[Mesa-dev] [PATCH v2] i915/aa: fixing anti-aliasing bug for thinnest width lines

[Brian Paul]

On 09/09/2015 07:59 AM, Marius Predut wrote:
> On PNV platform, for 1 pixel line thickness or less,
> the general anti-aliasing algorithm gives up, and a garbage line is generated.
> Setting a Line Width of 0.0 specifies the rasterization
> of the "thinnest" (one-pixel-wide), non-antialiased lines.
> Lines rendered with zero Line Width are rasterized using
> Grid Intersection Quantization rules as specified by bspec G45: Volume 2: 3D/Media,
> 7.3.13.1 Zero-Width (Cosmetic) Line Rasterization section.
>
> This patch follow the same rules as patches fixing the
> https://bugs.freedesktop.org/show_bug.cgi?id=28832
> bug.
>
> v1: Eduardo Lima Mitev:  Wrong indentation inside the if clause.
>
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=90367
>
> Signed-off-by: Marius Predut <marius.predut at intel.com>
> ---
>   src/mesa/drivers/dri/i915/i915_state.c | 15 +++++++++++++++
>   1 file changed, 15 insertions(+)
>
> diff --git a/src/mesa/drivers/dri/i915/i915_state.c b/src/mesa/drivers/dri/i915/i915_state.c
> index 4c83073..ebb4e9a 100644
> --- a/src/mesa/drivers/dri/i915/i915_state.c
> +++ b/src/mesa/drivers/dri/i915/i915_state.c
> @@ -599,6 +599,21 @@ i915LineWidth(struct gl_context * ctx, GLfloat widthf)
>
>      width = (int) (widthf * 2);
>      width = CLAMP(width, 1, 0xf);
> +
> +   if (ctx->Line.Width < 1.5 || widthf < 1.5) {

By using "1.5f" we can avoid some float/double conversion.


> +     /* For 1 pixel line thickness or less, the general
> +      * anti-aliasing algorithm gives up, and a garbage line is
> +      * generated.  Setting a Line Width of 0.0 specifies the
> +      * rasterization of the "thinnest" (one-pixel-wide),
> +      * non-antialiased lines.
> +      *
> +      * Lines rendered with zero Line Width are rasterized using
> +      * Grid Intersection Quantization rules as specified by
> +      * bspec G45: Volume 2: 3D/Media,

bspec?

> +      * 7.3.13.1 Zero-Width (Cosmetic) Line Rasterization section
> +      */
> +      width = 0;
> +   }
>      lis4 |= width << S4_LINE_WIDTH_SHIFT;
>
>      if (lis4 != i915->state.Ctx[I915_CTXREG_LIS4]) {
>