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@refX : The Marker Reference X Position Attribute

The refX attribute defines the horizontal reference point of a marker - the X coordinate within the marker’s coordinate system that aligns with the path vertex. This controls where the marker is positioned relative to the path point.

Usage

The refX attribute is used to:

  • Define the horizontal anchor point of the marker
  • Control how markers align with path vertices
  • Position marker content relative to the path
  • Create properly aligned arrowheads
  • Support data-driven marker positioning
  • Enable precise marker placement control
<svg xmlns="http://www.w3.org/2000/svg" width="400" height="200">
    <defs>
        <!-- Arrow with tip at path point -->
        <marker id="arrow" markerWidth="10" markerHeight="10"
                refX="10" refY="5" orient="auto">
            <polygon points="0,0 10,5 0,10" fill="#e74c3c"/>
        </marker>
    </defs>

    <line x1="50" y1="100" x2="350" y2="100"
          stroke="#2c3e50" stroke-width="2"
          marker-end="url(#arrow)"/>
</svg>

Supported Values

Value Type Description Example
<length> Number in marker units refX="5"
Default 0 if not specified (default)

Common Values 

<!-- Left edge (0) -->
refX="0"

<!-- Center (markerWidth / 2) -->
refX="5"    <!-- for markerWidth="10" -->

<!-- Right edge (markerWidth) -->
refX="10"   <!-- for markerWidth="10" -->

<!-- Decimal values -->
refX="7.5"

<!-- Negative values (outside marker) -->
refX="-2"

Supported Elements

The refX attribute is supported on:

Data Binding

Dynamic Reference Point

Adjust reference position based on marker size:

<!-- Model: { markerSize: 12, alignCenter: true } -->
<svg width="400" height="200">
    <defs>
        <marker id="dynamic-ref"
                markerWidth=""
                markerHeight=""
                refX=""
                refY=""
                orient="auto">
            <polygon points="0,0 , 0,"
                     fill="#3498db"/>
        </marker>
    </defs>

    <line x1="50" y1="100" x2="350" y2="100"
          stroke="#2c3e50" stroke-width="2"
          marker-end="url(#dynamic-ref)"/>
</svg>

Conditional Alignment

Change alignment based on marker type:

<!-- Model: { markerType: 'arrow', arrowTipAlign: true } -->
<svg width="400" height="200">
    <defs>
        <marker id="aligned-marker"
                markerWidth="10" markerHeight="10"
                refX=""
                refY="5"
                orient="auto">
            <polygon points="0,0 10,5 0,10" fill="#e74c3c"/>
        </marker>
    </defs>

    <line x1="50" y1="100" x2="350" y2="100"
          stroke="#2c3e50" stroke-width="2"
          marker-end="url(#aligned-marker)"/>
</svg>

Data-Driven Marker Positioning 

<!-- Model: {
    markers: [
        { size: 10, alignType: 'center', color: '#e74c3c' },
        { size: 12, alignType: 'tip', color: '#3498db' },
        { size: 14, alignType: 'base', color: '#2ecc71' }
    ],
    getRefX: function(m) {
        if (m.alignType === 'center') return m.size / 2;
        if (m.alignType === 'tip') return m.size;
        return 0;
    }
} -->
<svg width="300" height="250">
    <defs>
        <template data-bind="">
            <marker id="marker-"
                    markerWidth="" markerHeight=""
                    refX=""
                    refY=""
                    orient="auto">
                <polygon points="0,0 , 0,"
                         fill=""/>
            </marker>
        </template>
    </defs>

    <template data-bind="">
        <line x1="50" y1="50"
              x2="250" y2="50"
              stroke="#2c3e50" stroke-width="2"
              marker-end="url(#marker-)"/>
    </template>
</svg>

Notes

Reference Point Concept

The refX coordinate within the marker aligns with the path vertex:

<!-- Arrow tip at path point -->
<marker markerWidth="10" markerHeight="10" refX="10" refY="5">
    <!-- Point (10, 5) in marker aligns with path vertex -->
    <polygon points="0,0 10,5 0,10"/>
</marker>

<!-- Arrow center at path point -->
<marker markerWidth="10" markerHeight="10" refX="5" refY="5">
    <!-- Point (5, 5) in marker aligns with path vertex -->
    <polygon points="0,0 10,5 0,10"/>
</marker>

