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Old 02 March 2015, 06:57   #28
mc6809e
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Join Date: Jan 2012
Location: USA
Posts: 281
Quote:
Originally Posted by Mrs Beanbag View Post
i feel like you have cheated me a little here since the area to fill is only 24 words x 380 lines x 2 planes = 18240, or 54720 fill cycles + 182400 copy cycles = 237120 in total. So i get your point but it is a closer call than you thought.
Sorry

Quote:
Originally Posted by Mrs Beanbag View Post
You always have to calculate which polygons are behind the viewer, you can't draw those in any case. There are also many calculations that you have to do per-polygon whether they are visible in the final scene or not.
Oh, I just meant that since the CPU is usually busy with other calculations of all sorts while the blitter is less taxed, adding a cross product calculation for a surface normal plus dot product to see its relation to a ray from the camera just adds more calculation to an already burdened CPU. It might be worth it just to give the blitter more work even if the blitter would take more time, assuming it runs concurrently with the CPU. It would depend on how much internal operation the CPU was performing (plenty for multiplies and divides).

Quote:
Originally Posted by Mrs Beanbag View Post
But if you are not doing hidden surface removal, how do you order the polygons? Simple Z-sorting is not enough for something like an L-shaped object, for example. Whereas with hidden surface removal one can often use a fixed drawing order.
My intuition tells me something else, but that's not proof of course. I want to say that any object for which surface normals work should also work using Z-sorting. I have no proof though so I'll have to think about it more.

Quote:
Originally Posted by Mrs Beanbag View Post
When polygons are very distant it might be quicker to fill them than to do a couple of multiplies required for testing visibility, but we have to do some multiplies anyway to calculate the screen co-ordinates of all the points.

EDIT: also consider the fill operation includes an idle cycle, which can be used by CPU.
That's a good point. The extra plane means 9120 of those extra fill cycles are idle cycles, so it makes things even closer.
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