# Search:

Type: Posts; User: dolf

## Search: Search took 0.01 seconds.

by dolf
Replies
3
Views
1,793

### Re: Simple question

Simple. You use unscaled values for the texture coordinates (x1,....,y2) and scaled ones for the geometry coordinates (radius*x1,...,radius*y2).

But one thing is completely beyond my understanding...
2. ## Thread: How to find the target position?

by dolf
Replies
2
Views
208

### Re: How to find the target position?

I guess the D matrix is mysterious in the previous post, the original poster talked about angles in degrees. Let's say we are in the XY plane and have a heading rotation in the plane H and a pitch...

by dolf
Replies
10
Views
896

Just an uneducated guess: what if you take either one or both of

cgGLBindProgram(prog);
cgGLEnableProfile(fprog_profile);

out of Pass and place them in the program initialization code? It...
4. ## Thread: Scaling 3D points

by dolf
Replies
4
Views
235

### Re: Scaling 3D points

It appears to me that you want to fit the points' bounding box into that "grid", a rectangle with one corner at the origin and width/height/depth along X/Y/Z axes, respectively.

- determine the...

by dolf
Replies
3
Views
866

### Re: Stereographic Projection?

Sure stereoproj is linear: You have points on a sphere seen by a perspective viewer at the antipodal point. The only nonlinear part is the conversion from latitude and longitude (and altitude) into...

by dolf
Replies
5
Views
335

7. ## Thread: Rotation problems (object distortion)

by dolf
Replies
5
Views
335

### Re: Rotation problems (object distortion)

The following obvious bugs:
- in draw(), glPopMatrix is missing. This may lead to strange accumulations of matrices.
- in glFrustum, you have near==far. It is surprising to me that you see anything...
8. ## Thread: Gimbal Lock Problem

by dolf
Replies
10
Views
2,146

### Re: Gimbal Lock Problem

What you describe here sounds a lot like you apply pitch and roll in the wrong order.
9. ## Thread: transform 4x4 matrix into scale/rotation/move ?

by dolf
Replies
4
Views
1,690

### Re: transform 4x4 matrix into scale/rotation/move ?

After ripping out the translation of column 3, you could use singular value decomposition on the remaining 3x3 matrix.

This is the tool to deal with all the ugly cases that the literature usually...
10. ## Thread: Function to 'pinch' a mesh

by dolf
Replies
9
Views
1,808

### Re: Function to 'pinch' a mesh

Or try the height--dependent radius r(z)=1.1 + cos(z - 0.5*sin(z)) with z going from0 to 2*PI. That's how I imagine an hourglass.
11. ## Thread: Direction Vector from Plane

by dolf
Replies
3
Views
289

### Re: Direction Vector from Plane

Assume that you have 3 points p, q, r in the plane. One way to compute the plane normal is then e.g. n=cross(q-p,r-p).

You can use n as the rotation axis in glRotate, but also either of the...
12. ## Thread: Volume Rendering - projecting object-alined slices to viewpoint-aligned slices

by dolf
Replies
4
Views
497

### Re: Volume Rendering - projecting object-alined slices to viewpoint-aligned slices

You could, in addition to what hifuGL suggested, render all 3 object-aligned stacks from back to front, with opacity proportional to the dot product between surface normal and viewing vector.

The...

by dolf
Replies
12
Views
5,972

### Re: Adjustable rounded cube mesh generator

And it works with an Icosphere, too. This way, one gets nearly equal distribution of vertices on the rounded corners. I imagine that it will be tricky to generate this mesh with a program.

by dolf
Replies
12
Views
5,972

### Re: Adjustable rounded cube mesh generator

I did it interactively with Blender, making an UV sphere, extruding half the vertices along each of the 3 axes, and voilĂ*. I didn't get an equal distribution of the vertex density on the rounded...

by dolf
Replies
8
Views
524

### Re: L-systems, anyone?

Just a very rough idea: The ugly things with a cylinder-based rendering strategy are the branches. Now what about a metaball-like approach, like so: determine all the sticks going out from the branch...
16. ## Thread: Drawing Arcs Connecting Two Points on a Sphere

by dolf
Replies
1
Views
868

### Re: Drawing Arcs Connecting Two Points on a Sphere

Assume that you have two radius vectors v and w. Take the cross product r = cross(v,w) and its absolute value lr = |r| and determine the angle between v and w as a = arcsin(lr/(|v|*|w|)).

The...
17. ## Thread: Drawing a gradient fill in 2D vector based objects

by dolf
Replies
4
Views
3,169

### Re: Drawing a gradient fill in 2D vector based objects

Linear gradients are trivial. Generate a 1D texture, and assign 1d texcoords to all your mesh vertices increasing linearly along the progression direction of the gradient.

18. ## Thread: should I use slope or another metho

by dolf
Replies
1
Views
238

### Re: should I use slope or another metho

Slope doesn't work for 'vertical' lines. Better is the difference vector between adjacent road segment midpoints and its normalized perpendicular. What you need additionally are the angle bisectors...

by dolf
Replies
2
Views
277

### Re: plot circle

Normally, you'd be doing this with glRenderMode(GL_SELECT) etc.

Alternatively, you could compute the on-screen location of the circle center (cx,cy) and one point (rx,ry) on the circumference...
20. ## Thread: matrix manipulation optimization

by dolf
Replies
4
Views
237

### Re: matrix manipulation optimization

As usual, it depends - when you emit many glVertex'es without changing the transformation, it doesn't matter. Vertices will always be transformed by the current modelview matrix. But when you change...
21. ## Thread: finding contour lines that are closest

by dolf
Replies
3
Views
865

### Re: finding contour lines that are closest

This problem is not uniquely solvable, since a contour may either represent an increment or a decrement of altitude. Consequently, when you regard the contour lines of a mountain, they may as well be...
22. ## Thread: Roll Stabilized Camera w/Quaternion

by dolf
Replies
4
Views
322

### Re: Roll Stabilized Camera w/Quaternion

We want to formulate a rotation about the front direction that turns our roll into given_roll.

In order to do this, we perform a Gram-Schmidt normalization step of the up axis with respect to the...
23. ## Thread: strafe? ? ?

by dolf
Replies
5
Views
1,269

### Re: strafe? ? ?

Theoretically, one could use the modelview matrix generated by gluLookat (or any matrix for that matter) to strafe left by an amount of l.

double m[16];
double l;...
24. ## Thread: rotate onto a given vector

by dolf
Replies
3
Views
364

### Re: rotate onto a given vector

Assume your line to be given by the points P and Q, and your airplane reference direction to be heading=pitch=0. Assume further that Z is up.

Then