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

johnp
Running the examples in chapter 5 c under pytest 5.4.1 causes an AttributeError: ‘module’ object has no attribute ‘config’. In particula...
New
GilWright
Working through the steps (checking that the Info,plist matches exactly), run the demo game and what appears is grey but does not fill th...
New
jdufour
Hello! On page xix of the preface, it says there is a community forum "… for help if your’re stuck on one of the exercises in this book… ...
New
adamwoolhether
When trying to generate the protobuf .go file, I receive this error: Unknown flag: --go_opt libprotoc 3.12.3 MacOS 11.3.1 Googling ...
New
curtosis
Running mix deps.get in the sensor_hub directory fails with the following error: ** (Mix) No SSH public keys found in ~/.ssh. An ssh aut...
New
Charles
In general, the book isn’t yet updated for Phoenix version 1.6. On page 18 of the book, the authors indicate that an auto generated of ro...
New
hazardco
On page 78 the following code appears: <%= link_to ‘Destroy’, product, class: ‘hover:underline’, method: :delete, data: { confirm...
New
AufHe
I’m a newbie to Rails 7 and have hit an issue with the bin/Dev script mentioned on pages 112-113. Iteration A1 - Seeing the list of prod...
New
jwandekoken
Book: Programming Phoenix LiveView, page 142 (157/378), file lib/pento_web/live/product_live/form_component.ex, in the function below: d...
New
New

Other popular topics Top

AstonJ
I’ve been hearing quite a lot of comments relating to the sound of a keyboard, with one of the most desirable of these called ‘thock’, he...
New
AstonJ
I ended up cancelling my Moonlander order as I think it’s just going to be a bit too bulky for me. I think the Planck and the Preonic (o...
New
gagan7995
API 4 Path: /user/following/ Method: GET Description: Returns the list of all names of people whom the user follows Response [ { ...
New
AstonJ
We’ve talked about his book briefly here but it is quickly becoming obsolete - so he’s decided to create a series of 7 podcasts, the firs...
New
PragmaticBookshelf
Rails 7 completely redefines what it means to produce fantastic user experiences and provides a way to achieve all the benefits of single...
New
AstonJ
If you want a quick and easy way to block any website on your Mac using Little Snitch simply… File > New Rule: And select Deny, O...
New
New
sir.laksmana_wenk
I’m able to do the “artistic” part of game-development; character designing/modeling, music, environment modeling, etc. However, I don’t...
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
RobertRichards
Hair Salon Games for Girls Fun Girls Hair Saloon game is mainly developed for kids. This game allows users to select virtual avatars to ...
New

Sub Categories: