When I followed the tutorial in the book, I found that just before the turbulence is added I encountered some issues with my scene not rendering correctly.

I expected it to look like this:

What I actually got was this:

After continuing the tutorial to the turbulence section, I noticed that fabs() was used on the accumulated total. I wondered if this would fix my issue with the perlin_interp function (i.e. noise.noise() not noise.turb()), so I used it at the end there.

It did get rid of the black boxes but the result was also still not quite what was intended:

Perhaps this is because I used a scale value of 1, but setting it higher leads to results more similar to using turbulence.

Enjoying the book so far, though I am only very early on so far.

I believe there may be an unneeded semicolon in the following line:

inline float& operator[](int i) { return e[i]; };

I can't find the file named "float.h" in the project. Where can I download that file?

After working on the Cornell box, I noticed some trouble with the lighting, especially when I had a large light, which in the book said would help with the noise. I replaced one of the boxes with a glass sphere and noticed the obvious problem with the light of my image. Even with 1000 secondary rays, it didn't fix it.

I eventually figured out that there needed to be a value cap on the colors, so it wouldn't oversaturate. This might have been covered in the next book "Ray Tracing the Rest of Your Life", but with the final image of this book having a glass sphere and a very bright light, I figured it might be useful to mention it.
Here's my final image with that color cap:

p is never used in main.cc

89: vec3 p = r.point_at_parameter(2.0);
90: col += color(r, world,0);

should the r in 90: be p ?

can you upload the related images? thank you!!!

Although the use of ffmax and ffmin is advertised, for aabb surrounding_box(aabb box0, aabb box1) the functions fmax and fmin from the <math> library are used.

Working my way though book, and this error caught me up at the end of chapter 5.

I tried compiling the code here, and I got this error as well.

I ended up fixing this by using FLT_MAX instead of MAXFLOAT. I'm assuming they are equivalent, but I really don't know.

Any idea what could be causing this? I'm using Slackware Linux 14.1, using GCC 4.8.2.

The code for computing the ray-sphere intersection first appears incorrect, because a factor of two is introduced elsewhere. See commentary for issue #113.

Add code commentary to explain this easily-misunderstood line.

The code from line 42 (inluded) until line 49 (included) in the "sphere.h" is not needed? if it does can you please explain why? ( It does look to me as just a repetition of what has been already calculated.)

        temp = (-b + sqrt(discriminant)) / a;
        if (temp < t_max && temp > t_min) {
            rec.t = temp;
            rec.p = r.point_at_parameter(rec.t);
            rec.normal = (rec.p - center) / radius;
            rec.mat_ptr = mat_ptr;
            return true;
}

Within sphere::hit on Page 16

float discriminant = b*b - a*c;

should be

float discriminant = b*b - 4*a*c;

Similarly when expression is repeated in the two square root expressions a few lines below. Those should probably be sqrt(discriminant).

//cosine = ref_idx * dot(r_in.direction(), rec.normal) / r_in.direction().length();

---->

cosine = dot(r_in.direction(), rec.normal) / r_in.direction().length();
cosine = sqrt(1 - ref_idx*ref_idx*(1-cosine*cosine));

Hi! I ported this to Rust (https://github.com/adihodos/raytracer.git), all went pretty smooth (I even added multithreadead support) until I added lighting support. Raytracing the Cornell box results in this ugliness :
.
Can you give me some hints as to why this is happening ?

Hello Peter.
I have some question about Your "cross product" function.
wiki version of "cross product" is:
a×b=⟨a2b3−a3b2, a3b1 − a1b3, a1b2 − a2b1⟩
and Your is:
a×b=⟨a2b3−a3b2, -(a3b1 − a1b3), a1b2 − a2b1⟩
I'd be very grateful if You explain why your "y" is negative

Working my way though book, and this error caught me up at the end of chapter 5.

I tried compiling the code here, and I got this error as well.

I ended up fixing this by using FLT_MAX instead of MAXFLOAT. I'm assuming they are equivalent, but I really don't know.

Any idea what could be causing this? I'm using Slackware Linux 14.1, using GCC 4.8.2.

https://github.com/petershirley/raytracinginoneweekend/blob/0abfd4c3e0d6fcb932d087832706ac968675a72e/sphere.h#L32

float discriminant = b*b - a*c;

should be

float discriminant = b*b - 4*a*c;

cosine = m_refIdx * -Dot( In.m_direction , Rec.normal ) / In.m_direction.Length( );

multiplying refraction index to cosine got rid of a black pixel artifact I was seeing on my render.

P.S: notice the minus sign next to the Dot, this is for the else part where Dot product is <=0.

