Drawio Core Geometry

Draw.io Core Geometry

Purpose

This skill defines how to position shapes, route edges, and place labels in Draw.io mxGraph XML. Every visual element requires an <mxGeometry> child element. Getting geometry wrong causes shapes to overlap, edges to misroute, and labels to disappear.

Coordinate System

Draw.io uses a screen coordinate system:

• Origin: Top-left corner of the canvas is (0, 0)
• X-axis: Positive values go right
• Y-axis: Positive values go down
• Units: All values are in pixels

(0,0) ────────────► +X (right)
  │
  │
  │
  ▼
 +Y (down)

Vertex Geometry

Every vertex (shape) MUST have an <mxGeometry> with x, y, width, and height:

<mxCell id="2" value="Process" style="rounded=1;whiteSpace=wrap;html=1;"
        vertex="1" parent="1">
  <mxGeometry x="200" y="150" width="120" height="60" as="geometry" />
</mxCell>

Rules:

• ALWAYS specify width and height. Draw.io has NO implicit sizing — omitting dimensions produces a 0x0 invisible shape.
• ALWAYS set as="geometry" on the <mxGeometry> element.
• x and y default to 0 if omitted, placing the shape at the canvas origin.

Edge Geometry

Edges MUST use relative="1" on their geometry. The x and y attributes on edge geometry control label placement, NOT the edge path:

<mxCell id="4" value="Yes" style="edgeStyle=orthogonalEdgeStyle;"
        edge="1" source="2" target="3" parent="1">
  <mxGeometry relative="1" as="geometry" />
</mxCell>

Rules:

• ALWAYS set relative="1" on edge geometry. Without it, the edge rendering breaks.
• NEVER set width or height on edge geometry.

Edge Label Positioning

When relative="1", the x and y on <mxGeometry> position the edge label:

<!-- Label at midpoint, offset 15px perpendicular -->
<mxGeometry x="0" y="15" relative="1" as="geometry" />

Fine-Tuning with offset

Add an <mxPoint as="offset"> inside <mxGeometry> for pixel-level label adjustment:

<mxGeometry x="0.5" y="0" relative="1" as="geometry">
  <mxPoint x="10" y="-5" as="offset" />
</mxGeometry>

Unconnected Edge Endpoints

When an edge has no source or target attribute, use sourcePoint and targetPoint:

<mxCell id="5" edge="1" parent="1" style="edgeStyle=orthogonalEdgeStyle;">
  <mxGeometry relative="1" as="geometry">
    <mxPoint x="100" y="200" as="sourcePoint" />
    <mxPoint x="400" y="350" as="targetPoint" />
  </mxGeometry>
</mxCell>

These are absolute canvas coordinates.

Waypoints

Edges route through intermediate points using an <Array as="points"> inside <mxGeometry>:

<mxCell id="4" edge="1" source="2" target="3" parent="1"
        style="edgeStyle=orthogonalEdgeStyle;">
  <mxGeometry relative="1" as="geometry">
    <Array as="points">
      <mxPoint x="300" y="150" />
      <mxPoint x="300" y="250" />
    </Array>
  </mxGeometry>
</mxCell>

Rules:

• Waypoint coordinates are ALWAYS absolute canvas coordinates.
• The <Array> MUST have as="points".
• Each <mxPoint> defines one intermediate routing anchor.
• Order matters: edge routes source -> point1 -> point2 -> ... -> target.

Waypoint Behavior by Edge Style

Container-Relative Coordinates

When a cell is a child of a container (group or swimlane), its geometry coordinates are relative to the parent's top-left corner, NOT the canvas origin.

<!-- Container at canvas position (100, 100) -->
<mxCell id="10" value="Server Group" style="group" vertex="1" parent="1">
  <mxGeometry x="100" y="100" width="300" height="200" as="geometry" />
</mxCell>
<!-- Child at (20, 20) RELATIVE to parent = canvas position (120, 120) -->
<mxCell id="11" value="Web Server" style="rounded=1;" vertex="1" parent="10">
  <mxGeometry x="20" y="20" width="120" height="60" as="geometry" />
</mxCell>

Rules:

• NEVER use absolute canvas coordinates for children inside containers. The child's x and y are ALWAYS relative to the parent's top-left corner.
• A child at x="0" y="0" sits at the parent's top-left corner.
• Children CAN extend beyond the parent's bounds (they will be visually clipped in some styles but still exist).

Decision Tree: Absolute vs. Relative Coordinates

Is the cell a child of a container (parent != "1")?
├── YES → Use coordinates RELATIVE to parent's top-left
│         x=20, y=30 means 20px right and 30px down from parent origin
└── NO  → Use ABSOLUTE canvas coordinates
          x=200, y=150 means 200px right and 150px down from canvas origin

Collapsible Containers (alternateBounds)

Containers with collapsed="1" use alternateBounds to define their collapsed size:

<mxCell id="10" value="Server Group" style="swimlane;" vertex="1"
        collapsed="1" parent="1">
  <mxGeometry x="100" y="100" width="300" height="200" as="geometry">
    <mxRectangle x="100" y="100" width="160" height="30" as="alternateBounds" />
  </mxGeometry>
</mxCell>

• Expanded: renders at 300x200
• Collapsed: renders at 160x30

Connection Points (Style Properties)

Connection points control WHERE edges attach to shapes. They are style properties on the edge, using 0.0-1.0 relative coordinates on the source/target shape.

Reference Grid

(0,0)──────(0.5,0)──────(1,0)
  │                        │
(0,0.5)   (0.5,0.5)   (1,0.5)
  │                        │
(0,1)──────(0.5,1)──────(1,1)

Connection Point Style Properties

Common Connection Patterns

exitX=1;exitY=0.5;entryX=0;entryY=0.5;     → Right-to-left (horizontal flow)
exitX=0.5;exitY=1;entryX=0.5;entryY=0;     → Bottom-to-top (vertical flow)
exitX=1;exitY=0;entryX=0;entryY=1;         → Diagonal: top-right to bottom-left
exitX=0.5;exitY=0.5;entryX=0.5;entryY=0.5; → Center-to-center

Vertex Label Positioning

Label positioning on vertices uses style properties:

Critical rule: When labelPosition is NOT center, align MUST be the opposite direction:

labelPosition=left;align=right;                        → Label left of shape
labelPosition=right;align=left;                        → Label right of shape
verticalLabelPosition=top;verticalAlign=bottom;        → Label above shape
verticalLabelPosition=bottom;verticalAlign=top;        → Label below shape

Decision Tree: Label Position vs. Alignment

Is labelPosition set to something other than "center"?
├── YES → Set align to the OPPOSITE value
│         labelPosition=left → align=right
│         labelPosition=right → align=left
└── NO  → align controls text alignment within the shape (default: center)

Is verticalLabelPosition set to something other than "middle"?
├── YES → Set verticalAlign to the OPPOSITE value
│         verticalLabelPosition=top → verticalAlign=bottom
│         verticalLabelPosition=bottom → verticalAlign=top
└── NO  → verticalAlign controls text alignment within the shape (default: middle)

Perimeter Matching

Non-rectangular shapes NEED a matching perimeter style value for correct edge connection:

Rectangles and rounded rectangles use the default perimeter and need NO explicit value.

References

• methods.md - Complete attribute and property reference
• examples.md - Working XML examples for all geometry scenarios
• anti-patterns.md - Common mistakes and how to avoid them