# Rectangle moving along the z-axis
**URL:** https://discourse.processing.org/t/rectangle-moving-along-the-z-axis/8736
**Category:** Coding Questions
**Created:** [February 26, 2019, 3:22pm UTC](https://discourse.processing.org/t/rectangle-moving-along-the-z-axis/8736 "2019-02-26T15:22:53Z")
**Posts on this page:** 7
**Page:** 1
### Author:  [@Raoul](https://discourse.processing.org/u/Raoul)
#### Post date: [February 26, 2019, 3:22pm UTC](https://discourse.processing.org/t/rectangle-moving-along-the-z-axis/8736/1 "2019-02-26T15:22:53Z")
Hello,
I am learning Processing reading the Daniel Shiffman book and I just started the Chapter “Trasformation and 3D”. The following code is the first example about using the z axis.
I can not understand why once Z reached a value around 310 the rectangle is not drawn anymore. When z is set to 0 again the rectangle is draw again.
What I am missing here?
Thanks a lot for your support
Raoul
```auto
// A variable for the Z (depth) coordinate
float z = 0;
void setup() {
// When using (x,y,z) coordinates, we must tell Processing we want a 3D sketch.
// This is done by adding a third argument, P3D (or OPENGL), to the size() function.
size(400, 400, P3D);
frameRate(30);
}
void draw() {
background(255);
stroke(0);
fill(175);
// Translate to a point before displaying a shape there
translate(width/2, height/2, z);
rectMode(CENTER);
rect(0, 0, 8, 8);
// Increment z (i.e. move the shape toward the viewer)
z += 2;
println(z);
// Restart rectangle
if (z > 600) {
z = 0;
}
}
```
---
### Author:  [@kll](https://discourse.processing.org/u/kll)
#### Post date: [February 26, 2019, 5:11pm UTC](https://discourse.processing.org/t/rectangle-moving-along-the-z-axis/8736/2 "2019-02-26T17:11:48Z")
i see this too,
might be limit OR a bug??
anyhow you can try as workaround
```auto
// translate(width/2, height/2, z);
translate(width/2, height/2);
scale(z);
```
works with OR without P3D renderer.
---
### Author:  [@Raoul](https://discourse.processing.org/u/Raoul)
#### Post date: [February 26, 2019, 8:11pm UTC](https://discourse.processing.org/t/rectangle-moving-along-the-z-axis/8736/3 "2019-02-26T20:11:41Z")
Thank so much Kll for checking it out . I don’t know, I thought that maybe I was missing some information but now it seems it could be a bug.
Thank for the alternative solution.
---
### Author:  [@Chrisir](https://discourse.processing.org/u/Chrisir)
#### Post date: [February 26, 2019, 8:41pm UTC](https://discourse.processing.org/t/rectangle-moving-along-the-z-axis/8736/4 "2019-02-26T20:41:08Z")
Hello,
It’s not a bug.
The camera itself has a precise position in the 3D space (as has the rect).
When the rect moves through the camera and is BEHIND the camera, the rect is not visible anymore.
as a proof here is a slowly moving camera (attached to z, but moving slower than the rect)
- additionally I added a fixed box (that seems to move because the camera moves towards you)
- additionally I added avoidClipping with reduces the area a 3D shape would be cut of by the near camera
Chrisir
```auto
// A variable for the Z (depth) coordinate
float z = 0;
void setup() {
// When using (x,y,z) coordinates, we must tell Processing we want a 3D sketch.
// This is done by adding a third argument, P3D (or OPENGL), to the size() function.
size(400, 400, P3D);
frameRate(30);
}
void draw() {
camera(width/2.0, height/2.0, (height/2.0) / tan(PI*30.0 / 180.0) + z/2,
width/2.0, height/2.0, 0,
0, 1, 0);
avoidClipping();
background(255);
lights();
stroke(0);
fill(175);
pushMatrix();
fill(255, 0, 0);
translate(-100, -20, -200);
box(20, 20, 20);
popMatrix();
// Translate to a point before displaying a shape there
translate(width/2, height/2, z);
rectMode(CENTER);
rect(0, 0, 8, 8);
// Increment z (i.e. move the shape toward the viewer)
z += 2;
println(z);
// Restart rectangle
if (z > 600) {
z = 0;
}
}
void avoidClipping() {
// avoid clipping (at camera):
// https : //
// forum.processing.org/two/discussion/4128/quick-q-how-close-is-too-close-why-when-do-3d-objects-disappear
perspective(PI/3.0, (float) width/height, 1, 1000000);
}//func
//
```
---
### Author:  [@kll](https://discourse.processing.org/u/kll)
#### Post date: [February 27, 2019, 1:00am UTC](https://discourse.processing.org/t/rectangle-moving-along-the-z-axis/8736/5 "2019-02-27T01:00:39Z")
> [@Chrisir](#):
>
> When the rect moves through the camera and is BEHIND the camera, the rect is not visible anymore.
yes, i play that too,
but not find any info regarding that camera thinking and the specific numbers
- P3D
- z range 310 …0 … - ??
now i see
> **[perspective() / Reference](https://processing.org/reference/perspective_.html)**
>
> Sets a perspective projection applying foreshortening, making distant objects appear smaller than closer ones. The parameters define a viewing volume with the shape of truncated pyramid. Objects near …
> The default values are: perspective(PI/3.0, width/height, cameraZ/10.0, cameraZ_10.0) where cameraZ is ((height/2.0) / tan(PI_60.0/360.0));
and that is internal of P3D?