In chapter 6 of the book, it's mentioned that the image looks slightly wrong. After investigating further, I found out that there's an extra factor of 2 being multiplied in the x and y equations of the cosine-weighted hemisphere sampling code. I have details and pics in my PR at RayTracing/TheRestOfYourLife#8

Hi,

I was stuck in for a day and saw your nice mini-book. I thought it might be fun to see this working in kotlin, so I wrote it in kotlin....

I tried to keep variables etc the same as you mostly, so it should be very easy to compare.

There are a couple of changes - it uses coroutines (badly) (so uses all cores) and renders the image unto a UI window as its computing it (also badly!), so its a bit more interactive.

There may be some bugs in my conversion...

The code is at: https://github.com/time4tea/raytrace-in-a-weekend-kotlin

Hope that's useful.

Cheers

James

It seems that you are forgotten to pass the r_in.time into the constructor of the scattered ray in some of materials.

Hi,

Thank you for the books, they were very helpful! I signalled an issue on the blog, but you might not visit it often, so I'll put it here, too.

I implemented a ray tracer with help from your books and blog. I think I found an issue with the importance sampling. I'll try to describe it here in words.

The idea is that there is a list of objects that are 'important' (like the light in your book). Now, the same object also exists in the scene. It might happen that both the origin point and the generated target point to be on the same object, which for a rectangle for example means along the surface. But the pdf value for such a vector is zero, which means a division by zero. In my code I just checked for such a case and tried sampling again if that was the case, in a loop until success.

I cloned the repository and build the solution file. Its been 2 hours and the execution window is still open.
after running through chapter 7 anti aliasing, It takes more time to run the code.

Is there anyway to know how much time its taking to render the ppm image.

I've gotten to chapter seven, when my program has stopped at 20% of image generation with exit code 3221225725.
Above number is 0xc00000fd in hex, which is stack overflow error in windows.

Dev C++'s debugger shows me quite an interesting trace:

Here's the code I've written:

vec3 rius(mt19937_64 rng) {
	vec3 p;
	do {
		p = 2.0*vec3(unif(rng), unif(rng), unif(rng)) - vec3(1,1,1);
	} while (p.squaredLength() >= 1.0);
	return p;
}

vec3 color(const ray & r, hitable *world, mt19937_64 rng)
{
	HitRecord rec;
	if (world->hit(r, 0.0, FLT_MAX, rec))
	{
		vec3 target = rec.p	+ rec.normal + rius(rng);
		return 0.5*color(ray(rec.p, target-rec.p), world, rng);
	}
	else
	{
		vec3 unitDirection = unit(r.direction());
		float t = 0.5 * (unitDirection.y() + 1.0);
		return (1.0-t)*vec3(1.0, 1.0, 1.0) + t*vec3(0.2, 0.5, 1.0);
	}	
}

rng is just me passing a random number generator engine not to have scope issues.

From the backtrace provided, it would seem that the ray perhaps has hit the sphere on the inside?
The trace is very long and consists solely of the color() function, which would suggest me that it's due to function recursion.

Any help is appreciated, as I can't find any errors with the code above.

on line 33 in sphere.h
a little misleading perhaps...
if (discriminant > 0) -> if (discriminant >= 0) may be better?

Working my way though book, and this error caught me up at the end of chapter 5.

I tried compiling the code here, and I got this error as well.

I ended up fixing this by using FLT_MAX instead of MAXFLOAT. I'm assuming they are equivalent, but I really don't know.

Any idea what could be causing this? I'm using Slackware Linux 14.1, using GCC 4.8.2.

bool hitable_list::bounding_box(float t0, float t1, aabb& box) const {
    if (list_size < 1) return false;
    aabb temp_box;
    bool first_true = list[0]->bounding_box(t0, t1, temp_box);
    if (!first_true)
        return false;
    else 
        box = temp_box;
    for (int i = 1; i < list_size; i++) {
        if(list[0]->bounding_box(t0, t1, temp_box)) {
            box = surrounding_box(box, temp_box);
        }
        else
            return false;
    }
    return true;
}

at the loop of list
why the index is always zero ??

When I use two light source, the RGB value is very large, almost 987, which means it is not overflow when convert from reals to int. And I have tried some method to solve this, but only one of them work, but it is a website converter, so I do not like that. Could someone give me a suggestion?

Ah...I know...

