Re: [9fans] nvidia scrolling performance

["Artem Letko" <aletko@gmail.com>]

what if we use hardware to do blits with alpha?

-art

On 5/1/06, Russ Cox <rsc@swtch.com> wrote:
> > why does the framebuffer need to be consulted when the background is a known,
> > solid color?
>
> the underlying operation is just plain draw,
> and drawing text corresponds to drawing
> solid black through the font (as a mask)
> onto the destination image.  if the mask has
> fractional alpha, that requires reading the
> destination image to do the mixing.
>
> the destination image might in this case
> be a known solid color, but in general it
> need not be.
>
> you could address this by adding a fourth argument
> to memdraw and then using it inside devdraw
> to specify a "read from this instead of the destination"
> image.  it's not clear to me that this is worth the bother,
> and it makes the interface less clean.  you'd also have
> to redo libframe to use stringbg everywhere.
>
> russ
>
>