How to load channel as selection and fill with a color?

[henryanthony]

This is something I used a lot in my Photoshop work and am trying to replicate it in Affinity Photo. I think all the tools are available but I can't get my head around how to get this done. Here are the steps in Photoshop that I want to translate to Affinity Photo:

1. Starting with a blank page, create an alpha channel.
2. Edit the alpha channel to be 100% black.
3. Create some squares and fill them with various percentages of black other than 100%.
4. Return to the blank page (layer) and load the alpha channel as a selection. 
5. Fill the selection with a color. This would result in the squares created in Step 3 to be rendered in the fill color at the percentage dictated by the grayscale values in the alpha channel.

Does this make sense? Please let me know if I have not explained this clearly.

I'll throw one more question in:

When I make a circular or rectangular selection with the marquee tool, I cannot fill it with a color. This is one of the most basic things drawing programs do. When I use the rectangle or ellipse tool and others, I can fill it with color. So, what good is the marquee tool?

I am trying to figure all this out through Help but not able to so far. Looking for a bit of a nudge. 

Thanks

[Brian_J]

To fill a selection in Photo, create or select a Pixel Layer, make a pixel selection, then do one of the following:

• Edit > Fill (Shift+F5)
• Edit > Fill with Primary Color or Fill with Secondary Color
• Layer > New Fill Layer

I don't work much with alpha channels, so I'm sorry I can't answer that question.

[henryanthony]

Thanks Brian_J! I will practice your instructions since I'm having trouble just filling selections.

Another thing I have noticed is that, unlike Photoshop, the default "background" cannot be painted on. Is this assumption correct?

Regarding the alpha channels, looks like I'll have to learn it the old fashioned way and just figure it out. But first, there are about a million vids on YouTube I have to watch. 😉

[Old Bruce]

7 minutes ago, henryanthony said:

... I have noticed is that, unlike Photoshop, the default "background" cannot be painted on. Is this assumption correct?

Yes. You need a Pixel layer in order to paint pixels onto/into the document.

[henryanthony]

Thanks Old Bruce! 

I can build off that. Always helps to know if assumptions are correct or not. Now I can move on. Lots more to learn than I expected... but that's expected, right?