Guide Flow
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
Three ways to set direction
Pins are one of three. All feed the same solver, all are non-destructive, and they compose — pins take authority where they have it, the painted field owns everything else.
| Tool | What you do | Best for |
|---|---|---|
| Pins | Place and drag pins on the surface | Broad, sparse direction; a handful defines a style |
| Paint Flow | Drag a brush across the scalp | Fine control, partings, working into detail |
| Draw Flow Curves | Draw a stroke; the fur follows its direction | Long sweeps across a body; strokes stay editable |
Paint Flow
Press Paint Flow to comb by dragging directly on the scalp. The direction you drag is written per-vertex into the mesh and spread from there to everywhere you did not paint, so a few strokes cover a whole animal.
| Input | Action |
|---|---|
| Drag | Comb in the direction of the drag |
| Shift | Smooth — average the field with its neighbours |
| Ctrl | Erase back to no data (guides return to generated) |
| Wheel / [ ] | Brush radius |
| Shift + Wheel | Strength |
| D | Cycle the overlay: coverage tint → off → direction lines |
| X | Clear the whole painted field |
| Esc / RMB | Finish |
Reading the overlay. The coverage tint shades the scalp on the familiar weight ramp — blue where the field is weak, red where it is strong, and fully transparent where you have not painted at all, so it shows coverage rather than repainting the whole surface. The direction lines run dark at the root and bright at the tip, so you can see which way the flow points and not just which axis it lies on.
The paint is per-vertex, so its resolution is your scalp’s resolution. On a coarse mesh, subdivide before painting. The tool warns you when a mesh is too sparse to hold a stroke.
Draw Flow Curves
Press Draw Flow Curves and drag a stroke across the scalp — the fur follows the direction of the stroke, and the solver spreads it into everywhere you did not draw. Wheel resizes, Ctrl+Z undoes the last stroke, X clears all.
The difference from painting: the strokes are kept, so one can be removed later. Painting has no inverse — you can only paint over it.
Mirror
Mirror covers pins and the painted field. Paint or pin one half and the other reads the reflection — nothing is written into your paint, so turning it off gives back exactly what you drew. Where a half carries its own paint, that paint wins over its reflection. The plane follows the object transform, so it survives moving, rotating and scaling the scalp. Where the mesh is not symmetric, the reflection is refused rather than approximated.
Local Pins and symmetry tolerances
- Pin Local Extent — limits a pin’s authority to its own radius instead of letting it influence the whole surface. With it on, pins own their patches and the painted field owns every gap, which is what makes the two compose rather than compete. Off by default, so existing grooms are unchanged.
- Symmetry Threshold — how far a reflected pin may land from the real surface before the reflection is refused. Expressed as a fraction of the mesh size, so it means the same thing at any scene scale.
- Ignore Distance — pins closer to the symmetry plane than this are not mirrored, since their twin would land on top of them and double the field weight along the seam.
- Surface Field / Spread — enables the painted direction channel, and controls how far a painted stroke diffuses into the areas you did not paint.
Practical Examples
Natural Head Hair Flow
- Enter pin edit mode
- Place pins flowing backward from forehead
- Place pins flowing downward on sides
- Place a swirl pin at the crown
- Adjust radii so pins overlap smoothly
- Exit pin mode
Center Parting
- Place two pins on either side of the center line
- Point left pin to the left, right pin to the right
- Adjust radii to create a clean separation
Beard with Curl-Under
- Place pins pointing downward on chin
- Use Bend Profile "Late" preset
- Tips curl under naturally due to late bending
Short Fur (Surface Hugging)
- Place pins following body contours
- Use high strength
- 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.