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H34D

Move one Vertex to another in D3D

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Hello board, im having a problem with a calculation - dunno why but my brain is completly out of order at this point :O There are two vectors in d3d space, lets say: Vector a = (100,200,1000)(x,y,z) Vector b = (-300,-200,0)(x,y,z) vector a should move to vector b in a smooth and direct way, like a ray, how do i calculate that ? thanks in advance Head [edited by - H34D on May 19, 2004 4:43:28 AM]

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two ways. exponential way (moves rapidely first, and settles down to b's position)

decay = 0.25f;
Vector Diff = (b - a);
a += Diff * decay;

not frame rate independent (the faster the framerate, the faster a will reach b).

or a linear movement, frame rate independent

float speed = 1.0f; // 1 unit a second movement
Vector Diff = (b - a);
Diff.Normalise();
a += Diff * (speed * time_step);

for the second one, you can't guarantee that a will reach b exactly (basically, get very close), depending on the frame rate, A might shuffle around B for a while on low frame rates. So, you need to cap the maximum amount A can move towards B, by the vertex radius. This depends on the frame rate.

Don;t know if this would work, but it would be something along those lines.


float vertex_radius = 0.1f; // vertices have a 0.01 unit in radius.

//when A reaches that radius, A and

// B are considered at the same position

// and A is snapped straight onto B

float max_speed = 1.0f; // max particle speed, one unit a second

float max_dt = (vertex_radius / max_speed) * 0.99f; // make sure the vertex won't move more

// than the radius of a vertex in one frame


Vector Dir = (B - A);
float distance = Diff.Magnitude();

if (distance <= vertex_radius)
{
A = B;
return;
}

Dir /= distance;
if (dt > max_dt) dt = max_dt;
float speed = distance / dt;
if (speed > max_speed) speed = max_speed;
A += Dir * speed * dt;


[edited by - oliii on May 19, 2004 6:40:40 AM]

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Guest Anonymous Poster
eeek thanks so much

the result is now a "3 line solution"

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