Common Alignment Patterns

Tip alignment (arrows):

<!-- Arrow tip exactly at path end -->
<marker markerWidth="10" markerHeight="10"
        refX="10" refY="5" orient="auto">
    <polygon points="0,0 10,5 0,10"/>
</marker>

Center alignment (dots, circles):

<!-- Circle center at path point -->
<marker markerWidth="10" markerHeight="10"
        refX="5" refY="5">
    <circle cx="5" cy="5" r="4"/>
</marker>

Base alignment:

<!-- Base at path point, marker extends outward -->
<marker markerWidth="10" markerHeight="10"
        refX="0" refY="5" orient="auto">
    <polygon points="0,0 10,5 0,10"/>
</marker>

Relationship with markerWidth

refX should be within the range 0 to markerWidth:

<!-- For markerWidth="10" -->
refX="0"    <!-- Left edge -->
refX="5"    <!-- Center -->
refX="10"   <!-- Right edge -->

Values outside this range position the reference point outside the marker viewport (valid but uncommon).

Default Value

If refX is not specified, the default is 0 (left edge):

<!-- These are equivalent -->
<marker id="m1" markerWidth="10" markerHeight="10">
<marker id="m2" markerWidth="10" markerHeight="10" refX="0">

Coordinate System

refX uses the marker’s own coordinate system:

  • Independent of markerUnits
  • Always relative to marker viewport (0 to markerWidth)
  • Not affected by stroke width or scaling

Visual Impact

Different refX values change where the marker appears:

<!-- refX="0": marker starts at path point -->
<marker refX="0" refY="5">
    <!-- Marker extends forward from point -->
</marker>

<!-- refX="5": marker centered on path point -->
<marker refX="5" refY="5">
    <!-- Marker straddles the point -->
</marker>

<!-- refX="10": marker ends at path point -->
<marker refX="10" refY="5">
    <!-- Marker extends backward to point -->
</marker>

Orient Interaction

With orient="auto", the marker rotates, but refX always refers to the marker’s local coordinate system before rotation.

Precision

Use decimal values for precise positioning:

<!-- Fine-tuned alignment -->
<marker refX="9.5" refY="5.25">

Examples

Arrow with Tip Alignment (refX = markerWidth) 

<svg width="400" height="150">
    <defs>
        <marker id="tip-aligned" markerWidth="12" markerHeight="12"
                refX="12" refY="6" orient="auto">
            <polygon points="0,0 12,6 0,12" fill="#e74c3c"/>
        </marker>
    </defs>

    <line x1="50" y1="75" x2="350" y2="75"
          stroke="#34495e" stroke-width="2"
          marker-end="url(#tip-aligned)"/>
    <text x="200" y="50" text-anchor="middle" font-size="11">refX="12" (tip at path point)</text>
</svg>

Arrow with Center Alignment (refX = markerWidth / 2) 

<svg width="400" height="150">
    <defs>
        <marker id="center-aligned" markerWidth="12" markerHeight="12"
                refX="6" refY="6" orient="auto">
            <polygon points="0,0 12,6 0,12" fill="#3498db"/>
        </marker>
    </defs>

    <line x1="50" y1="75" x2="350" y2="75"
          stroke="#34495e" stroke-width="2"
          marker-end="url(#center-aligned)"/>
    <text x="200" y="50" text-anchor="middle" font-size="11">refX="6" (center at path point)</text>
</svg>

Arrow with Base Alignment (refX = 0) 

<svg width="400" height="150">
    <defs>
        <marker id="base-aligned" markerWidth="12" markerHeight="12"
                refX="0" refY="6" orient="auto">
            <polygon points="0,0 12,6 0,12" fill="#2ecc71"/>
        </marker>
    </defs>

    <line x1="50" y1="75" x2="350" y2="75"
          stroke="#34495e" stroke-width="2"
          marker-end="url(#base-aligned)"/>
    <text x="200" y="50" text-anchor="middle" font-size="11">refX="0" (base at path point)</text>
</svg>

