Derender

Not every useful vector drawing should be produced programmatically. A Bezier-heavy logo, traced illustration, or hand-adjusted path may be easier and more faithful to author in a visual editor. Derender brings that SVG or XML into Sevgi's element model, where editor-authored geometry can participate in Ruby-driven composition, styling, layout, and output.

Use Derender when SVG/XML is a real input artifact, not as a detour for shapes or relationships that are clearer in the Sevgi DSL. Convert inline content or a file, generate source, include part of it, or inspect its tree.

The round trip

SVG/XML content or file → immutable Derender node → Sevgi source → evaluated SVG tree

The conversion keeps element names, attributes, text, comments, CDATA, and child order. It represents the XML tree as Ruby. It cannot recover the loops, helper methods, or other higher-level code that may have produced the original file.

Choose source generation when the converted Ruby should become the maintained representation. Choose evaluation or Include when the editor file should remain the source of its geometry and Sevgi should compose it at runtime.

Library code uses the capitalized facade operations. For example, a consumer can inspect a node and generate only that subtree without installing script-mode names:

xml = '<svg><g id="mark" style="fill: red"><rect width="4"/></g></svg>'
mark = SVG.Decompile(xml, id: "mark")
source = mark.derender

raise unless mark.name == "g"
raise unless source.include?("rect width: 4")

Generate source

In a .sevgi script, Derender converts inline content and returns formatted Ruby:

source = Derender '<path id="mark" d="M 0 0 L 8 3"/>', id: "mark"
puts source

Library code writes the same operation as SVG.Derender(...).

Use DerenderFile when the source already lives on disk:

source = DerenderFile "badge.svg", id: "mark"

The optional id selects one subtree. Without it, the document root is used. Pass one attribute name or an array to omit when editor metadata should not survive the conversion:

source = DerenderFile "badge.svg", id: "mark", omit: %i[id style]

Attribute names may be strings or symbols and match exactly across the selected subtree. Selection happens before omission, so an id may select a node without appearing in the result. Namespace declarations and style elements are preserved when attributes are omitted.

The companion igves command prints a file conversion from the shell and accepts a repeatable option:

igves --omit id --omit style badge.svg

Both conversion commands read standard input when the file is omitted or -, which makes the same conversion usable in a pipeline:

igves --omit id < badge.svg

When normalized SVG is the desired result rather than generated Ruby, the umbrella sevgi gem provides igsev. It performs the complete SVG-to-Sevgi-to-SVG round trip and accepts the same repeatable omission option:

igsev --omit id --omit style badge.svg > normalized.svg

This is a structural formatter, not a byte-preserving XML rewrite: Sevgi rendering determines declaration, whitespace, attribute spelling, and other serialized details.

Inspect

Decompile stops one step earlier and returns an immutable node. The node owns snapshots of its attributes, namespaces, metadata, content, and descendants:

xml = <<~SVG
  <svg xmlns="http://www.w3.org/2000/svg" xmlns:_="https://sevgi.roktas.dev/meta">
    <g id="mark" _:role="icon"><rect width="4"/></g>
  </svg>
SVG

root = SVG.Decompile(xml)
mark = root.find("mark")

raise unless root.root?
raise unless root.namespaces["xmlns"] == "http://www.w3.org/2000/svg"
raise unless root.children.first.equal?(mark)
raise unless mark.attributes["id"] == "mark"
raise unless mark.meta["role"] == "icon"
raise unless mark.children.map(&:name) == ["rect"]
raise unless mark.derender.include?("rect width: 4")

The file counterpart is explicit:

node = DecompileFile "badge.svg", id: "mark"

Use these methods when you need to examine a selection, its attributes, or its children without generating source.

Evaluate and include

Evaluate imports inline content directly into an existing SVG tree. EvaluateChildren imports only the selected node's children:

drawing = SVG :minimal
SVG.Evaluate '<circle id="mark" r="4"/>', drawing, id: "mark"
drawing.Render

Use EvaluateFile or EvaluateChildrenFile for file input. All conversion and evaluation forms accept omit. Inside an SVG block, the established Include and IncludeChildren drawing words remain convenient file-oriented forms because their target is already the current element:

SVG do
  Include "badge.svg", "mark", omit: %i[id style]
end

Applications depending only on sevgi-derender can use the lowercase component API under Sevgi::Derender: decompile, derender, evaluate, and evaluate_children accept content; their _file counterparts accept paths.

All these APIs parse XML as data and build immutable snapshots or graphics elements; they do not execute the generated Ruby. This is distinct from Sevgi.execute, which deliberately runs trusted Ruby with the process's authority. Parsing untrusted XML still deserves normal resource limits, but it does not grant the source a Ruby execution path.

The catalog links its Derender entries back here because selection, conversion, and evaluation all use this same mechanism.