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**ray****Member**- Registered: 2005-11-03
- Posts: 2

Hi !

I am writing a 3D shader and I got this graph and I just can't figure out the function

The result value (given in greyscale values between 0=black and 1=white) depends on the two variables a and b.

It is for example,

0.5 when a=b

1 when a=1

0 when b=1

0.5+(a/2) when b=0

0.5+(b/2) when a=0

(is there a name for this kind of graph btw.?)

I think it must be a quite simple function.

Thanks in advanced for help

Ray

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**MathsIsFun****Administrator**- Registered: 2005-01-21
- Posts: 7,684

Calculate the slope (or angle) from any point to (1,1) and base it on that.

Example: (0.2,0.2) ==> Slope = (1-0.2)/(1-0.2) = 1 = 45°

Example: (0.9,0.2) ==> Slope = (1-0.2)/(1-0.9) = 8 = 83°

So you could say the first point was 45°/90° = 0.5, and the second 83°/90° = 0.92

That should get you close.

"The physicists defer only to mathematicians, and the mathematicians defer only to God ..." - Leon M. Lederman

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**ray****Member**- Registered: 2005-11-03
- Posts: 2

Thanks!

I have the solution now as:

if( (1-a) < (1-b) )

r = 1 - ( (1-a) / (1-b) ) / 2;

else

r = ( (1-b) / (1-a) ) / 2;

Ray

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