Comparison of Different refX Values 

<svg width="400" height="300">
    <defs>
        <marker id="ref-0" markerWidth="16" markerHeight="10"
                refX="0" refY="5" orient="auto">
            <polygon points="0,0 16,5 0,10" fill="#e74c3c"/>
            <circle cx="0" cy="5" r="1" fill="white"/>
        </marker>
        <marker id="ref-8" markerWidth="16" markerHeight="10"
                refX="8" refY="5" orient="auto">
            <polygon points="0,0 16,5 0,10" fill="#3498db"/>
            <circle cx="8" cy="5" r="1" fill="white"/>
        </marker>
        <marker id="ref-16" markerWidth="16" markerHeight="10"
                refX="16" refY="5" orient="auto">
            <polygon points="0,0 16,5 0,10" fill="#2ecc71"/>
            <circle cx="16" cy="5" r="1" fill="white"/>
        </marker>
    </defs>

    <line x1="50" y1="60" x2="300" y2="60" stroke="#34495e" stroke-width="2" marker-end="url(#ref-0)"/>
    <circle cx="300" cy="60" r="3" fill="orange"/>
    <text x="320" y="65" font-size="10">refX="0"</text>

    <line x1="50" y1="150" x2="300" y2="150" stroke="#34495e" stroke-width="2" marker-end="url(#ref-8)"/>
    <circle cx="300" cy="150" r="3" fill="orange"/>
    <text x="320" y="155" font-size="10">refX="8"</text>

    <line x1="50" y1="240" x2="300" y2="240" stroke="#34495e" stroke-width="2" marker-end="url(#ref-16)"/>
    <circle cx="300" cy="240" r="3" fill="orange"/>
    <text x="320" y="245" font-size="10">refX="16"</text>
</svg>

Circle Marker with Center refX 

<svg width="400" height="150">
    <defs>
        <marker id="centered-circle" markerWidth="14" markerHeight="14"
                refX="7" refY="7">
            <circle cx="7" cy="7" r="6" fill="#9b59b6" stroke="#8e44ad" stroke-width="1"/>
            <circle cx="7" cy="7" r="1" fill="white"/>
        </marker>
    </defs>

    <line x1="50" y1="75" x2="350" y2="75"
          stroke="#34495e" stroke-width="2"
          marker-end="url(#centered-circle)"/>
    <circle cx="350" cy="75" r="3" fill="orange"/>
    <text x="200" y="50" text-anchor="middle" font-size="11">Centered circle: refX="7" (half of 14)</text>
</svg>

Diamond with Different refX Alignments 

<svg width="400" height="250">
    <defs>
        <marker id="diamond-left" markerWidth="12" markerHeight="12"
                refX="0" refY="6" orient="auto">
            <path d="M 0,6 L 6,0 L 12,6 L 6,12 Z" fill="#f39c12"/>
            <circle cx="0" cy="6" r="1" fill="white"/>
        </marker>
        <marker id="diamond-center" markerWidth="12" markerHeight="12"
                refX="6" refY="6" orient="auto">
            <path d="M 0,6 L 6,0 L 12,6 L 6,12 Z" fill="#f39c12"/>
            <circle cx="6" cy="6" r="1" fill="white"/>
        </marker>
        <marker id="diamond-right" markerWidth="12" markerHeight="12"
                refX="12" refY="6" orient="auto">
            <path d="M 0,6 L 6,0 L 12,6 L 6,12 Z" fill="#f39c12"/>
            <circle cx="12" cy="6" r="1" fill="white"/>
        </marker>
    </defs>

    <line x1="50" y1="50" x2="300" y2="50" stroke="#34495e" stroke-width="2" marker-end="url(#diamond-left)"/>
    <circle cx="300" cy="50" r="3" fill="orange"/>
    <text x="320" y="55" font-size="9">refX="0"</text>

    <line x1="50" y1="125" x2="300" y2="125" stroke="#34495e" stroke-width="2" marker-end="url(#diamond-center)"/>
    <circle cx="300" cy="125" r="3" fill="orange"/>
    <text x="320" y="130" font-size="9">refX="6"</text>

    <line x1="50" y1="200" x2="300" y2="200" stroke="#34495e" stroke-width="2" marker-end="url(#diamond-right)"/>
    <circle cx="300" cy="200" r="3" fill="orange"/>
    <text x="320" y="205" font-size="9">refX="12"</text>
</svg>

