GSoC: proposal for transformation tool

[Sven Langkamp]

On Sat, Apr 3, 2010 at 11:52 PM, Marc <pe.marc at free.fr> wrote:

> Hi,
> here is the first version of my proposal for a new transformation tool
> for krita. I'd like some comments !
>
> Title: Image Tranformation Tool for Krita
>
> Abstract:
>
> Since Krita is to be used also for shading and texturing, there are some
> image transformations that it needs to provide. Indeed, a professional
> even reported that, for texturing, image manipulations were the most
> basic and important tools used.
>
> While Krita already covers most of the essential features concerning
> color correction, layering, and painting, the current image
> transformation tool lacks crucial features such as shearing image,
> changing image perspective, or warping image (plus some pre-written
> transformations using warping).
> What's more, the current tool shows some problems in conception : the
> transformation process is done each time the user rotates or scales the
> selection, which deterioriates the image each time a little bit more.
> The tool should work and perform each transformation on a temporary low
> quality representation of the selection, and perform the complete
> transformation on the initial selection only once.
> Ultimately, the current transformation tool is not functional nor
> ergonomic : a tool like that needs to have shortcuts, key modifiers, and
> some buttons (even if it is just a few) to facilitate its use.
>
> Hence the aim is to develop from scratch a new transformation tool for
> krita, which will be at the same time fast, quite exhaustive, and
> comfortable to use.
>
> Implementation :
>
> -First, I will focus on rewriting from scratch the current
> transformation tool (only the code for the already-existing scale and
> rotation transformation will likely be re-used), so that it keeps the
> original shapes of the selection, and records all the modifications done
> by the user (basically this will be done by updating a QMatrix at each
> step). When the user is finished with the transformation, the tool will
> then apply the complete resulting operation on the original shapes,
> which will replace the current ones.
>
> -Then, I will add the shear transformation (which will be immediate from
> an algorithmic point of view, since it is simply a linear transformation
> that Qt can perform for us using a QMatrix). To shear the image, the
> user will only have to hold a key modifier and click on the side he
> wants to move. I will also add a center for the rotation, which can be
> moved by the user.
>
> -Then comes the "change perspective" transformation, which won't be as
> easy as shearing : since it is not a 2D transformation, it cannot be
> done using a 2x2 matrix like QMatrix. However, such a transformation can
> be done using a 3x3 matrix, and projecting the coordinates on the plan
> of the screen. Perhaps the best way to implement it is to change
> directly the KoShape class to accept 3D transformations. Thus, this may
> take some time : I will have to create a 3x3 Matrix class with basic
> operations such as multiplication, inversion, determinant and
> changePerspective, and then write the methods for 3D transformations in
> KoShape. In Krita the user will be able to rotate the image around an x
> axis and around an y axis by holding a key modifier and moving the mouse
> (movement in the x direction will perform a rotation around the y axis
> and vice versa).
>
> -Finally, I will implement warping. Warping enables the user to
> transform the image by modifying some of its points : a grid is
> displayed temporarily on the selection and the user moves its
> intersection points to deform the image. This will likely take a great
> amount of time in proportion to the other transformations. It is really
> a challenge from an algorithmic point of view : it is not a linear
> transformation, and thus cannot be done simply by multiplying matrices.
> So first i will have to do some research, read some papers to come up
> with an algorithm. Implementing the interface will also be quite
> challenging.
>
> -If i have some time left, I will add some pre-written transformations
> using the warping transformation.
>
> Some details about how the user will use the different transformations
> on this scheme :
> http://dl.free.fr/bUw3Loddg
> And a mockup for the Tool Options widget :
> http://dl.free.fr/qqX3RkbjD
>
> Timeline :
>
> Although my exams finish the 21th of May, I will still have to work on a
> project for school until the 11th of June (but then I will be entirely
> free until september). Hence, I would start working on my transformation
> tool before the official beginning of the Google Summer of Code, in
> parallel of school.
> This would be a preliminary schedule :
> Apr 20 - I start right away with rewriting the current transformation
> tool.
> May 3 - The tool should be rewritten, enabling like before the user to
> rotate and scale the image. I will be taking 10 days to prepare for the
> exams. My exams will then take 10 days. Afterwards I will have 3 weeks
> to work on a project which will close the school year.
> June 11 - implement the shear transformation and the change perspective
> transformation (2 weeks).
> July 2 - work on the details of the interface to have something polished
> for the midterm evaluation.
> July 9 - begin the work on the warping transformation. The
> investigations will likely take about 1 week and the implementation of
> the algorithm and the interface will take easily 2 weeks.
> July 30th - polish the interface, bug corrections, adding pre-written
> transformations using warping (until the pencils down date).
>
> About me :
>
> I am a first-year french student in a school of engineering (Ensimag :
> National Superior School of Computer Science and Applied Mathematics). I
> have been using essentially open source programs for approximately 5
> years now, and, since January, i have made several small contributions
> for Krita (for example i fixed/added the local selections). Thus, I am
> already familiar with krita's code.
> I have grown an interest in image manipulation and transformation since
> last year, while I was working on image resizing techniques and basic
> edge detection methods for a school project last year. This project
> resulted in a small program written in Qt, which means I am comfortable
> using Qt and C++, and I am not afraid to read scientific algorithmic
> papers which may be needed to complete my project.
>
>
Have a look at QTransfrom that is a 3x3 matrix allowing perspective
transformations. I think changing KoShape is beyond the scope for this
project and it shouldn't be needed for it. Did you take a look a the
specification for the new Gimp transform tool? That can provide some ways to
avoid forcing the user to always use shortcuts.

I the timeline I noticed a small gap where is says "(2 weeks)", but it's
actually three weeks till July 2nd.

Otherwise it looks good.
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