PDA

View Full Version : Dynamic Vertex ?

DanDanger
11-17-2002, 07:54 AM
Hi,

is there any way to draw a Mathematical Curve in OpenGL with Dynamic Arrays ???

I interpolate the Curve by Calculating different Points along the x-Axis, and Connect them via
GL_LINES :

glBegin(GL_LINES) ;

... Here must be a "Dynamic" Vertex-Array
... Adding more and more Points....

glEnd() ;

The Problem is: I don't know, how many Points I need, to draw the Curve, so, i mus dynamical add another Point to the Line.

Does Anyone know, how to implement this ???

Greeting's
DanDanger

jwatte
11-17-2002, 01:22 PM
I would suggest generating your vertices into some structure supporting easy insert, such as a list. Then, inside the glBegin(), just walk the list and issue the vertices, as stored in the list.

DanDanger
11-18-2002, 05:03 AM
Yeah,
I think, that should do it.

But, is there any other way to implement it ?
I just want to draw a Curve ;-)

Greetings
DanDanger

knackered
11-18-2002, 06:20 AM
If you just want to add vertices to the end of the array, just do this:-

float* array=0;
int mem=0;
int count=0;

{
if (count>=mem)
{
mem = count+100;
array = (float*)realloc(array, sizeof(float)*3*mem);
}

array[count*3]=x;
array[count*3+1]=y;
array[count*3+2]=z;

count++;
}

jwatte
11-18-2002, 12:01 PM
I don't understand why linked lists are "overloaded" (or, I believe he meant to say, "overkill").

If he wants to subdivide a curve to some specific tolerance (which it sounds like he wants to do) then he just needs to find a good data structure for doing that. If you don't want to be memcpy()-ing a vector out towards the end, to insert in the middle, a linked list is the right data structure.

Of course, you can't submit a linked-list as-is to OpenGL; you need to somehow traverse it when you're done, whereas a vector can be submitted as-is, so it's all in which case ends up being better for your specific case.

However, if you find yourself with a problem, and there's some common data structure that will solve the problem, I would consider that "great" rather than "overkill," because if I can use a data structure I understand, that means I probably won't be writing a bunch of buggy code I'll have to debug.