v4.0.1 (2024-08-31)

Common

• Change -- Include hittable.h from material.h; drop hit_record forward declaration (#1609)
• Change -- Refactor sphere to use ray representation for animate center (#1621)
• Change -- All headers assume implicit rtweekend.h include (#1628)
• Fix -- Big improvement to print version listing font size (#1595) and more compact line
  height for code listings in both print and browser.
• Fix -- Slight improvement to rotate_y::hit() function (#1484)
• Fix -- Fixed possible bogus values from random_unit_vector() due to underflow (#1606)

In One Weekend

• Fix -- Fixed usage of the term "unit cube" for a cube of diameter two (#1555, #1603)
• Fix -- Fixed broken highlighting on some code listings (#1600)

The Next Week

• Fix -- Add missing ellipsis in listing 2.62 (#1612)

The Rest of Your Life

• Fix -- Fix typo of "arbitrary" (#1589)
• Fix -- Fix X-axis label for figure 3.08 (Approximating the nonuniform f()) (#1532)
• Fix -- Corrected scatter angle theta range in section 3.5.3 (The Scattering PDF) (#1331)
• Fix -- Clarify the distinction between average and expected value (#1535)
• New -- Added a bit more explanation of Buffon's needle problem (#1529)

v4.0.0 (2024-07-26)

From our last official v3.2.3 release (three and a half years ago!), this major release includes all
changes in the v4.0.0-alpha.1 and v4.0.0-alpha.2 releases, plus the changes listed immediately
below. Generally, this represents a large overhaul of all three books and their code, and will
require large changes to any code you've based on the prior v3.2.3 version. Going forward, we plan
to avoid such massive, long-running development branches, at the expense of more frequent minor and
major releases.

There's still a fair amount of work remaining on book three, which we'll work on after this release.

Common

• New -- Add explicit std:: namespacing almost everywhere (#1487)
• Change -- Use delegating constructors where helpful (#1489)
• Change -- Standardized our use of begin/end standard C++ iterators (#1551)
• Fix -- CSS reformatting and fixes (#1567)
• Fix -- Add workaround for image and figure captions using latest Markdeep versions (#1583)
• New -- Add DOCTYPE declaration to all Markdeep documents (#1566)

The Next Week

• Delete -- Remove debug output code from constant_medium::hit() function (#1495)
• Change -- Convert perlin class to use static arrays instead of dynamically allocated (#1483)
• Fix -- Workaround Markdeep issue for code listings with tag-like tokens (#1463)

The Rest of Your Life

• Change -- Simplified the onb class, and renamed or deleted functions (#1080)
• Change -- Many small updates following walkthrough of book 3 (#988, #1317)
• Change -- Use plain array for estimate_halfway program (#1523)
• Change -- Refactored the ONB class to remove unused methods and generally simplify (#1088)
• Change -- Use ICD(d) instead of f(d) for inverse cumulative distribution for clarity (#1537)
• Fix -- Add missing signature updates for material::scatter() functions
• Fix -- Avoid hittable_list of lights in book until code is ready (#1318)

v4.0.0-alpha.2 (2024-04-07)

This alpha wraps up most of the major changes we expect to make to book 2 for the impending v4.0.0
release, along with a bunch of updates to the other two books. Since the alpha.1 release last
August, we've been lucky to have onboarded two new contributors: Arman Uguray and Nate Rupsis.
They've been helping out a ton with this release, and Arman is also developing his GPU Ray Tracing
book at the same time!

This release is a bit faster, thanks to some new BVH optimizations. We've eliminated the negative
radius sphere hack to model hollow spheres, instead accomplishing this with refraction indices. This
eliminates a bunch of places in the code where we had to accomodate this, and probably a bunch of
bugs we still haven't found. We now load texture images in linear color space, fixing a long-running
bug where we were gamma-correcting our textures twice -- you'll notice object texture maps look a
bit darker and less washed out. Refraction text has gotten a bit of an overhaul, and a better
example of total internal reflection. Of course, this also includes a load of small fixes, tweaks,
and improvements.

Our current plan is to get the final v4.0.0 release out the door by SIGGRAPH 2024, targeting July
28. With that, here are the latest changes since our alpha.1 release:

Common

• Delete -- Removed rtw_stb_image.h header from book 1 source, as it's unused there.
• Change -- Increase compile warning levels for MSVC, and corrected newly-flagged code.
• Change -- Default to using post-increment everywhere
• Change -- We've removed the few cases where we used C++ default constructors. Instead, we either
  require all parameters, or use operator overloading to use default values.
• Change -- For clarity across audiences with broad programming backgrounds, we now use
  double(x) instead of static_cast<double>(x), and similarly for other types, for
  easier readability for non-C++ programmers.
• Change -- The ray class constructors no longer use C++ default parameter values
• Change -- Remove pixel sampling knowledge from write_color(). This simplifies write_color()
  to take only the desired output color, and made each phase in color computation easier
  to understand.
• Change -- ray::origin() and ray::direction() getters now return const references, avoiding
  unnecessary copies.
• Change -- Cleaned up the use of the hit_record class in material.h
• Change -- All books now point to the project wiki instead of the in1weekend blog for further
  reading links.
• Change -- New BVH optimization splits the bounds according to the longest bounding box
  dimension, yielding a 15-20% speedup (#1007)
• Change -- Reversed the ray-sphere direction and calculations throughout equations and code for
  all books. This ended up simplifying equations and code in several places (#1191)
• Change -- Pass vec3, point3, ray, and color parameters by const reference where
  possible (#1250)
• Change -- Changed BVH construction (removed const qualifer for objects vector) so sorting is
  done in place, and copying of vector is avoided, yielding better BVH build performance
  (#1327, #1388, #1391)
• Change -- Implement hollow spheres using refraction index instead of negative radii.
  Additionally, we now block negative radius spheres. This fixes a bunch of corner
  cases with inverted spheres (#1420)
• Change -- Refactor pixel subsampling to make the sampling functions simpler and better focused
  in scope (#1421)
• Change -- All constructor parameter names now match their member names if assigned directly. C++
  can handle this without ambiguity, and it means we don't have to come up with
  alternate names for everything (#1427)
• Change -- material::scatter() gets a trivial default implementation (#1455)
• Fix -- Fixed section describing total internal reflection. It turns out that spheres with
  refraction index greater than the surrounding atmosphere cannot exhibit total internal
  reflection. Changed example to instead model a bubble of air in water, and updated the
  rendered images to match (#900)
• Fix -- Fix references from random_in_hemisphere() to random_on_hemisphere() (#1198)
• Fix -- The linear_to_gamma() function has been hardened against negative inputs (#1202)
• Fix -- Fixed default camera look-from and look-at values (#1341)
• Fix -- The quad bounding box now considers all four vertices instead of erroneously only
  using two (#1402)
• New -- Added PRINTING.md to give information about how to print these books to PDF or paper.
  We will also be including PDFs of each book with each new GitHub release going
  forward.

