[SOLVED] Incorrect node rotation

[santosh.a]

Hi all. While coding I came up with an issue involving incorrect node rotation which, for the life of me, I'm not able to figure out. If would be helpful if someone could point out where the issue is. Basically I'm trying to create and align a shell along the barrel of an artillery. The final line of world transformation is incorrectly rotating the shell. Kindly find pics attached. Code for spawning and aligning shell is like this :

 

void spawnShell()

{

    // Create shell node.

 

    m_cRefNode = class_remove( new NodeReference( "nodes/weapons/ammunition/155mm_shell.node" ) );

    engine.editor.addNode( m_cRefNode );

    assert( m_cRefNode != NULL );

    m_cRefNode.setName( "he_shell" );

    m_cRefNode.setProperty( "HEShell" );

 

    // Find and assign necessary nodes.

 

    Node container = m_cRefNode.getNode();

    m_cObject = node_cast( container );

    int id = container.findChild( "nose" );

    m_cNoseNode = node_cast( container.getChild( id ) );

    id = container.findChild( "base" );

    m_cBaseNode = node_cast( container.getChild( id ) );

    assert( m_cObject != NULL );

    assert( m_cBaseNode != NULL );

    assert( m_cNoseNode != NULL );

 

    // Place and align the shell w.r.t artillery barrel

 

    NodeDummy barrelEnd = m_cOwnerArtillery.getBarrelEnd();

    m_cRefNode.setWorldPosition( barrelEnd.getWorldPosition() );                                                        // Rot_Issue_2/2A.jpg

 

    m_cRefNode.setWorldRotation( m_cOwnerArtillery.getWorldRotation() );                                         // Rot_Issue_3/4.jpg

 

    vec3 v1 = m_cNoseNode.getWorldPosition() - m_cBaseNode.getWorldPosition();

    vec3 v2 = m_cOwnerArtillery.getLaunchDirection();

    if( v1 != v2 && length( v1 ) != 0.0f && length( v2 ) != 0.0f ) {

 

        v1 = normalize( v1 );

        v2 = normalize( v2 );

 

        vec3 v3 = cross( v1, v2 );

        v3 = normalize( v3 );

 

        float angle = acos( dot( v1, v2 ) ) * RAD2DEG;

        m_cRefNode.setWorldTransform(  m_cRefNode.getWorldTransform() * rotate( v3, angle ) );       // Rot_Issue_5/5A.jpg

    }

}

 

 

 

rotation_issue.rar

[silent]

Hi,

 

For quick test you can try to replace:

vec3 v3 = cross( v1, v2 );

 with 

vec3 v3 = cross( v2, v1 );

If this doesn't help, I'm afraid we will need to check the whole scene with actual content.

 

Thanks!

[santosh.a]

Thanks for the quick reply, Silent. That is fixing the rotation partially but not fully. Also, cross( v2, v1 ) would mean that we want the node to be rotated from v2 direction to v1, which is an incorrect assumption. I will set a test case asap and get back, thanks again!

[santosh.a]

I've set up a test case, kindly find the zipped file attached. Create new project, place test_case folder inside data folder and do turn visualizer on too. Thanks.

test_case.rar

[silent]

Great! I will report as soon as I will have a feedback from the developers.

 

Thanks!

[silent]

Hi,

 

The reason you get such rotation issue is in line 142 of shell.h script. If you remove this line shell will be aligned correnly in the world coordinates.

 

Thanks!

[santosh.a]

I'm already aware that there would not be any problem if shell rotation is done in 1 step without line 142. But I had to add it for a reason :) I prefer to maintain the local Z axis of shell in upwards direction for further trajectory calculations, so if I remove line 142 the shell would be awkwardly rotated. That is the reason for rotating it horizontally first and then vertically. Anyway, the code snippet 144-162 should theoretically work correctly on its own especially since the vectors are all correct. That's where my concern is.

 

Edit : Another reason that I cannot just remove line 142 and fix the issue is that the code of trajectory movement (that I haven't shared yet) also has this same issue. So I need to know the exact problem (or whether I'm doing some silly mistake).

[silent]

Hi,

 

Please, try to change line 159 in shell.h script:

m_cRefNode.setWorldTransform( translate(m_cRefNode.getWorldPosition()) * rotate( v3, angle ) * rotation(m_cRefNode.getWorldTransform()) );

At first we rotate shell in it's local coordinates, then we apply world transformations.

 

Thanks! 

[santosh.a]

That worked perfectly. Thanks Silent, that was big help. So what lesson can I learn here? I mean, whenever I need to rotate a node around an axis, I should always apply translate first and current world rotation last? Should I never directly apply getWorldTransform() value? Kindly let me know the reasoning behind it so that I can avoid this issue in the future. Thanks again!

[binstream]

It is the way 3D math works, the issue is not related to the engine.

[santosh.a]

Okay I will figure it out. Thanks.