avfilter/vf_drawvg: support color expressions as setvar/call arguments.

The arguments for `setvar` and `call` commands can be colors (like `#rrggbb`).
This replaces the previous trick of using `0xRRGGBBAA` values to use colors as
procedure arguments.

The parser stores colors as the value expected by Cairo (a `double[4]`). This
array is allocated on the heap so the size of the union in `VGSArgument` is
not increased (i.e. it is still 8 bytes, instead of 32).

Signed-off-by: Ayose <ayosec@gmail.com>

tests/ref/fate/filter-drawvg-interpreter

@@ -76,6 +76,16 @@ cairo_fill
 cairo_set_source #a8d8f0e6
 cairo_set_fill_rule 0
 cairo_fill
+cairo_set_source #abcdef66
+cairo_stroke
+cairo_set_source #123456ff
+cairo_stroke
+cairo_set_source #abcdef66
+cairo_stroke
+av_log[32]: [104:45] a0 = 1.000000 | [104:48] a2 = 123.000000
+cairo_set_source #50a0f033
+cairo_stroke
+av_log[32]: [104:45] a0 = -1.000000 | [104:48] a2 = -123.000000
 cairo_rel_line_to 1.0 3.0
 cairo_rel_line_to nan 0.0
 

tests/ref/lavf/drawvg.all

@@ -93,6 +93,18 @@ defhsla c1 200 0.7 0.8 0.9
 setcolor c0 fill
 setcolor c1 fill
 
+// Colors as arguments for setvar/call.
+setvar color0 #123456
+setvar color1 #abcdef@0.4
+setvar color2 color1
+setvar a 123
+
+setcolor color2 stroke
+setcolor color0 stroke
+proc f3 a0 a1 a2 { setcolor a1 stroke print a0 a2 }
+call f3 1 color1 a
+call f3 -1 #50A0F0@0.2 (-a)
+
 // Frame metadata
 getmetadata md0 m.a
 getmetadata md1 m.b