feat: add option to only draw whitespace if it is within selection (#1312)

* refactor: remove sort_positions usage
* refactor: move draw conditional to has_any_selection and other changes
  - snake case (sssss)
  - break after finding selection
* fix: typo of config plugins
* fix: do check for show selected only properly
* feat: only draw within selection per substitution
* `drawwhitespace`: Make `show_selected_only` work properly

---------

Co-authored-by: Guldoman <giulio.lettieri@gmail.com>

data/plugins/drawwhitespace.lua

@@ -1,5 +1,6 @@
 -- mod-version:3
 
+local core = require "core"
 local style = require "core.style"
 local DocView = require "core.docview"
 local common = require "core.common"
@@ -11,6 +12,7 @@ config.plugins.drawwhitespace = common.merge({
   show_leading = true,
   show_trailing = true,
   show_middle = true,
+  show_selected_only = false,
 
   show_middle_min = 1,
 
@@ -64,6 +66,13 @@ config.plugins.drawwhitespace = common.merge({
       type = "toggle",
       default = true,
     },
+    {
+      label = "Show Selected Only",
+      description = "Only draw whitespaces if it is within a selection.",
+      path = "show_selected_only",
+      type = "toggle",
+      default = false,
+    },
     {
       label = "Show Trailing as Error",
       description = "Uses an error square to spot them easily, requires 'Show Trailing' enabled.",
@@ -292,11 +301,41 @@ function DocView:draw_line_text(idx, x, y)
   for i=1,#cache,4 do
     local tx = cache[i + 1] + x
     local tw = cache[i + 2]
-    if tx <= x2 then
     local sub = cache[i]
     local color = cache[i + 3]
-      if tx + tw >= x1 then
+    local partials = {}
-        tx = renderer.draw_text(font, sub, tx, ty, color)
+    if config.plugins.drawwhitespace.show_selected_only and self.doc:has_any_selection() then
+      for _, l1, c1, l2, c2 in self.doc:get_selections(true) do
+        if idx > l1 and idx < l2 then
+          -- Between selection lines, so everything is selected
+          table.insert(partials, false)
+        elseif idx == l1 and idx == l2 then
+          -- Both ends of the selection are on the same line
+          local _x1 = math.max(cache[i + 1], self:get_col_x_offset(idx, c1))
+          local _x2 = math.min((cache[i + 1] + tw), self:get_col_x_offset(idx, c2))
+          if _x1 < _x2 then
+            table.insert(partials, {_x1 + x, 0, _x2 - _x1, math.huge})
+          end
+        elseif idx >= l1 and idx <= l2 then
+          -- On one of the selection ends
+          if idx == l1 then -- Start of the selection
+            local _x = math.max(cache[i + 1], self:get_col_x_offset(idx, c1))
+            table.insert(partials, {_x + x, 0, math.huge, math.huge})
+          else -- End of the selection
+            local _x = math.min((cache[i + 1] + tw), self:get_col_x_offset(idx, c2))
+            table.insert(partials, {0, 0, _x + x, math.huge})
+          end
+        end
+      end
+    end
+
+    if #partials == 0 and not config.plugins.drawwhitespace.show_selected_only then
+      renderer.draw_text(font, sub, tx, ty, color)
+    else
+      for _, p in pairs(partials) do
+        if p then core.push_clip_rect(table.unpack(p)) end
+        renderer.draw_text(font, sub, tx, ty, color)
+        if p then core.pop_clip_rect() end
       end
     end
   end