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Box2D is just way too much fun!

Working on IPhone, btw.

I'm trying to make it such that I can touch a fixture to make it active and then touch again later to make it inactive.

Init body and fixture:



All works fine. But then I try in ccTouchEnded:



I get an error saying "no matching function for call to b2Fixture::TestPoint(CGPoint&)"

I checked b2Fixture.h and it's in there.

What am I doing wrong here?

Box2D doesn't know about CGPoint. TestPoint expects a b2Vec2.

Thanks for the reply.

I just got back to this feature and tried your suggestion.

I converted touch position to b2Vec2 & tried TestPoint again


Never registers that MyFixture is touched when I touch it ...

I decided to printf some values for convertedTouch.
Top right edge of the screen (landscape mode) the values for convertedTouch are roughly x=14.9, y=9.8. Seem reasonable?

Also tried:

But I get an error during compile:

:1279: error: no matching function for call to 'b2Fixture::TestPoint(b2Transform&, b2Vec2&)'

Perhaps I'm not using transform correctly?

You should just go to the Box2D code on your machine and look at the function interface.

That's usually the first thing I try (along with the manual & google search) and most of the time I get it myself.
This is my first attempt at programming so apologize if I come off annoying ...

I assume this is what you mean by the function interface?
in b2Fixture.h:


It would seem I could just pass the fixture's corresponding body to GetTransform ...

So I tried:

error: no matching function for call to 'b2Fixture::TestPoint(b2Transform&, b2Vec2&)'
Started trying different permutations of calls with no luck.

Searching the forum I see plenty of examples of doing something like this but I don't see what I'm doing wrong here.

This example does the same thing I do believe within the code snippet:

http://www.box2d.org/forum/viewtopic.php?f=3&t=5582&p=26037&hilit=GetTransform#p26037

Again sorry for the noobish whining ...

Actually it DOES in fact work, sorta.



At first it only registers when I click the far right of screen.

My fixture is a car always centered at x=240 (actually the camera "follows" it). I achieve scrolling the rest of world with the camera.

If I then move the fixture (with camera following) in one direction the registered click area moves to where the fixture is but then passes it. Move back in opposite direction and it lines up again then passes.

Not sound corny but like 2 ships passing each other.

If I test touch point with a stationary fixture and scroll side to side the stationary fixture scrolls but the click area always remains at only one area of the screen.

Seems I DO need to do a transform of some sort so back to previous problem of why this:

gives error: no matching function for call to 'b2Fixture::TestPoint(b2Transform&, b2Vec2&)'

Any clues because I think I'm doing it as others are. I AM passing the proper b2Transform and b2Vec2.

Aren't I?

To use TestPoint(transformation, location) you need to access the TestPoint() from shape. So it need to be like this:



Just add the GetShape() there and it should work. Just remember that you need to go through all the fixtures in the fixtureList. Hope fully some one finds this useful

You don't need to use the transform.

If the "camera" follows the car, then the convertedTouch also needs to be offset by the same offset you use to offset the camera. b2Vec2 does not automatically adjust along with the screen. When you use TestPoint(b2Vec2), it's testing in the physics world coordinates. So if you don't offset the b2Vec2 point to reflect the camera following the car, the b2Vec2 point will not coincide with the point you're touching.

It should be something like this (pseudocode):



You may need to subtract by the cameraOffset values instead of adding, depending on how the camera offsetting works. Also, is dividing by the PTM_RATIO correct? PTM means pixel to meter, and usually you multiply some pixel value to get a meter value. If the PTM_RATIO is less than 1.0, then you should be multiplying.