Issues with transparency with psevents

[Esteban82]

I created an earthquake animation (similar to Animation 8) and wanted the events to appear with transparency. I noticed a few issues: currently, transparency is only supported during the coda phase, which only exists for events with finite duration.

What confuses me is that transparency behaves differently from other properties, such as size or color (see figure below). I’m wondering if there’s a deeper reason why transparency was implemented this way and I’m just not seeing it.

I think I could make the modifications in the source file, but I might need some help.

Issues observed

1. The -t option is not available for events.
2. Transparency is hard-wired to 0 in the plateau, decay, and normal phases. See lines 839, 846, and 851.
3. Two transparency values can be set with -Mtval1[+cval2]. It seems that the first value (val1) is only used in the previous phase (with a transition in the rise phase). For symbols, this makes little sense since their size is set to 0 at that point—perhaps it’s more relevant for text?
4. Transparency works fine in the fade and coda phases.

Help needed

I believe I can implement the required changes, but right now I would appreciate:

1. Any comments on how transparency is supposed to work—how Paul originally intended it.
2. Confirmation that I can safely use the undocumented psevents -/ options to get the event functions at t = 0. See line 629.

[Esteban82]

For the records, in this other issue Paul said (#8328 (comment)):

How are you passing in stroke and fill transparency for the text? With extra columns and -t[+f][+s] ?

So, Paul tought that the -t option was available in events.

[remkos]

Just for info. What you need here is indeed the -t option.
The way it is implemented (I did quite a bit of the work at the time) is that it adds command to the Postscript output that is interpreted by Ghostscript in the conversion to PDF (or raster formats) to have the next layer be transparent. (This does actually not work for Postscript (printers) but works great with Ghostscript, as you can see.)