# The VBTTuning interface

This interface defines values that can be changed to maximize Trestle's performance on particular systems.

    INTERFACE VBTTuning;

    IMPORT Word;

    CONST
      BatchSize: CARDINAL = 325;
      BatchLatency: CARDINAL = 50000;
      HVParlim: CARDINAL = 100000;
      ZParlim: CARDINAL = 100000;
      ResumeLength: CARDINAL = 1;
      CombineLimit: CARDINAL
        = (BatchSize * ADRSIZE(Word.T)) DIV 2;

The value `BatchSize` is the number of `Word.T`'s in a standard painting batch.

The value `BatchLatency` is the number of microseconds before a paint batch is automatically forced.

The values `HVParlim` and `ZParlim` are the default minimum child areas (in pixels) for which `ZSplit` and `HVSplit` will fork separate repaint or reshaping threads.

`ResumeLength` is the size that a queue of paint batches must shrink to before a cross-address space filter will unblock a thread that painted into an overfull queue. It must be at least 1.

The value `CombineLimit` is the number of addressable units (e.g., bytes) in a batch beyond which Trestle will not consider combining another batch into it.

    END VBTTuning.