Don't paint invisible background-colored rounded corners (#7046)

* Don't paint invisible background-colored rounded corners

Made obvious when testing #7042

* Only enforce a highlight radius on buttons that don't already set a
custom one ;).

(Mostly, square buttons with a 0 radius ^^).

ffi/blitbuffer already handles radius being nil, which suits us just fine
:)

frontend/ui/widget/button.lua

@@ -44,7 +44,7 @@ local Button = InputContainer:new{
     margin = 0,
     bordersize = Size.border.button,
     background = Blitbuffer.COLOR_WHITE,
-    radius = Size.radius.button,
+    radius = nil,
     padding = Size.padding.button,
     padding_h = nil,
     padding_v = nil,
@@ -233,6 +233,11 @@ function Button:onTapSelectButton()
             --       c.f., #4554 & #4541
             -- NOTE: self[1] -> self.frame, if you're confused about what this does vs. onFocus/onUnfocus ;).
             if self.text then
+                -- We only want the button's *highlight* to have rounded corners (otherwise they're redundant, same color as the bg).
+                -- The nil check is to discriminate the default from callers that explicitly request a specific radius.
+                if self[1].radius == nil then
+                    self[1].radius = Size.radius.button
+                end
                 UIManager:widgetRepaint(self[1], self[1].dimen.x, self[1].dimen.y)
             end
             UIManager:setDirty(nil, function()
@@ -245,11 +250,13 @@ function Button:onTapSelectButton()
                     -- widget no more there (destroyed, re-init'ed by setText(), or not inverted: nothing to invert back
                     return
                 end
+
                 self[1].invert = false
-                UIManager:widgetRepaint(self[1], self[1].dimen.x, self[1].dimen.y)
-                if self.text then
-                    UIManager:widgetRepaint(self[1], self[1].dimen.x, self[1].dimen.y)
+                -- Since we kill the corners, we only need a single repaint.
+                if self[1].radius == Size.radius.button then
+                    self[1].radius = nil
                 end
+                UIManager:widgetRepaint(self[1], self[1].dimen.x, self[1].dimen.y)
                 UIManager:setDirty(nil, function()
                     return "fast", self[1].dimen
                 end)

frontend/ui/widget/container/framecontainer.lua

@@ -28,7 +28,7 @@ local FrameContainer = WidgetContainer:new{
     background = nil,
     color = Blitbuffer.COLOR_BLACK,
     margin = 0,
-    radius = 0,
+    radius = nil,
     inner_bordersize = 0,
     bordersize = Size.border.window,
     padding = Size.padding.default,