[Cuis-dev] Best way to draw arcs

[Juan Vuletich]

Hi Jon,

Long time, no see!

(Jon was a very active member of the Squeak community many years ago).

Welcome to Cuis!

On 3/3/2023 9:36 PM, Jon Hylands via Cuis-dev wrote:
>
> Hi everyone,
>
> New to the list, new to Cuis (just downloaded it today).
>
> I'm designing some gauges for an ultralight plane that will run on a 
> Raspberry Pi 4 with a 10" LCD panel. Right now, this is what I have:
>
> Cuis-Gauges.png
>
> I love the anti-aliasing, vector-based properly scalable graphics!
>

This looks really nice!

> The part that I'm not happy with is the green, yellow and red 
> indicator bands on the airspeed gauge. They look nice, but I'm drawing 
> them by drawing a sequence of filled polygons.
>
> The code looks like this:
>
> drawShadeFrom: startSpeed to: endSpeed color: color on: aCanvas
>   | ratio |
>   ratio := self angleToValueRatio.
>   aCanvas strokeWidth: 1 color: color fillColor: color do: [
>     startSpeed to: endSpeed - 2 do:[:each |
>       | startAngle endAngle |
>       startAngle := (90 - (each * ratio)) degreesToRadians.
>       endAngle := (90 - ((each + 2) * ratio) degreesToRadians.
>       aCanvas
>         moveTo: (Point rho: 85 theta: startAngle);
>         lineTo: (Point rho: 95 theta: startAngle);
>         lineTo: (Point rho: 95 theta: endAngle);
>         lineTo: (Point rho: 85 theta: endAngle);
>         lineTo: (Point rho: 85 theta: startAngle)]].
>
> I tried using the #arcTo: method, but I just couldn't get it to work 
> at all (not to mention the line ends of the arc are round, which 
> doesn't work here anyways).
>
> Is there a more reasonable way to do this?
>
> Thanks,
> Jon
>

The #arcTo: method was done following the way to specify arcs in SVG. 
Yes, it is a bad api. Pretty hard to use. I guess I'm late to answer 
about this, as others (thanks folks!) have already answered.

WRT the ends being round, yes, Cuis Vector Graphics only support a round 
pen nib. The solution is to draw the border of the arc with small, or 
zero pen width, and use fill.

Cheers,

-- 
Juan Vuletich
cuis.st
github.com/jvuletich
researchgate.net/profile/Juan-Vuletich
independent.academia.edu/JuanVuletich
patents.justia.com/inventor/juan-manuel-vuletich
linkedin.com/in/juan-vuletich-75611b3
twitter.com/JuanVuletich

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