Square Marker with Corner Reference 

<svg width="400" height="150">
    <defs>
        <marker id="square-corner" markerWidth="12" markerHeight="12"
                refX="12" refY="12">
            <rect width="12" height="12" fill="#e74c3c" stroke="#c0392b" stroke-width="1"/>
            <circle cx="12" cy="12" r="1.5" fill="white"/>
        </marker>
    </defs>

    <line x1="50" y1="75" x2="350" y2="75"
          stroke="#34495e" stroke-width="2"
          marker-end="url(#square-corner)"/>
    <circle cx="350" cy="75" r="3" fill="orange"/>
    <text x="200" y="50" text-anchor="middle" font-size="11">Square corner at path point: refX="12", refY="12"</text>
</svg>

Star with Center Reference 

<svg width="400" height="150">
    <defs>
        <marker id="star-center" markerWidth="20" markerHeight="20"
                refX="10" refY="10">
            <path d="M 10,2 L 12,8 L 18,8 L 13,12 L 15,18 L 10,14 L 5,18 L 7,12 L 2,8 L 8,8 Z"
                  fill="#f1c40f" stroke="#f39c12" stroke-width="1"/>
            <circle cx="10" cy="10" r="1" fill="white"/>
        </marker>
    </defs>

    <line x1="50" y1="75" x2="350" y2="75"
          stroke="#34495e" stroke-width="2"
          marker-end="url(#star-center)"/>
    <circle cx="350" cy="75" r="3" fill="orange"/>
    <text x="200" y="50" text-anchor="middle" font-size="11">Star centered: refX="10", refY="10"</text>
</svg>

Custom Icon with Precise Positioning 

<svg width="400" height="150">
    <defs>
        <marker id="custom-icon" markerWidth="24" markerHeight="24"
                refX="12" refY="12">
            <rect x="2" y="2" width="20" height="20" rx="4" fill="#3498db" stroke="#2980b9" stroke-width="2"/>
            <path d="M 8,12 L 11,15 L 16,10" fill="none" stroke="white" stroke-width="2" stroke-linecap="round"/>
            <circle cx="12" cy="12" r="1.5" fill="yellow"/>
        </marker>
    </defs>

    <line x1="50" y1="75" x2="350" y2="75"
          stroke="#34495e" stroke-width="3"
          marker-end="url(#custom-icon)"/>
    <circle cx="350" cy="75" r="3" fill="orange"/>
    <text x="200" y="50" text-anchor="middle" font-size="11">Complex icon centered: refX="12"</text>
</svg>

Decimal refX Value 

<svg width="400" height="150">
    <defs>
        <marker id="decimal-ref" markerWidth="15" markerHeight="10"
                refX="13.5" refY="5" orient="auto">
            <polygon points="0,0 15,5 0,10" fill="#9b59b6"/>
            <circle cx="13.5" cy="5" r="1" fill="white"/>
        </marker>
    </defs>

    <line x1="50" y1="75" x2="350" y2="75"
          stroke="#34495e" stroke-width="2"
          marker-end="url(#decimal-ref)"/>
    <circle cx="350" cy="75" r="3" fill="orange"/>
    <text x="200" y="50" text-anchor="middle" font-size="11">Precise positioning: refX="13.5"</text>
</svg>

Offset Reference (negative refX) 

<svg width="400" height="150">
    <defs>
        <marker id="offset-ref" markerWidth="12" markerHeight="12"
                refX="-3" refY="6" orient="auto">
            <polygon points="0,0 12,6 0,12" fill="#e74c3c"/>
            <circle cx="-3" cy="6" r="1.5" fill="white" stroke="black" stroke-width="0.5"/>
        </marker>
    </defs>

    <line x1="50" y1="75" x2="350" y2="75"
          stroke="#34495e" stroke-width="2"
          marker-end="url(#offset-ref)"/>
    <circle cx="350" cy="75" r="3" fill="orange"/>
    <text x="200" y="50" text-anchor="middle" font-size="11">Negative refX="-3" (offset from marker)</text>
</svg>

