What Doesn't MELT

Transformations

Shaderlight will retrace if you transform (move, rotate or scale) geometry, or if you move the camera's viewpoint. Transforming an object means that the pixels in the image no longer have an accurate picture of what parts of the 3D scene might affect them. Moving the camera means that the contents of every pixel change, because every pixel is now “looking” at a different part of the scene.

Materials

Although the majority of parameters in Materials, Environment, Lights and Textures can be altered without causing a retrace, there are some that will. As a general rule, items that change the direction or number of rays traced will invalidate the render and cause a retrace. Examples are:

Things that change the number of rays traced in the scene:

•	Making a surface reflective where it was previously matte.

•	Increasing the number of samples to improve the appearance of glossy reflections.

•	Altering the reflection falloff distance.

•	Introducing transparency where an object was previously opaque.

•	Increasing Ambient Occlusion samples.

•	Changing Ambient Occlusion maximum distance.

Things that alter the direction of rays traced in the scene:

•	Increasing the roughness of a reflective Art Professional material.

•	Increasing the amount or position of a bump map on a reflective surface.

•	Changing the amount or position of a displacement map.

•	Changing the Index of Refraction of a transparent object.

Although these will cause a full retrace at present, future releases will be capable of partial retrace so that only invalid parts of an image will be re-rendered.

Miscellaneous

There are a number of actions which have no influence on the image, yet will cause a full retrace as the change makes the scene state “undefined”. For example grouping or un-grouping objects, or adding a modifier to a mesh. For this release, Shaderlight will always retrace if it thinks there has been a change in the scene state, but we will be introducing more control over this in future.

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