Overview of Terminal UI (TUI) development for WvdS FPC RAD Studio.

Terminal User Interface (TUI) enables graphical interfaces in the terminal:

• Text-based display - Characters instead of pixels
• Cross-platform - Runs on Windows Terminal, WezTerm, iTerm2, Linux Console
• Resource-efficient - Ideal for servers, SSH, containers
• Accessible - Screen reader compatible

The WvdS TUI standard targets Ratatui-level quality or better:

┌─────────────────────────────────────────────────────────────┐
│  PXAML (Markup)                                             │
├─────────────────────────────────────────────────────────────┤
│  Control Model (TWvdS*) - Target-neutral                    │
├─────────────────────────────────────────────────────────────┤
│  TUI Renderer - Target-specific                             │
├─────────────────────────────────────────────────────────────┤
│  Render Surface → CellBuffer → DiffEngine                   │
├─────────────────────────────────────────────────────────────┤
│  Terminal IO (ANSI Escape Sequences)                        │
└─────────────────────────────────────────────────────────────┘

Control models contain no terminal-specific logic:

(* CORRECT - Target-neutral *)
TWvdSButton = class(TWvdSControl)
private
  FCaption: string;
  FOnClick: TNotifyEvent;
public
  property Caption: string read FCaption write SetCaption;
  property OnClick: TNotifyEvent read FOnClick write FOnClick;
end;
 
(* FORBIDDEN - Terminal-specific in model *)
TWvdSButton = class(TWvdSControl)
  procedure WriteAnsiSequence;  (* FORBIDDEN! *)
end;

Renderers draw the model to the CellBuffer:

TWvdSTUIButtonRenderer = class(TWvdSTUIRenderer)
public
  procedure Measure(AControl: TWvdSControl; AAvail: TSize): TSize; override;
  procedure Paint(AControl: TWvdSControl; ASurface: TRenderSurface); override;
  function HandleInput(AControl: TWvdSControl; AEvent: TInputEvent): Boolean; override;
end;

Every control has anchoring enabled by default:

Anchors: Left, Top, Right, Bottom

Default: Left+Top (stable position)
Left+Right: Width stretches with parent
Top+Bottom: Height stretches with parent
All four: Rect stretches in both directions

unit WvdS.UI.Controls.MyControl;
 
type
  TWvdSMyControl = class(TWvdSControl)
  private
    FValue: string;
  public
    property Value: string read FValue write SetValue;
  end;

unit WvdS.UI.TUI.Renderers.MyControl;
 
type
  TWvdSTUIMyControlRenderer = class(TWvdSTUIRenderer)
  public
    procedure Measure(AControl: TWvdSControl; AAvail: TSize): TSize; override;
    procedure Paint(AControl: TWvdSControl; ASurface: TRenderSurface); override;
  end;

{
  "id": "mycontrol",
  "renderers": {
    "tui": {
      "unit": "WvdS.UI.TUI.Renderers.MyControl",
      "class": "TWvdSTUIMyControlRenderer"
    }
  },
  "targetCaps": {
    "requires": ["keyboard"],
    "optional": ["mouse"]
  }
}

Every TUI implementation must be verified:

[ ] No flicker during repeated repaint
[ ] Resize produces stable layout
[ ] TextEdit caret is stable with wide/combining chars
[ ] Table/List renders 10k rows with smooth scroll
[ ] Images behave correctly per TerminalCaps
[ ] Focus remains stable through reflow

• TUI Engine
• TUI Controls
• TUI Layout
• Build Targets
• Control Development