Re: [png-mng-implement] Blending pngs

[Ssagarr P. <hug...@ou...>]

Hi,

> this is what I did... you may require clamping to avoid overly intense colors 
>  
> The output alpha is a combination of the alphas in the image; it's  
> a1*a2 which keeps merged alphas more transparent.  Works for several  
> overlays stacked pretty well. 
>  
> but basically it's out = top * a + under * ( 1 - a ) 
>  
> foreach( pixel ) 
> { 
> int r, g, b, aout; 
> if( !a ) 
> return over; 
> //if( a> 255 ) 
> //   a = 255; 
> if( a == 255 ) 
> return (in | 0xFF000000); // force alpha full on. 
> aout = AlphaTable[a][AlphaVal( over )] << 24; 
>  
> r = ( (( ((in & 0x00FF0000)>> 8)  *(a+1)) + ( ( (over & 0x00FF0000)>>  
> 8)*(256-(a)))) ); 
> if( r & 0xFF000000 ) 
> r = 0x00FF0000; 
> else 
> r &= 0x00FF0000;  // trim low bits 
>  
> g = ( (( ((in & 0x0000FF00)>> 8)  *(a+1)) + ( ( (over & 0x0000FF00)>>  
> 8)*(256-(a)))) ); 
> if( g & 0x00FF0000 ) 
> g = 0x0000FF00; 
> else 
> g &= 0x0000FF00;  // trim low bits 
>  
> b = ( ((in & 0x000000FF )*(a+1)) + ( ( over & 0x000000FF)*(256-(a))) )>> 8; 
> if( b & 0x0000FF00 ) 
> b = 0x000000FF; 
> //else 
> // b &= 0x000000FF; 
> } 
>  
can you please elaborate on  AlphaTable and what are in pixels and out pixels ?

Thanks,
Sagar