[Savage40] Image flip - Pro savage

[Tim Roberts]

Young Kim wrote:

> HI, we are developing a system that based on Windows XP embedded.
> The graphics chip we are using is S3 twister.
>
> We are trying to make 780x780 resolution and tried to twick some
> register.
> But the system occasionally flip the image horizontally and vertically
> - like a mirror diagonally.
> Then it flips back after some time.
>
> I am wondering if there are any register to flip the image - probably
> horizontal flip and vertical flip at the same time.
> We want to lock them right after boot up or monitor why those
> registers are changing.


Are you talking about the whole image flipping without any action on
your part?  That would be fascinating, because the Savage chips have no
registers to do that.  Indeed, many folks have asked for that feature,
to support notebook computers with displays that swivel.  It does have
the ability to do flipping during a blit operation; there are bits in
the blit command that specify which direction to blit in both X and Y.

What have you set the screen stride to?  That is, how many bytes from
the start of scanline 0 to scanline 1?  Remember that the Savages
require that the frame buffer stride be a multiple of 16 pixels.  That's
why, for example, on a laptop with a 1400x1050 panel, we have to set the
width of the frame buffer at 1408 pixels, even though we only display
the first 1400.  Those last 8 pixels are wasted.

In your case, you probably need to set up the frame buffer for a width
of 800 pixels, although 784 probably works, too.

Why on earth do you need a 780x780 display?

-- 
Tim Roberts, timr at probo.com
Providenza & Boekelheide, Inc.