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Re: [etoys-notify] [JIRA] Created: (SQ-1141) Sector does not always display straight lines when heading is not 0.

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dcorking

Re: [etoys-notify] [JIRA] Created: (SQ-1141) Sector does not always display straight lines when heading is not 0.

> To re-create:
> 1) Set a sector to angle=90
> 2) increase angle by 90
>
> When heading is not 0 the straight lines in the sector, are not straight.

I played with sectors for a while and I could not reproduce this. For
me, it was never more than one or two pixels from straight.

Could you provide more detail please?

David
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Steve Thomas

Re: [etoys-notify] [JIRA] Created: (SQ-1141) Sector does not always display straight lines when heading is not 0.

My problem was it was more than 1 pixel from straight. See image below:

So I guess I don't understand why the X value for pts A and B can't be equal (same for the Y value of A and C).

Below is a 180 degree angle that is a pixel off.

WARNING - I am about to make a comment on code I do NOT fully understand (let alone the vagueries of sin/cos or floating point arithmetic is Squeak, but that never stopped me before :D)

Perhaps if we started with 3 vertices instead of two and calculated only the points on the Circle.

Cheers,

Stephen

On Sat, Dec 8, 2012 at 12:22 PM, David Corking <[hidden email]> wrote:

> To re-create:
> 1) Set a sector to angle=90
> 2) increase angle by 90
>
> When heading is not 0 the straight lines in the sector, are not straight.

I played with sectors for a while and I could not reproduce this. For
me, it was never more than one or two pixels from straight.

Could you provide more detail please?

David
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dcorking

Re: [etoys-notify] [JIRA] Created: (SQ-1141) Sector does not always display straight lines when heading is not 0.

Steve Thomas wrote:
> My problem was it was more than 1 pixel from straight.
....
>
> Perhaps if we started with 3 vertices instead of two and calculated only the points on the > Circle.

You are right: there is more than one way to calculate the vertices.
However, open an inspector on a Sector and look at the vertices. It
turns out that only a very small error accumulates from the step by
step method Etoys uses. (For me it was only the last 2 or 3 decimal
places.) That error is several decimal places too small to be visible
on the screen.

Set your sector's border width to zero. When I tried this, the sector
looked pixel perfect.

So as far as I can see, this isn't a bug in Sector, but there could be
an opportunity for a small improvement in the way Etoys draw borders.

Just my thoughts. David
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Steve Thomas

Re: [etoys-notify] [JIRA] Created: (SQ-1141) Sector does not always display straight lines when heading is not 0.

David,

Thanks for your thoughts and your activity (here and in tracker).

Good to see you back and active!!!

Stephen

On Mon, Dec 10, 2012 at 12:32 PM, David Corking <[hidden email]> wrote:

Steve Thomas wrote:
> My problem was it was more than 1 pixel from straight.

....

>
> Perhaps if we started with 3 vertices instead of two and calculated only the points on the > Circle.

You are right: there is more than one way to calculate the vertices.
However, open an inspector on a Sector and look at the vertices. It
turns out that only a very small error accumulates from the step by
step method Etoys uses. (For me it was only the last 2 or 3 decimal
places.) That error is several decimal places too small to be visible
on the screen.

Set your sector's border width to zero. When I tried this, the sector
looked pixel perfect.

So as far as I can see, this isn't a bug in Sector, but there could be
an opportunity for a small improvement in the way Etoys draw borders.

Just my thoughts. David

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etoys-dev mailing list
[hidden email]
http://lists.squeakland.org/mailman/listinfo/etoys-dev