Drawio Impl Swimlanes

Draw.io Swimlane Implementation

Purpose

This skill enables correct generation of swimlane diagrams, cross-functional flowcharts, and pool/lane layouts in Draw.io mxGraph XML. It enforces the container-relative coordinate system and prevents the most common AI mistake: placing child shapes at absolute page coordinates instead of container-relative coordinates.

Critical Rules (Memorize These)

1. ALWAYS set container=1 in every swimlane and pool style — Without it, child shapes will NOT move with the lane when repositioned.
2. ALWAYS use container-relative coordinates for children — A child at x="40" y="35" is 40px from the lane's left edge and 35px from the lane's top edge (below the header). NEVER use absolute page coordinates.
3. ALWAYS set parent to the container ID for child shapes — A shape inside "lane1" MUST have parent="lane1". NEVER set parent="1" for shapes that belong inside a container.
4. ALWAYS set cross-lane edge parent to the common ancestor — When an edge connects shapes in different lanes, set the edge's parent to the pool (the shared ancestor). NEVER set it to one of the individual lanes.
5. ALWAYS include collapsible=0 on lanes — Without it, users can accidentally collapse lanes in the editor, hiding all contents.
6. NEVER use absolute page coordinates for shapes inside a container — This is the #1 swimlane mistake. Shapes will render at the wrong position and will NOT move with their parent lane.

Container Hierarchy

Swimlane diagrams use a strict parent-child hierarchy:

Root (id="1")
  Pool (container=1, parent="1")           <-- absolute coordinates
    Lane A (container=1, parent="pool")     <-- relative to pool
      Shape 1 (parent="lane_a")             <-- relative to Lane A
      Shape 2 (parent="lane_a")             <-- relative to Lane A
    Lane B (container=1, parent="pool")     <-- relative to pool
      Shape 3 (parent="lane_b")             <-- relative to Lane B
    Edge (parent="pool", source/target)     <-- cross-lane edges on pool

Pool Style

The pool is the outermost container that holds all lanes. Use shape=table for structured pool layouts:

shape=table;startSize=30;container=1;collapsible=0;childLayout=tableLayout;fixedRows=1;rowLines=0;fontStyle=1;strokeColor=#6c8ebf;fillColor=#dae8fc;

Alternative: use swimlane;startSize=30;container=1;collapsible=0; for a simpler pool without table layout.

Lane Style

Each lane is a child container inside the pool:

swimlane;startSize=30;container=1;collapsible=0;horizontal=1;fillColor=#f5f5f5;strokeColor=#666666;fontStyle=1;

Horizontal vs. Vertical Orientation

Important: The horizontal property controls the header orientation, NOT the lane stacking direction. horizontal=0 means the header text is horizontal (rendered at the top), and lanes stack side by side — this is the most common layout for cross-functional flowcharts with top-to-bottom flow.

When to Use Which

• horizontal=0 (vertical lanes, top-to-bottom flow): Use for cross-functional flowcharts where the process flows downward and lanes represent departments/roles side by side. This is the DEFAULT for most business process diagrams.
• horizontal=1 (horizontal lanes, left-to-right flow): Use when lanes stack vertically and the process flows left-to-right. Common for value stream maps and horizontal process flows.

Header Sizing (startSize)

The startSize property controls the header band height (for horizontal=0) or width (for horizontal=1):

Coordinate impact: The usable area for child shapes starts AFTER the header. For startSize=30, the first child shape's y-coordinate starts at y=0 relative to the lane (the header occupies the top 30px visually, but child y=0 is at the top-left of the content area after the header in practice). In Draw.io's XML, child y-coordinates are relative to the lane's top-left corner INCLUDING the header. Place children with y >= startSize to avoid overlap.

Lane Geometry Rules

Pool Positioning

The pool uses absolute page coordinates:

<mxCell id="pool1" value="Order Process" style="shape=table;startSize=30;container=1;..."
        vertex="1" parent="1">
  <mxGeometry x="40" y="40" width="700" height="400" as="geometry" />
</mxCell>

Lane Positioning

Lanes use coordinates relative to the pool. The first lane starts at y=startSize (below the pool header):

<!-- First lane: y = pool's startSize (30) -->
<mxCell id="lane1" value="Sales" style="swimlane;..." vertex="1" parent="pool1">
  <mxGeometry y="30" width="700" height="130" as="geometry" />
</mxCell>

<!-- Second lane: y = 30 + height of lane1 (130) = 160 -->
<mxCell id="lane2" value="Warehouse" style="swimlane;..." vertex="1" parent="pool1">
  <mxGeometry y="160" width="700" height="140" as="geometry" />
</mxCell>

Width rule: ALWAYS set lane width equal to pool width. Lanes span the full width of the pool.

Height rule: The sum of all lane heights plus the pool header startSize MUST equal the pool height:

• Pool height = startSize + lane1.height + lane2.height + ...

