Re: Shading to transparent using withshademethod

[Hans Hagen <pragma@wxs.nl>]

On 1/28/2016 11:45 AM, Marco Patzer wrote:
> On Thu, 28 Jan 2016 09:43:24 +0100
> Hans Hagen <pragma@wxs.nl> wrote:
>
>> On 1/27/2016 10:05 PM, Marco Patzer wrote:
>>> The new code appears to work in general, but only if no shading to
>>> transparent is being used:
>>>
>>> \definecolor [trans] [a=multiply, t=.5, s=.5]
>>> \starttext
>>>     \startMPcode
>>>       % works
>>>       fill fullcircle scaled 10cm withcolor \MPcolor{trans};
>>>
>>>       fill fullsquare xyscaled (15cm, 15cm)
>>>         withshademethod "linear"
>>>         withshadevector (0,1)
>>>         % works
>>>         withshadecolors (red,\MPcolor{blue})
>>>         % fails
>>>         %% withshadecolors (red,\MPcolor{trans})
>>>         ;
>>>     \stopMPcode
>>> \stoptext
>>>
>>> How to make transparent shadings work with the new mechanism?
>>
>>         withtransparency (1,.5)
>
> However, this makes the entire shade transparent. How to shade from
> one colour to transparent using withtransparency to achieve an
> effect like in the example below?

that isn't how shading works, it's a vector from one color to the other 
(same color space eventually) and transparency is a property of the whole

> \definecolor      [trans] [a=multiply, t=0]
> \setupbackgrounds [page]  [background=color, backgroundcolor=lightgray]
>
> \starttext
>    \startMPcode
>    fill fullsquare xyscaled (15cm, 15cm)
>      withshademethod "linear"
>      withshadevector (0, 1)
>      %% colour doens't match
>      %% withshadecolors (red, lightgray)
>      %% output is ok with \MPcolor
>      withshadecolors (red, \MPcolor{lightgray})
>      %% ??
>      %% withtransparency (1, .5)
>      ;
>    \stopMPcode
> \stoptext
>
> Furthermore, why do the tex and MP colours differ? Wouldn't it make
> sense to use the same colour definitions? Or was that intentional?

it's already hard enough to have what we have now (tex and mp are 
different species)


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