Need Explain camera vector

[feelthat]

//outer code setting
ICameraSceneNode* camera = smgr->addCameraSceneNodeFPS(0, 100.0f, .02f, 0, 0, 0, true, 1.0f);
camera->setPosition(core::vector3df(0,0,20));
camera->setTarget(core::vector3df(0,0,21));

//irrlicht kernel
//in CSceneNodeAnimatorCameraFPS::animateNode
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target.set(0, 0, core::max_(1.f, pos.getLength()));
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mat.transformVect(target);
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target += pos;
camera->setTarget(target);
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My queestion is I already set camera target outer code
why animateNode get camera position length in target z then add pos to be a target???
//target.set(0, 0, core::max_(1.f, pos.getLength())); this
//target += pos; and this

[thanhle]

Hi,
Because you are using FPS camera instead of normal camera.
With FPS camera, the target is updated as you press the keyboard keys.

Regards
Thanh

[feelthat]

1.
I can understand do the rotation
mat.setRotationDegrees(core::vector3df(relativeRotation.X, relativeRotation.Y, 0));
mat.transformVect(target);

2.
but why use pos.getLength() setting target z then add pos
reason why?

if pos(0,0,20) then target=(0,0,20); add pos, target=(0,0,40);

if pos(0,0,40) then target=(0,0,40); add pos, target=(0,0,80);

[feelthat]

Finally I got answer~~~

//here get target HorizontalAngle
core::vector3df relativeRotation = target.getHorizontalAngle();

//set target length = pos length
target.set(0, 0, core::max_(1.f, pos.getLength()));

//rotation target length to HorizontalAngle
mat.setRotationDegrees(core::vector3df(relativeRotation.X, relativeRotation.Y, 0));
mat.transformVect(target);

//add pos to do the compare target-z with camera pos length, after add
//target-z + => positive mean forward,
//target-z - => negtive or zero mean backward
target += pos;

1.
I can understand do the rotation
mat.setRotationDegrees(core::vector3df(relativeRotation.X, relativeRotation.Y, 0));
mat.transformVect(target);

2.
but why use pos.getLength() setting target z then add pos
reason why?

if pos(0,0,20) then target=(0,0,20); add pos, target=(0,0,40);

if pos(0,0,40) then target=(0,0,40); add pos, target=(0,0,80);