Dewey Anderson (dewey++at++evt.com)
Thu, 25 Jul 1996 12:14:57 -0700
In a simple example program, I have two planes (rectangles) perpendicular to
the line of sight with one moving up while the other moves down. The one
moving down is 5 units behind the one moving up. There is NO depth buffer.
(Running on a high impact with visual 43 (0x2b). We HAVE to have 8 bit RGBA
double buffer.)
At first things look OK. This would indicate that the plane behind (moving
down) is getting drawn first and then is overdrawn by the one in front (moving
up). At one point, you can see the one behind begin to appear below the one in
front.
Then, suddenly, the one in back appears to jump "in front", i.e. it appears
that the one in FRONT (moving UP) is drawn first and the one behind (moving
down) overdraws it. With no depth buffer to mask out pixel drawing, the
illusion is that the one in back jumped to the front.
I was hoping that the statement in the manual that traversal happens
left-to-right would apply to drawing as well but my example seems to indicate
that the drawing order can change.
Is there any way to control this? I can imagine that no one ever expected
performer to be used in a situation where there is no depth buffer so I
wouldn't be surprised to hear that it's not consistent or controllable.
Dewey Anderson
dewey++at++evt.com
Evolving Video Technologies
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