afaict, this is a limitation of the "particle API" used by Gem.

while the `pColor()` function (as used in `part_color.cpp:56`) has indeed an "alpha" value, this is only a scalar, and not part of the 3D(sic! there's now 4th dimension for the alpha) space that forms a domain.

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** [bugs:#228] part_color ignores alpha component**

**Status:** open **OS:** any **Release:** unknown **Labels:** particles **Created:** Tue Aug 19, 2014 04:24 PM UTC by Anonymous **Last Updated:** Wed Aug 20, 2014 02:53 PM UTC **Owner:** nobody

Using Gem 0.93.3 on Windows 7 32bit.

I noticed that when using a part_color, the 4th value (alpha component) is ignored. I looked at the code, and I think it is line 56 of part_color.cpp. When rendering, the color is not passed into the function.

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On 2014-08-19 18:24, Ticket 228 wrote:

Using Gem 0.93.3 on Windows 7 32bit.

I noticed that when using a part_color, the 4th value (alpha component) is ignored. I looked at the code, and I think it is line 56 of part_color.cpp. When rendering, the color is not passed into the function.

i was wondering whether you think that making [part_color] respect the alpha-value (of the 1st color) is a useful feature for Gem (or whether it might break your patches).

for a short discussion see [228].

to tear it down: [part_color] allows to specify a domain to "blend" between two colors. unfortunately only RGB values are taken into account (Alpha is ignored). more unfortunate, the current API (as used internally) would only allow to pass a single alpha-value, so the "blending" would not extend to opacity. instead we could use the alpha-value of the first color (instead of the currently fixed value of "1")

what do you think?

fgmasdr IOhannes

[228] https://sourceforge.net/p/pd-gem/bugs/228/