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feat(D.2b): UiChatScrollbar — track/thumb/buttons driving UiScrollable

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Implements the right-side chat scrollbar widget. Ports retail
UIElement_Scrollbar::UpdateLayout @0x4710d0 (thumb sizing + placement)
and HandleButtonClick @0x470e90 (step ±1 line, page on track click).

Dat element ids sourced from chat LayoutDesc 0x21000006 (base layout
0x2100003E): up-button sprite 0x06004C69, down-button 0x06004C6C, track
0x06004C5F, thumb middle 0x06004C63. Up/down buttons occupy the top and
bottom ButtonH (16px) regions of the widget height, matching element
positions Y=0 and Y=32 in the base scrollbar template.

Adds 6 pure ThumbRect tests (no GL): sizing, clamping to MinThumb,
position at start/mid/end, no-overflow full-fill.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
This commit is contained in:
Erik 2026-06-15 22:31:12 +02:00
parent 0eaef67b9d
commit 2940b4e3b2
2 changed files with 245 additions and 0 deletions
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164
src/AcDream.App/UI/UiChatScrollbar.cs Normal file
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using System;
using System.Numerics;
namespace AcDream.App.UI;
/// <summary>
/// Right-side chat scrollbar: a track sprite, a draggable thumb sized to the
/// content/view ratio, and up/down step buttons. Drives a linked
/// <see cref="UiScrollable"/>. Ports retail <c>UIElement_Scrollbar::UpdateLayout
/// @0x4710d0</c> (thumb size = trackLen * ThumbRatio, min 8px; thumb pos from
/// PositionRatio) and <c>HandleButtonClick @0x470e90</c> (step ±1 line).
/// </summary>
/// <remarks>
/// Dat element ids (chat LayoutDesc 0x21000006): track 0x10000012 (X=474 Y=6 W=16 H=68),
/// thumb 0x1000048C. The track is instanced from base layout 0x2100003E which contains
/// the full scrollbar widget with distinct up/down button children:
/// Up button element 0x10000071 — Y=0, 16×16, Normal sprite 0x06004C69.
/// Down button element 0x10000072 — Y=32, 16×16, Normal sprite 0x06004C6C.
/// Track body sprite: 0x06004C5F (48px tall in the base template; stretched to H=68 in chat).
/// Thumb is a 3-slice: top cap 0x06004C60, middle 0x06004C63, bottom cap 0x06004C66.
/// For Task H wiring: up/down regions occupy the top and bottom ButtonH (16px) of the
/// rendered scrollbar's height; the widget responds to those regions directly via hit
/// comparison in OnEvent without requiring separate child elements.
/// </remarks>
public sealed class UiChatScrollbar : UiElement
{
/// <summary>The scroll model this bar reflects + drives (shared with the transcript).</summary>
public UiScrollable? Model { get; set; }
/// <summary>RenderSurface id → (GL tex, w, h). 0 id = skip.</summary>
public Func<uint, (uint tex, int w, int h)>? SpriteResolve { get; set; }
/// <summary>Track background sprite id (0x06004C5F from layout 0x2100003E element 0x10000455).</summary>
public uint TrackSprite { get; set; }
/// <summary>Thumb sprite id (3-slice middle tile: 0x06004C63; the widget draws
/// a single stretched sprite for simplicity — Task H can upgrade to 3-slice).</summary>
public uint ThumbSprite { get; set; }
/// <summary>Up-arrow button sprite id (0x06004C69 Normal state, element 0x10000071).</summary>
public uint UpSprite { get; set; }
/// <summary>Down-arrow button sprite id (0x06004C6C Normal state, element 0x10000072).</summary>
public uint DownSprite { get; set; }
/// <summary>Retail attribute 0x89 floor: minimum thumb height in pixels.</summary>
private const float MinThumb = 8f;
