Hi,
while using shading in metapost I cannot get transparency work.
The transparency is simply ignored and the result is the same colour as with
no transparency specified.
Here's an example that demonstrates the problem:
\definecolor [a] [darkyellow]
\definecolor [b] [r=1, g=1, b=1, a=1, t=0]
\definecolor [c] [r=1, g=1, b=1, a=1, t=.5]
\definecolor [bg] [r=.8, g=.8, b=1]
% Define test background to see transparency (not) working
\defineoverlay[bg][\uniqueMPgraphic{bg}]
\startuniqueMPgraphic {bg}
fill unitsquare
xyscaled (\overlaywidth, \overlayheight) withcolor \MPcolor{bg};
picture pic; pic := nullpicture;
addto pic contour fullcircle scaled .5mm withcolor .2white;
for i=1 upto 52:
for j=1 upto 73:
addto currentpicture also pic shifted (4mm*i, 4mm*j);
endfor;
endfor;
\stopuniqueMPgraphic
\setupbackgrounds [page] [background=bg]
\starttext
\startMPcode
path p[];
p1 := unitsquare xyscaled (4cm, 2cm);
p2 := p1 yshifted -2.5cm;
p3 := p2 yshifted -2.5cm;
% Transparency does not work, background is white instead of full alpha
linear_shade(p1,0,\MPcolor{a},\MPcolor{b});
% Setting 2nd colour to background colour works only with plain coloured
% backgrounds not with patterns
linear_shade(p2,0,\MPcolor{a},\MPcolor{bg});
% Transparency with simple »fill« works as expected
fill p3 withcolor \MPcolor{c};
\stopMPcode
\stoptext
Thanks for any hints
Marco
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