Re: RFC: bitmap line alignment

[Knut Petersen <Knut_Petersen@t-online.de>]

Hi Tony,

>If you create your own info->pixmap and an info->pixmap.scan_align = 4, the
>driver will be fed a bitmap that have a scanline that is 32-bit aligned.
>The default if you don't specify anything, of course, will be an 8-bit
>aligned bitmap which, for the sake of code efficiency, is the alignment
>assumed by the cfb_* drawing functions.
>
>(An example usage is in the patch I attached just a few days ago when
>I commented how the cyberblade should be intelligent enough to handle
>bitmaps with variable widths.)
>  
>
Well, here is what I did:  A quick look at the changes in 
cyblafb_imageblit made
it very clear to me that the code could not work as I assumed a totaly 
wrong format
for the image data. To me it was obvious from a look at skeletonfb that 
the data was
a continous bit field without anything like alignment gaps. Anyway, I 
was already
in the process of repeatedly locking up my PC with an accel function 
that was based
on that wrong assumption (I sent data until I reached the erroneously 
calculated end
of the data buffer, the accel engine waited for more data, got a new 
command in
between and locked everything). Yesterday I even attached an old VT 220 for
debugging, and that showed me that the data is byte aligned. Then it was 
easy to write
a much too complicated bitblit for that data with 8 bit pixelline alignment.

I assume by now you are ROTFL ;-)

I think a comment in skeletonfb would be a good idea.

cu,
 Knut




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