merman-render

merman-render is the low-level layout and SVG crate behind merman. It consumes merman-core parse results and produces layout JSON or Mermaid-like SVG.

Most applications should start with the merman crate and merman::render::HeadlessRenderer. Use merman-render directly when you need lower-level control over layout, text measurement, SVG options, or SVG postprocessing.

What It Provides

• Headless layout for parsed Mermaid diagrams.
• Mermaid-parity SVG emission.
• LayoutOptions::headless_svg_defaults() for editor/export use cases.
• Text measurement hooks through TextMeasurer.
• Math rendering hooks through MathRenderer.
• SvgPipeline presets and postprocessors for readable or rasterizer-friendly SVG.

Direct Rendering Example

use merman_core::{Engine, ParseOptions};
use merman_render::{layout_parsed_render_layout_only, LayoutOptions};
use merman_render::svg::{
    render_layout_svg_parts_for_render_model_with_config, SvgPipeline, SvgRenderOptions,
};

fn main() -> Result<(), Box<dyn std::error::Error>> {
    let engine = Engine::new();
    let parsed = engine
        .parse_diagram_for_render_model_sync(
            "flowchart TD\nA[API] --> B[DB]",
            ParseOptions::strict(),
        )?
        .expect("diagram detected");

    let layout_options = LayoutOptions::headless_svg_defaults();
    let layout = layout_parsed_render_layout_only(&parsed, &layout_options)?;

    let svg_options = SvgRenderOptions {
        diagram_id: Some("example-diagram".to_string()),
        ..SvgRenderOptions::default()
    };

    let svg = render_layout_svg_parts_for_render_model_with_config(
        &layout,
        &parsed.model,
        &parsed.meta.effective_config,
        parsed.meta.title.as_deref(),
        layout_options.text_measurer.as_ref(),
        &svg_options,
    )?;

    let svg = SvgPipeline::resvg_safe().process_to_string(&svg)?;
    println!("{svg}");

    Ok(())
}

SVG Output Pipelines

The default SVG renderer aims for Mermaid DOM parity. Host applications can opt into an output pipeline after rendering:

• SvgPipeline::parity() leaves the SVG unchanged.
• SvgPipeline::readable() keeps fallback text for <foreignObject> labels.
• SvgPipeline::resvg_safe() prepares SVG for common usvg / resvg rasterization paths.
• ScopedCssPostprocessor, CssOverridePostprocessor, and custom SvgPostprocessor implementations let applications inject host-specific styling without forking the renderer.

See docs/rendering/SVG_OUTPUT_PIPELINE.md for the higher-level integration guide.

Relationship To merman

merman re-exports the common render APIs behind its render feature and adds HeadlessRenderer, SVG id sanitization helpers, and optional raster helpers. Direct merman-render users get the same layout/SVG engine with less convenience wrapping and more explicit control over each phase.