# 256 cube help plz

ok. im extremely new to openGL so please be as “layman” as possible when it comes to help. any help however is much appreciated

im creating a 16x16x16 cube filled with smaler cubes. ivew managed to do this. ive also implemented a zoom and rotate feature. my problem is this.
i need to be able to draw a plane through any point and set everything in front of that as either transparent or as background so it becomes invisible.
if need be i will show my code for the cube.
kind regards
rborob

Hi,

SOunds like you need a clip-plane. Basically, you can define a plane that will not allow anything drawn behind it (plane direction is defined by the normal vector).

FROM THE REDBOOK:

void glClipPlane(GLenum plane, const GLdouble *equation);

Defines a clipping plane. The equation argument points to the four coefficients of the plane equation, Ax+By+Cz+D = 0. All points with eye coordinates (xe, ye, ze, we) that satisfy (A B C D)M-1 (xe ye ze we)T >= 0 lie in the half-space defined by the plane, where M is the current modelview matrix at the time glClipPlane() is called. All points not in this half-space are clipped away. The plane argument is GL_CLIP_PLANEi, where i is an integer between 0 and 5, specifying which of the six clipping planes to define.

So, the trickiest part is determining the coefficients for the plane. A simple example would to clip fragments with a negative X would be:

``````GLdouble coefs[4] = { 1.0, 0.0, 0.0, 0.0 };

glClipPlane( GL_CLIP_PLANE0, coefs );
glEnable( GL_CLIP_PLANE0 );
// Draw geometry to clip
glDisable( GL_CLIP_PLANE0 );
``````

Hope that helps!
-Rawk

ok ill try that during the weekend
thanks for help ill let you know how it goes

ok so how would i go about setting an input in my interface to handle any arguments? would i have an x, y, z input and have it draw the normal at those coordinates then clip it? what sort of code would i be looking at to do that for me if thats the case?

ok that methos wasn’t so good since the view of the cube is changing with rotate etc. heres what i think should work…any ideas?

given 3 cubes in tesseral form, plot a plane through these and determine what is displayed. thats to say everything in front of it is displayed as background (black)

help plz

bump

please can someone help…ive found some info on other posts but cant tell if its relevant or not. i just want my interface to be able to input 3 sets of coordinates, draw a plane through all of them and set all in front as background. please help

bumpety bump

Stop bumping with silly posts.

1. You have been answered correctly : use clip planes.
2. A problem with rotation/scaling ? Read the docs better.
3. … and stop bumping with silly posts. If you don’t show you make some work, why would one want to help you again ?