[Gllug] Faster maths?

[salsaman]

salsaman wrote:

> salsaman wrote:
>
>> salsaman wrote:
>>
>>> Adrian McMenamin wrote:
>>>
>>>> On Fri, 2007-03-09 at 00:49 +0100, salsaman wrote:
>>>>  
>>>>
>>>>> Adrian McMenamin wrote:
>>>>>   
>>>>
>>>>
>>>>
>>>>
>>>>  
>>>>
>>>>> Perhaps you could do some optimising while the index is being 
>>>>> created ? How do you generate the 8 bit palette ?
>>>>>
>>>>>   
>>>>
>>>>
>>>>
>>>>
>>>> Median cut
>>>>
>>>>  
>>>>
>>>
>>> I'm not familiar with that method, but it appears you will make 
>>> cubes in RGB space which contain equal numbers of colour pixels.
>>>
>>> When you are counting the pixels, then you know which box they 
>>> belong in.
>>>
>>> Or am I missing something ?
>>>
>>> Gabriel.
>>>
>>
>>
>> OK, now I see where the problem lies; when you add the dithering, 
>> each pixel moves a random amount.
>>
>> To calculate this quickly, you should make a 3d map of all the cubes: 
>> each cube has 6 faces which connect to another cube. So you need an 
>> array of 256*6 connections. You will also store the side length of 
>> each cube (256*3 array).
>>
>> Now when a point moves, you can track it's position as it crosses 
>> from one cube into the next, first in the R direction, then G, then 
>> B. You will then know which cube it ends up in, and you can map it to 
>> your indexed palette.
>>
>> Gabriel.
>>
>
>
>
>
>
> Hmmm...actually it's not quite so simple as I thought. Each face can 
> connect to multiple other cubes, so for each face you need to store an 
> array of four ints (the opposite corners of the intersection with 
> connecting cubes).
>
> You can still use the same algorithm, it's just a little more complex 
> to see which cube a pixel moves to when it crosses a face.
>
> Gabriel.
>


OK, I see one final problem, and that is - unmapped space between 
blocks. To compensate for this, you should still map the blocks as 
touching, even if there is a gap between them. Then when you move from 
block A to block B, it only enters B if it has crossed the mid point 
between them. Since you store the side length of each block, it is 
trivial to determine the mid point between two faces.

Hope this helps.

Gabriel.
http://lives.sourceforge.net



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