Hi all
I'm trying to create graded transparency over an area similar to the
effect produced using lmt_shade, where one colour goes to another colour
over a continuum, but with graded transparency we would go from say 0 to
1 transparency, for a single colour. See the MWE below.
I have tried this by creating a loop which draws a linear path, yshifted
the thickness of the pen, with transparency calculated for each step
over the a predetermined height on the page. I have also tried a similar
way for a circular path but in this case the path is repeatedly drawn
scaled in a loop. The MWE below works OK but when I zoom into the graded
transparency areas lines begin to appear which would suggest that their
is a better way to do what I want. This is borne out if you zoom into a
lmt-shade area, one colour smoothly becomes another colour. I've put
examples of this in the MWE. I'm guessing the way lmt_shade areas are
drawn is the way to go. Is this likely to be easy to code for what I
want to do?
Best Wishes
Keith McKay
%%%MWE%%
\setuppapersize[A4,portrait]
\usecolors[crayola]
\starttext
\startMPpage %page 1
StartPage;
numeric maxTransp;% Must be between 0 and 1
numeric opHeight; % Opaque area height on page
path t;
string p[]; p[5] = "RadicalRed"; p[10] = "LemonYellow"; p[15] =
"MiddleGreen"; p[20] = "CadetBlue"; p[25] = "white";
maxTransp := 1;
opHeight := 2.5; %cm
for k= 5, 10, 15, 20, 25:
draw lmt_text [
text = "opaque",
color = "black",
style = "bold",
anchor = "lft",
position = (-1mm,2mm),
] xsized .95TextWidth ysized 7cm shifted(22cm,(k - 2)*cm);
t := (1cm, k*cm) -- (20cm, k*cm); %Square opaque area
draw t withpen pensquare scaled .25pt withcolor p[k]
withtransparency("normal",maxTransp);
for i = 0 step 0.25until (opHeight*72/2.54):
r := (i/(opHeight*72/2.54))*maxTransp; %calculate transparency
draw t yshifted (-i-.25)*pt withpen pensquare scaled .25pt withcolor
p[k] withtransparency("normal",(maxTransp-r));
draw t yshifted (i+.25)*pt withpen pensquare scaled .25pt withcolor p[k]
withtransparency("normal",(maxTransp-r));
endfor;
endfor;
draw lmt_shade [
path = fullsquare xyscaled(19cm,2cm),
direction = "up",
alternative = "linear",
colors = { "red", "blue" },
] shifted(10.5cm,1.5cm);
StopPage;
\stopMPpage
\page
\startMPpage %page 2
StartPage;
numeric maxTransp;% Must be between 0 and 1
numeric opHeight; % Opaque area height
path t, u;
string p[]; p[5] = "RadicalRed"; p[10] = "LemonYellow"; p[15] =
"MiddleGreen"; p[20] = "CadetBlue"; p[25] = "white";
maxTransp := 1;
opHeight := 2.5; %centimeters
opHeightpt := (opHeight /2.54)*72.27;
draw lmt_text [
text = "\rotate{opaque}",
color = "black",
style = "bold",
anchor = "lft",
position = (-1mm,2mm),
] xsized .25TextHeight shifted(12cm,10cm);
for k= 5, 10, 15, 20, 25:
t := (1cm, k*cm)--(20cm, k*cm) ; %Square opaque area
draw t withpen pensquare scaled .25pt withcolor p[k]
withtransparency("normal",maxTransp);
for i = 0 step 0.25 until opHeightpt:
r := (i/(opHeight*72.27/2.54))*maxTransp;
draw t yshifted (i+0.25)*pt withpen pensquare scaled 0.25pt withcolor
p[k] withtransparency("normal",(maxTransp-r));
draw t yshifted (-i-0.25)*pt withpen pensquare scaled .25pt withcolor
p[k] withtransparency("normal",(maxTransp-r));
endfor;
endfor;
draw lmt_shade [
path = fullsquare xyscaled(19cm,2cm),
direction = "up",
alternative = "linear",
colors = { "red", "blue" },
] shifted(10.5cm,1.5cm) ;
StopPage;
\stopMPpage
\page
\startMPpage %page 3
StartPage;
draw lmt_text [
text = "opaque",
color = "black",
style = "bold",
anchor = "lft",
position = (-1mm,2mm),
] xsized .95TextWidth ysized 7cm shifted(22cm,13cm);
draw lmt_text [
text = "opaque",
color = "black",
style = "bold",
anchor = "lft",
position = (-1mm,2mm),
] xsized .95TextWidth ysized 7cm shifted(22cm,3cm);
path t, u;
t := (11cm, 15cm) -- (20cm, 15cm); %Square opaque area
u := fullcircle scaled 5cm shifted (5cm,16cm); %Circular opaque area
for j = (5*72.27/2.54) step -0.25 until 1:
r := (j/(5*72.27/2.54)) *0.5;
s := -r + 0.5;
draw fullcircle scaled (j*pt) shifted (5cm,16cm) withpen pencircle
scaled 0.25pt withcolor ("RadicalRed") withtransparency ("normal",s);
endfor;
fill fullcircle scaled .25pt shifted (5cm,16cm) withpen pencircle scaled
0.25pt withcolor ("RadicalRed") withtransparency ("normal",s);
for i = 0.0001 step 0.25 until (10*72.27/2.54):
r := (i/(10*72.27/2.54));
draw t yshifted -i*pt withpen pensquare scaled 0.25pt withcolor
("SpringGreen") withtransparency ("lighten",(1-r));
draw t yshifted i*pt withpen pensquare scaled 0.25pt withcolor
("RadicalRed") withtransparency ("lighten",(1-r));
endfor;
draw lmt_shade [
path = fullcircle scaled 5cm,
alternative = "circular",
colors = { "red", "blue" },
] shifted(5cm,5cm) withtransparency("normal",0.85);
StopPage;
\stopMPpage
\stoptext
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