Wfpokorny: Adding content for howto for loop over while loop.

2016-11-23T13:27:53Z

Adding content for howto for loop over while loop.

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===Loops===
Traditionally in POV-Ray the <code>#while</code> directive has been the way to implement loops. In 3.7 a new <code>#for</code> directive was added that makes coding counting loops much simpler.

===Nested Loops===
Loops can of course be nested. This capability is often used to lay out very large numbers of objects using an economical amount of code.

First, here's a very simple, complete scene file containing a nested <code>#while</code> loop with which you can play:

<source lang=pov>
#include "colors.inc"
#include "woods.inc"

camera {location <-1.5,0.9,-0.08> look_at <0,0.7,0.5>}
light_source {<-20,75,-100> White}
background {LightBlue}
plane {y,0 pigment {color GreenYellow}

#declare RandomSeed = seed(1);
#declare XCount=0;
#while (XCount < 200)
#declare ZCount=0;
#while (ZCount < 200)
box {<-0.05,0,-0.05><0.05,1,0.05>
rotate <3*rand(RandomSeed),5*rand(RandomSeed),3*rand(RandomSeed)>
texture {T_Wood1 translate <rand(RandomSeed),ZCount,rand(RandomSeed)> rotate x*90 scale 0.07}
translate <XCount,0,ZCount>
}
#declare ZCount=ZCount+1;
#end
#declare XCount=XCount+1;
#end
</source>

Here's the same looping accomplished with the new <code>#for</code> loop directive:

<source lang=pov>
#include "colors.inc"
#include "woods.inc"

camera {location <-1.5,0.9,-0.08> look_at <0,0.7,0.5>}
light_source {<-20,75,-100> White}
background {LightBlue}
plane {y,0 pigment {color GreenYellow}

#declare RandomSeed = seed(1);
#for (XCount,0,199)
#for (ZCount,0,199)
box {<-0.05,0,-0.05><0.05,1,0.05>
rotate <3*rand(RandomSeed),5*rand(RandomSeed),3*rand(RandomSeed)>
texture {T_Wood1 translate <rand(RandomSeed),ZCount,rand(RandomSeed)> rotate x*90 scale 0.07}
translate <XCount,0,ZCount>
}
#end
#end
</source>

These example uses 2 nested loops. Each nested loop has its own control variable. It starts with both XCount and YCount equal to zero. With XCount at zero, YCount loops from 0 to 199, then XCount is incremented to 1, YCount is reset to zero and the second loop repeats.

This example also introduces a degree of randomness in each iteration using the POV-Ray seed and rand functions. When generating a large number of objects using loops you'll find that a little randomness goes a long way. This example generates 40,000 wooden posts, each with a little bit of a wobble and each with a slightly different wood texture pattern. It should take about 10 or 20 seconds to render

HowTo:Use for loop over traditional while loop - Revision history

Wfpokorny: Adding content for howto for loop over while loop.