Irrlicht Engine

Posted: **Wed Jun 18, 2008 2:18 pm**

Hi,

Ive been looking all over for a way of doing this, but i cant seem to find anything.

I have a node in a map(the quake2 map that comes with the download) I need to find the distance from the node to the wall in front of it. Eventually I will have to find the distance to walls around the node, but ill start with just one for now. Im new to irrlicht and I really have no idea how to go about doing this. If the wall was another node, I could get it done, but since it is the map I dont know where to go or what to use.

example:

Code: Select all


       Wall
------------------------------------
                        ^
                        |
                        |
                        | distance
                        |
                        |
                   _______
                  |       |
                  |   Node|
                  |_______|

any help would be greatly appreciated,

thank you.

Posted: **Wed Jun 18, 2008 2:31 pm**

You should read collisions tutorial.

To find distance you can create vector from you node. Set it's length to "infinity", change direction and find point, where it hit wall.

Posted: **Wed Jun 18, 2008 2:42 pm**

could you not just send out a ray and then get the point of intersection with the wall.

Once you have intersection deduct the z value of the vector from your current z value position, boom, thats your distance?

Posted: **Wed Jun 18, 2008 3:40 pm**

Specifically, what you're looking for is example 07.Collision/main.cpp

The significant code is:

Code: Select all

		selector = smgr->createOctTreeTriangleSelector(q3levelmesh->getMesh(0), q3node, 128);

...

		core::line3d<f32> line;
		line.start = camera->getPosition();
		line.end = line.start + (camera->getTarget() - line.start).normalize() * 1000.0f;

		core::vector3df intersection;
		core::triangle3df tri;

		if (smgr->getSceneCollisionManager()->getCollisionPoint(
			line, selector, intersection, tri))
		{
			// Then you'll need the distance, which is just...
			f32 distance = (intersection - line.start).getLength();
		}

However, instead of creating the line from the camera position, create it from the node's position. You'll need to determine a direction as well. If you assume that "in front of" is dependent of the node's rotation, and +Z is forwards, then this will get you a direction vector (and the line to use in the collision check):

Code: Select all

	core::matrix4 nodeMatrix = node->getAbsoluteTransformation();
	core::vector3df forwards(0, 0, 1000);
	nodeMatrix.rotateVect(forwards);

	core::line3d<f32> line;
	line.start = node->getAbsolutePosition();
	line.end = line.start + forwards;

Posted: **Thu Jun 19, 2008 4:11 am**

I would place a core::line3df along the parameter of the wall, and then use the "getClosestPoint()" method to find the closest point on the wall.

Posted: **Thu Jun 19, 2008 10:13 am**

"the wall"? Which wall?

Posted: **Thu Jun 19, 2008 3:44 pm**

Hey all,

thanks a lot. I was picking through the collision tutorial, but i guess i missed that, or i had no idea what it did. Thanks for pointing it out. Ill go have a look and give it a shot.

thanks a lot.

Posted: **Thu Jun 19, 2008 6:45 pm**

No problem. Collision detection can be tricksy, so give us a shout if you run into problems.

Posted: **Fri Jun 20, 2008 2:43 am**

cp51, what you're trying to do is similar to something rogerborg helped me with a couple of months ago. See here:

http://irrlicht.sourceforge.net/phpBB2/ ... hp?t=26765

I use getIntersectionWithLimitedLine() for the triangles in the wall. It's considerably faster than getCollisionPoint().

Posted: **Wed Jun 25, 2008 1:20 pm**

hey,

thanks for the info. Im going to look at that right now.

I have a question though. Currently i have 16 range finders in a circle. I created a rangeFinder objectthat i pass a pointer to the selector to and what angle it will be looking in.

However, i also have a simple CubeSceneNode that uses selector for collision detection with the world. When i have just the box(no rangeFinder object), everything is fine, however, when i add in the range finder stuff, the box just drops through the floor...

Does this have something to do with reusing the selector? Do I need multiple selectors? is that even possible?

Thanks for the help everyone.

Posted: **Wed Jun 25, 2008 1:23 pm**

Create an IMetaTriangleSelector (big basket for triangle selectors) and put all your triangle selectors in there and use it as you were using triangle selectors previously.

Posted: **Wed Jun 25, 2008 2:06 pm**

wow you guys are fast.

thanks a lot, that worked. So excited lol.

-Thanks again everyone.

Irrlicht Engine

Range Finding To Wall

Range Finding To Wall