Hi Andrew,

First of all, i would suggest to use:
st:= arctime (laenge+cur/2) of P; instead of
st:= arctime (laenge+cur)/2 of P;

for the direction of the last block. Otherwise this will use the direction near the middle of the path, and not at the location of the last block. But I am not sure if this is related to your issue.

I remember having this issue also back then, when generating the AUT symbol-set. Though I don't remember the details anymore, I believe it always had something to do with determining the scale_factor for the last block, or the calculated location for the last block.

You can check that by adding the line "scale_factor" before " if scale_factor > 0:", to print out the value of scale factor (when omitting the ';', it will print out the stated value). Then you should see if this value gets <=0 sometimes.

But note that it is not feasible to do this on a big dataset, as there will be an enormous amount of output then.

hope that helps,

Georg.

On Mon, Sep 21, 2015 at 9:39 AM, Andrew Atkinson <andrew@wotcc.org.uk> wrote:

I think this started life at the AUT line symbol for Blocks. My metapost
is at the stage where I can just about edit it to get small changesm but
that is about it.

With the AUT symbol you got blocks at funny angle when going round a
tight curve, I think this was because it took it angle from the start of
the place that it was drawing the block, so I added the st variable as
well as reducing the randomness of the angle. I also increased the
length of the blocks, plus added an extra point on the block and added a
bit of space between. All well and good, but now occasionally, probably
about 1/4 of the time, the last block in a line is drawn on top of the
second last block in a line then a space the size of the last bock is
left. No idea why this should be controlled by position t which is the
same as the rest of the blocks that work fine.

If anyone could help solve this I would be most greatful, trying to
print the survey for HE in 5 days time, so printing needs to be sent off
asap

thanks Andrew

def l_wall_blocks_CHED (expr P) =

T:=identity;
pickup PenC;
laenge := arclength P;

path block;
path old_block;

cur := 0;

#draw first block
old_block := punked ((
(.65u,-.15u)--(.72u,0.05u)--(.55u,.15u)--(.23u,.17u)--(.0u,.03u)--(.05u,-.1u))randomized
(0.1u))
scaled (uniformdeviate(0.3)+.65);
block_width := (xpart urcorner old_block - xpart ulcorner old_block);
t:= arctime (cur+block_width/2) of P;
old_block:=old_block rotated angle( direction t of P) shifted point 0
of P;
thclean (old_block--cycle);
thdraw old_block;

cur := cur + block_width + 0.04u;

forever:
# generate random block
block := punked (
((.65u,-.15u)--(.72u,0.05u)--(.55u,.15u)--(.2u,.17u)--(.0u,.03u)--(.05u,-.1u)
)
randomized (0.1u) )
scaled (uniformdeviate(0.3)+.65)
rotated (uniformdeviate(20)-10);
# check width of block
block_width := (xpart urcorner block - xpart ulcorner block);

exitif cur > (laenge- 3*block_width/2);
# find next position where the block fits in without intersecting
the previous one
forever:
exitif xpart ( ((block--cycle) rotated angle(direction t of P)
shifted point t of P) intersectiontimes old_block) < 0;
cur:=cur+0.01u;
t:= arctime cur of P;
st:= arctime (cur+block_width/2) of P;
exitif cur > (laenge- 3*block_width/2);
endfor;
exitif cur > (laenge- 3*block_width/2);

old_block:= block rotated angle(direction st of P) shifted point t of P;
thclean (old_block--cycle);
thdraw old_block;

cur := cur + block_width + 0.04u;

endfor;

# generate last block

block :=
(((.65u,-.15u)--(.72u,0.05u)--(.55u,.15u)--(.2u,.17u)--(.0u,.03u)--(.05u,-.1u))
);
block_width := (xpart urcorner block - xpart ulcorner block);

# scale last block to fit in the remaining gap
scale_factor:=(laenge-cur)/block_width;
t:= arctime cur of P;
st:= arctime (laenge+cur)/2 of P;
forever:
exitif scale_factor < 0;
exitif xpart ( ( (block) rotated angle (direction st of P) scaled
scale_factor shifted (point t of P) ) intersectiontimes old_block) < 0;
scale_factor:=scale_factor-0.001;
endfor;
if scale_factor > 0:
thclean (block--cycle) rotated angle (direction st of P) scaled
scale_factor shifted (point t of P);
thdraw (block) rotated angle (direction st of P) scaled
scale_factor shifted (point t of P);
fi;
enddef;

initsymbol ("l_wall_blocks_CHED");
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