Re: miext/shadow/shrotate.c speedup and question

On Tue, 21 Sep 2005, Staffan Ulfberg wrote:

> I have a Sharp Zaurus C3100, where X normally runs rotated 90 degrees,
> using a shadow framebuffer.  I've been hacking a bit on getting the
> code that blits a rotated shadow onto the display a bit faster and
> came up with the included patch.

> Blitting in rotated mode is about 4x the previous speed.  Non-rotated
> copies are about the same speed; maybe up to 10% slower for small
> rectangles (on the Zaurus).

> The idea is to copy the area in blocks of 32x32 pixels, to reduce the
> number of cache misses, which are unavoidable when walking either the
> source or the destination bitmap across the scanlines.  16x16, 24x24,
> andd 32x32 yields about the same result, so I chose 32x32 since it
> seems best for the non-rotated modes.

> Any comments on this patch?

This looks good to me.  I have committed it.

> I have a question myself about the original code: This is the function
> call to get the address in the destination frame buffer to write to:

> 	  win = (FbBits *) (*pBuf->window) (pScreen,
> 					    scr_y,
> 					    scr_x << 2,
> 					    SHADOW_WINDOW_WRITE,
> 					    &winSize,
> 					    pBuf->closure);

> The "scr_x << 2" part seems, to me, to assume that
> sizeof(FbBits) == 4.  Am I missing something, or is this really
> correct?  Anyway, my patch does not make this problem either better
> or worse, but this is a chance to fix it if it is a bug...

As we compile this, FbBits will always be a CARD32.

Thanks for the patch.

Marc.

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