Cannot find anything named "loc" error? Why?

Programming Questions

stevenq

Cannot find anything named "loc" error? Why?

in Programming Questions • 1 year ago

Hello, I'm working on a little project for school.

Eventually this program should have 'Agents' (ellipses) which are following my mouse movement. They should also bounce off black colored objects (this is not yet included in current coding).

This is my current code

Line 4 is where I define 'loc'

but at line1 of the other code part it gives the error: Cannot find anything named "loc"

Why?

Copy code

class Agent {
PVector loc = new PVector(width/2,height/2); //Here I defined "loc"
PVector vel = new PVector(0, 0, 0);
PVector acc = new PVector(1, 1, 0);
Agent(PVector _loc) {
loc = _loc;
}
void run() {
display();
update();
followMouse();
}
void followMouse() {
PVector target = new PVector(mouseX, mouseY, 0);
PVector dif = PVector.sub(target,loc);
float distance = dif.mag();
dif.normalize();
dif.div(100);
acc.add(dif);
}
void update() {
vel.add(acc);
vel.limit(7);
loc.add(vel);
acc = new PVector();
}
void display() {
stroke(0);
fill(255);
ellipse(loc.x, loc.y, 10, 10);
}
void botsen() {
if ((loc.x == 622) || (loc.x == 25))
{
vel = vel*-1;
}
}
}

Along with this:

Copy code

Agent myAgent = new Agent(loc); // Error: "cannot find anything named "loc" " I defined "loc" above right?
void setup() {
size (647, 694);
PImage img1;
smooth();
img1 = loadImage("Klembord01.gif");
}
void draw() {
fill(255, 10);
PImage img1;
img1 = loadImage("Klembord01.gif");
image(img1, 0, 0);
a.run();
}

Thanks in advance!

Replies(13)

Chrisir

Re: "Cannot convert from void to PVector" ?

1 year ago

Meaning sub doesn't return a vector

It returns nothing (void).

It just makes target smaller I think.

So divide the line into two - One being

target.sub(loc);

The other

PVector dif = target;

or so.

stevenq

Re: Re: "Cannot convert from void to PVector" ?

1 year ago

Thanks, it helped. But only to find the next problem.

I'll try to figure it out myself, I don't want to have a working program without know how

tishan_pu..

Re: "Cannot convert from void to PVector" ?

1 year ago

Try

PVector target = new PVector(mouseX, mouseY);

instead of line 22

Also refer this[1] to make your life easy.

[1] http://processing.org/learning/objects/

tishan_pu..

Re: "Cannot convert from void to PVector" ?

1 year ago

@Chrisir

Have a look at this[1].

According to it vec1.sub(vec2) should return a vector. I think the problem is in trying to subtract a 3 dimensional vector from a 2 dimensional vector.

[ 1 ] http://processing.org/reference/PVector_sub_.html

stevenq

Re: Re: "Cannot convert from void to PVector" ?

1 year ago

I changed the code into:

PVector dif = target;

target.sub(loc);

Now it does not give an error anymore, but I do not yet know if it does what it has to do because there are some other errors in my code. I'll try to fix them and see if it works!

Thanks for the references by the way :)

tishan_pu..

Re: "Cannot convert from void to PVector" ?

1 year ago

Oh...my bad.

Only PVector.sub(v1,v2) returns a Pvector.

stevenq

Re: Re: "Cannot convert from void to PVector" ?

1 year ago

Mind if I ask you another question? ^_^

Now it says: the function scaleSelf(float) does not exist at line 30.

Do you know another way to put this 'scaleSelf(float)' function?

I think it gives an error because all the PVectors were Vec3D's.

I sort of 'translated' them into PVectors, this because I do not know anything about Vec3D's (I'm working on this project with a classmate of mine, he came up with the code with Vec3D's, but the Vec3D code needed a library and that somehow did not work on my computer)

quarks

Re: "Cannot convert from void to PVector" ?

1 year ago

PVector dif = target.sub(loc);

The problem is that the sub method does not return a new PVector. The result of the above statement is to subtract the xyz values of loc from the xyz values in target. In other words the PVector target is changed from
target.x, target.y, target.z
to
target - loc.x, target.y - loc.y, target.z - loc.z
but the actual method always returns void which cannot be stored in diff hence the error message.

The soultion is to use the following method.
PVector dif = PVector.sub(target, loc);

In this statement target and loc are unchanged but this it will return a PVector object whcih is the difference between them.

stevenq

Re: Re: "Cannot convert from void to PVector" ?

1 year ago

Many replies suddenly, but thanks a lot!

If it does not work I'll try this :)

tishan_pu..

Re: "Cannot convert from void to PVector" ?

1 year ago

scaleSelf() is a method provided by the library you are using. So clearly you can not apply that method to a PVector object. It is something like asking a car to fly. Car does not have the method fly. You should use a plane instead. Hope you got my point

stevenq

Re: Re: "Cannot convert from void to PVector" ?

1 year ago

got it, thanks :)

I think I'm almost there, I fixed the scaleSelf() function.

I'll read those references and try to fix what's left :)

I hope you don't mind if I ask some questions if I'm stuck. :)

stevenq

Re: Re: "Cannot convert from void to PVector" ?

1 year ago

Could you please look at the code above, i edited it.

It says : Cannot find anything named "loc"

But I defined "loc"as:

PVector loc = new PVector(width/2,height/2);

quarks

Re: Cannot find anything named "loc" error? Why?

1 year ago

The problem is that loc is part of the class Agent so is not 'visible' outside the class. Also you want to avoid using loadImage insdie the draw method which is executed 60 times a second.

So change the code to

Copy code

Agent myAgent;
PImage img1;
void setup() {
size (647, 694);
smooth();
img1 = loadImage("Klembord01.gif");
myAgent = new Agent(new PVector(width/2, height/2);
}
void draw() {
fill(255, 10);
image(img1, 0, 0);
a.run();
}

In the Agent class I would change the constructor to

Copy code

Agent(PVector _loc) {
loc.set(_loc);
}

since you have already created an object for the attribute loc.

HTH

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