We now link the third menu button from the VTS root menu to the slide show 3.1 as following. We want to be able to choose randomly one slide show from the group of five shows 3.1 through 3.5 when this menu button is pressed. The random selection logic is performed by the pre-commands of the slide show 3.1 described in the next section.

DVD-Lab stores the required data structures of each slide show in a separate program chain (PGC). Before a slide show is displayed, any DVD virtual command if present in the pre-command section of the PGC is executed. The DVD virtual machine instruction "Rnd" is used here to generate a random number from a specified range. Since we want to select randomly from five individual slide shows, we use this virtual command to randomize five values from 1 to 5. The generated number decides which slide show to play back. If we have a large number of slide shows, we can provide additional enhancements to the random generation logic such as no repetition of the last selected slide show, uneven distribution of random numbers, etc. By programming the virtual commands in this pre-command section, there are many other possibilities to customize the playback requirements. The following screen shot shows how to generate and edit the required virtual commands for the slide show 3.1 (right click to display the context menu).

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