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pcb-rnd - the [square] patch

Most of my PCBs end up in toner transfer. There are a lot of tricks around prototyping at home. One of the problems I often face is small rings peeling off during rework (and rework tend to happen on the first prototypes). The solution for this is increasing ring size - which is not suitable if traces are passing between pins. Another solution is to increase the area of the pin:

square pin: while it makes the pin slightly larger still letting traces pass between pins, it's too symmetrical and can not use up extra room
DJ's teardrop plugin: this increases the area only toward the trace, whereas very often there's more room on the opposite side
manually add an extra poly around the pin; with multiple pins it's hard to get the polys separate
manually add a short extra track on the pin, width matching the size of the pin; this is very close, but increases workload when components are moved, layers are changed

[demo showing DIP with different pin shapes]

The patch takes an octagon pin and stretches points in various directions. There are 4 bits (for left, right, up and down) to indicate in which directions the stretch applies. Pressing 'q' on a pin cycles thru round pin, square pin, 16 stretched octagons and the original octagon.

The code is also patched to handle clearances, shorts and connections (find.c).

Thermals are not fully working for funny shaped pins, but it has low priority: they still work fine for rounded and square pins and if there is a poly around the pin, I wouldn't use shaped pins anyway.

save/load and compatibility

This patch introduces a new pin flag called shape(n), where n is an integer selecting the shape of the pin when the square flag is also set:

Pin[40000 60000 6000 3000 6600 2800 "8" "8" "square,shape(3)"]

Mainline PCB will load the design ignoring the custom shape and will use a square pin. As long a traces end in the center point of the pin, this should not break connections.

Mainline PCB doesn't save shape() - once the design is loaded and saved with mainline PCB pin shape info is lost.

plans

In the original code there are separate code paths for round, octagonal and square pins. The separation repeats for at least:

drawing the pin shape
calculating the clearance
checking whether things overlap or connect (pin vs pin, pin vs line, etc.)
autorouter

In most cases a set of hardwired constants are written in the C code. A notable exception was the octagon pin draw function, that had x and y offsets in a const table for 8 points and a loop to create the poly (or line segments in thin draw).

The [square] feature is a good base for cleaning up the code a bit and for moving toward a generic pin shape patch:

hardwired octagon calculations should be replaced to use the same x;y const offset table
the table should be replaced by a struct that describes length (number of points) - alternatively use POLYAREA
square pin should be renamed to polygon pin
octagon flag shall be removed - it should be a configuration of the x;y const table
square flag shall be removed - it should be a configuration
the only flag remaining should be shape(); if a pin is not shaped, it's round
the pin shape struct should have a field for compatibility - to mark the entry corresponding to the original square and octagon pins so PCB-rnd format can be converted to and from the mainline PCB format.
there should be a set of pin shapes in a default configuration table, including square and octagonal; these should be static
the PCB file format should be extended with an option to expand the pin shape table with custom shapes
UI: shapes could be imported (converted) from polys around vias
UI: since there may be a lot of pin shapes, a GUI selector alternative shall be offered while also keeping the cycle-thru 'q' key