Evaluating Expressions From Hdk

[jhiggins]

I was just curious, if anyone knew a way to evaluate an expression from within the hdk.

for instance, if I have a string input parameter on a custom SOP that is "rand(0)" , how would

I evaluate it and use it in my cook method.

thanks,

jeff

[Wolfwood]

I was just curious, if anyone knew a way to evaluate an expression from within the hdk.

for instance, if I have a string input parameter on a custom SOP that is "rand(0)" , how would

I evaluate it and use it in my cook method.

thanks,

jeff

20540[/snapback]

In OP/OP_Parameters.h there are methods like evalString.

As long as your expression is formated correctly it should evaluate the parameter.

`rand("0")`

If.....you want to pass a actual string to your custom SOP and then evaluate that expression internally....then I think you can use CMD_Manager::execute() to evalute the expression.

Ie:

UT_String foo("echo `");

foo += myExpression;

foo += "`"';

CMD_Manager::execute(foo);

There is probably a better way.......

Ed?

[edward]

You could use CH_Manager::evaluate(). Local variables won't work though.

eg. OPgetDirector()->getManager()->evaluate("rand(0)");

[jhiggins]

You could use CH_Manager::evaluate(). Local variables won't work though.

eg. OPgetDirector()->getManager()->evaluate("rand(0)");

20545[/snapback]

thanks... that worked great!!!!!

one problem though, which i expected is that when i call rand(0) and a set of points, all the random values are exactly the same, b/c the seed is the same.

Is there a good way to either expose the $PT variable.

I can just override "$PT" by replacing it with whatever i want, but it seems wrong to do it this way.

thanks

jeff higgins

[edward]

Where are you calling this? If you're within the cook codepath of a SOP, then you could try:

evaluate(my_expr, current_time, getChannels()).

This is all assuming that you've already set up use of local variables of course. See the SOP_Flatten.C in the HDK examples.

[jhiggins]

You could use CH_Manager::evaluate(). Local variables won't work though.

eg. OPgetDirector()->getManager()->evaluate("rand(0)");

20545[/snapback]

revisting this after a while, I wouldn't mind being able to get local variables working.

would you know how to get this working.

The CH_Collection* local on the evaluate method looks like what i should be using, but

so far my attempts have been fruitless.

[edward]

As previously mentioned, see SOP_Flatten.C in the HDK examples.

[jhiggins]

i was looking at an older SOP_Flatten.C (ala v7), i still seem to be having a problem.

maybe i can explain more, because maybe local variables isn't really what i want.

i want a custom sop the will assign attributes based on an expression using other variables.

I will need to do more with them after this is established, which will require the use of the HDK.

so if in my network i have three point attribs X, Y, Z with (local variables $X, $Y, $Z), then I want to be able to have in my custom op set Z to an expression like sqrt($X*$X+$Y*$Y).

So my custom sop will have to iterate over all of the points and evaluate the string "sqrt($X*$X+$Y*$Y)".

I was thinking evalFloat would be what i need, but it doesn't seem to be working for me!

Thanks!

[edward]

evalFloat() should work provided you've setup the use of variables correctly. Here's the relevant code portions from SOP_Flatten.C.

eg. you need to do this first:

setVariableOrder(3, 2, 0, 1);
myCurGdp[0] = gdp;
setupLocalVars();

Then you need to do this for each point prior to calling evalFloat():

myCurPt[0] = ppt;

And finally, clean up when done:

resetLocalVarRefs();

[jhiggins]

evalFloat() should work provided you've setup the use of variables correctly. Here's the relevant code portions from SOP_Flatten.C.

eg. you need to do this first:

setVariableOrder(3, 2, 0, 1);
myCurGdp[0] = gdp;
setupLocalVars();

Then you need to do this for each point prior to calling evalFloat():

myCurPt[0] = ppt;

And finally, clean up when done:

resetLocalVarRefs();

22409[/snapback]

using the follow in my cook method:

UT_String a = "$PT";

UT_String b = "rand($PT)";

setVariableOrder(3, 2, 0, 1);

myCurGdp[0] = gdp;

setupLocalVars();

GEO_Point* ppt;

FOR_ALL_GPOINTS(gdp, ppt)

{

myCurPt[0] = ppt;

cout << evalFloat( a, 0, context.myTime ) << " --> "

<< evalFloat( b, 0, context.myTime ) << endl;

}

resetLocalVarRefs();

but i would get the following error for every point in my grid

evalFloat: Invalid parameter name $PT

0 --> core_berkleydb1 evalFloat: Invalid parameter name rand($PT)

j.h.

[sibarrick]

Surely thats because you are passing an "actual" expression as a string rather than the name of a parameter which the user may have typed a parameter string into.

Are you doing this just to test the result or because you want to always evaluate rand($PT)?

[jhiggins]

Surely thats because you are passing an "actual"  expression as a string rather than the name of a parameter which the user may have typed a parameter string into.

Are you doing this just to test the result or because you want to always evaluate rand($PT)?

22470[/snapback]

i'm doing this to test the result. I want to the user to be able to enter any valid expression as a string,

and then in my custom node i want to be able evaluate it for every point.

ideally i would have 2 such expressions (key, value) which would store values to a berkleydb.

[sibarrick]

I would just go ahead and set up your user parameters then, once you have that pointing your evalFloat functions at them should make it work.