The perspective filter in Affinity Photo can be found in the distort menu beneath the filters menu in Affinity Photo. The effect is a wonderful powerful perspective distortion tool that can distort any image in many ways in single plane or duo plane mode.
You can use the Affinity Photo perspective filter with images as well as type and also resources such as patterns and brush strokes
1) Go to the image
2) filter and distort and perspective filter
3) Grid appears as well as panel. Select planes and mode
4) Move grid as required
OK, there is a lot more to the Affinity Photo perspective filter such as the source mode and autoclip as well as two types of planes (single and dual plane) and you can also use the perspective filter to create subtle shifts of an image as well as truly extreme distortions, really depends on what you want to do such as add an object / layer in the same perspective as the background.
5) click apply
You can find many tutorials on the site such as how to use
and many others
You can also use the perspective effect as a live filter layer by going to the layer menu and using that above existing layers or applied to a single layer (if layer selected) as well as using blending modes with the effect to see the underlying image and effect combined as well as preserving the alpha. I think the layer approach works best for many projects but the destructive filter approach requires less thought to the underlying layers etc
The perspective tool is also available via the toolbar with the same functionality as the filter. As soon as you select that tool in the toolbar, you will see the panel which can then be used to manipulate the grid (it is easier if you use the show grid option)
You can use the perspective live filter layer as well as the normal filters with layers. You can add subtle shifts of perspective to a layer / element in an image such as distorting a house etc to match another house in the image background. You can use it also for interesting and more extreme collages of images and layers in Affinity Photo.
1) open image
2) file menu and place
3) apply the filter menu and distort menu perspective filter to the new placed layer (single or dual plane).
This can be done with a couple of layers as well as many layers.
In the image on the left, only two layers are present but you could easily have 10 layers and the perspective filter applied to each and every layer and distorting them all to create a truly abstract design.
The great thing about the layers is that they can be used with blending modes as well to create even more interesting color effects as well as adding masks and layer effects into the mix.
With the single plane, you can move the four corners which by default fill the entire image or layer. With dual plane, you can move the four corners as well as the central line (two points) but sadly there is no rotation ability for the line though the four corners can be twisted over themselves to create some truly extreme distortion of images.
All kinds of extreme distortion can be created as well as subtle changes in both plane types. Personally, I like to work on a layer as you can see the original image behind the distortion in the left image (it is a dual plane image with the left half hardly distorted and the right half stretched to the near limits)
You can also use the single as well as the dual (but I think the single works best for basic transforms) just to add a subtle scaling of a layer as well as add some elements of perspective such as on the right and it can be combined with layer effects as well. To have the image slightly shift into the distance, as a plane on the ground.
1) select image
2) duplicate layer
3) use filter menu and distort and perspective and single plane
4) shift the corners down into the bottom half of the image and slightly distort
5) use the effect menu and add an outer shadow (such as on the right image
Probably the oddest, the destination mode gives a more visual feedback as the grid moves as you move the points. With the source option, you can't see anything but the results can be even more dramatic (though perhaps not so predictable). As with all filters in Affinity Photo, you can re-apply the perspective filter either using different settings or just the same settings via the filter menu and repeat. The repeat with the source as well as destination mode can result in even more extreme image effects with the distortion fragmenting the original image.
Opposite, the image and the effect has been repeated a number of times to fragment the artwork and the repeat works best with the source mode. If you apply the repeat with the destination mode you just end up with the perspective adding the same perspective shift but without any fragmentation
In the image on the right, the mode has been set to destination and with two layers you can only still see the image twice, that does not happen with the mode set to source
You don't have to use the entire layer, you can use the perspective filter with a selection.
1) Open image
2) go to the elliptical marquee tool in toolbar
3) go to the filter menu and distort and perspective filter
You can now distort just the selection part. Weirdly, you can create interesting echo or fragmented effects with the destination mode such as on the left (the source mode still does the same fragmentation with the selection as with the full layer). Anyway, you can use the selection approach with the Affinity Photo perspective filter to create some subtle changes to a particular area of an image but also for some really unusual distortions of an image. Of course, you can also use different selections and not just circular ones
The image on the right used multiple selections and multiple applications of the destination mode / dual plane perspective filter.