dib fixes

[Rein Klazes]

On Sat, 09 Apr 2005 07:15:43 +0200, you wrote:


> > I am looking into a couple of crashes in dlls/x11drv/dib.c caused by a
> > patch from you. The patch (attached) is only 5 years old, I am sure you
> > remember all the details ;)
> sure... since RLE encoding can have holes (ie, it can jump a couple of pixels or 
> lines ahead),

That is what I was wondering about.

> when you need to render a RLE image, you need to:
> - paint the pixels from RLE (for the ones that are defined in RLE)
> - and keep the previous pixels (from the underlying bitmap) for the ones not in RLE
> The aim of the patch is to implement this by:
> - first getting a whole copy of the old bitmap
> - then paint the RLE pixels on it
> This can be really suboptimal when the RLE contains all the pixels (they get 
> changed twice)

I see.

> 
> > To be precise, I get X-errors in the calls to XGetSubImage caused by out
> > of range parameters. Fixing this by some parameter checking is not the
> > big problem, but I wonder if it is still necessary to have those calls
> > there.
> > 
> > You call it a "quick hack", would it not be better to remove it now and
> > properly fix any problems that may surface? The patch that I sent in
> > yesterday ( "fix decoding compressed dibs") is an example of such
> > problem..
> 
> IMO, what you're seeing is that getting the bitmap isn't cropped against all 
> possible dimensions & boundaries.

Are you suggesting more checks then that the pixels are within the
dimensions of the drawable?

> So the fixes are either:
> - check the boundaries
> - rewrite the RLE expander to behave properly pixels not defined in RLE

Thanks for the clarification.

Rein.