How to draw a 3D vector in OpenGL?

Question

I'm making a 3D simulation of the motion of particles, and I want to draw arrows representing the electric field at certain positions. I made an arrow mesh in Blender and exported it as a .obj so I can use it in my code (I made a .obj loader), but I can't seem to rotate it properly so that it points in the right direction, even though I checked that the electric field vector was calculated properly. I am getting some weird results as well. For example, if the vector should be pointing upwards, it points downwards, but when I comment out the code that rotates in the x axis, the arrow points downwards like intended. Then if it's supposed to point to the right, it points inwards (towards negative z axis), but when I comment out the rotation in the y axis, it points to the right.

Here's my code for rotation and rendering of the arrows:

void Render(Vector3 cameraPos)
{
    glScalef(field.length() * ArrowLength,1.0,1.0);
    glTranslatef(0,0,_zdefault);
    glRotatef(Entity::yangle,0,1,0);
    glTranslatef(pos.getX() + cameraPos.getX(), pos.getY() + cameraPos.getY(), pos.getZ() + cameraPos.getZ() - _zdefault);

    glRotatef(atan2(field.getZ(),field.getY()) * 180/M_PI, 1.0,0.0,0.0);
    glRotatef(atan2(field.getX(),field.getZ()) * 180/M_PI, 0.0,1.0,0.0);
    glRotatef(atan2(field.getY(),field.getX()) * 180/M_PI, 0.0,0.0,1.0);

    glBindTexture(GL_TEXTURE_2D,arrowTexture);

    glCallList(arrow);
    glLoadIdentity();
};

field is the Vector that represents the electric field. The lines

glTranslatef(0,0,_zdefault);
glRotatef(Entity::yangle,0,1,0);

Are there so that I can rotate the entire scene, kind of like orbiting around it in Blender. Also, Vector3 is just a simple Vector class that I wrote with very basic functionality. Like I said though, there is no problem with the vector calculations, I checked that, I just can't use the Vectors to rotate things properly.

I have a feeling my angles are a little screwed up for the glRotatef's where I use atan2, but I still can't understand how that would affect the rotations as described before.

Is there any way to rotate something based only on vector components?

Answer 1

first you should probably not use the glRotatef glTranslatef etc. legacy pipeline and use shaders and manage your own matrices instead.

Besides that it's better to use a lookAt transformation using the field as your direction direction and some up as the up vector

For rotating the entire scene you just define a center and rotate all vectors around that with the same transformation after you translate them