Child Shape Positioning

Shapes inside lanes use coordinates relative to the lane's top-left corner:

<!-- This shape is 40px from lane's left edge, 35px from lane's top -->
<mxCell id="task1" value="Receive Order" style="rounded=1;whiteSpace=wrap;html=1;..."
        vertex="1" parent="lane1">
  <mxGeometry x="40" y="35" width="120" height="60" as="geometry" />
</mxCell>

Place children with y >= startSize of the lane to avoid overlapping the lane header.

Cross-Lane Connections

Edges that connect shapes in different lanes MUST use the pool as their parent:

<!-- task2 is in lane1, task3 is in lane2 — edge parent is pool1 -->
<mxCell id="e1" style="edgeStyle=orthogonalEdgeStyle;endArrow=classic;html=1;"
        edge="1" parent="pool1" source="task2" target="task3">
  <mxGeometry relative="1" as="geometry" />
</mxCell>

Edges that connect shapes within the SAME lane MAY use either the lane or the pool as parent. For consistency, ALWAYS use the pool as edge parent.

Nested Lanes

Lanes can contain sub-lanes for finer granularity:

<mxCell id="lane1" value="Engineering" style="swimlane;startSize=30;container=1;..."
        vertex="1" parent="pool1">
  <mxGeometry y="30" width="700" height="200" as="geometry" />
</mxCell>

<!-- Sub-lane inside lane1 -->
<mxCell id="sublane1a" value="Frontend" style="swimlane;startSize=25;container=1;..."
        vertex="1" parent="lane1">
  <mxGeometry y="30" width="700" height="85" as="geometry" />
</mxCell>

<mxCell id="sublane1b" value="Backend" style="swimlane;startSize=25;container=1;..."
        vertex="1" parent="lane1">
  <mxGeometry y="115" width="700" height="85" as="geometry" />
</mxCell>

Rule: Sub-lane coordinates are relative to the parent lane. Sub-lane widths MUST equal the parent lane width.

Auto-Expand Behavior

When container=1 is set, Draw.io auto-expands the container if a child shape extends beyond its boundaries. To prevent unwanted expansion:

• ALWAYS size the pool and lanes large enough to contain all children.
• Add resizable=1 to allow manual resizing in the editor.
• Add recursiveResize=0 on the pool to prevent child lanes from auto-resizing when the pool resizes.

Complete Example: 3-Lane Order Processing

<mxGraphModel>
  <root>
    <mxCell id="0" />
    <mxCell id="1" parent="0" />

    <!-- Pool -->
    <mxCell id="pool1" value="Order Processing" style="shape=table;startSize=30;container=1;collapsible=0;childLayout=tableLayout;fixedRows=1;rowLines=0;fontStyle=1;strokeColor=#6c8ebf;fillColor=#dae8fc;" vertex="1" parent="1">
      <mxGeometry x="40" y="40" width="700" height="430" as="geometry" />
    </mxCell>

    <!-- Lane 1: Sales -->
    <mxCell id="lane_sales" value="Sales" style="swimlane;startSize=30;container=1;collapsible=0;horizontal=1;fillColor=#f5f5f5;strokeColor=#666666;fontStyle=1;" vertex="1" parent="pool1">
      <mxGeometry y="30" width="700" height="130" as="geometry" />
    </mxCell>

    <mxCell id="t1" value="Receive&lt;br&gt;Order" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#d5e8d4;strokeColor=#82b366;" vertex="1" parent="lane_sales">
      <mxGeometry x="40" y="35" width="120" height="60" as="geometry" />
    </mxCell>

    <mxCell id="t2" value="Validate&lt;br&gt;Order" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#dae8fc;strokeColor=#6c8ebf;" vertex="1" parent="lane_sales">
      <mxGeometry x="220" y="35" width="120" height="60" as="geometry" />
    </mxCell>

    <mxCell id="d1" value="Valid?" style="rhombus;whiteSpace=wrap;html=1;fillColor=#fff2cc;strokeColor=#d6b656;" vertex="1" parent="lane_sales">
      <mxGeometry x="400" y="25" width="100" height="80" as="geometry" />
    </mxCell>

    <!-- Lane 2: Warehouse -->
    <mxCell id="lane_warehouse" value="Warehouse" style="swimlane;startSize=30;container=1;collapsible=0;horizontal=1;fillColor=#f5f5f5;strokeColor=#666666;fontStyle=1;" vertex="1" parent="pool1">
      <mxGeometry y="160" width="700" height="130" as="geometry" />
    </mxCell>

    <mxCell id="t3" value="Pick&lt;br&gt;Items" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#dae8fc;strokeColor=#6c8ebf;" vertex="1" parent="lane_warehouse">
      <mxGeometry x="220" y="35" width="120" height="60" as="geometry" />
    </mxCell>