/// <summary>Up/down button height in pixels. Matches element height 16px from
/// the up/down button children in base layout 0x2100003E.</summary>
private const float ButtonH = 16f;
private bool _draggingThumb;
private float _dragOffsetY;
public UiChatScrollbar() { CapturesPointerDrag = true; }
/// <summary>
/// Computes the thumb rectangle (local y origin and height) within the track area
/// between the two end buttons. Ports retail <c>UIElement_Scrollbar::UpdateLayout
/// @0x4710d0</c>: thumb height = max(MinThumb, trackLen * ThumbRatio); thumb top
/// offset = trackTop + (trackLen - thumbH) * PositionRatio.
/// </summary>
/// <param name="m">The scroll model.</param>
/// <param name="trackTop">Y of the top of the usable track area (below up-button).</param>
/// <param name="trackLen">Pixel length of the usable track area (between up and down buttons).</param>
/// <returns>Local Y of the thumb's top edge, and its pixel height.</returns>
public static (float y, float h) ThumbRect(UiScrollable m, float trackTop, float trackLen)
{
float h = MathF.Max(MinThumb, trackLen * m.ThumbRatio);
float travel = trackLen - h;
float y = trackTop + travel * m.PositionRatio;
return (y, h);
}
protected override void OnDraw(UiRenderContext ctx)
{
if (Model is not { } m || SpriteResolve is not { } resolve) return;
// Track background, full element bounds.
DrawSprite(ctx, resolve, TrackSprite, 0f, 0f, Width, Height);
// Up button — top ButtonH rows.
DrawSprite(ctx, resolve, UpSprite, 0f, 0f, Width, ButtonH);
// Down button — bottom ButtonH rows.
DrawSprite(ctx, resolve, DownSprite, 0f, Height - ButtonH, Width, ButtonH);
// Thumb — only when content overflows the view.
if (m.HasOverflow)
{
float trackTop = ButtonH;
float trackLen = Height - 2f * ButtonH;
var (ty, th) = ThumbRect(m, trackTop, trackLen);
DrawSprite(ctx, resolve, ThumbSprite, 0f, ty, Width, th);
}
}
private void DrawSprite(UiRenderContext ctx, Func<uint, (uint tex, int w, int h)> resolve,
uint id, float x, float y, float w, float h)
{
if (id == 0) return;
var (tex, _, _) = resolve(id);
if (tex == 0) return;
ctx.DrawSprite(tex, x, y, w, h, 0f, 0f, 1f, 1f, Vector4.One);
}
public override bool OnEvent(in UiEvent e)
{
if (Model is not { } m) return false;
switch (e.Type)
{
case UiEventType.MouseDown:
{
// e.Data1 = local X, e.Data2 = local Y (int pixel coords, see UiRoot hit dispatch).
float ly = e.Data2;
// Up-button region: top ButtonH rows.
if (ly <= ButtonH) { m.ScrollByLines(-1); return true; }
// Down-button region: bottom ButtonH rows.
if (ly >= Height - ButtonH) { m.ScrollByLines(1); return true; }
// Track interior: start a thumb drag or page-scroll.
float trackTop = ButtonH;
float trackLen = Height - 2f * ButtonH;
var (ty, th) = ThumbRect(m, trackTop, trackLen);
if (ly >= ty && ly <= ty + th)
{
// Clicked inside the thumb — begin drag with offset from thumb top.
_draggingThumb = true;
_dragOffsetY = ly - ty;
}
else
{
// Clicked above or below thumb — page scroll (HandleButtonClick page case).
m.ScrollByPage(ly < ty ? -1 : 1);
}
return true;
}
case UiEventType.MouseMove when _draggingThumb:
{
// Map current local Y (minus drag offset from thumb top) back to a
// position ratio across the available travel distance.
float trackTop = ButtonH;
float trackLen = Height - 2f * ButtonH;
float thumbH = MathF.Max(MinThumb, trackLen * m.ThumbRatio);
float travel = MathF.Max(1f, trackLen - thumbH);
float newRatio = ((float)e.Data2 - _dragOffsetY - trackTop) / travel;
m.SetPositionRatio(newRatio);
return true;
}
case UiEventType.MouseUp:
_draggingThumb = false;
return true;
}
return false;
}
}