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Translucent Sphere

Posted on 2003-10-22
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Anybody can guide in how to draw a translucent sphere? Pls show my some code. Thanks.
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Question by:KeithTeo
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by:sunnycoder
ID: 9604451
Hi KeithTeo,

two things ... what platform/library?
is this your homework ?

Cheers!
Sunny:o)
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by:KeithTeo
ID: 9625017
I'm working on Win2K using standard opengl library.

I understand that GLUquadricObj allows me to draw a spherical object and glColor4f allows me to draw an alpha object. But I still landed up with an opaque object. Why? Whats wrong? Can show me some code?

No. Its not my homework. Its just an interest.
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sunnycoder earned 125 total points
ID: 9670248
Ok, you should find some code as well explanation here

http://nehe.gamedev.net/data/lessons/lesson.asp?lesson=08
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by:effectstudios
ID: 9816471
well, I dont't have the code right now, but the problem is really simple. You first have to enable blending.


If that is all you need, please go ahead and skip the rest.

To understand this, you have to know just a couple of things.
1. Every geometric primitive that you draw, has finally to be represented on a raster - scan display, and thus all geometry is finally computed into pixels.

2. The entire 3D scene is projected onto a 2D plane, thus many objects end up overlapping each other.

3. When OpenGL is writing pixels to the frame buffer, it checks if a pixel is already there.
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by:effectstudios
ID: 9816486
(Sorry, pressed a couple of wrong keys!)

        a. if no, then it simply writes to the buffer.
        b. If yes, then it checks if the pixel in the buffer has come from a primitive that is closer to the camera than the current one. If the new one is closer, the value is overwritten, if the previous one is closer, then the new value is discarded.

4. However, this is in case of opaque objects, now suppose that you have to make something look transparent. In such a case, logic says that a pixel coming from the transparent/translucent primitive will not overwrite the previous pixel but change its colour (lets say in case of coloured glass). This modification of the colour of the previous pixel by the new one is termed blending.

Thus, you first have to enable blending. Then you select one of the various blending modes available and finally you precisely specify how you want the 'modification' to be done.

Regards
Vin
 
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by:sunnycoder
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