Shadoka

Shadoka

The Ray Tracer Challenge: Gradient pattern is not a gradient

Hello @jamis and everyone,

I’ve implemented the gradient pattern as described in the book and it gives me this output:

The code for pattern_at (I’ve renamed it to ColorAt) is the following:

func (gp *GradientPattern) ColorAt(point math.Point) math.Color {
	distance := gp.ColorB.Subtract(gp.ColorA)
	fraction := point.X - gomath.Floor(point.X)

	return gp.ColorA.Add(distance.Mul(fraction))
}

As you can see it is not exactly a gradient, but the output makes sense to me.
Our spheres are centered at 0, 0, 0 in object space and at x = 0 the fraction evaluates to 0, which in turn means that we just return colorA.

But I highly suspect that this function is supposed to return an image of a smooth gradient from A to B.
I’m going mildly insane about this issue and if anyone got any advice I would greatly appreciate that.

Thanks! :slight_smile:

Marked As Solved

jamis

jamis

Author of Mazes for Programmers and 1 other title

The issue here is that your pattern space needs to be translated and scaled so that the [0,1] range fits the object you’re applying it to. If your sphere has radius 1, and is centered at (0,0), then the pattern (by default) will be covering [-1, 1] (from -x to +x), which means the gradient will be doubled (running once from [-1,0] and again from [0,1]). If you scale the pattern space by 2 (so the gradient runs from [0,2]) and then translate it by -x (so it runs from [-1,1]), it should look more like what you’re expecting.

Hopefully that helps! If you’d like me to restate/clarify anything, let me know.

Also Liked

Shadoka

Shadoka

Thank you so much, that indeed fixes it!

I am facepalming really hard right now, because I already tried scaling by 2 and translating by -1, but I never thought of having to combine those two…

Thanks again for your help and for writing that book, having a blast with it!

Where Next?

Popular Pragmatic Bookshelf topics Top

brianokken
Many tasks_proj/tests directories exist in chapters 2, 3, 5 that have tests that use the custom markers smoke and get, which are not decl...
New
Alexandr
Hi everyone! There is an error on the page 71 in the book “Programming machine learning from coding to depp learning” P. Perrotta. You c...
New
lirux
Hi Jamis, I think there’s an issue with a test on chapter 6. I own the ebook, version P1.0 Feb. 2019. This test doesn’t pass for me: ...
New
conradwt
First, the code resources: Page 237: rumbl_umbrella/apps/rumbl/mix.exs Note: That this file is missing. Page 238: rumbl_umbrella/app...
New
HarryDeveloper
Hi @venkats, It has been mentioned in the description of ‘Supervisory Job’ title that 2 things as mentioned below result in the same eff...
New
Chrichton
Dear Sophie. I tried to do the “Authorization” exercise and have two questions: When trying to plug in an email-service, I found the ...
New
leba0495
Hello! Thanks for the great book. I was attempting the Trie (chap 17) exercises and for number 4 the solution provided for the autocorre...
New
hazardco
On page 78 the following code appears: <%= link_to ‘Destroy’, product, class: ‘hover:underline’, method: :delete, data: { confirm...
New
andreheijstek
After running /bin/setup, the first error was: The foreman' command exists in these Ruby versions: That was easy to fix: gem install fore...
New
SlowburnAZ
Getting an error when installing the dependencies at the start of this chapter: could not compile dependency :exla, "mix compile" failed...
New

Other popular topics Top

PragmaticBookshelf
Rust is an exciting new programming language combining the power of C with memory safety, fearless concurrency, and productivity boosters...
New
AstonJ
Thanks to @foxtrottwist’s and @Tomas’s posts in this thread: Poll: Which code editor do you use? I bought Onivim! :nerd_face: https://on...
New
AstonJ
Saw this on TikTok of all places! :lol: Anyone heard of them before? Lite:
New
AstonJ
Biggest jackpot ever apparently! :upside_down_face: I don’t (usually) gamble/play the lottery, but working on a program to predict the...
New
PragmaticBookshelf
Author Spotlight: Karl Stolley @karlstolley Logic! Rhetoric! Prag! Wow, what a combination. In this spotlight, we sit down with Karl ...
New
DevotionGeo
I have always used antique keyboards like Cherry MX 1800 or Cherry MX 8100 and almost always have modified the switches in some way, like...
New
New
PragmaticBookshelf
Develop, deploy, and debug BEAM applications using BEAMOps: a new paradigm that focuses on scalability, fault tolerance, and owning each ...
New
PragmaticBookshelf
Get the comprehensive, insider information you need for Rails 8 with the new edition of this award-winning classic. Sam Ruby @rubys ...
New
AstonJ
This is a very quick guide, you just need to: Download LM Studio: https://lmstudio.ai/ Click on search Type DeepSeek, then select the o...
New

Sub Categories: