Re: Re: bits_per_pixel query

Re: Re: bits_per_pixel query

[Linux PPC]

On Mon, 09 Sep 2002 Antonino Daplas wrote :
>Just pad the pitch/line_length/stride of the buffer to the next 
>byte
>alignment your hardware is capable of.  It is acceptable to have 
>excess
>bits/bytes which theoretically your hardware will ignore.

The padding is at the end of the line_length, or
at the end of the pixel data? I tried both ways,
but I'm getting a skewed square, which I draw
using a user space application.

>For static pseudocolor and truecolor, that is true, since 0 is 
>hardwired
>to black.  For pseudocolor and directcolor, that depends on how 
>the
>DAC/palette is loaded. In most cases, it will produce a black 
>screen.

For psuedocolor and direct color, does the pixel
data, have the index into the colormap or does it
have actual colors? If it has the index, then the size of the 
buffer would be lesser: right?

Thanks,

- navin.

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Re: Re: bits_per_pixel query

[Geert Uytterhoeven]

On 11 Sep 2002, Linux  PPC wrote:
> On Mon, 09 Sep 2002 Antonino Daplas wrote :
> >Just pad the pitch/line_length/stride of the buffer to the next 
> >byte
> >alignment your hardware is capable of.  It is acceptable to have 
> >excess
> >bits/bytes which theoretically your hardware will ignore.
> 
> The padding is at the end of the line_length, or
> at the end of the pixel data? I tried both ways,
> but I'm getting a skewed square, which I draw
> using a user space application.

The padding is at the end of the line.

If fix.line_length != 0, the line length (in bytes) is fix.line_length, and the
padding is fix.line_length-var.xres_virtual*var.bits_per_pixel/8.
If fix.line_length == 0, the line length (in bytes) is
var.xres_virtual*var.bits_per_pixel/8 and there is no padding.
 
> >For static pseudocolor and truecolor, that is true, since 0 is 
> >hardwired
> >to black.  For pseudocolor and directcolor, that depends on how 
> >the
> >DAC/palette is loaded. In most cases, it will produce a black 
> >screen.
> 
> For psuedocolor and direct color, does the pixel
> data, have the index into the colormap or does it
> have actual colors? If it has the index, then the size of the 
> buffer would be lesser: right?

In pseudocolor and directcolor, the pixel data is a colormap index. Pixels
always have a size of var.bits_per_pixel bits.

Gr{oetje,eeting}s,

						Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
							    -- Linus Torvalds



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