Add vertical slider support to bevy_ui_widgets slider

[DuckyBlender]

Objective

• Fixes the issue of vertical sliders not being functional. Previously, when creating a vertical slider, the slider drag behavior was still horizontal, meaning dragging left/right would change the value instead of dragging up/down. Additionally, clicking on the slider track was offset and didn't correctly map to the clicked position.

Solution

The slider widget now automatically detects its orientation based on the node's dimensions (height > width for vertical, otherwise horizontal) and adjusts its interaction behavior accordingly:

1. Orientation Detection: Added automatic detection of slider orientation by comparing node.size().y to node.size().x in both slider_on_pointer_down and slider_on_drag functions.

2. Drag Direction Fix:

   • For vertical sliders, the drag calculation now uses the Y-axis (distance.y) instead of X-axis
   • The Y coordinate is properly inverted (since screen Y increases downward) to match expected behavior (dragging up increases value)
   • Thumb size calculation uses thumb.size().y for vertical sliders instead of always using thumb.size().x

3. Click Position Fix:

   • Fixed coordinate conversion from Bevy's center-origin coordinate system to top/left-origin coordinates
   • For vertical sliders: converts local_pos.y from [-height/2, +height/2] to [0, height] before calculating the slider value
   • Accounts for thumb size offset to center the calculation properly
   • Inverts the Y coordinate for vertical sliders since Y increases downward

4. Track Size Calculation: Uses node.size().y - thumb_size for vertical sliders and node.size().x - thumb_size for horizontal sliders when calculating the available track space.

The changes are backward compatible - horizontal sliders continue to work exactly as before, and the orientation detection is transparent to users of the API.

Testing

• Manual Testing: Created test application with both vertical and horizontal sliders to verify:

  • Vertical sliders respond correctly to vertical drag movements (up = increase, down = decrease)
  • Horizontal sliders continue to work correctly with horizontal drag movements
  • Clicking anywhere on the slider track correctly snaps to that position for both orientations
  • Thumb positioning updates correctly during drag operations
  • Multiple sliders can coexist without interfering with each other

• Edge Cases Tested:

  • Clicking at the very top/bottom of vertical sliders
  • Clicking at the very left/right of horizontal sliders
  • Dragging from one extreme to the other
  • Rapid clicking and dragging interactions

Areas that may need more testing:

• Sliders with non-standard aspect ratios (very wide vertical sliders or very tall horizontal sliders)
• Sliders with custom transforms/rotations applied
• Sliders in nested UI hierarchies with complex transforms

How reviewers can test:

1. Create a vertical slider (height > width) and verify:
   • Dragging up increases the value
   • Dragging down decreases the value
   • Clicking anywhere on the track snaps to that exact position
2. Create a horizontal slider (width > height) and verify it still works as before
3. Test with multiple sliders of both orientations simultaneously

Platforms tested:

• macOS (Apple Silicon)

Showcase

Before

• Vertical sliders were unusable - dragging would move horizontally instead of vertically
• Clicking on vertical slider tracks was offset, with clicks near the bottom snapping to the middle instead

before.mov

After

• Vertical sliders work correctly with intuitive up/down drag behavior
• Clicking anywhere on the slider track accurately snaps to the clicked position
• Both vertical and horizontal sliders work seamlessly together

after.mov

Code Example

// Vertical slider - now works correctly!
commands.spawn((
    Node {
        width: Val::Px(12.0),
        height: Val::Px(300.0),  // height > width = vertical
        ..default()
    },
    Slider::default(),
    SliderValue(50.0),
    SliderRange::new(0.0, 100.0),
    // ... thumb and track children
));

// Horizontal slider - continues to work as before
commands.spawn((
    Node {
        width: Val::Px(300.0),
        height: Val::Px(12.0),  // width > height = horizontal
        ..default()
    },
    Slider::default(),
    SliderValue(50.0),
    SliderRange::new(0.0, 100.0),
    // ... thumb and track children
));

The orientation is automatically detected based on the node dimensions - no API changes required!

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