>>So my question: is there an easy way of selecting only visible objects in my zone?? I was thinking of rendering a scene with indexes colors indicating the object''s ID, then going through all rendered pixels. How can this be easily achieved? Is there a better/easier way??<<

yes this is an easy way, watch out though if u have dithering enabled

http://uk.geocities.com/sloppyturds/kea/kea.html
http://uk.geocities.com/sloppyturds/gotterdammerung.html

u dont need to, just draw each primative (object) in a different color watch out though with 16bit color window u are limited to 65535 different objects though with 32bit u can do 4billion.

heres basically what u do (16 bit will need to be treated differently)

drawobject()
{
warning these bit operations are most likely wrong but it should give u the idea
r = indexcounter%256; // or &255
g = (indexcounter<<8)%256;
b = (indexcounter<<16)%256;

glcolorub(r,g,b)
draw the object
indexcounter++
}

indexcounter=0;
drawobject()
drawobject()
drawobject()



(btw ive used this method to pick objects when theres been over 2million different on the screen so it does scale very well)

http://uk.geocities.com/sloppyturds/kea/kea.html
http://uk.geocities.com/sloppyturds/gotterdammerung.html