gui: improve scroll bar thumb size and appearance

Author: eruvanos

arcade/gui/experimental/scroll_area.py

@@ -18,7 +18,7 @@
     UIMouseReleaseEvent,
     UIMouseScrollEvent,
     UIWidget,
-    bind,
+    bind, UIKeyPressEvent,
 )
 from arcade.types import LBWH
 
@@ -42,7 +42,7 @@ def __init__(self, scroll_area: UIScrollArea, vertical: bool = True):
         self.with_border(color=arcade.uicolor.GRAY_CONCRETE)
         self.vertical = vertical
 
-        self._scroll_bar_size = 20
+        # self._scroll_bar_size = 20
 
         bind(self, "_thumb_hover", self.trigger_render)
         bind(self, "_dragging", self.trigger_render)
@@ -52,6 +52,10 @@ def __init__(self, scroll_area: UIScrollArea, vertical: bool = True):
         bind(scroll_area, "content_width", self.trigger_full_render)
 
     def on_event(self, event: UIEvent) -> Optional[bool]:
+        # check if we are scrollable
+        if not self._scrollable():
+            return EVENT_UNHANDLED
+
         # detect if event is mouse down and inside the scroll thumb
         # if so, start dragging the thumb
         thumb_rect_relative = self._thumb_rect()
@@ -68,20 +72,20 @@ def on_event(self, event: UIEvent) -> Optional[bool]:
         # if so, update the scroll position
         if isinstance(event, UIMouseDragEvent) and self._dragging:
             sx, sy = event.pos - self.rect.bottom_left
-            sx -= self._scroll_bar_size / 2
-            sy -= self._scroll_bar_size / 2
+            sx -= self._scroll_bar_size() / 2
+            sy -= self._scroll_bar_size() / 2
 
             scroll_area = self.scroll_area
 
             if self.vertical:
-                available_track_size = self.content_height - self._scroll_bar_size
+                available_track_size = self.content_height - self._scroll_bar_size()
                 target_progress = 1 - sy / available_track_size
                 target_progress = max(0, min(1, target_progress))
 
                 scroll_range = scroll_area.surface.height - scroll_area.content_height
                 scroll_area.scroll_y = -target_progress * scroll_range
             else:
-                available_track_size = self.content_width - self._scroll_bar_size
+                available_track_size = self.content_width - self._scroll_bar_size()
                 target_progress = sx / available_track_size
                 target_progress = max(0, min(1, target_progress))
                 scroll_range = scroll_area.surface.width - scroll_area.content_width
@@ -95,7 +99,28 @@ def on_event(self, event: UIEvent) -> Optional[bool]:
             self._dragging = False
             return True
 
+        if isinstance(event, UIKeyPressEvent):
+            print(self._scroll_bar_size())
+
         return EVENT_UNHANDLED
+    
+    def _scroll_bar_size(self):
+        # based on: https://stackoverflow.com/a/16367035
+
+        content_size = self.scroll_area.surface.height if self.vertical else self.scroll_area.surface.width
+        view_size = self.scroll_area.content_height if self.vertical else self.scroll_area.content_width
+        ratio = view_size / content_size
+
+        scoll_range = self.content_height if self.vertical else self.content_width
+
+        return scoll_range * ratio
+
+    def _scrollable(self):
+        return (
+            self.scroll_area.surface.height - self.scroll_area.content_height
+            if self.vertical
+            else self.scroll_area.surface.width - self.scroll_area.content_width
+        ) > 0
 
     def _thumb_rect(self):
         """Calculate the rect of the thumb."""
@@ -108,24 +133,24 @@ def _thumb_rect(self):
             else scroll_area.surface.width - scroll_area.content_width
         )
 
-        if scroll_range <= 0:
-            # content is smaller than the scroll area, no need for a thumb
-            return XYWH(0, 0, 0, 0)
+        if not self._scrollable():
+            # content is smaller than the scroll area, full size thumb
+            return LBWH(0,0, self.content_width, self.content_height)
 
         scroll_progress = -scroll_value / scroll_range
 
         content_size = self.content_height if self.vertical else self.content_width
-        available_track_size = content_size - self._scroll_bar_size
+        available_track_size = content_size - self._scroll_bar_size()
 
         if self.vertical:
-            scroll_bar_y = self._scroll_bar_size / 2 + available_track_size * (1 - scroll_progress)
+            scroll_bar_y = self._scroll_bar_size() / 2 + available_track_size * (1 - scroll_progress)
             scroll_bar_x = self.content_width / 2
-            return XYWH(scroll_bar_x, scroll_bar_y, self.content_width, self._scroll_bar_size)
+            return XYWH(scroll_bar_x, scroll_bar_y, self.content_width, self._scroll_bar_size())
 
         else:
-            scroll_bar_x = self._scroll_bar_size / 2 + available_track_size * scroll_progress
+            scroll_bar_x = self._scroll_bar_size() / 2 + available_track_size * scroll_progress
             scroll_bar_y = self.content_height / 2
-            return XYWH(scroll_bar_x, scroll_bar_y, self._scroll_bar_size, self.content_height)
+            return XYWH(scroll_bar_x, scroll_bar_y, self._scroll_bar_size(), self.content_height)
 
     def do_render(self, surface: Surface):
         """Render the scroll bar."""