On Mon, 2013-07-22 at 06:06 +0200, Grigori Goronzy wrote:
> Subpixel text rendering is typically done with a solid src and a
> pixmap mask. Traditionally, this cannot be accelerated in a single
> pass and requires two passes [1]. However, we can cheat a little
> with a constant blend color.
>
> We can use:
>
> const.A = src.A / src.A
> const.R = src.R / src.A
> const.G = src.G / src.A
> const.B = src.B / src.A
>
> dst.A = const.A * (src.A * mask.A) + (1 - (src.A * mask.A)) * dst.A
> dst.R = const.R * (src.A * mask.R) + (1 - (src.A * mask.R)) * dst.R
> dst.G = const.G * (src.A * mask.G) + (1 - (src.A * mask.G)) * dst.G
> dst.B = const.B * (src.A * mask.B) + (1 - (src.A * mask.B)) * dst.B
>
> This only needs a single source value. src.A is cancelled down in
> the right places.
>
> [1] http://anholt.livejournal.com/32058.html
Like Roland, I wonder if this trick couldn't be done in EXA instead of
in the driver?
> diff --git a/src/evergreen_exa.c b/src/evergreen_exa.c
> index 5b8a631..ee5b06b 100644
> --- a/src/evergreen_exa.c
> +++ b/src/evergreen_exa.c
> @@ -704,6 +704,14 @@ static uint32_t EVERGREENGetBlendCntl(int op, PicturePtr
> pMask, uint32_t dst_for
> } else if (dblend == (BLEND_ONE_MINUS_SRC_ALPHA <<
> COLOR_DESTBLEND_shift)) {
> dblend = (BLEND_ONE_MINUS_SRC_COLOR << COLOR_DESTBLEND_shift);
> }
> +
> + /* With some tricks, we can still accelerate PictOpOver with solid src.
> + * This is commonly used for text rendering, so it's worth the extra
> + * effort.
> + */
> + if (sblend == (BLEND_ONE << COLOR_SRCBLEND_shift)) {
> + sblend = (BLEND_CONSTANT_COLOR << COLOR_SRCBLEND_shift);
> + }
Is this correct for all cases where (sblend == (BLEND_ONE <<
COLOR_SRCBLEND_shift))?
> if (EVERGREENBlendOp[op].src_alpha &&
> (EVERGREENBlendOp[op].blend_cntl & COLOR_SRCBLEND_mask) !=
> (BLEND_ZERO << COLOR_SRCBLEND_shift)) {
> - RADEON_FALLBACK(("Component alpha not supported with source
> "
> - "alpha and source value blending.\n"));
> + if (pSrcPicture->pDrawable || op != 3)
> + RADEON_FALLBACK(("Component alpha not supported with
> source "
> + "alpha and source value blending.\n"));
> }
> }
Please use PictOpOver instead of the magic number 3.
--
Earthling Michel Dänzer | http://www.amd.com
Libre software enthusiast | Debian, X and DRI developer
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