www.jpct.net

jPCT-AE - a 3d engine for Android => Support => Topic started by: Knuffi on April 16, 2012, 10:40:51 pm

Title: Rotating a cylinder in a direction given by a simple vector
Post by: Knuffi on April 16, 2012, 10:40:51 pm

I don't get it. :(

I have a cylinder representing a line. And on building it, I want to translate it to a certain point (working) and rotate it, that it looks into the same direction as a given vector. The last thing does not work.
When I give the vector
* (1/0/0), the cylinder's direction is the z-axis (or -z, I could not see),
* (0/1/0) the cylinder's direction is also the z-axis (or -z)
* (0/0/1) the cylinde's direction is the x-axis.

I changed the coordinate system to an "upright" as needed in school.

Code: [Select]

public static void addGerade(Gerade g){
Object3D gt = Primitives.getCylinder(6, 0.1f, 150);

// Changing the ccordinates from the calculated line to the ones needed to draw it
double ax = g.getA().getX1();
double ay = -g.getA().getX3();
double az = g.getA().getX2();

double rx = g.getV().getX();
double ry = -g.getV().getZ();
double rz = g.getV().getY();

SimpleVector Aufpunkt = new SimpleVector (ax, ay, az);
SimpleVector Richtung = new SimpleVector(rx, ry, rz);
Matrix r = Richtung.getRotationMatrix();
gt.setRotationMatrix(r);
gt.translate(Aufpunkt);

gt.setTexture("linet");
gt.build();
world.addObject(gt);

buffer.clear(java.awt.Color.DARK_GRAY);
world.renderScene(buffer);
// world.drawWireframe(buffer, Color.WHITE);
world.draw(buffer);
buffer.update();
}

Almost the same code works fine with points (as already said, translating works) and even planes (translating and rotating so that the normal vector looks into a given direction.

Can anybody help?

Title: Re: Rotating a cylinder in a direction given by a simple vector
Post by: EgonOlsen on April 16, 2012, 10:59:26 pm

You have to keep in mind that the cylinder created by the Primitives class doesn't point into z-direction. If you ensure this by doing something like

Code: [Select]

cyly = Primitives.getCylinder(6, 0.1f, 150);
cyly.rotateX((float) Math.PI/2f);
cyly.rotateMesh();
cyly.clearRotation();

and then apply your rotation, it should work.

Title: Re: Rotating a cylinder in a direction given by a simple vector
Post by: Knuffi on April 17, 2012, 07:14:09 am

Thanks, it worked! :)

I tried rotating around x-axis, but I did not know that I had to clear the Rotation.