What is the relationship between the "brush width" of a textured intensity brush and stroke weight on canvas?

[ForeverAflame]

I want to know how Affinity Designer decides what the stroke weight of strokes for shape tools should be when applying a textured intensity brush as the stroke with the Brushes panel/studio.

In the default set of textured intensity brushes in the Brushes panel/studio, "Classic Pencil HB" from the "Pencils" category (the one that appears at the top of the list for me) has a default brush width of 128. If I select the Vector Brush Tool and then the Classic Pencil HB in the Brushes panel, the "Width:" value in the Context Toolbar says "128 px".

However, when I actually draw a curve with the Vector Brush Tool and select the curve with the Move Tool or the Node Tool, the stroke width for that curve says "64 pt"—exactly half. Why isn't it 128 px, like Classic Pencil HB says in the Brushes panel?

Likewise, when I create a shape using one of the shape tools, like the Rectangle Tool, and then apply Classic Pencil HB as the stroke, it's also 64 pt.

Is this somehow related to the DPI value in the "Document Setup…" dialog box? If so, what is the relationship—how do the mechanics of this work? There appears to be some relationship between pt, px, and DPI that I don't understand.

[lepr]

2 hours ago, ForeverAflame said:

There appears to be some relationship between pt, px, and DPI that I don't understand.

I'm going to write PPI instead of DPI because PPI is the correct abbreviation when talking about pixels per inch (and Serif knows that but have deliberately chosen to not use the correct term).

1 point equals 1/72th of an inch

1 point equals PPI/72 pixels

There is an option labelled "Show lines in points" in the UI section of the app preferences. If disabled, stroke sizes will be displayed in the document measurement unit instead of points. However, the Brushes panel always shows brush size in pixels and the brush editor won't accept size entry with a unit other than pixel. Absence of a unit there will default to pixel but defaults to the document measurement unit elsewhere. Yes, the UI is an inconsistent mess in places.

[carl123]

1 hour ago, ForeverAflame said:

However, when I actually draw a curve with the Vector Brush Tool and select the curve with the Move Tool or the Node Tool, the stroke width for that curve says "64 pt"—exactly half. Why isn't it 128 px, like Classic Pencil HB says in the Brushes panel?

Point (pt) sizes only exactly match Pixel (px) sizes when the document's DPI is 72

Your document's DPI is 144 (twice 72) hence your point size will be displayed at exactly half the corresponding pixel size

1pt = 1px at 72DPI
1pt = 2px at 144DPI  (2x72)
1pt = 3px at 216DPI  (3x72)

etc
etc

[ForeverAflame]

Thank you, @anon2 and @carl123! I wonder why 72 PPI is the default; maybe because it's the usual web display resolution, or something…

I have one additional question. When I'm creating a custom textured intensity brush, what determines the default brush width? I've tried to make a few, and most came out as 64, but not all of them—I think.