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FERNANDO-BRASIL

Object position

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Hi there people! I have a question but I don''t know how to explain... I would like to get a vertex position (I think). FOr example: glLoadIdentity(); glTranslatef(1.0f, 0.0f, 0.0f); glBegin(xxxx); glVertex3f(0.0f, 1.0f, 0.0f); glEnd(); Specifying this simple commands, we know that glVertex3f (in this case) will draw a point at position 2.0f (in X). We can arrive to this conclusion by adding 1.0f (of glTranslatef) + 1.0f (of glVertex3f) = 2.0f. All that we have to do is add what we passed to glTranslatef and glVertexf, and we get the position of the painted object. But a problem will occur if we inform rotations... We cannot prediscover the vertex position if we rotate the object... I would like to know if there is a command to get this values, or a way to do this by hand... Any help will be appreciated! Fernando.

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I had the same problem yesterday... I needed to find out where exactly my objects where after I rotated/translated them etc., so that I could do my own manual sorting to make blending look right.

What I ended up doing is just not use the glRotate/glTranslate functions. Instead, I made my own, which wasn''t very hard.

Just rotate/translate the objects yourself and you will get the same results, however (probably) slower than glRotate/glTranslate. If you don''t know the trig required (cosine and sin is all), then just look at some of the tutorials on rotation on gamedev.net

I found out can get the current matrix that GL uses after glRotate/translate, though... Then you can just apply that matrix to all your points, and viola, you have their new positions. glGet(something-matrix) is the function you need to get that...

Right now I''m doing it the first way, though, since I know nothing about how you would apply a matrix to a point...

So I have a question of my own...

How do you apply a 4 by 4 matrix to a point? I know NOTHING about matrix math stuff :-( Cuz like I said before, I can get the matrix that GL uses, but I don''t know what to do with it once I have it.

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