[lua] Add Image:clear(Rectangle, color) overload (fix #3799)

We can use:

  Image:clear()
  Image:clear(color)
  Image:clear(rectangle)
  Image:clear(rectangle, color)

If the color is not specified it will be the transparent color of the
image.

Co-authored-by: David Capello <david@igara.com>

src/app/script/image_class.cpp

@@ -220,13 +220,25 @@ int Image_clear(lua_State* L)
   auto obj = get_obj<ImageObj>(L, 1);
   auto img = obj->image(L);
   doc::color_t color;
-  if (lua_isnone(L, 2))
+  gfx::Rect rc;
+  int i = 2;
+
+  if (auto rcPtr = may_get_obj<gfx::Rect>(L, i)) {
+    rc = *rcPtr;
+    ++i;
+  }
+  else {
+    rc = img->bounds();         // Clear the whole image
+  }
+
+  if (lua_isnone(L, i))
     color = img->maskColor();
-  else if (lua_isinteger(L, 2))
-    color = lua_tointeger(L, 2);
+  else if (lua_isinteger(L, i))
+    color = lua_tointeger(L, i);
   else
-    color = convert_args_into_pixel_color(L, 2, img->pixelFormat());
-  doc::clear_image(img, color);
+    color = convert_args_into_pixel_color(L, i, img->pixelFormat());
+
+  doc::fill_rect(img, rc, color); // Clips the rectangle to the image bounds
   return 0;
 }
 

tests/scripts/image.lua

@@ -41,6 +41,27 @@ do
   assert(not a:isEmpty())
 end
 
+-- Clear
+do
+  local spec = ImageSpec{
+    width=2, height=2,
+    colorMode=ColorMode.INDEXED,
+    transparentColor=1 }
+
+  local img = Image(spec)
+  img:clear()
+  expect_img(img, { 1, 1,
+                    1, 1 })
+
+  img:clear(img.bounds)
+  expect_img(img, { 1, 1,
+                    1, 1 })
+
+  img:clear(Rectangle(1, 0, 1, 2), 2)
+  expect_img(img, { 1, 2,
+                    1, 2 })
+end
+
 -- Clone
 do
   local c = Image(a)