```auto
float cameraZ = (height/2.0)/ tan(PI * 60.0/360.0) ;
float fovy, aspect, zNear, zFar;
void my_perspective(){
fovy = PI/3.0;
aspect = width/height;
zNear = cameraZ/10.0;
zFar = cameraZ*10.0;
perspective(fovy, aspect, zNear, zFar);
}
```
now with above code i can see rect up to z = 330
with zNear = 1; ( instead z = 340 )
( using perspective but not camera !)
test code:
```auto
// check on https://discourse.processing.org/t/rectangle-moving-along-the-z-axis/8736/4
int step=10, z = 0;
void setup() {
size(400, 400, P3D);
stroke(200, 0, 0);
fill(0, 200, 0);
rectMode(CENTER);
}
void draw() {
my_perspective();
background(200, 200, 0);
translate(width/2, height/2, z);
// translate(width/2, height/2);
// scale(z);
rect(0, 0, 8, 8); // rect(0, 0, 400, 400);
}
void keyPressed() {
println("key "+key+" keyCode "+keyCode);
if ( keyCode == 38 ) z +=step; // key UP 310 . 320 green to yellow (rect or background/rect invisible )
if ( keyCode == 40 ) z -=step; // key DOWN
println("z "+z+" cameraZ "+cameraZ+" fovy "+fovy+" aspect "+aspect+" zNear "+zNear+" zFar "+zFar);
}
float cameraZ = (height/2.0)/ tan(PI * 60.0/360.0) ;
float fovy, aspect, zNear, zFar;
void my_perspective() {
fovy = PI/3.0;
aspect = width/height;
zNear = cameraZ/10.0; //z 330 cameraZ 86.60254 fovy 1.0471976 aspect 1.0 zNear 8.660254 zFar 866.0254
// zNear = 1; //kll test z 340 cameraZ 86.60254 fovy 1.0471976 aspect 1.0 zNear 1.0 zFar 866.0254
zFar = cameraZ*10.0;
perspective(fovy, aspect, zNear, zFar);
}
float cameraZ = (height/2.0)/ tan(PI * 60.0/360.0) ;
float fovy, aspect, zNear, zFar;
void my_perspective() {
fovy = PI/3.0;
aspect = width/height;
zNear = cameraZ/10.0; //z 330 cameraZ 86.60254 fovy 1.0471976 aspect 1.0 zNear 8.660254 zFar 866.0254
// zNear = 1; //kll test z 340 cameraZ 86.60254 fovy 1.0471976 aspect 1.0 zNear 1.0 zFar 866.0254
zFar = cameraZ*10.0;
perspective(fovy, aspect, zNear, zFar);
}
```
and that looks like with this you would still not be able to zoom in
( like to see some details on the rect surface… )
as it works with
```auto
translate(width/2, height/2);
scale(z);
```
---
### Author:  [@Chrisir](https://discourse.processing.org/u/Chrisir)
#### Post date: [February 27, 2019, 8:30am UTC](https://discourse.processing.org/t/rectangle-moving-along-the-z-axis/8736/6 "2019-02-27T08:30:55Z")
you can find information about the camera in the reference:
[https://www.processing.org/reference/camera\_.html](https://www.processing.org/reference/camera_.html)
The camera has an initial position.
The default values are
```auto
camera(width/2.0, height/2.0, (height/2.0) / tan(PI*30.0 / 180.0), // its position
width/2.0, height/2.0, 0, // where it's looking at
0, 1, 0); // whether it's rotated / don't change this
```
You can just change the camera’s z-position so it’s more far away from the rectangle (closer to you).
**OR**
you can leave the camera where it is
you can just start the rectangle more far away from you by setting its initial value to -300 (the negative means, it’s more far away from you) and let it fly to +300.
Instead of a rect use box(), looks better. Use also lights().
Chrisir
---
### Author:  [@Raoul](https://discourse.processing.org/u/Raoul)
#### Post date: [March 4, 2019, 3:55pm UTC](https://discourse.processing.org/t/rectangle-moving-along-the-z-axis/8736/7 "2019-03-04T15:55:28Z")
Thanks a lot for the explanation Chrisir!! This camera concept is new to me, I will look at it in the reference.
Raoul