XenoDream Tutorials

Clip and Object Distance

On the VIEW tab within XenoDream, just beside the Camera's X, Y, and Z Position indicators, there are four fields which may be used for some really interesting images, especially for those objects that are more "solid" in appearance. These fields specify the "Clip Front" and "Clip Back", and the "Closest Point" and "Furthest Point" of the object.

XD View tab

fig.1
Both the "Closest Point" and "Furthest Point" indicators are read-only fields, which means that the User is unable to modify the value represented. When viewing an object, it is done so from what is known as the Camera Position. And the space in front of the camera, where the object exists, is all part of the viewing distance. When the 3-D object has a portion nearest the camera "lens", then that area from the camera to the object is the Closest Point. The Furthest Point is from the camera lens to the very back of the 3-D object.

The "Clip Front" and "Clip Back" indicators show the values at which point two verticle "planes" exist within the viewing distance, one in front of and the other behind the object. It is probably best to think about these planes as sheets of glass, something like window panes, with the object between them. The object, when being created/rendered, can not go past these planes, either towards the camera or away from it. If the Clip Front is the same value as the Closest Point, then this plane is touching the object at the portion nearest to the camera. If the Clip Front value is greater than the Closest Point (further out and past it), then this plane actually cuts through the object being viewed, just like a knife slicing an apple. Nothing of the object on the camera side of the "plane" will be visible, only what is on the other side. It works in the opposite way for the other Clip Back and Furthest Point variables.

As an example, try bringing up the XEP file for the "Untitled-34" image, which was made available in one of my earlier collection uploads (see the FILES section of either of the Yahoo XD eGroups). You will notice that the camera's X and Y Positions are set at zero, meaning they are horizontally and vertically positioned right in the very center. And that the camera Z Position is at a value of 4.000 (a direction relative to the camera orientation), and means that it is along the depth axis from the center. Now you will also notice that the Clip Front has a value of 0.010 and the Closest Point indicates 3.03. NOTE: When modifications are made to the Z Position value, this will affect both the Closest Point and Furthest Point indicator values, since this is altering the position of the camera to the object.

First try setting the Clip Front to the same value as the Closest Point, which is 3.03. The object should still appear the same as before. Now adjust the Clip Front to a value of 3.50. This will make the front "plane" cut through the object showing only what is on the other side of that plane, everything on the camera side of the plane becomes non-existent (see figure 2 below). If you now set the Clip Front to a value of 4.00 then you have cut the object in half, just like slicing through the center of an apple, as in the second example (see figure 3 below). If you further increase the Clip Front to a value of 4.96 then you have reached the far side of the object, at which point nothing more than a tiny spot is left.

fig.2

fig.3

Now let us try something a little different. Set the Clip Front to a value of 2.75 (away from the object) and then drag the camera's Z Position so that it decreases in value. Stop at every value some where around a tenth of the original 4.0, such as 3.9, 3.8, 3.7, 3.6, etc. You will notice that the Closest Point indicator's value has also been changing, decreasing as well. This will eventually cause the Clip Front to be within the object and not outside of it, effectively cutting through the object.

By the way, using the Camera Zoom field does not alter any of the fields and values discussed above. This control is only for magnification purposes, and does not affect the position of the camera or the object. It is like using a stronger magnification lens on your camera (a zoom lens), making the object appear closer, even though it really is not.

As an added note, another item on the VIEW tab, which has some significance with these fields, is the Fisheye Lens checkbox. When checked, it then makes full use of the Clip Front rather than the Z camera position. The amount of fisheye applied may be controlled by adjusting the Clip Front towards the Closest Point value, without moving the camera. This feature may cause the object to expand off the edges of the viewing area, so by reducing the Camera Zoom value, it should become whole again. In figure 4 below, this example of the same XEP file has the Zoom set to a value of 22 and the Clip Front set to a value of 3.

Untitled-34-Ex-3

fig.4
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