[Mesa-dev] [PATCH 2/2] draw: fix line stippling with aa lines

[sroland at vmware.com]

From: Roland Scheidegger <sroland at vmware.com>

In contrast to non-aa, where stippling is based on either dx or dy
(depending on if it's a x or y major line), stippling is based on
actual distance with smooth lines, so adjust for this.

(It looks like there's some minor artifacts with mesa demos
line-sample with wide lines, I think there might be some issues
with wide lines and very short line segments (when the original
line segment length is below half a pixel) but it may be related
to aa lines rather than stippling.)
---
 src/gallium/auxiliary/draw/draw_pipe_stipple.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/src/gallium/auxiliary/draw/draw_pipe_stipple.c b/src/gallium/auxiliary/draw/draw_pipe_stipple.c
index 3a84d6c..8fa8274 100644
--- a/src/gallium/auxiliary/draw/draw_pipe_stipple.c
+++ b/src/gallium/auxiliary/draw/draw_pipe_stipple.c
@@ -50,6 +50,7 @@ struct stipple_stage {
    float counter;
    uint pattern;
    uint factor;
+   bool smooth;
 };
 
 
@@ -136,9 +137,15 @@ stipple_line(struct draw_stage *stage, struct prim_header *header)
    float dx = x0 > x1 ? x0 - x1 : x1 - x0;
    float dy = y0 > y1 ? y0 - y1 : y1 - y0;
 
-   float length = MAX2(dx, dy);
+   float length;
    int i;
 
+   if (stipple->smooth) {
+      length = sqrtf(dx*dx + dy*dy);
+   } else {
+      length = MAX2(dx, dy);
+   }
+
    if (header->flags & DRAW_PIPE_RESET_STIPPLE)
       stipple->counter = 0;
 
@@ -205,6 +212,7 @@ stipple_first_line(struct draw_stage *stage,
 
    stipple->pattern = draw->rasterizer->line_stipple_pattern;
    stipple->factor = draw->rasterizer->line_stipple_factor + 1;
+   stipple->smooth = draw->rasterizer->line_smooth;
 
    stage->line = stipple_line;
    stage->line(stage, header);
-- 
2.7.4