New subject: transparent colours in custom symbols not any more transparent than standard colours

10 Nov 2012

      Taking inspiration from Martins recent post on transparent colours I thought
I might make my custom point water and area water transparent, or at least
behave better with 'transparency on' than the standard non-transparent
colours.  Alas the code compiles without fuss, but the result is identical
to the result when using standard (opaque) colour definitions.

In my layout I have, in the order called.

Define the area and point water 

def p_water (expr pos,theta,sc,al)=

    U:=(.425u,.3u);

    T:=identity aligned al rotated theta scaled sc shifted pos;

    pickup PenD;

    p:=fullcircle xscaled (1.2u) yscaled (0.8u) randomized (0.1u) rotated
uniformdeviate (-45);

    %if known colour_water_bg: thfill p withcolor colour_water_bg; else:
thfill p withcolor white; fi; 

    if known tr_colour_water_bg: thfill p withtransparentcolor
tr_colour_water_bg; else: thfill p withtransparentcolor tr_white; fi;

    thfill p withpattern pattern_water; %%% withcolor black;  %but with
failed attempt at black hatch

    thdraw p;   %outline

enddef; 

def a_water (expr Path) =

  T:=identity;

  % thclean Path;

  pickup PenD;

  % if known colour_water_bg: thfill Path withcolor colour_water_bg; else:
thfill Path withcolor white; fi; 

   if known tr_colour_water_bg: thfill Path withtransparentcolor
tr_colour_water_bg; else: thfill Path withtransparentcolor tr_white; fi;   

  thfill Path withpattern pattern_water;  

  %%thdraw Path;  %outline, not needed as area drawn is defined by line
border anyway

enddef;

Optionally define the colours (the tr_white not needed as it is defined in
the default distribution)

                        !color colour_water_bg; %! forces interpretation as
metapost

                        colour_water_bg := (0.86,1,1);      %light blue

                        def_transparent_rgb(tr_colour_water_bg, 0.86, 1, 1);

and then

             transparency on     

             opacity 50         

Everything in these examples is in a single scrap.

I have checked that my code is being used by changing the colours, for
example from tr_white to tr_black etc and these changes are reflected
properly, it's just that they are not transparent.

In Adobe Reader it looks like this (below) (the water on the right is
definitely not transparent - the rock place bottom is obscured)

Adobe also seems to make the colours and line weights different to the
others - incorrectly I suspect.

If I run this example with transparency off (but still using my custom
transparent colours), the result is identical EXCEPT all the colours are
much more intense.

In Foxit Reader it looks like this (below) with transparency on (Foxit
always makes everything transparent when transparency is on, so it is not
really a test)  So again, no difference whether using transparent colour
definitions or non-transparent.

When transparency is off, it looks exactly the same as in Adobe.

In Evince it looks like this (after about 1 minute to load the modest
file-Evince also behaves just like Foxit, but has a problem with hatches
extending out into the bounding box as well)

So as you can see the viewing software may be masking (a little) what
Therion is really trying to do, however it seems to be somewhat like either
almost everything is opaque, or almost everything is transparent, and the
promise that transparent colours seem to offer some more control cannot be
realised?

What I would like is something closer to what Adobe is rendering (with the
finer line work of Foxit) , but with the 'rock-border place bottom' showing
through the water when the water is defined with a transparent colour.

I guess when transparency is on, water and sump should always be transparent
to underlying objects, but closed rock-borders and the rocks in 'area
blocks' should never be.  After all that maybe I need to be looking at the
rock-border and area blocks definitions?

Any ideas why transparent colours make no difference at all?

Any ideas how to make the rocks in area blocks and closed rock-borders
opaque to any objects (in the same scrap) beneath them without messing up
the transparency of other objects?

Bruce

transparent colours in custom symbols not any more transparent than standard colours

Bruce

Martin Budaj

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