crop: Add light curtain to make out selection in dark areas

Previously, it was impossible to see the crop selection over dark
backgrounds. Remedy it by adding another bright shade. The default
`shade_opacity` has been updated to keep a similar brightness
before the change. Also fixes the `opts.shade_opacity` condition
as reviewed by the script author.

Ref: Sneakpeakcss/mpv-scripts@b617d20
     occivink/mpv-scripts#63

Author: Sneakpeakcss

script-opts/crop.conf

@@ -13,7 +13,8 @@ draw_frame=yes
 frame_border_width=1
 frame_border_color=EEEEEE
 # hexadecimal: 00 is opaque, FF is transparent
-shade_opacity=77
+shade_opacity=44
+light_opacity=CC
 mouse_support=yes
 disable_window_dragging=yes
 

scripts/crop.lua

@@ -1,7 +1,8 @@
 local opts = {
     mode = "hard", -- can be "hard" or "soft". If hard, use video-crop, if soft use zoom + pan. Or a bonus "delogo" mode
     draw_shade = true,
-    shade_opacity = "77",
+    shade_opacity = "44",
+    light_opacity = "CC",
     draw_frame = false,
     frame_border_width = 2,
     frame_border_color = "EEEEEE",
@@ -119,14 +120,14 @@ function video_norm_to_screen(point, dim)
     }
 end
 
-function draw_shade(ass, unshaded, window)
+function draw_shade(ass, unshaded, window, color, opacity)
     ass:new_event()
     ass:pos(0, 0)
     ass:append("{\\an7}")
     ass:append("{\\bord0}")
     ass:append("{\\shad0}")
-    ass:append("{\\c&H000000&}")
-    ass:append("{\\1a&H" .. opts.shade_opacity .. "}")
+    ass:append("{\\c&H" .. color .. "&}")
+    ass:append("{\\1a&H" .. opacity .. "}")
     ass:append("{\\2a&HFF}")
     ass:append("{\\3a&HFF}")
     ass:append("{\\4a&HFF}")
@@ -232,7 +233,12 @@ function draw_crop_zone()
                     top_left = { x = 0, y = 0 },
                     bottom_right = { x = dim.w, y = dim.h },
                 }
-                draw_shade(ass, frame, window)
+                if opts.light_opacity:lower() ~= "ff" then
+                    draw_shade(ass, frame, window, "FFFFFF", opts.light_opacity)
+                end
+                if opts.shade_opacity:lower() ~= "ff" then
+                    draw_shade(ass, frame, window, "000000", opts.shade_opacity)
+                end
             end
             if opts.draw_frame then
                 draw_frame(ass, frame)