[PATCH] D29363: [XRAY] A Color Choosing helper for XRay Graph

[Alexis Shaw via llvm-commits]

Hi Chandler
I was wondering Which color schemes I should keep, I am using OrRd for the
hard-coded scheme tight now, and PiYg for the Hard coded scheme for graph
differences in D29320
I was, on acceptance of those patches going to allow the choice of color
scheme by the user in a new patch.
But if you want a subset of the color-schemes in that patch, which ones
would you like?


On 23 February 2017 at 11:58, Chandler Carruth via Phabricator <
reviews at reviews.llvm.org> wrote:

> chandlerc added inline comments.
>
>
> ================
> Comment at: tools/llvm-xray/xray-color-helper.cc:22-35
> +// Static Polynomials for the ColorHelper.
> +//
> +// In order to calculate these polynomials,
> +//   1. Convert the color scheme samples from sRGB to LAB color space.
> +//   2. Interpolate between the descrete colors in LAB space using a cubic
> +//      spline interpolation.
> +//   3. Sample this interpolation at 100 points and convert to sRGB.
> ----------------
> varno wrote:
> > chandlerc wrote:
> > > varno wrote:
> > > > chandlerc wrote:
> > > > > I really think this is more complexity than is reasonable to add
> to LLVM for this use case.
> > > > >
> > > > > IMO, we don't need perfectly accurate color interpolation here. We
> need roughly accurate, *simple* interpolation so that it is useful even
> where it isn't perfect.
> > > > >
> > > > > I would strongly suggest switching to what I understand is the
> very common scheme of RGB -> HSV, linear interpolate, HSV -> RGB process
> for interpolating colors. That seems likely to be good enough for all
> realistic usages LLVM will have, and much easier to understand and maintain
> going forward.
> > > > Hi Chandler.
> > > >
> > > > Colors are hard. Really hard. Especially when you want perceptual
> uniformity, as we do here. We want our perception of color to present a
> sense of distance quality. This is an attempt to have good perceptual
> uniformity in the least complicated way possible.
> > > >
> > > > I have not heard of anyone interpolating in HSV, can you show an
> example. Everyone who does this sort of thing interpolates either in RGB
> very, very carefully (with many had chosen intermediate pointe) or in LAB
> like I am doing (or using bisection in delta-E).
> > > I understand that colors are hard. I just don't believe that it is
> actually important to have (perfect) perceptual uniformity for these
> particular use cases.
> > >
> > > I think that for tools like this, being close or having a rough
> correspondence is more than enough. If someone wants to get precise, they
> should use the actual data and not colors. The colors are to help *at a
> glance*.
> > >
> > > Interpolating using HSV is the first answer to the first SO question I
> find when I search on Google for "interpolating between two colors":
> > > http://stackoverflow.com/questions/13488957/
> interpolate-from-one-color-to-another
> > >
> > > So, I guess not everyone?
> > >
> > > Still, my comment remains in essence: this is too complicated for the
> value it brings. We should use a simpler solution with lower quality
> because the qualitative difference won't matter here. SO suggests one
> approach that seems reasonably simple. I'm happy for you to suggest other
> approaches, but they need to be similarly simple.
> > Hi Chandler
> >
> > This patch implements the interpolation in HSV as requested.
> Thanks, this is already tremendously simpler.
>
> I'd also suggest starting with a fairly small set of colors / schemes. I
> think 2 or 3 are fine. IT is easy to add more if and when we have a
> compelling use case for more color schemes. Until then, YAGNI -- we
> shouldn't add the code.
>
>
> https://reviews.llvm.org/D29363
>
>
>
>
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