Guide Flow Modifier

The Guide Flow modifier controls which way hair flows across the surface using a pin-based system. Think of it like combing hair — you place pins on the surface that define direction and bend, and guides smoothly follow them.

What is Guide Flow?

Guide Flow is a guide-level modifier that shapes guide curves using FlowPins. Each pin defines a direction and influence radius on the surface. Guides within a pin's radius are bent to follow the pin's direction, with smooth blending between overlapping pins.

Visual effect: Hair flows in specific directions you define. Strands rotate and bend to follow your flow pattern.

When to use: Almost always. Natural hair has flow direction — forward on top, downward on sides, swirled at the crown. Use this for partings, swirls, styled looks, or natural flow patterns.

How It Works

You place pins on the mesh surface by clicking and dragging. Each pin has:

  • A position on the surface
  • A direction it points toward
  • A radius of influence

Guides within a pin's radius smoothly bend to follow the pin's direction. When multiple pins overlap, their directions blend together naturally — no hard edges or sudden transitions.

The system processes each point along a guide individually, so you get smooth, flowing curves rather than rigid rotations.

Note: This replaced the old arrow-based "Flow Direction" modifier. Old scenes load fine but the legacy modifier is inactive. Use Guide Flow for all new work.

FlowPin Editor

The FlowPin editor is the primary interaction mode.

Entering Pin Edit Mode

Click the "Edit Pins" button in the Guide Flow modifier panel.

Controls

| Action | Effect | |--------|--------| | LMB click + drag on surface | Place new pin (drag sets direction) | | LMB drag existing pin | Move pin position | | RMB drag pin handle | Adjust pin direction | | Scroll wheel on pin | Adjust pin radius | | DEL / X | Delete selected pin | | Ctrl+Z | Undo | | ESC / Enter | Exit pin edit mode |

Pin Placement Tips

  • Drag in the direction you want hair to flow
  • Longer drag = clearer direction (doesn't affect strength)
  • Pins update guides in real-time as you place them
  • Changes apply instantly — no need to click "Apply"

Two Passes: Direction + Shape

Guide Flow has two independent passes that can be toggled:

Enable Direction

Rotates guides to face the pin direction (the "combing" effect). This controls which way hair points.

Enable Shape

Applies the Bend Profile curve to shape how guides bend from root to tip. This controls the physical bending behavior.

Both are enabled by default. You can disable either for specific effects.

Bend Profile

The Bend Profile curve controls how much guides bend along their length.

Default (Smooth):

  • Root: 0.0 (no bending — stays fixed to scalp)
  • Mid: gradual increase
  • Tip: 1.0 (full bending)

Preset buttons:

  • Linear — Straight ramp from 0 to 1
  • Smooth — Natural S-curve (default)
  • Late — Straight until tips, then bend
  • Early — Bend near root, straight tips

Tip: The default Smooth profile is most natural. Roots stay fixed, tips bend fully — just like real hair.

Options Panel

Strength

Overall flow effect strength (0.0–1.0, default 1.0).

Preserve Length

Keep strand segment lengths constant after flow is applied. Default: ON. Leave this on to prevent unnatural stretching.

Use Pin Length

When enabled, dragging a longer pin stretches guides inside its radius proportionally. Default: OFF.

Useful for creating length variation driven by flow — e.g., longer hair where you comb it back, shorter where it's pushed forward.

Mask Support

Guide Flow supports texture masks like all modifiers:

  • Paint a mask to control where flow has effect
  • White = full flow, Black = no flow
  • Useful for blending styled areas with natural areas

Practical Examples

Natural Head Hair Flow

  1. Enter pin edit mode
  2. Place pins flowing backward from forehead
  3. Place pins flowing downward on sides
  4. Place a swirl pin at the crown
  5. Adjust radii so pins overlap smoothly
  6. Exit pin mode

Center Parting

  1. Place two pins on either side of the center line
  2. Point left pin to the left, right pin to the right
  3. Adjust radii to create a clean separation

Beard with Curl-Under

  1. Place pins pointing downward on chin
  2. Use Bend Profile "Late" preset
  3. Tips curl under naturally due to late bending

Short Fur (Surface Hugging)

  1. Place pins following body contours
  2. Use high strength
  3. Combine with Surface Offset modifier for clearance

Tips

  • Few pins go a long way. Pins blend smoothly, so 5–10 well-placed pins can define an entire hairstyle.
  • Use large radii for broad flow, small radii for local control.
  • Scroll to resize — quickly adjust pin radius without leaving edit mode.
  • Preserve Length ON — always keep this on unless you specifically want stretching.
  • Combine with Clumping — Flow defines direction, Clumping adds structure on top.

Common Mistakes

  • Too many pins: Overlapping pins with conflicting directions create chaos. Use fewer, well-placed pins.
  • Forgetting to exit pin mode: ESC or Enter to exit. Changes apply in real-time during editing.
  • Disabling Preserve Length: Causes unnatural stretching. Keep it on.
  • Not using Bend Profile: The default Smooth profile is natural. A flat profile (uniform bending) looks artificial.