Scarpe/Shoes Incompatibilities

This document outlines known incompatibilities between Scarpe and classic Shoes3 (the original _why implementation and its successors).

Unsupported Shoes3 Widgets

These widgets exist only in Shoes3 and have no Scarpe equivalent:

• plot - Graphing/charting widget
• terminal - Embedded terminal emulator
• systray - System tray icon
• spinner - Loading spinner widget
• switch - Toggle switch widget (use check instead)
• video - Video player (VLC-based in Shoes3)
• svghandle - SVG rendering (Scarpe uses image with SVG data URIs)

Unsupported Shoes3 APIs

Global App Settings (Shoes. methods)

• Shoes.settings - Application preferences
• Shoes.monitor - Display/monitor detection
• Shoes.show_manual - Built-in manual viewer (stub only in Scarpe)
• RELEASE_* constants - Version/release info

Event System

• shoesevent - Programmatic event creation
• event block - Global event capture/replay
• Event capture/replay system

Decoration & Theming

• decoration - Window decoration control
• cache - Asset caching system

Native Menus

• menu, menubar - Native OS menus

Behavioral Differences

Scripts Without Shoes.app

Classic Shoes allowed calling ask(), alert(), and other builtins at the top level without wrapping in Shoes.app:

# This works in classic Shoes, NOT in Scarpe
guess = ask "What's your name?"
alert "Hello, #{guess}!"

Scarpe requires Shoes.app because builtins need a WebView context:

# Scarpe-compatible version
Shoes.app do
  guess = ask "What's your name?"
  alert "Hello, #{guess}!"
end

Method Definition Order

Methods defined AFTER Shoes.app are not available inside the block:

# This will FAIL - to_radians doesn't exist when Shoes.app runs
Shoes.app do
  angle = to_radians(45)  # NoMethodError!
end

def to_radians(deg)
  deg * Math::PI / 180
end

Solution: Define helper methods BEFORE Shoes.app:

# This WORKS
def to_radians(deg)
  deg * Math::PI / 180
end

Shoes.app do
  angle = to_radians(45)  # Works!
end

Widget Positioning

In classic Shoes, widgets knew their position after layout. In Scarpe, self.left and self.top inside Widget#initialize return nil because browser layout hasn’t occurred yet.

class MyWidget < Shoes::Widget
  def initialize
    @x = self.left  # nil in Scarpe, had value in classic Shoes
  end
end

ask() Cancel Behavior

• Classic Shoes: ask() returned nil on cancel
• Scarpe: ask() returns empty string "" on cancel (more predictable for string operations)

Pre-app Dialogs

Calling confirm(), ask(), or alert() before Shoes.app exists doesn’t work in Scarpe:

# Works in classic Shoes, fails in Scarpe
if confirm("Continue?")
  Shoes.app { ... }
end

External Dependencies

Some Shoes3 examples require gems that are dead or incompatible with modern Ruby:

• hpricot - Dead HTML parser (use Nokogiri)
• bluecloth - Markdown renderer (use kramdown or redcarpet)
• observer - Removed from Ruby 3.4 stdlib

Migration Tips

1. Wrap all code in Shoes.app - Don’t rely on top-level builtins
2. Define helpers before Shoes.app - Method order matters in Ruby
3. Use check instead of switch - Similar functionality
4. Replace svghandle with image - SVG data URIs work well
5. Use Nokogiri instead of hpricot - For HTML/XML parsing
6. Test ask() cancel handling - Now returns "" not nil

What Works Well

Scarpe has excellent compatibility with core Shoes features:

• Layout: stack, flow, background
• Drawing: rect, oval, line, arc, star, shape, mask
• Text: para, title, subtitle, tagline, caption, inscription, banner
• Styles: span, strong, em, link, code, ins, del, sub, sup
• Interaction: button, click, hover, leave, keypress, motion
• Input: edit_line, edit_box, list_box, check, radio
• Timing: animate, timer, every
• Dialogs: alert, confirm, ask, ask_color, ask_open_file, ask_save_file
• Graphics: fill, stroke, strokewidth, nofill, nostroke, rotate
• Custom: Shoes::Widget subclasses
• Navigation: URL routing with url and visit
• Turtle graphics: Full Turtle.draw / Turtle.start support

The Hackety Hack samples are a good test suite - 9 of 12 run unmodified on Scarpe.