crop: Improve click-and-drag crop selection

Second take of d5306ca because I noticed Sneakpeakcss didn't fully
implement click-and-drag crop selection exactly as in the original PR.
Previously, you had to click the first point before you can hold and
drag to crop.

This commit integrates po5's complex keybinds changes, allowing you to
start, select and submit the crop in a single hold-and-drag operation!

One of the roadblock to patching po5's PR directly was the condition
`or (crop_first_corner.x == corner_video.x and crop_first_corner.y ==
corner_video.y)`. It was causing errors due to a missing `corner_video`
variable, which was removed in occivink/mpv-scripts@af360f3. Thus, I've
partially restored the variable to fix this.

Note: Unlike Sneakpeakcss's version, click-and-drag and point-and-click
are mutually exclusive. You can't click to start the crop, then
hold-and-drag to select the area. It was unintuitive anyways.

Ref: occivink/mpv-scripts#62

Author: po5

scripts/crop.lua

@@ -345,8 +345,11 @@ function update_crop_zone_state()
         return
     end
     cursor = clamp_point(cursor, dim)
-    if crop_first_corner == nil then
-        crop_first_corner = screen_to_video_norm(cursor, dim)
+    local corner_video = screen_to_video_norm(cursor, dim)
+    if crop_first_corner == nil or
+       (crop_first_corner.x == corner_video.x and
+        crop_first_corner.y == corner_video.y) then
+        crop_first_corner = corner_video
         redraw()
     else
         local c1, c2 = rect_from_two_points(
@@ -362,23 +365,24 @@ function update_crop_zone_state()
 end
 
 local bindings = {}
+local bindings_complex = {}
 local bindings_repeat = {}
 
 function cancel_crop()
     crop_first_corner = nil
     for key, _ in pairs(bindings) do
         mp.remove_key_binding("crop-"..key)
     end
+    for key, _ in pairs(bindings_complex) do
+        mp.remove_key_binding("crop-"..key)
+    end
     for key, _ in pairs(bindings_repeat) do
         mp.remove_key_binding("crop-"..key)
     end
     mp.unobserve_property(redraw)
     mp.unregister_idle(draw_crop_zone)
     mp.set_osd_ass(1280, 720, '')
     active = false
-    if opts.disable_window_dragging and not mp.get_property_bool("window-dragging") then
-        mp.set_property_bool("window-dragging", true)
-    end
 end
 
 -- adjust coordinates based on previous values
@@ -539,6 +543,9 @@ function start_crop(mode)
     for key, func in pairs(bindings) do
         mp.add_forced_key_binding(key, "crop-"..key, func)
     end
+    for key, func in pairs(bindings_complex) do
+        mp.add_forced_key_binding(key, "crop-"..key, func, { complex = true })
+    end
     for key, func in pairs(bindings_repeat) do
         mp.add_forced_key_binding(key, "crop-"..key, func, { repeatable = true })
     end
@@ -577,7 +584,18 @@ if opts.mouse_support then
     bindings["MOUSE_MOVE"] = function() cursor.x, cursor.y = mp.get_mouse_pos(); redraw() end
 end
 for _, key in ipairs(opts.accept) do
-    bindings[key] = update_crop_zone_state
+    if string.find(key:lower(), "btn") then
+        bindings_complex[key] = function(mouse)
+            if opts.disable_window_dragging then
+                mp.set_property_bool("window-dragging", mouse["event"] ~= "down")
+            end
+            if crop_first_corner == nil or mouse["event"] ~= "down" then
+                update_crop_zone_state()
+            end
+        end
+    else
+        bindings[key] = update_crop_zone_state
+    end
 end
 for _, key in ipairs(opts.cancel) do
     bindings[key] = cancel_crop