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Index › Programming Questions & Help › Syntax Questions › Set the alpha of a color variable
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Set the alpha of a color variable? (Read 889 times)
FoodEater
Set the alpha of a color variable?
Dec 18th, 2009, 12:37am  
The only thing in the reference I can find is the alpha() function, which returns the alpha, but I don't know how to assign a new alpha to it.
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blindfish
Re: Set the alpha of a color variable?
Reply #1 - Dec 18th, 2009, 1:29am  
The color documentation is perhaps a little unclear.  You can set the alpha of a colour along with the colour values by passing an additional parameter:

color(150,125); // grey, half-transparent

color(255,0,0,50); // red, fairly transparent
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Where is the what if the what is in why?
 
Cedric
Re: Set the alpha of a color variable?
Reply #2 - Dec 18th, 2009, 5:50am  
i was looking through the references too cause i was not sure if this is the aswer he was looking for...
How would you change a colors alpha asigned to a color variable.

lets say

color c = color(255,0,0);

now i want to change it to color(255,0,0,100);

i tried color color(c,100), doesnt work...
other idea would be:
color(red(c),green(c),blue(c),100);
maybe its the easiest way. dont know...
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subpixel
Re: Set the alpha of a color variable?
Reply #3 - Dec 18th, 2009, 9:01am  
If speed is a concern, you can avoid using the red(), green(), blue() and colour() by manipulating the 32bit ARGB value for the colour:

Code:
color newColor = (oldColor & 0xffffff) | (newAlpha << 24);


where newAlpha is in the range 0 to 255.

That is, keep the existing RGB bits of the colour and merge in the new alpha bits.
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