🚀 go-pugleaf

In article <1992Nov23.151933.21308@bmw.mayo.edu>
	Kall@Mayo.EDU writes:
>What I am trying to do is display a moving 3d cursor in a PHIGS image,
>interactively.

Ah.  Now I understand.  3D cursors are non-trivial to implement
correctly.  With a 2D cursor, most video DACs have a feature that
overlays the cursor on top of the video stream so that the cursor
image doesn't have to be written into the frame buffer.  Older
machines xor the cursor image directly into the frame buffer (I think
this is the case for monochrome Suns; it definately is the case for
the Mac).

>I thought having two
>(exactly the same) workstations on the same drawable would enable me
>to have a 3d cursor in one and my other structures in another and only
>update the workstation that my 3d cursor is moving in.  Not having
>been able to implement this idea, I'm not sure if the idea is totally
>out to lunch?

You want to avoid redrawing the big structures because of the time it
takes to render them, yet the image of the big structures will be
"damaged" by the rendering of the 3D cursor.  The only thing I can
think of is to use "quick update methods" when moving the cursor
interactively.  There is also the problem of what to do when the
cursor should be occluded by some object in the scene.  Another
solution might be to turn off lighting and shading (i.e. line-only
renderings) of the big structure while you interactively move the
cursor and then redraw with lighting and shading turned back on when
the interaction is deigned complete.

>Any suggestions??  Any better approaches?? (Besides do it outside of Phigs?)

I don't know any way you could do a 3D cursor outside of a 3D system,
unless you just kludged the 3D cursor up via the 2D cursor mechanisms
of X.  One such hack is to size the image of the cursor based on how
deep into the screen the cursor is.  This doesn't get you 3D occlusion
like you might want and the cursor always appears "on top" no matter
how far into the screen it is, but at least its changing size
indicates its depth.

							-- Rich
-- 
		      Don't blame me; I voted Libertarian
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