In One Weekend

• Change -- Update reference to "Fundamentals of Interactive Computer Graphics" to "Computer
  Graphics: Principles and Practice". This is the name used by newer editions of the
  book.
• Change -- Updated the "Next Steps" section at the end of book 1 (#1209)
• Change -- Update rtweekend.h header introduction and use (#1473)
• Fix -- Fix code listing ordering bug with lambertian texture support (#1258)
• New -- Improved help for the very first build and run.
• New -- Define albedo prior to first use (#1430)

The Next Week

• Change -- Lots of miscellaneous edits and clarifications to book two as we encountered them.
  This also includes various improvements to code listings to provide better context and
  address discrepancies between the listings and the actual source code.
• Change -- perlin::turb() no longer defaults the value for the depth parameter.
• Change -- AABB automatically pads to mininmum size for any dimension; no longer requires
  primitives to call aabb::pad() function.
• Change -- Switch from ray = A + tb to ray = Q + td in AABB text.
• Change -- Update checker scale to 0.32
• Change -- Refactor AABB class. Renamed aabb::axis() to aabb::axis_interval(). Minor
  refactoring of aabb::hit() function. (#927, #1270)
• Change -- Reworked the AABB chapter. Created skippable sections for planar coordinates
  derivation (#1236)
• Fix -- Updated book 2 images to match the latest code.
• Fix -- Images loaded for texture mapping are now converted from their original gamma to
  linear color space for use. Rendered images are still gamma corrected to 2.0 on
  output (#842)
• Fix -- Fix regression in calls to Perlin turb() functions with scaled points (these should
  be unscaled). (#1286)
• New -- Add section on alternative 2D primitives such as triangle, ellipse and annulus (#1204,
  #1205)

The Rest of Your Life

• Fix -- Add missing backslash for LaTeX operatorname (#1311)
• Fix -- Fix LaTeX functions with underscore (#1330)

v4.0.0-alpha.1 (2023-08-11)

It's been quite a while since our last release of v3.2.3 at the end of 2020. For this cycle, we've tackled a load of significant backlog items, including rewrites of much of our underlying code. As always, the primary idea isn't to provide the best or most optimal implemntation, but instead to put out simple, sometimes crude first approximations of the main components of writing a ray tracer.

Highlights include large rewrites and expansions of the book text, a large refactoring of our camera class, folding moving_sphere functionality into sphere, adding a new interval class for use in multiple contexts, creating a new general quad primitive to replace the old *_rect primitives, and the addressing of hundreds of issues and requested features. The line-item changes below should give you an idea of v4 includes.

In order to drive this release to resolution, we're releasing our alpha.1 version to coincide with the start of SIGGRAPH 2023. We've pretty much finished with book one, though there's a fair amount left for books two and three. Our plan is to keep crunching for a final v4.0.0 release by the end of 2023.

Since this is an alpha, we would greatly appreciate any feedback you might have. Let us know by creating issues up on the GitHub project.

Common

• Fix - CSS fix for cases where code listing overflows; change to fit content (#826)
• Fix - Enabled compiler warnings for MSVC, Clang, GNU. Cleaned up warnings as fit (#865)
• Fix - Remove redundant virtual keyword for methods with override (#805)
• Fix - rect hit returning NaNs and infinities (#681)
• Fix - Add \mathit to italic math variables to fix slight kerning issues in equations (#839)
• Fix - Fixed issues in Bib(La)TeX entries.
• Change - Use class instead of struct throughout for simpler C++ (#781)
• Change - Moved all class method definitions inside class definition (#802)
• Change - Class public/private access labels get consistent two-space indents (#782)
• Change - Updated classes to use private access for class-private variables (#869)
• Change - Made our code inline clean. We now use inline in all header function definitions to
  guard against copies in multiple C++ translation units (#803)
• Change - Retired the src/common/ directory. Each book now has complete source in one directory
• Change - Significant rewrite and expansion of the camera class
• Change - aabb class constructor treats two params as extreme points in any orientation (#733)
• Change - hittable:hit() methods use new interval class for ray-t parameter
• Change - interval::clamp() replaces standalone clamp utility function
• Change - aabb class uses intervals for each axis (#796)
• Change - hittable member variable ptr renamed to object
• Change - general rename of mat_ptr to mat (material)
• Change - hittable::bounding_box() signature has changed to always return a value (#859)
• Change - replaced random vector in isotropic with random_unit_vector
• Change - