graphics

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• 1. polygon problem
Hi: I am working on a CAFM project in AutoCAD system. right now I have problem relate to polygon. 1. island (hole) detect: How I can detect if a island (hole) of a polygon, inside or outside ? This is general example: ---------------------- | | | ------------- | | | | | | | | | | | | | | |------------- | | | | | | | ---------------------- also I need to check if this is self intersect, how I can do this? 2. polygon offset: for any 2 adjace polygon, there are 3 situation there: Polygon A take all space, polygon B take none; A and B take 50% B take all, A take none I am not going work with ARC segment right now. If you give any direction, algorithm, code sample, reference site, I will really appreciate it. Thank you very much Happy Valentine's Day Wes
• 2. *why* are rational beziers projective-invariant?
I can see how rational beziers curves would be invariant under affine transformations: the 4-D nonrational equivalents rely entirely on repeated linear interpolation, i.e. barycentric combination, which itself is invariant under affine transformations. But exactly *why* are they invariant under projective transformations? These transformations do *not* preserve barycentric combinations. Every text I see says that these curves are invariant inthis way, but none provesit, or even offers a deeper explanation. If someone has a clear explanation, please illuminate!
• 3. Review on isosurface/isocurve algorithms?
Greetings! There a lot of ideas and algorithms to deal with the problem of computing isocurves/isosurfaces ... Is there some review comparing isosurface/isocurve algorithms? What is the fast? What is the most precise? What is most suitable for scattered data? What is the most suitable when functions are provided? Any directions are welcome! Thanks in advance, Humberto.
• 4. Skinned Animation w/o Inverse Bone Transforms?
I'm curious to know if there are any documented methods for doing skinned animation without needing to store inverse bone transforms. Most people seem to calculate the bone offset then apply it just before passing the matrices to their software skinning routine/vertex program. But if there is a way to avoid this I would prefer to do so. I've seen reference to the topic of "offset-based animation", but not a lot of discussion about it. Does anyone have any information?
• 5. Getting x,y coordinates on a perspective transformed plane
For example, say you have chess board rotated 22deg and you want to map coordinates in the 3D view to 2D coordinates on that plane. I've googled as much as I can stand, I just can't find the right answer. I thought I could do it with gluUnProject() and gluProject() - in the code below, my[Un]Project() is just shorthand for getting the gl matricies and terse code: // draw glLoadIdentity(); glTransformf( 0, 0, -10 ); glRotatef( -67, 1, 0, 0 ); glutSolidCube( 1 ); // get the 3D point in space at the mouse position myUnProject( winX, winY, &objX, &objY, &objZ ); // inverse the transform to flatten the 3D point glLoadIdentity(); glTransformf( 0, 0, 10 ); glRotatef( 67, 1, 0, 0 ); // get the x,y point at the 2D point in space myProject( objX, objY, objZ, &winX, &winY ); The opengl group is not as active, hence the posting here. Thanks much, Mike

```Hi,
i'm trying to implement the tone mapping algorithm used in radiance.
looking at the source code of radiance (color.h), it calculates the
luminance as:
Luminance(col) = WHITEEFFICACY * bright(col);
where bright(col) is the y chromacicity component and WHITEEFFICACY =
179.0;
i'm trying to figure out where that value comes from, i would expect it
to be 683.0 wich is the maximum efficacy (reached for 555nm
wavelenghts).
does anybody have any idea how this value (179) was calculated?

thanks.

```

```After I have converted a photo to line art (Black and White 1-bit
depth), can I convert it to full color but where all the black pixels
get turned into a color of my choice, like pure red? or blue? or
yellow?
I would want all the white pixels to stay white, of course.  If there
is a way, could someone show me which tabs and options it would be
under?  littleberry

```

```I have it formatted for a fade effect with black and white, it looks that way
in word, but when I print it, it prints with a blue and white fade effect
instead of black and white.  How do I change it to print the way I have it
formatted and why does it do this?
```

```Hi, I'm studying the Precomputed Radiance Transfer method that is in the
directx sdk.

How does it work. Does it perform a monte carlo integration of the texture?
```

```Usually when light refracts into a medium with a higher index of
refraction the radiance measure for the light increases (as shown on
page 143 of Veach's thesis).  However, if the angular distribution of
light is a delta function, as is the case for a directional light, is
this still true?  Veach derives the increase in radiance by
differentiating Snell's law and looking at the respective differential
solid angles for the incoming and outgoing ray, but is that valid for
a directional light?  Or perhaps, have I posed a faulty question by
mixing the radiance measurement and a directional light source?

Here's a small thought experiment.  Say you have a disk that provides
a perfectly directed thick beam of light with some amount of power.
Also suppose that you have a pool of water with a a perfectly flat
specular surface and a perfectly flat diffuse bottom.

Is it possible to describe the light coming from the disk using the

Assuming the disk is above the water facing directly down, how does
the radiance change as it enters the water, hits the pool, and exits
the water?

Assuming the disk is UNDERNEATH the water facing directly down, how
does the radiance change as it hits the pool, and exits the water?

Any help would be much appreciated.  Thanks!

Kevin

```