[PATCH xserver 1/4] glamor: fix repeat-reflect case in linear gradient shader

[Jeff Smith]

If _pt_distance is negative, it causes the final distance to be negative
in the repeat-reflect case.  Moving the scaling by _pt_distance earlier
avoids this problem, and simplifies some equations as a bonus.

Bugzilla: https://bugs.freedesktop.org/98508
Signed-off-by: Jeff Smith <whydoubt at gmail.com>
---
 glamor/glamor_gradient.c | 11 ++++-------
 1 file changed, 4 insertions(+), 7 deletions(-)

diff --git a/glamor/glamor_gradient.c b/glamor/glamor_gradient.c
index 2f2a5cc9b..d492f6951 100644
--- a/glamor/glamor_gradient.c
+++ b/glamor/glamor_gradient.c
@@ -456,7 +456,6 @@ _glamor_create_linear_gradient_program(ScreenPtr screen, int stops_count,
 	    "float get_stop_len()\n"\
 	    "{\n"\
 	    "    vec3 tmp = vec3(source_texture.x, source_texture.y, 1.0);\n"\
-	    "    float len_percentage;\n"\
 	    "    float distance;\n"\
 	    "    float _p1_distance;\n"\
 	    "    float _pt_distance;\n"\
@@ -482,19 +481,17 @@ _glamor_create_linear_gradient_program(ScreenPtr screen, int stops_count,
 	    "        _pt_distance = pt_distance * source_texture_trans.z;\n"\
 	    "    } \n"\
 	    "    \n"\
-	    "    distance = distance - _p1_distance; \n"\
+	    "    distance = (distance - _p1_distance) / _pt_distance;\n"\
 	    "    \n"\
 	    "    if(repeat_type == %d){\n" /* repeat normal*/\
-	    "        distance = mod(distance, _pt_distance);\n"\
+	    "        distance = fract(distance);\n"\
 	    "    }\n"\
 	    "    \n"\
 	    "    if(repeat_type == %d) {\n" /* repeat reflect*/\
-	    "        distance = abs(mod(distance + _pt_distance, 2.0 * _pt_distance) - _pt_distance);\n"\
+	    "        distance = abs(fract(distance * 0.5 + 0.5) * 2.0 - 1.0);\n"\
 	    "    }\n"\
 	    "    \n"\
-	    "    len_percentage = distance/(_pt_distance);\n"\
-	    "    \n"\
-	    "    return len_percentage;\n"\
+	    "    return distance;\n"\
 	    "}\n"\
 	    "\n"\
 	    "void main()\n"\
-- 
2.14.3