Knockout Layers

[ESPR]

In one of his recent tutorials, Graphical showed how to use text as a mask, by using the Erase Blendmode and inverting it with a Curves Adjustment set to Alpha.

Photoshop has a similar feature called knockout, and i was wondering if the Affinity workaround could be implemented more directly. For example by adding an Inverted Erase Mode.

 

 

[Zero1]

Instead of introducing a new blend mode (Inverted Erase or Keep), i would suggest to introduce a "Custom" Blend mode. (I think i have mentioned this earlier in the forums) When setting to custom, one would be able to specify the formula similar to Apply Image / Procedural Texture. Idea would be to specify per channel the formula (and maybe even save local presets similar to procedural textures). For the formulas, procedural functions are not very easy with IF THEN ELSE, so i would suggest implement a scripting language  (eg. lua) or at least implement a condition, true formula and a false formula as most blend modes do have a condition.

This way, you can easily create presets like the requested KEEP blend mode or any other blend mode that is missing. By having 1 "custom" blend mode, it will also keep the list of blend modes compact and definitely open up new possibilities. This needs to be completely non-destructive of course so you can easily adjust and play with the formula. In a sense it will be an improved and live version of the apply image filter with more possibilities and without having to select an image/layer (as the current layer will be treated as source1, and the under-laying layer results  as source2)

 

PS.
Personally i would even go a step further and make it possible to use pixel values from the whole image, eg. source(0,0) = current source value, source(-1,-1) = pixel 1 position to the left and 1 position to the top. Also having some helper functions would definitely help, like canvaswidth, etc. Again this is a bit over the top, i guess, but having a scripting engine can be very interesting for creatives. I am pretty sure the Affinity community would come with a lot of cool effects (and filters).

[Old Bruce]

Just make a Curves preset called Inverted Alpha and use that whenever you want to achieve this.