# Difference Map

The Difference Map feature stores the influence of the deformer on each point in a vertex map, by converting the distance moved by each point into a value from 0% to 100%. You can then use that information to control the influence of other effects and materials (eg by using the vertex map in a 'Restriction' tag on later deformers). All of the Mega Deformer Pack deformers have a 'Difference Map' tab to access these features.

Difference Maps can only be used on polygon objects (you'll need to make primitives editable before applying vertex map tags).

This sphere is being deformed by an Impact Deformer, and thanks to the 'Difference Map' feature the influence of that deformer can be seen in a vertex map. To the right are the settings used to control how the map is created.

## Options

1. Tag - the Vertex Map tag to store the difference information in. Any vertex map tag of the same name on an object influenced by this deformer will be altered by the Difference Map functions.
2. Create Tags – use this button to quickly create new vertex map tags on the polygon objects that are influenced by this deformer, and use them to fill the 'Tag' field. This will always create new tags with a unique name, even if tags already exist.
3. Maximum length – the Difference Map function fills the vertex map with values from 0% to 100% depending on how far the points have been moved by the deformer. Use this setting to determine how far a point has to be moved before the vertex map will be set to 100% - points that move further will be capped at 100%.
4. Spline – this spline controls how the distances are mapped to vertex map values, the default is linear.

Some of the deformers additionally have a 'Mode' option in their 'Difference Map' tabs, use it to choose whether to calculate the difference map from the 'Distance' points move (the default mode), or the 'Angle' they are rotated by the deformer.

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