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Can someone explain stride to me? (VertexPointer)

Posted on 2004-09-19
Medium Priority
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void glVertexPointer(
GLint size,
GLenum type,
GLsizei stride,
const GLvoid *pointer
);

Parameters

size
The number of coordinates per vertex. The value of size must be 2, 3, or 4.
type
The data type of each coordinate in the array using the following symbolic constants: GL_SHORT, GL_INT, GL_FLOAT, and GL_DOUBLE.
stride
The byte offset between consecutive vertices. When stride is zero, the vertices are tightly packed in the array.
pointer
A pointer to the first coordinate of the first vertex in the array.

I find the definition of stride very vague. Could someone explain what it exactly means? For example, if i have an array of vertices... array { x, y, z, x, y, z, x, y, z } and the stride is set to 12 does this mean that if i call glArrayElement (1) it will draw the first set of x, y, z? (array[0], array[1], array[2])?
Or

does it mean the data is represented like this:
array { x, x, x, y, y, y, z, z, z }?

Thanks
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Question by:zekard
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Accepted Solution

str_ek earned 150 total points
ID: 12103713
stride (and so named offset spacing) is used to reduce the actual need to have more than one table descrypting a "something" you just can agregate extra verticle properities, and it lets you have all info you want in just one array ! (helps a lot when it comes to manipulating)

so you may have a

x,y,z,x,y,z form
as well as
x,y,z,alpha,type,x,y,z,alpha,type,

it's an array, so the type is constat, but it's also a linear memory so you can contain data of any virtualy constat-length type between the coordinates set :) all you need to know for furher operations is the offset of every "extra info" and total length of pack descrybing a verticle :) it may be extra coords (ie texture), calculated light, or any other junk

gl is only interested in the coords, because only coords it can use, so he makes assuption, that coords come firtst (well it's just a array you can shift it a bit, and cos it's cyclic it will always look good for gl), and lets you tell how many of array units ( this is also up to you) is he to skip each time he traces next vertice

co the cycle ( totla verticle description length) is
(stride+size)*sizeof(type) :)

got it?
0

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