Drawing in alpha channel

Programming Questions

claumm

in Programming Questions • 2 years ago

Hello,

I am trying to achieve an image revealing effect with lines drawn by the user. To do this, I am placing a white square above the image to be revealed. What I would like to know is if it is possible to paint the alpha channel of this square in the space around the lines.

This would be better explained with an image:

I would appreciate any help!

Thank you

Replies(3)

PhiLho

Re: Drawing in alpha channel

2 years ago

Sorry, but I did,'t understand the question, even with the image.
But, basically, you can alter the alpha channel of any image. In general, it is done on the pixels[] array, with some binary manipulations.

claumm

Re: Re: Drawing in alpha channel

2 years ago

Hello,

What I want to achieve is:

- There is an image that fills the entire canvas.
- The image has an alpha mask, completely hiding it at the beginning.
- The user draws a line.
- A rectangle with the width of the line and +/- 10px height will be positioned below the line, in the alpha mask, revealing this part of the image.

How could I insert a white rectangle in the alpha mask?

Thank you!

fjenett

Re: Drawing in alpha channel

2 years ago

Simply draw into a PGraphics and use that with mask() on your image.

http://processing.org/reference/createGraphics_.html

http://processing.org/reference/PImage_mask_.html

F

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