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Planets, and Apple Video...

Posted by BGB, 17 September 2013 · 431 views

Planets:
I have decided to change my voxel engine from being an "infinite" 2D plane, to being a bounded 2D region, which I will assert as being a "planet".

this basically consisted of adding wrap-around, and generating a topographical map for the world.
currently, the world size is fairly small, roughly a space about the size of the surface of Phobos, or otherwise, about 64km around (65536 meters).

an issue with planets:
there is no really obvious "good" way to map a 2D plane onto a sphere.
some people try, but things get complicated.

I took the easy route though, and simply made it wrap around, effectively making the ground-level version of the planet have a torus as its topology.

then, for those who notice that the ground-level view of the planet is geometrically impossible, I can be like "actually, the planet is a Clifford Torus", and the spherical view represents the part of the torus passing through normal 3D space...

kind of a hand-wave, but oh well...


meanwhile, went and threw together an implementation of the Apple Video codec (FOURCC='rpza').

http://en.wikipedia.org/wiki/Apple_Video
http://wiki.multimedia.cx/index.php?title=Apple_RPZA


reasons:
I was thinking "you know, Apple Video and DXT1 are pretty similar...".

basically, they are sufficiently similar to where moderately fast direct conversion between them is possible.
granted, the size/quality tradeoff for this codec isn't particularly good.

while I was implementing support for the codec, I did add alpha-support, so this particular variant supports transparent pixels.

quick test:
I am decoding frames from a test video at around 432 Mpix/s, or a 320x240 test video decoding at around 5700 frames/second. the above is with a vertical flip as a post-step (omitting the flip leaves the decoder running at 470 Mpix/s, and 6130 frames/second).


and, then even as fast as it is going, checking in the profiler reveals a spot which is taking a lot of cycles, causing me to be like "MSVC, FFS!!"


the expressions:
tb[6]=0; tb[7]=0;

compile to:
0xfe08c6a mov edx,00000001h BA 01 00 00 00 0.44537419
0xfe08c6f imul eax,edx,06h 6B C2 06
0xfe08c72 mov [ebp-44h],eax 89 45 BC 0.21256495
0xfe08c75 cmp [ebp-44h],10h 83 7D BC 10
0xfe08c79 jnb $+04h (0xfe08c7d) 73 02 1.38335919
0xfe08c7b jmp $+07h (0xfe08c82) EB 05 0.19569471
0xfe08c7d call $+00018ce1h (0xfe2195e) E8 DC 8C 01 00
0xfe08c82 mov ecx,[ebp-44h] 8B 4D BC
0xfe08c85 mov [ebp+ecx-14h],00h C6 44 0D EC 00 0.25305352
0xfe08c8a mov edx,00000001h BA 01 00 00 00 0.50273299
0xfe08c8f imul eax,edx,07h 6B C2 07
0xfe08c92 mov [ebp-3ch],eax 89 45 C4 0.30703825
0xfe08c95 cmp [ebp-3ch],10h 83 7D C4 10
0xfe08c99 jnb $+04h (0xfe08c9d) 73 02 1.26189351
0xfe08c9b jmp $+07h (0xfe08ca2) EB 05 0.2598016
0xfe08c9d call $+00018cc1h (0xfe2195e) E8 BC 8C 01 00
0xfe08ca2 mov ecx,[ebp-3ch] 8B 4D C4
0xfe08ca5 mov [ebp+ecx-14h],00h C6 44 0D EC 00 0.00337405


which is actually, pretty much, just plain ridiculous...

ADD:
yes, the above was for debug code...
but, there is presumably some limit to how wacky code built in debug mode should get.


otherwise:
http://cr88192.dyndns.org:8080/wiki/index.php/BTIC1C

the implementation of Apple Video was extended slightly, with this extended version hereby dubbed BTIC1C.

the primary additions are mostly alpha support and some LZ77 related features.




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