    <mxCell id="t4" value="Pack&lt;br&gt;Shipment" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#dae8fc;strokeColor=#6c8ebf;" vertex="1" parent="lane_warehouse">
      <mxGeometry x="400" y="35" width="120" height="60" as="geometry" />
    </mxCell>

    <!-- Lane 3: Finance -->
    <mxCell id="lane_finance" value="Finance" style="swimlane;startSize=30;container=1;collapsible=0;horizontal=1;fillColor=#f5f5f5;strokeColor=#666666;fontStyle=1;" vertex="1" parent="pool1">
      <mxGeometry y="290" width="700" height="140" as="geometry" />
    </mxCell>

    <mxCell id="t5" value="Generate&lt;br&gt;Invoice" style="shape=document;whiteSpace=wrap;html=1;fillColor=#f5f5f5;strokeColor=#666666;" vertex="1" parent="lane_finance">
      <mxGeometry x="400" y="35" width="120" height="60" as="geometry" />
    </mxCell>

    <mxCell id="t6" value="Process&lt;br&gt;Payment" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#dae8fc;strokeColor=#6c8ebf;" vertex="1" parent="lane_finance">
      <mxGeometry x="560" y="35" width="120" height="60" as="geometry" />
    </mxCell>

    <!-- Reject path -->
    <mxCell id="t_reject" value="Reject&lt;br&gt;Order" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#f8cecc;strokeColor=#b85450;" vertex="1" parent="lane_sales">
      <mxGeometry x="560" y="35" width="120" height="60" as="geometry" />
    </mxCell>

    <!-- Connections (all parent="pool1" for cross-lane routing) -->
    <mxCell id="e1" style="edgeStyle=orthogonalEdgeStyle;endArrow=classic;html=1;" edge="1" parent="pool1" source="t1" target="t2">
      <mxGeometry relative="1" as="geometry" />
    </mxCell>
    <mxCell id="e2" style="edgeStyle=orthogonalEdgeStyle;endArrow=classic;html=1;" edge="1" parent="pool1" source="t2" target="d1">
      <mxGeometry relative="1" as="geometry" />
    </mxCell>
    <mxCell id="e3" value="Yes" style="edgeStyle=orthogonalEdgeStyle;endArrow=classic;html=1;" edge="1" parent="pool1" source="d1" target="t3">
      <mxGeometry relative="1" as="geometry" />
    </mxCell>
    <mxCell id="e4" value="No" style="edgeStyle=orthogonalEdgeStyle;endArrow=classic;html=1;" edge="1" parent="pool1" source="d1" target="t_reject">
      <mxGeometry relative="1" as="geometry" />
    </mxCell>
    <mxCell id="e5" style="edgeStyle=orthogonalEdgeStyle;endArrow=classic;html=1;" edge="1" parent="pool1" source="t3" target="t4">
      <mxGeometry relative="1" as="geometry" />
    </mxCell>
    <mxCell id="e6" style="edgeStyle=orthogonalEdgeStyle;endArrow=classic;html=1;" edge="1" parent="pool1" source="t4" target="t5">
      <mxGeometry relative="1" as="geometry" />
    </mxCell>
    <mxCell id="e7" style="edgeStyle=orthogonalEdgeStyle;endArrow=classic;html=1;" edge="1" parent="pool1" source="t5" target="t6">
      <mxGeometry relative="1" as="geometry" />
    </mxCell>
  </root>
</mxGraphModel>

This example demonstrates:

• 3 lanes (Sales, Warehouse, Finance) inside one pool
• 7 shapes across 3 lanes with container-relative coordinates
• Cross-lane connections with parent="pool1"
• Decision diamond with labeled Yes/No branches
• Document shape for invoice generation
• Consistent left-to-right flow within horizontal lanes

Checklist: Before Outputting a Swimlane Diagram

1. Every pool and lane has container=1 in its style.
2. Every lane has collapsible=0 in its style.
3. Every child shape has parent set to its containing lane ID.
4. Every child shape uses coordinates relative to its lane (NOT absolute page coordinates).
5. Every cross-lane edge has parent set to the pool (common ancestor).
6. Lane widths equal the pool width.
7. Pool height = startSize + sum of all lane heights.
8. Child shapes have y >= startSize of their lane to avoid header overlap.
9. Both structural cells (id="0" and id="1") are present.
10. All cell IDs are unique.
11. All edges have valid source and target attributes.

Cross-References

• XML fundamentals: See drawio-core-xml-format for file structure and structural cells.
• Style syntax: See drawio-syntax-styles for the complete style property reference.
• Connection details: See drawio-syntax-connections for edge routing and waypoints.
• Geometry: See drawio-core-geometry for coordinate system and positioning.
• Flowchart shapes: See drawio-impl-flowcharts for ISO 5807 shapes used inside lanes.

Reference Links

• Complete Reference
• Working Examples
• Anti-Patterns