Do u see the pucture? When character from picture moving, then it's leaves a trail.
I only have array of pictures to pass to wxGIFHandler::SaveAnimation. It's need to me to take valid gif animation from picture array.

I mean that if gif is diff-based format, then it's seems to wxwidgets don't correct makes these "diffs" when there is transparent pixels.

[doublemax]

It's possible that this is bug. You may even be the first one to have tried this

[Randajad]

Okay. This is bug in wx.
imaggif.cpp:729:
Change

Code: Select all

buf[3] = (maskIndex != wxNOT_FOUND) ? 1 : 0;   // has transparency

To

Code: Select all

buf[3] = (maskIndex != wxNOT_FOUND) ? 1 | 2 << 2 : 0;   // has transparency

It's also need to set proper disposal flag.
http://www.u229.no/stuff/GIFFormat/

Now image goes in right way.

[doublemax]

Nice

If you found a bug in the wx sources (and even a fix for it), please report at http://trac.wxwidgets.org/

Also, could you show some complete, working code for what you did?