Multi-Marker Path with Different refX 

<svg width="400" height="200">
    <defs>
        <marker id="start-ref" markerWidth="10" markerHeight="10"
                refX="5" refY="5">
            <circle cx="5" cy="5" r="4" fill="#2ecc71"/>
            <circle cx="5" cy="5" r="1" fill="white"/>
        </marker>
        <marker id="mid-ref" markerWidth="8" markerHeight="8"
                refX="4" refY="4">
            <circle cx="4" cy="4" r="3" fill="#3498db"/>
        </marker>
        <marker id="end-ref" markerWidth="12" markerHeight="12"
                refX="12" refY="6" orient="auto">
            <polygon points="0,0 12,6 0,12" fill="#e74c3c"/>
            <circle cx="12" cy="6" r="1" fill="white"/>
        </marker>
    </defs>

    <polyline points="50,150 120,50 200,120 280,60 350,150"
              fill="none" stroke="#34495e" stroke-width="2"
              marker-start="url(#start-ref)"
              marker-mid="url(#mid-ref)"
              marker-end="url(#end-ref)"/>
</svg>

Wide Marker with Different Alignments 

<svg width="400" height="250">
    <defs>
        <marker id="wide-left" markerWidth="24" markerHeight="12"
                refX="0" refY="6" orient="auto">
            <rect width="24" height="12" rx="2" fill="#3498db"/>
            <circle cx="0" cy="6" r="1.5" fill="white"/>
        </marker>
        <marker id="wide-center" markerWidth="24" markerHeight="12"
                refX="12" refY="6" orient="auto">
            <rect width="24" height="12" rx="2" fill="#3498db"/>
            <circle cx="12" cy="6" r="1.5" fill="white"/>
        </marker>
        <marker id="wide-right" markerWidth="24" markerHeight="12"
                refX="24" refY="6" orient="auto">
            <rect width="24" height="12" rx="2" fill="#3498db"/>
            <circle cx="24" cy="6" r="1.5" fill="white"/>
        </marker>
    </defs>

    <line x1="50" y1="50" x2="300" y2="50" stroke="#34495e" stroke-width="2" marker-end="url(#wide-left)"/>
    <circle cx="300" cy="50" r="3" fill="orange"/>

    <line x1="50" y1="125" x2="300" y2="125" stroke="#34495e" stroke-width="2" marker-end="url(#wide-center)"/>
    <circle cx="300" cy="125" r="3" fill="orange"/>

    <line x1="50" y1="200" x2="300" y2="200" stroke="#34495e" stroke-width="2" marker-end="url(#wide-right)"/>
    <circle cx="300" cy="200" r="3" fill="orange"/>
</svg>

Gradient Marker with Centered refX 

<svg width="400" height="150">
    <defs>
        <linearGradient id="grad-h" x1="0%" y1="0%" x2="100%" y2="0%">
            <stop offset="0%" stop-color="#667eea"/>
            <stop offset="100%" stop-color="#764ba2"/>
        </linearGradient>

        <marker id="gradient-centered" markerWidth="18" markerHeight="18"
                refX="9" refY="9">
            <circle cx="9" cy="9" r="8" fill="url(#grad-h)" stroke="#5a67d8" stroke-width="1"/>
            <circle cx="9" cy="9" r="1.5" fill="white"/>
        </marker>
    </defs>

    <line x1="50" y1="75" x2="350" y2="75"
          stroke="#34495e" stroke-width="3"
          marker-end="url(#gradient-centered)"/>
    <circle cx="350" cy="75" r="3" fill="orange"/>
    <text x="200" y="50" text-anchor="middle" font-size="11">Gradient marker centered: refX="9"</text>
</svg>

Complex Shape with Custom refX 

<svg width="400" height="150">
    <defs>
        <marker id="complex-ref" markerWidth="20" markerHeight="16"
                refX="20" refY="8" orient="auto">
            <path d="M 0,8 L 10,0 L 20,8 L 10,16 Z" fill="#e74c3c" stroke="#c0392b" stroke-width="1"/>
            <circle cx="20" cy="8" r="1.5" fill="white" stroke="black" stroke-width="0.5"/>
        </marker>
    </defs>

    <line x1="50" y1="75" x2="350" y2="75"
          stroke="#34495e" stroke-width="2"
          marker-end="url(#complex-ref)"/>
    <circle cx="350" cy="75" r="3" fill="orange"/>
    <text x="200" y="50" text-anchor="middle" font-size="11">Complex shape: refX="20" (right tip)</text>
</svg>

See Also