[Therion] metapost help - line Blocks

[Georg Pacher]

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 at 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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