ortho() near and far parameters?

Programming Questions

matteosis..

ortho() near and far parameters?

in Programming Questions • 2 years ago

Hi,

Does anybody know what the near and far parameters (last two parameters) of the ortho() function are supposed to change?

Whatever value I use for them I can't see any difference in the results.

The projection doesn't seem to change, nor does it affect which shapes are or aren't drawn.

See for example the following code:

float DEPTH=117;
size(100, 100, P3D);
noFill();
smooth();
ortho(0, width, 0, height, -10, 10);
translate(100, 100, DEPTH);
box(45);

Whatever values I choose for the near and far parameters, the box is always drawn (as a square in this case) if DEPTH <=117, and it disappears for DEPTH>117.

Why 117? And why doesn't it depend on near and far?

Besides the clipping, if I add rotations, the result doesn't change a bit by changing the values for near and far.

Is this expected behavior? If so what am I missing?
What are the near and far parameters for?

Thanks
m.

Replies(5)

kooogy

Re: ortho() near and far parameters?

2 years ago

from the reference

"The parameters to this function specify the clipping volume where left and right are the minimum and maximum x values, top and bottom are the minimum and maximum y values, and near and far are the minimum and maximum z values."

http://processing.org/reference/

so just the clipping. i'd've said that's expected behaviour - ortho has no perspective so things won't get smaller with distance from the camera.

matteosis..

Re: ortho() near and far parameters?

2 years ago

Yes I read the reference. Ok so we expect it to affect just the clipping.

The problem is, I don't observe any difference in clipping either...

matteosis..

Re: Re: ortho() near and far parameters?

2 years ago

When I said "besides the clipping" I meant "in addition to _not_ observing any difference in clipping"

kooogy

Re: ortho() near and far parameters?

2 years ago

had a look at the code and it looks ok, matches the wikipedia page ( http://en.wikipedia.org/wiki/Orthographic_projection_%28geometry%29 )

public void ortho(float left, float right,
float bottom, float top,
float near, float far) {
float x = 2.0f / (right - left);
float y = 2.0f / (top - bottom);
float z = -2.0f / (far - near);
float tx = -(right + left) / (right - left);
float ty = -(top + bottom) / (top - bottom);
float tz = -(far + near) / (far - near);
projection.set(x, 0, 0, tx,
0, y, 0, ty,
0, 0, z, tz,
0, 0, 0, 1);
updateProjection();
frustumMode = false;
}

(but curiously updateProjection is empty)

[edit, that code is from Aug 2010]

the 117 is curious. and it changes with width and height. i think this has been raised before.

oh, here http://forum.processing.org/topic/is-ortho-working-as-it-should

matteosis..

Re: ortho() near and far parameters?

2 years ago

Well that seems to be a different problem, that the translation along the x and y axis is not as expected, but it doesn't seem to mension a clipping in the z axis.

It must be that I misunderstand the meaning of "clipping volume" in this sentence (from the reference):

The parameters to this function specify the clipping volume where left and right are the minimum and maximum x values, top and bottom are the minimum and maximum y values, and near and far are the minimum and maximum z values.

What I understand by "clipping volume" is that everything inside that volume is drawn, and everything outside that volume is not. But that is not the case for near and far, as the real distance at which things stop being drawn does not change when you change near and far, or at least, it is not true that things are drawn if and only if near<z<far.

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