D3PLOT 22.1

3D_OPTIONS... Further 3D Options

The 3D_OPTS... button gives a control panel for further 3D options. These options are described below.

Soft clip Clipping graphics outside the current screen window

If you are dealing with a very large model, but are only looking at a small part of it, the 3D graphics driver can work unnecessarily slowly in its default mode of operation. This is because the whole model is sent to and manipulated by the graphics driver, despite the fact that you are only looking at a small part of it, in anticipation of your wanting to zoom out to see the whole of it.

If you turn Soft Clip on , and redraw the image, the graphics will run faster. This is because the software has "clipped" (ie removed) those parts of the image not visible in the current window before sending it to the 3D graphics driver, so the 3D driver has to process fewer graphics entities. However this also means that if you zoom out those parts of the image outside the previous window will not be there. This is illustrated in the figures below.

In this example the user has zoomed in on the neck and upper chest region of a side-impact dummy (left hand image), and then zoomed out to what should show the full dummy. This exposes the jagged edges left by the 3D clipping algorithm.

To see the missing elements you need to issue an explicit drawing command at the new scale to recalculate the clipping and send more elements to the 3D graphics driver.

SHOW_PROJ Showing the viewing frustrum

On 3D devices it is possible to show the current viewing "frustrum" at the bottom left corner of the plot by turning SHOW_PROJ on.

This shows the information in the figure below.

The frustrum shown here assumes perspective projection.

The Z clipping plane locations are shown when SHOW_PROJ is on, and this can be very helpful when using Z clipping, as otherwise it is easy to "lose" the clipping planes.

The default near and far plane positions are drawn in green, and the plane locations in blue. So you can visualise movement relative to initial locations.

Using the Z clipping planes

The Z clipping planes are shown in the figure above. There are two planes: a "near" and a "far" one, which the hardware uses to clip the image in the +/- screen Z axis.

By default they are set just outside the +/-Z limits of the structure (shown as green lines in the projection box), so that no clipping takes place, but when the 3D options box is mapped you can move them (shown as blue lines in the box) using the following mouse and keyboard meta-key combination:
<right shift> + <left mouse>	Moves the near clipping plane.	Cursor symbol is
<right shift> + <right mouse>	Moves the far clipping plane.	Cursor symbol is
<right shift> + <mid mouse>	Moves the both clipping planes.	Cursor symbol is

(Note that when the 3D options box is not mapped then the <right shift> and <right control> keys act exactly like their <left> equivalents, meaning that either side of the keyboard can be used for normal dynamic viewing.)

In all cases moving the mouse up moves the plane(s) away from you, and down moves towards you. This is a form of dynamic viewing: the planes move and the image gets updated as the cursor moves. It is recommended that you turn the SHOW_PROJ switch, described above, on as this will enable you to see the planes moving in the projection box.

To reset the planes to their default positions use the Reset Z clip NEAR and FAR buttons. This will reset them to their initial positions (shown by the blue lines in the projection box).

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