Having trouble making a fade in black border

[kiokoyasu]

I'm still pretty new to Affinity despite have Design, Photo, and Publisher. I'm trying to make a large document (60"x80") that will have a black frame around it that fades into a transparency so that I can then put a collage of photos behind it. I know in Adobe I could achieve this by making a square and an inner glow, but attempting to do the same thing with Affinity, the 100px glow does not create the desired effect on such a large document. Doing a gradient makes the fade either circular or linear and I want the fade to maintain it's square shape. There must be a way to do this that I'm just failing to find, right? Can anyone help me out? I'm currently attempting this in Publisher since I assumed it would be easier to create the collage in. Should I be using a different program?

[firstdefence]

You can type in larger px than 100px the slider just goes up to that but typing a figure in such as 500px should give you a larger glow.

inputting a figure will only allow up to 1024px

[firstdefence]

You could try duplicating the rectangle and placing it as a child layer then applying a large stroke set to inner aligned to the child layer and then hefty gaussian blur up to a max of 1024px, although you should only need about 500px for a good blur.

[thomaso]

4 hours ago, kiokoyasu said:

a black frame around it that fades into a transparency so that I can then put a collage of photos behind it.

Left: How about just a rectangle with a black stroke + a blur effect? Optionally with a separate rectangle as image background.

Right: If the black frame around the images should not be fading with the placed collage you can just place your images on a blurred black filled rectangle, instead of behind a frame.

[NotMyFault]

Just a small note: using blur with huge radius (e.g. 1024) impacts performance. Not for one single layer, but if you start to use it for many layers, your document will slow down drastically. So best practice it to use it with care. 
In many cases you can use 

• color gradients 
• layers rasterized (if target is a raster format)

to avoid this effect.

[GarryP]

An alternative to the suggestions above could be to use a Contour Outline Effect on a Rectangle as in my attached image.
It doesn’t look very nice for this particular use but it’s something worth knowing about.

[Apple Cinema]

I think Affinity have to rework the way to make a coloured border. It is impossible to make the top/buttun and sides same size. It is also impossible to colour the canvas afterwards.If Affinity can not make this easier I will stay with Phoshop. It's very easy in Photoshop.

[thomaso]

On 11/20/2022 at 4:31 PM, Apple Cinema said:

make a coloured border. It is impossible to make the top/buttun and sides same size. It is also impossible to colour the canvas afterwards.

Hm? – Both is possible & easy in Affinity, too. Just do it. For instance by using the Context Toolbar / Stroke Panel / Transform Panel / Shape Tools / Fill Layer …