I can use this to add a color cap:

inline int colCap(int x) {
	return x > 255 ? 255 : x;
}

||=== 构建文件: "无目标" 在 "无项目" 中 (编译器: 未知的) ===|
C:\Users\asus\Downloads\Compressed\raytracingtherestofyourlife-master\raytracingtherestofyourlife-master\pdf.h||In function 'vec3 random_cosine_direction()':|
C:\Users\asus\Downloads\Compressed\raytracingtherestofyourlife-master\raytracingtherestofyourlife-master\pdf.h|7|error: 'drand48' was not declared in this scope|
C:\Users\asus\Downloads\Compressed\raytracingtherestofyourlife-master\raytracingtherestofyourlife-master\pdf.h||In function 'vec3 random_to_sphere(float, float)':|
C:\Users\asus\Downloads\Compressed\raytracingtherestofyourlife-master\raytracingtherestofyourlife-master\pdf.h|17|error: 'drand48' was not declared in this scope|
C:\Users\asus\Downloads\Compressed\raytracingtherestofyourlife-master\raytracingtherestofyourlife-master\pdf.h||In function 'vec3 random_in_unit_sphere()':|
C:\Users\asus\Downloads\Compressed\raytracingtherestofyourlife-master\raytracingtherestofyourlife-master\pdf.h|30|error: 'drand48' was not declared in this scope|
C:\Users\asus\Downloads\Compressed\raytracingtherestofyourlife-master\raytracingtherestofyourlife-master\pdf.h||In member function 'virtual vec3 mixture_pdf::generate() const':|
C:\Users\asus\Downloads\Compressed\raytracingtherestofyourlife-master\raytracingtherestofyourlife-master\pdf.h|81|error: 'drand48' was not declared in this scope|
C:\Users\asus\Downloads\Compressed\raytracingtherestofyourlife-master\raytracingtherestofyourlife-master\hitable_list.h||In member function 'virtual vec3 hitable_list::random(const vec3&) const':|
C:\Users\asus\Downloads\Compressed\raytracingtherestofyourlife-master\raytracingtherestofyourlife-master\hitable_list.h|28|error: 'drand48' was not declared in this scope|
C:\Users\asus\Downloads\Compressed\raytracingtherestofyourlife-master\raytracingtherestofyourlife-master\camera.h||In function 'vec3 random_in_unit_disk()':|
C:\Users\asus\Downloads\Compressed\raytracingtherestofyourlife-master\raytracingtherestofyourlife-master\camera.h|8|error: 'drand48' was not declared in this scope|
C:\Users\asus\Downloads\Compressed\raytracingtherestofyourlife-master\raytracingtherestofyourlife-master\camera.h||In member function 'ray camera::get_ray(float, float)':|
C:\Users\asus\Downloads\Compressed\raytracingtherestofyourlife-master\raytracingtherestofyourlife-master\camera.h|36|error: 'drand48' was not declared in this scope|
C:\Users\asus\Downloads\Compressed\raytracingtherestofyourlife-master\raytracingtherestofyourlife-master\perlin.h||In function 'vec3* perlin_generate()':|
C:\Users\asus\Downloads\Compressed\raytracingtherestofyourlife-master\raytracingtherestofyourlife-master\perlin.h|59|error: 'drand48' was not declared in this scope|
C:\Users\asus\Downloads\Compressed\raytracingtherestofyourlife-master\raytracingtherestofyourlife-master\perlin.h||In function 'void permute(int*, int)':|
C:\Users\asus\Downloads\Compressed\raytracingtherestofyourlife-master\raytracingtherestofyourlife-master\perlin.h|65|error: 'drand48' was not declared in this scope|
C:\Users\asus\Downloads\Compressed\raytracingtherestofyourlife-master\raytracingtherestofyourlife-master\material.h||In member function 'virtual bool dielectric::scatter(const ray&, const hit_record&, scatter_record&) const':|
C:\Users\asus\Downloads\Compressed\raytracingtherestofyourlife-master\raytracingtherestofyourlife-master\material.h|84|error: 'drand48' was not declared in this scope|
C:\Users\asus\Downloads\Compressed\raytracingtherestofyourlife-master\raytracingtherestofyourlife-master\aarect.h||In member function 'virtual vec3 xz_rect::random(const vec3&) const':|
C:\Users\asus\Downloads\Compressed\raytracingtherestofyourlife-master\raytracingtherestofyourlife-master\aarect.h|39|error: 'drand48' was not declared in this scope|
C:\Users\asus\Downloads\Compressed\raytracingtherestofyourlife-master\raytracingtherestofyourlife-master\main.cc||In function 'vec3 color(const ray&, hitable*, hitable*, int)':|
C:\Users\asus\Downloads\Compressed\raytracingtherestofyourlife-master\raytracingtherestofyourlife-master\main.cc|29|error: 'MAXFLOAT' was not declared in this scope|
C:\Users\asus\Downloads\Compressed\raytracingtherestofyourlife-master\raytracingtherestofyourlife-master\main.cc||In function 'int main()':|
C:\Users\asus\Downloads\Compressed\raytracingtherestofyourlife-master\raytracingtherestofyourlife-master\main.cc|99|error: 'drand48' was not declared in this scope|
||=== 构建 失败: 13 error(s), 0 warning(s) (0 分, 0 秒) ===|

This repo could really use a short README that explains how to run the program when compiled. Thanks for writing the book and making this code available.

where can I find the earthmap?

