# Thinking of writing a perspective tool for krita

Wolthera griffinvalley at gmail.com
Sat Apr 25 09:36:41 UTC 2015

```Sorry, the ellipse's horizontal component needs to be aligned to the
horizon of that particular plane.

There's a thread here which goes into the complexer details:

Resize your toolbox: there's a bug where it doesn't allow you to click
transform when crop isn't touching the toolbox border.
For the line-tool, it's supossed to be laggy, as it takes your tablet
sensors into account. Tick 'preview' in the tool box to get a quicker
previewing line.

On Sat, Apr 25, 2015 at 10:42 AM, Brendan Scott <
disposableemail at apps.opensourcelaw.biz> wrote:

> [resend with attachment removed and hosted at
> http://www.tiikoni.com/tis/view/?id=bfd5b0a]
>
> On 25/04/15 00:59, Wolthera wrote:
>
>> I see.
>>
>> The reason the vanishing point assistant was set up the way it was is
>> because of the way I understand perspective: All parallel lines share a
>> single vanishing point, and making the horizon is actually a lot easier
>> than you'd think: Just turn on snapping and draw a line from one vanishing
>> point to the other. (Though shift+snapping is on my todo list for the
>> parallel lines :) )
>>
>> As far as I know I wasn't eyeballing the distances: You can check these by
>> drawing diagonals, and maybe I haven't drawn enough diagonals in the video
>> itself. It was my third take or something, but I did take into account the
>> diagonals.
>>
>> But, in regards to that link: let me make your life a whole lot more easy:
>> A perfect circle in perspective is always an ellipse. An ellipse in
>> perspective in turn becomes an egg-shaped ellipsoid. What's more, any
>> perfect circle fits perfectly in a perfect square. What this means is
>> that,
>> if any given perfect circle is an ellipse, we can draw our lines around
>> it,
>> then we have a perfect square! I'm attaching an image with this in Krita.
>> Sounds a lot easier than following that link's guide for a perfect square
>> each and every time, doesn't it?
>>
>
> I'm sorry. I don't follow. If I have a length that I want to transfer from
> one axis to another, I don't see how an ellipse will help.
>
> For example, assume that you _only_ have edge G (and the two vanishing
> points
> and vanishing lines) in the attached image.
>
> How could you use an ellipse to create edge A or E (and therefore
> implicitly C/B/D/F)?
> In particular, there are multiple ellipses which are tangent to both
> vanishing lines.
> Even if I put one of the axes of the ellipse passing through both the the
> centre of G
> and (when extended) through the vanishing point.
>
> See: http://www.tiikoni.com/tis/view/?id=bfd5b0a
> (expires in 28 days)
> There is no basis for distinguishing between the ellipse on the left hand
> side of edge G and that on the right hand side. Is there?
>
> This is my use case:
>
> At the moment I'm trying to draw a person in perspective and I want to do
> the
> perspective properly basically to try to train my eye for the right
> perspective
> proportions.
>
> The person I want to do has "heroic" proportions - which means they're 9
> tall and 2.66 heads across their shoulders. The length of the head is the
> yardstick.
> I am doing them from waist to head, so I need to map out a prism: 4.5 heads
> high, 2.66 heads wide (ie across shoulders)  and 1.4 heads deep (roughly
> front of chest to
> back of backside).
>
> I did this on a piece of paper then scanned it into Krita. I'd like to do
> it
> natively within Krita.
>
>
>  Similarly, you can use the perspective transform to deform any given
>> imagine to a perspective plane(you can even drag around the vanishing
>> points in the perspective transform for precision).(This isn't cheating,
>> Krita isn't a videogame)
>>
>> You can use the distance measure tool to measure pixels. In the future I
>> hope to get a concentric circle assistant working, which you could then
>> use
>> to draw a perfect circle around each vanishing point so you don't have to
>> go and measure things.
>>
>
> Yeah, I think my build didn't work properly. That block of tools (crop,
> move,
> transform, measure) doesn't work for me. My line tool is also laggy.
>
>  I hope this e-mail doesn't sound flippant, but I want to make your life
>> easier, or at the least bearable till I have time to work on the
>> assistants
>> again. :)
>>
>
>
>
>
>
>
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> https://mail.kde.org/mailman/listinfo/kimageshop
>

--
Wolthera
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