Touch Location on a CC3MeshNode « cocos2d for iPhone

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Touch Location on a CC3MeshNode

(5 posts) (2 voices)

Started 3 months ago by blulightjr
Latest reply from blulightjr

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blulightjr
Member

From the CC3DemoMashUp demo project, it has a feature where you touch the plane and it adds a burning teapot at the location you touched. I wanted to do that with a POD file and noticed that there wasn't a method available. You're able to get a CC3Ray with the direction and starting point of the touch location, but I need to be able to get the location on the object.

Basically, I have a box, and I want to be able to know the point the user touches on it so I can add something at that point, like a circle on the texture indicating where the user touches. I appreciate any help in advance.

Posted 3 months ago #
Bill Hollings
Moderator

@blulightjr

Once you know which node has been touched, use the node's inverted transform matrix (in the transformMatrixInverted property) to transform the startLocation and direction of the CC3Ray returned from the camera's unprojectPoint: method into the local coordinate system of the node. Use the transformLocation: and transformDirection: methods on the matrix, respectively.

This will move the ray into the local coordinate system of the node, and then you can use some basic intersection math (check online or book references) to find where the ray intersects the localContentBoundingBox of the node.

The next version of cocos3d will include this capability in the base library.

...Bill

Posted 3 months ago #

blulightjr
Member

Thank you very much for your help, Bill. I followed what you said, hopefully correctly. What I'm confused with is finding the solution to the "basic intersection math" you mentioned. You see, I'm very inexperienced with 3D programming and I looked up some things on the Web and tried to use Ray-Box Intersection formulas but the values I was getting didn't seem right. Is there another hint you or anyone can provide?

-(void) nodeSelected: (CC3Node*) aNode byTouchEvent: (uint) touchType at: (CGPoint) touchPoint {
     CC3Ray touchLoc = [self.activeCamera unprojectPoint:touchPoint];
     if(aNode) {
        CC3GLMatrix *mat = aNode.transformMatrixInverted;
        CC3Vector loc = [mat transformLocation:touchLoc.startLocation];
        CC3Vector dir = [mat transformDirection:touchLoc.direction];
        CC3MeshNode* meshNode = (CC3MeshNode*)[self getNodeNamed: @"boxNode"];
        CC3BoundingBox box = meshNode.localContentBoundingBox;
     }
}

Posted 3 months ago #

Bill Hollings
Moderator

@blulightjr

You're on the right track.

Are you sure that the node that was touched (aNode) is the same as the meshNode that you are retrieving by name (@"boxNode")? If so, why are you bothering to retrieve it again? If not...then you're transforming the ray into the wrong node's coordinate system.

You're code doesn't include the ray-box intersection code itself, so I can't tell what's going wrong there.

I haven't done this in detail myself yet (it's scheduled for development soon), so I can't provide much more in the way of further specific guidance...yet.

...Bill

Posted 3 months ago #

blulightjr
Member

@Bill Hollings

Sorry, I didn't include the ray-box intersection code, before. But, I've included it here in this post. Anyhow, I've been reading up more on the subject and I guess the correct term in 3D game development for what I'm trying to do is creating "Decals". And, it looks like there's more to this than just figuring out the coordinates a user touched on a 3D object. You mentioned that this is a feature that's in development and I look forward to that feature in a future cocos3d release. But in the meantime, I guess I'll challenge myself into figuring this out.

thanks for your help.

-(void) nodeSelected: (CC3Node*) aNode byTouchEvent: (uint) touchType at: (CGPoint) touchPoint {
     CC3Ray touchLoc = [self.activeCamera unprojectPoint:touchPoint];

     CC3MeshNode* meshNode = (CC3MeshNode*)[self getNodeNamed: @"boxNode"];
     CC3GLMatrix *mat = meshNode.transformMatrixInverted;

     CC3Vector loc = [mat transformLocation:touchLoc.startLocation];
     CC3Vector dir = [mat transformDirection:touchLoc.direction];
     CC3BoundingBox box = meshNode.localContentBoundingBox;

     GLfloat txMin,txMax,tyMin,tyMax,tzMin,tzMax;
     BOOL intersect;

     if(dir.x >= 0) {
        txMin = (box.minimum.x - loc.x)/dir.x;
        txMax = (box.maximum.x - loc.x)/dir.x;
     }
    else {
        txMin = (box.maximum.x - loc.x)/dir.x;
        txMax = (box.minimum.x - loc.x)/dir.x;
    }
    if(dir.y >= 0) {
        tyMin = (box.minimum.y - loc.y)/dir.y;
        tyMax = (box.maximum.y - loc.y)/dir.y;
    }
    else {
        tyMin = (box.maximum.y - loc.y)/dir.y;
        tyMax = (box.minimum.y - loc.y)/dir.y;
    }

    if(txMin > tyMax || tyMin > txMax) {
        intersect = NO;
    }
    else {
        intersect = YES;
    }

    if(tyMin > txMin) txMin = tyMin;
    if(tyMax < txMax) txMax = tyMax;

    if(dir.z >= 0) {
        tzMin = (box.minimum.z - loc.z)/dir.z;
        tzMax = (box.maximum.z - loc.z)/dir.z;
    }
    else {
        tzMin = (box.maximum.z - loc.z)/dir.z;
        tzMax = (box.minimum.z - loc.z)/dir.z;
    }

    if (txMin > tzMax || tzMin > txMax) intersect = NO;
    if (tzMin > txMin) txMin = tzMin;
    if (tzMax < txMax) txMax = tzMax;

    LogInfo(@"txMin = %f | txMax = %f | tyMin = %f | tyMax = %f | tzMin = %f | tzMax = %f", txMin,txMax,tyMin,tyMax,tzMin,tzMax);
}

Posted 2 months ago #

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