In one of the code snippets in chapter 5 there is this line of code (page 18, Version 1.54):

vec3 p = r.point_at_parameter(2.0);

There is a write to variable p but no read. It is an unused variable. Delete this code line!

The bounding_box virtual function is declared in the bvh_node class as

virtual bool bounding_box(float t0, float t1, aabb& box) const;

but is defined outside the class as

bool bvh_node::bounding_box(float t0, float t1, aabb& b) const { b = box; return true; }

where box is a member variable of the class. I think the member should be declared as m_box and the last parameter of the function as box (as it is in the pure virtual function).

I spotted an issue on page 15.

Maybe the equation should be Color = A * color(direction)?

Working my way though book, and this error caught me up at the end of chapter 5.

I tried compiling the code here, and I got this error as well.

I ended up fixing this by using FLT_MAX instead of MAXFLOAT. I'm assuming they are equivalent, but I really don't know.

Any idea what could be causing this? I'm using Slackware Linux 14.1, using GCC 4.8.2.

At line number 100 of "main.cc" :
vec3 p = r.point_at_parameter(2.0);
I think this is not needed at all, is it?

In chapter 7, we have the sentences:

"Pick a random point s from the unit radius sphere that is tangent to the hitpoint, and send a ray
from the hitpoint p to the random point s. That sphere has center (p+N)."

After puzzling over this for a while (even with the picture) it finally dawned on me that it is the unit sphere itself that is tangent to the hitpoint p, and not the point s. It seems obvious in retrospect, but I think this point could be made clearer. I think my confusion comes from two facts:

1. hitpoint p (and the ray that generates it) is not labeled in the diagram (so it was not obvious to me that the surface underneath the unit sphere is what is actually being hit by the ray)
2. point s would be secant to hitpoint p

To trace my confusion: I originally imagined that the unit sphere was at the center of the sphere being hit and could therefore approximate a sphere of any size; then I imagined the unit sphere's center was at hitpoint p and we were looking for a point on the sphere tangent to it (which made no sense to me); and then finally I partially understood the unit sphere's tangency to p, but still thought point s would be secant to p and that the modifier "tangent" applied to s and not the sphere.

The Lambertian brdf uses random_in_unit_sphere, however this induces a cosine squared brdf rather than a Lambertian one. To correct this, one has to use random_on_unit_sphere (this can be achieved through normalize(random_in_unit_sphere)). For more information see: https://github.com/vchizhov/Derivations/blob/master/Probability%20density%20functions%20of%20the%20projected%20offset%20disk%2C%20circle%2C%20ball%2C%20and%20sphere.pdf
Note that this is a mistake in both the book and the code.

There is a small issue with the materials introduced in chapters 7, 8 and 9 (lambertian, metal, dielectric). Due to floating point error, it may happen that the intersection of a ray with some geometry (in this case a sphere) may be "on the wrong side" (let the ideal intersection be at t0, however due to precision error let one get t1: t1>t0, then r_in.point_at_parameter(t1) would be "on the wrong side"). That means that when we try to scatter a ray, it will start inside of the sphere resulting in self-intersection and a black pixel contribution in the final image (akin to shadow acne). This is valid for both lambertian and metal materials, it is especially obvious for perfect mirror materials (fuzz==0.0) when they are introduced in chapter 8 since we get black pixels where we're not supposed to. To mitigate this issue, one can define epsilon = 0.01 (depending on the scale of your geometry this value may have to be smaller or larger) and when returning the scattered ray, make it have origin not rec.p, but rather rec.p + epsilon*normal. Which leads me to another issue - if an object is intersected "from inside", the wrong normal is used for lambertian scattering and reflection (fortunately the right normal is used for refraction). To fix this, use this normal for lambertian scattering, reflection and refraction: normal = dot(r_in,rec.normal)<0.0f? rec.normal : -rec.normal. For refraction the scattered ray should rather start from rec.p - epsilon*normal (we want to be on the opposite side, to avoid self-intersection).
Another thing that may look like a mistake is: schlick(cosine, ref_idx) since based on the definition it should be schlick(cosine, ni_over_nt). However, in this case it is lucky that schlick(cosine, 1.0/ni_over_nt) == schlick(cosine, ni_over_nt) since ((1-ni_over_nt)/(1+ni_over_nt))^2 == ((1-1/ni_over_nt)/(1+1/ni_over_nt))^2.