Write/Read Masks

[Tylertron1998]

How does one achieve write/read masks using your api?

[antonfirsov]

@Tylertron1998 can you be more specific? This can mean many things for me.

[Tylertron1998]

for example, say I want to write a 100x100 image onto another 100x100 image, but I want only a 25x25 circle in the middle to be 'written', in other frameworks (namely, imagemagik) I would put down a mask on the image to be written to of a 25x25 circle, and then write, and then only any pixel that lies within the circle would be written over by the image that is being written from. The same with reading

[tocsoft]

This isn't directly possible in our current API, however you could adapt the techniques from one of our samples (linked below) where you can make use of the ImageBrush to fill a shape of your choosing with the image/effect you want to apply.

Process is roughly;

1. Create an IPath that represents your desired region.
2. Make sure you have 2 image instances, src(buffer you want draw) and destination(buffer you want to draw to) (clone destination if you are just apply an effect and not drawing a 2nd image).
3. Apply any effects etc to src as required.
4. Crop down src so it fits the IPath.Bounds of your region.
5. Fill your IPath using an ImageBrush taking your now cropped src in its constructor.
6. ...
7. Profit.

Working sample applying a Gaussian Blur to only the inside of a Star
https://github.com/SixLabors/Samples/blob/master/ImageSharp/ApplyEffectInsideShape/Program.cs

[Tylertron1998]

Awesome! Thanks for the answer. Will read/write masks ever be supported? Is this process less efficient then a typical read/write mask implementation?

[antonfirsov]

With an arbitrary IPath yes. A more efficient method would be probably to alter the alpha channel of src according to the shape you want to draw (making the non drawable, "background" pixels transparent), and draw it as a rectangular region on destination.