The Render Buffer is used to generated Effects data onto. For each Model/Group/Submodel, xLights creates a Rectangular Grid to render effects on to. The size of the buffer depends on the model type and settings. 16 strand by 40 pixels Mega Tree will have a 16x40 render buffer.
The Effect is overlaid onto the render buffer to calculate the color data of the individual pixels or lights.
Matix Render Buffer
Custom Model Render Buffer
Default Minimal Grid will Draws a 2D grip over the models in the group and attempt to put each pixel in its own box, Up to the Max Grid Size, Normally 400x400.
Credit: Keith Westley