Multipass

Compositing in multiple passes is the way that professionals create visual effects. Compositing in passes is the process of use multiple transforms to generate special visual effects. The multipass composition is divided into several stages as initial, stage₀, stage₁, ..., and final. The initial is the warm-up stage to make source images ready. Then the first transforms are completed in the stage₀. The outputs of stage₀ could be the inputs of the next stages. The final stage may render or store the result.

A Multipass Pattern

This diagram shows an example of the multipass. The P0, P1, P2 are input images. T0, T1, T2 are transforms. S is the final result. Each transform has two inputs, one output, and a progress value.

This is the output of the Fade transform T0 in stage₀ with value 0.7. The first input picture is the grass and the second is the bug.

This is the output of the Fade transform T1 in stage₀ with value 0.6. The first input picture is the bug and the second is the blue rainbow map. Notice the lighting on the left-bottom and right-top corners.

This is the output of the Fade transform T2 in stage₁ with value 0.7. The first input picture is the output of transform₀ and the second is the output of transform₁. It is the composition of three initial pictures: grass, bug, and blue rainbow.

mCL can easily implement this multipass pattern with snap command.

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Multipass

A Multipass Pattern