Hi all, I got this problem with walking in 3D:

import processing.opengl.*;
float a=0;
int f=-1600;
float Y=0;
float s=512;
float mx=512;
float my=300;
float mxa=512;
int ground = 1024;

void setup()
{
size(1024,600,OPENGL);
background(0);
framerate(80);
stroke(255,255,255);
}

void draw()
{
background(0);  

pushMatrix();
translate(0,height);

rotateX(PI/2);
fill(0,055,0);
rect(0,0,ground,-ground);

pushMatrix();
rotateX(PI/2);
translate(768,0,256);
fill(0,210,0);
box(100,300,100);
popMatrix();

pushMatrix();
rotateX(PI/2);
translate(256,0,256);
fill(0,110,0);
box(100,300,100);
popMatrix();

pushMatrix();
rotateX(PI/2);
translate(768,0,768);
fill(0,0,100);
box(100,300,100);
popMatrix();

pushMatrix();
rotateX(PI/2);
translate(256,0,768);
fill(100,0,0);
box(100,300,100);
popMatrix();

popMatrix();


if(keyPressed && keyCode==UP)f+=3;
if(keyPressed && keyCode==DOWN)f-=3;
if(keyPressed && keyCode==LEFT)mx+=3;
if(keyPressed && keyCode==RIGHT)mx-=3;
if(mousePressed)
{
beginCamera();
camera(mx, my, f, mx, my,2000, 0, 1, 0);
if(mouseButton == RIGHT)a=a+0.02;
if(mouseButton == LEFT)a=a-0.02;
rotateY(a);
endCamera();
}
else
{
beginCamera();
camera(mx, my, f, mx, my,2000, 0, 1, 0);
rotateY(a);
endCamera();
}
}


Now the problem is about walking in direction I am looking at. It always walks in the same direction, no matter where camera is looking. I was thinking to rotate coordinate system so Z axis rotates with a camera, if you know what I mean. Well, have a look, its easy to understand once you look at it running. Thanks for your help in advance.