Re: [Plplot-devel] More alpha values

[Hazen B. <hba...@ma...>]

On Jan 16, 2008, at 9:14 PM, Alan W. Irwin wrote:

> On 2008-01-16 20:03-0500 Hazen Babcock wrote:
>>
>> I tried that, as you can see in the code in example 30, but it  
>> does not work for me. I can still see faint black lines separating  
>> the different colors. Does it work for you?
>
> I attach the result for the second page for the png (not pngcairo)  
> device so
> you can be the judge.  I don't see any extraneous black lines here,  
> but
> OTOH, it is mostly just a big red blob with some minor transparency  
> effects
> so perhaps something is not working quite correctly for the second  
> page for
> the png device.  Alternatively, it may be working correctly and you  
> just
> haven't yet had a chance to design a dramatic range of colours to  
> accentuate
> the transparency effects.

It looks like this driver scales alpha values in a different way than  
the cairo drivers.

> I also tried it for the psc device.  That device is not alpha- 
> enabled yet,
> but it was interesting that the second page (literally just a red  
> rectangle
> for this special case of non-enabled device) had black lines in it  
> (where
> the black background leaked through) with antialiasing turned on.   
> The lines
> disappeared with antialiasing turned off so you may also need to  
> turn off
> antialiasing to get rid of the black lines for cairo devices.

That (anti-aliasing) does seem to be the problem, thanks! I've  
attached example 30 page 2 from pngcairo for comparison purposes with  
the png device.

-Hazen