[GuiScrollbar] Scrollbar limits fixed (#2022)

* [GuiScrollbar] Move copy/paste updates to onDraw, persist values

* [GuiScrollbar] Prevent draggable bar from dropping to below bottom arrow button

* [GuiScrollbar] Enable full range on large lists

* Problems with range calculations prevented access to full range in large lists
* These adjustments allow drag-scrolling to the end without any slop
* Tested on:
** Comms smaller than the window
** Comms larger than the window
** A log smaller than the window
** A log with 10,000 entries

---------

Co-authored-by: oznogon <[email protected]>

src/gui/gui2_scrollbar.cpp

@@ -24,24 +24,21 @@ void GuiScrollbar::onDraw(sp::RenderTarget& renderer)
 
     renderer.drawStretched(rect, back.texture, back.color);
 
-    int range = (max_value - min_value);
-    float arrow_size = rect.size.x / 2.0f;
-    float move_height = (rect.size.y - arrow_size * 2);
-    float bar_size = move_height * value_size / range;
-    if (bar_size > move_height)
-        bar_size = move_height;
-    renderer.drawStretched(sp::Rect(rect.position.x, rect.position.y + arrow_size + move_height * getValue() / range, rect.size.x, bar_size), front.texture, front.color);
+    // Update the bar's range, size, and draggable bar size.
+    range = max_value - min_value - value_size;
+    arrow_size = rect.size.x / 2.0f;
+    move_height = rect.size.y - arrow_size * 2;
+    // Clamp the size of the draggable bar to no less than 20px.
+    bar_size = std::clamp(move_height * value_size / (range + value_size), 20.0F, move_height);
+    // Set the bottom of the draggable bar no lower than the top of the bottom arrow.
+    const float bar_y = std::min((rect.position.y + arrow_size + (move_height - bar_size) * getValue() / range), rect.position.y + rect.size.y - arrow_size - bar_size);
+
+    renderer.drawStretched(sp::Rect(rect.position.x, bar_y, rect.size.x, bar_size), front.texture, front.color);
 }
 
 bool GuiScrollbar::onMouseDown(sp::io::Pointer::Button button, glm::vec2 position, sp::io::Pointer::ID id)
 {
-    int range = (max_value - min_value);
-    float arrow_size = rect.size.x / 2.0f;
-    float move_height = (rect.size.y - arrow_size * 2);
-    float bar_size = move_height * value_size / range;
-    if (bar_size > move_height)
-        bar_size = move_height;
-    float bar_y = rect.position.y + arrow_size + move_height * getValue() / range;
+    float bar_y = rect.position.y + arrow_size + (move_height - bar_size) * getValue() / range;
     if (position.y >= bar_y && position.y <= bar_y + bar_size)
     {
         drag_scrollbar = true;
@@ -56,39 +53,25 @@ void GuiScrollbar::onMouseDrag(glm::vec2 position, sp::io::Pointer::ID id)
 {
     if (drag_scrollbar)
     {
-        float arrow_size = rect.size.x / 2.0f;
-        int range = (max_value - min_value);
-        float move_height = (rect.size.y - arrow_size * 2);
-        float bar_size = move_height * value_size / range;
-        if (bar_size > move_height)
-            bar_size = move_height;
-
         float target_y_offset = position.y - drag_select_offset - (rect.position.y + arrow_size);
         target_y_offset = std::max(target_y_offset, 0.0f);
         target_y_offset = std::min(target_y_offset, move_height - bar_size);
 
         if (bar_size < move_height)
-            setValue(int(target_y_offset / move_height * range + 0.5f));
+            setValue(int(target_y_offset / (move_height - bar_size) * range + 0.5f));
     }
 }
 
 void GuiScrollbar::onMouseUp(glm::vec2 position, sp::io::Pointer::ID id)
 {
     if (!drag_scrollbar)
     {
-        float arrow_size = rect.size.x / 2.0f;
-        int range = (max_value - min_value);
-        float move_height = (rect.size.y - arrow_size * 2);
-        float bar_size = move_height * value_size / range;
-        if (bar_size > move_height)
-            bar_size = move_height;
-
         float target_y_offset = position.y - bar_size / 2.0f - (rect.position.y + arrow_size);
         target_y_offset = std::max(target_y_offset, 0.0f);
         target_y_offset = std::min(target_y_offset, move_height - bar_size);
 
         if (bar_size < move_height)
-            setValue(int(target_y_offset / move_height * range + 0.5f));
+            setValue(int(target_y_offset / (move_height - bar_size) * range + 0.5f));
     }
 }
 
@@ -126,6 +109,7 @@ int GuiScrollbar::getValue() const
         value = max_value - value_size;
     if (value < min_value)
         value = min_value;
+
     return value;
 }
 

src/gui/gui2_scrollbar.h

@@ -20,6 +20,11 @@ class GuiScrollbar : public GuiElement
     bool drag_scrollbar;
     float drag_select_offset;
 
+    int range;
+    float arrow_size;
+    float move_height;
+    float bar_size;
+
     const GuiThemeStyle* back_style;
     const GuiThemeStyle* front_style;
 public: