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This is what's wrong with the brush in affinity photo


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I've had a hard time adjusting the brush to act in a natural way for drawing. I've compared with mainly photoshop and sketchbook pro and posted numerous reports about this. There are a few issues like jagged lines on low zoom levels and general inconsistent behaviour of hardness and size. Things you only notice when drawing or writing by hand on a tablet or Cintiq.

Now I think I found what causes the latter! I was able to isolate what is going on by setting the shape to a narrow ellipse and the stroke to large spacing. Look what the preview shows. There are 2 things going on here:

1 Inconsistent size toward the beginning/ending of the stroke, causing a sort of 'arrow head' effect

2 The increase of the amount of dots towards the ending is too steep. Meaning the spacing between the dots in the end is near zero and in the middle pretty large. Some decay in spacing is useful since the relative spacing between dots should stay the same. But it seems that AP does not take the dot size into account and at certain settings the decay is much to steep, causing too many dots to overlap. I noticed that in photoshop and sketchbook pro this decay is far less and generally in better balance with the shape size. This presumably results in their smoother line behaviour. One result of this steep decay in AP is that soft lines are much harder in the endings than in the middle and pressure sensitivity feels a bit 'off'.

All in all this explains the strange behaviour I was experiencing. This arrowhead effect is nearly invisible in the preview when the shapes are rounder, but in practice I always notice the inconsistent line behaviour because of this. 

Affinity photo:

91272214_Screenshot2021-03-31at10_57_00.png.adb6ea52db1be2c55df694cde2fe2a41.png

A drawn line to show it's not just the preview:

417331492_Screenshot2021-03-31at10_59_29.png.caee81f3f97e541ac293706412c18212.png

 

photoshop:

1636677911_Screenshot2021-03-31at10_48_44.png.8068d4bd53e9d7fd2b8928c74a39f0f8.png

sketchbook

383952487_Screenshot2021-03-31at11_09_44.png.233c5599a772fd291882a9075834054a.png

 

lastly look at this soft line and how hard it gets near the endings. The steep decrease of dot spacing is what causes this. 

1209126695_Screenshot2021-03-31at11_55_38.png.f148589736aa8c49b6f2497e9fe30a93.png

 

In all examples these are the dynamics settings:

image.png

In my opinion two things need to change:

1 The arrow head behaviour is just off and needs to be fixed.

2 The spacing between the dots needs to be rebalanced in order to have a consistent line behaviour throughout different settings of spacing, dynamics, hardness etc. Generally speaking the dot SPACING needs to be in balance with the dot SIZE and SHAPE. E.g. the thinner part of a pressure sensitive line should be equally soft as the broader part of the line. Also when pressure sensitivity is set to linear, the line thickness change should also be linear. This is currently not the case and my guess is the inconsistent dot spacing causes this. 

I hope this helps refine the brush behaviour for AP!

 

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This could also possibly explain a bit why there is such a huge delay when doing fast brush strokes with Hardware Acceleration on Windows. The amount of dots created at the beginning and end of each stroke is likely making the computing skyrocket. Of some reason this slowdown doesn't happen to the same extent with regular CPU computing, but the inconsistent brush stroke spacing likely doesn't help.

Good detective work, by the way! :)

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