PDA

View Full Version : Questions about rotation



Amit5
11-26-2009, 01:54 PM
Hello,

I was wondering if there is a way of retriveing the vertecies
after preforming glRotatef() on them (without using sin() / cos() ) ?

I was also wondering if it is posible to draw a circle around
the Y-axis using a given vertex and the glRotatef() function ?
(i know it can be done using cos() and sin()...)

Thanks :)

mikau
11-26-2009, 06:59 PM
In my experience, the transformations you set up, such as glRotate, glTranslate, and glScale, specify what operations are applied to the 'primitives', or shapes that you draw. When you draw a shape, it is sent down the pipeline and you really don't see or get the results of the calculations until it appears on the screen. OpenGL is not intended to be a calculation library to perform vector operations. There are a few helpful functions, like one that allows you to find out where an onscreen object originated, but they all relate to graphics in some way.

I don't know why you don't want to use sin and cos. My best guess
is that you're not familiar with trigonometry. That is kind of a prerequisite for OpenGL, and it will be difficult to do pretty much anything without knowing the basics there. It isn't hard to learn though. In my oppinion the only thing scary about Trigonometry is its name. :]

scratt
11-26-2009, 08:21 PM
Following on from mikau's reply here are a couple of links you might find helpful :

http://www.swiftless.com/tutorials/opengl/circle.html

http://www.gamedev.net/community/forums/topic.asp?topic_id=329897&whichpage=1&#2136549

Amit5
11-27-2009, 04:03 AM
I realy don't like trigonometry but that is not why i wanted to
my project using opengl function, it's a project for my university
and i thought it should be done only using opengl functions..

thanks for your answers! , now i see it's impossible to do the project without using a bit of trigonometry..