Venn Diagrams

A Venn diagram is 2 or 3 overlapping sets with an optional title, optional region labels, and an optional legend.

Overview

The model lives in Atelier\Diagram\Venn\: VennDiagram and VennSet (id, label, optional cardinality). All model classes are immutable.

Sets receive the ids A, B, C in declaration order. Regions are addressed by the ids of the sets they intersect: A, B, C for the exclusive regions, AB, AC, BC for the pairwise intersections, ABC for the center.

Reach for it to show membership overlap between a small number of categories: skills shared across roles, features across plans, tags across documents. Cardinalities are carried by the model but the schematic layout does not size regions by them.

Format

This type has no Mermaid grammar; it is built through the PHP builder only. See Parse.

Builder API

VennDiagramBuilder (or Diagram::venn(), which returns it) is the one way to build the model:

use Atelier\Diagram\Diagram;

$diagram = Diagram::venn()
    ->title('Web skills')
    ->set('Frontend', 42)        // becomes set A
    ->set('Backend', 35)         // becomes set B
    ->regionLabel('A', 'CSS')    // Frontend only
    ->regionLabel('B', 'SQL')    // Backend only
    ->regionLabel('AB', 'HTTP')  // intersection
    ->withLegend()
    ->build();

Diagram::of($diagram)->saveSvg('skills.svg');

• set($label, $cardinality) - adds a set (first call is A, second B, third C); the fourth call throws InvalidDiagramException. Cardinality is optional and ignored by the schematic layout.
• regionLabel($region, $text) - labels a region; last call wins per region. Unknown region keys throw immediately; references to undeclared sets (e.g. BC in a 2-set diagram) are checked on build().
• title($text) - sets a title (not part of any text form).
• withLegend() - opts in to a set-to-color legend (off by default).
• targetSize($width, $height) - constrains the schematic into an exact canvas.
• paddingPercent($percent) - reserves outer canvas padding, resolved from the target size.
• innerPaddingPercent($percent) - reserves label padding inside each circle safe area.
• circleStrokeWidth($px) - draws a fixed-width contained circle stroke.
• build() - throws InvalidDiagramException for fewer than 2 sets or a region referencing an undeclared set.

Options

• Determinism: layout is source-order based and deterministic; the same model always yields the same SVG.

Layout\Venn\VennLayoutEngine uses fixed schematic geometry: 2 sets as equal circles side by side, 3 sets on an equilateral triangle. Set labels sit outside the circles, region labels at approximate region centroids. The radius grows automatically when a region label is wider than the default circle.

Two sets instead of three. The layout engine places circles and region labels from the set count, so a Venn diagram is never hand-positioned.

Themes

Venn diagrams fill the circles with accentColors at 0.5 opacity so intersections stay readable; the same palette drives the legend swatches. They also use nodeStrokeColor for circle strokes, textColor for set and region labels, and fontFamily / fontSize for text. A palette of at least 2 (3 for a triple diagram) distinct accent colors reads best; colors are cycled by set index.

All presets apply (Theme::default(), dark(), blueprint(), mono(), neutral()). See Theming.

Parse

Not applicable: this type has no Mermaid grammar, so toMermaid() / toMarkdown() throw and Diagram::fromMermaid() never returns one. SVG output works like for any other type.

Debug

The builder throws InvalidDiagramException on invalid input (a fourth set, an unknown region key, a region referencing an undeclared set, or fewer than 2 sets). There is no parser, so no parser diagnostics apply.