avfilter/vf_drawvg: round color values to avoid differences on some platforms

This ensures consistent color conversion between double and u8 and
guarantees that values remain consistent across different platforms,
especially when x87 math is used.

Note that libcairo also performs rounding internally when converting
doubles to integers, see _cairo_color_double_to_short().

Fixes: fate-filter-drawvg-interpreter
Signed-off-by: Kacper Michajłow <kasper93@gmail.com>

libavfilter/tests/drawvg.c

@@ -167,7 +167,7 @@ void cairo_set_source(cairo_t *cr, cairo_pattern_t *source) {
     printf("%s", __func__);
 
 #define PRINT_COLOR(prefix) \
-    printf(prefix "#%02x%02x%02x%02x", (int)(r*255), (int)(g*255), (int)(b*255), (int)(a*255))
+    printf(prefix "#%02lx%02lx%02lx%02lx", lround(r*255), lround(g*255), lround(b*255), lround(a*255))
 
     switch (cairo_pattern_get_type(source)) {
     case CAIRO_PATTERN_TYPE_SOLID:

libavfilter/vf_drawvg.c

@@ -1981,7 +1981,7 @@ static int vgs_eval(
                 b = numerics[3];
             }
 
-            #define C(v, o) ((uint32_t)(av_clipd(v, 0, 1) * 255) << o)
+            #define C(v, o) ((uint32_t)lround(av_clipd(v, 0, 1) * 255) << o)
 
             state->vars[user_var] = (double)(
                 C(r, 24)

tests/ref/fate/filter-drawvg-interpreter

@@ -64,16 +64,16 @@ cairo_set_dash [ -1.0 ] 4.0
 cairo_set_dash [ ] 0.0
 cairo_move_to 1.0 2.0
 cairo_rel_line_to -1.0 -2.0
-cairo_set_source #19334c66
+cairo_set_source #1a334d66
 cairo_set_fill_rule 0
 cairo_fill
-cairo_set_source #475b3d66
+cairo_set_source #475c3d66
 cairo_set_fill_rule 0
 cairo_fill
-cairo_set_source #7f99b2cc
+cairo_set_source #8099b3cc
 cairo_set_fill_rule 0
 cairo_fill
-cairo_set_source #a8d7efe5
+cairo_set_source #a8d8f0e6
 cairo_set_fill_rule 0
 cairo_fill
 cairo_rel_line_to 1.0 3.0