magicmarker

Woah- thanks so much for this info! This is a game-changer. 

In both Designer and Photo you can use Blend Ranges to make the white background transparent:
 

Ok thanks! Meanwhile, congrats for Designer, I completely switched to it from AI CC. Maybe something missing but much more intuitive and productive...

HI Kip
 
In all fairness to Affinity the release nots for the the beta made it absolutely clear in advance that there was no backward compatibility and gave an equally clear advice not to use it for production work.
 
That being said here's a possible workaround. 1.5 has an excellent PSD export. Export your 1.5 beta files to PSD and then open these in 1.4.3. I have tried this on a couple of quite complex images and it seems to work fine with everything preserved intact. Inevitably there are probably going to be some incompatibilities with certain features but I haven't discovered them yet. I must however caution that I have only tried this with 8 bit images.
 
Worth a try maybe?

I am a little confused that in the release notes it says that I won't be able to open my Photo 1.5 files in Photo 1.4. I got stuck into using the beta because when I installed Design 1.5 I was under the impression that I would still be able to open my files in Photo 1.4. At this time it seems like I am forced into using the unstable 1.5 photo beta for production work. I guess I am still not 100% sure what to do now.

Preferences > User Interface > Show brush preview

Make a new pixel layer, and in the channels panel, lock each of the R, G and B composite channels by deselecting the little pencil icon to the right of the eyeball icon. Then, with your new pixel layer active, you can make a selection and use the paint bucket to fill it. If you are only painting on the alpha, it always goes to white regardless of what color you have selected (even if black or gray) because you are basically making a 100% alpha of the filled area.
 
You can also paint with black, white or any shade of gray on your pixel layer by locking the R, G or B channels you don't want to paint on. It will add color value only from the active channel.
 
This thread may also be helpful: https://forum.affinity.serif.com/index.php?/topic/17438-using-channels-as-non-destructive-way-to-color-wallcovering-patterns/?hl=channels

Thanks for the help everyone!
I understand that I'm using Photo in a slightly unorthodox way.  
 
I have been using the paintbrush & "protect alpha" mode, but to save time I was looking for an "locked pixels/alpha channel" fill method. Sometimes it's just easier to fill in a large area, rather than manually paint it. 
 
It's actually helpful to hear that there is no such feature at this time, so I can stop hunting around looking for it.
 
I'm curious about the Fill layer method that Pierrick mentioned though, I will explore that. 

If you just wanna fill pixels that are on a transparent layer and you want to "lock" the transparency, there is no direct equivalent yet like you described. A workaround that I was suggested was to use the paintbrush on the layer but to click on Protect Alpha, and then you'd have to manually brush over your layer, not a big deal I guess, but I do too wish it was available in Photo.

Hi All!
 
I too am making the leap from Adobe to Affinity. I use Photo from an illustration perspective, working with scanned-in drawings, removing the white backgrounds, and then going crazy cutting things out, resizing, arranging, coloring, etc. 
It's been great so far, just getting used to where things are in Affinity Photo. 
 
My question here is:
 
I see how one can paint an alpha channel only (equivalent to locking pixels on a layer in PS), but how do you bulk fill an alpha channel (i.e. locked pixels) on a layer?
 
In PS, you can select the layer (with locked pixels), choose a color, and either select "fill"from the drop-down menu, or "option/command-delete". 
Does anyone know the equivalent in Affinity Photo?
 
I hope that makes sense!
 
Thanks in advance!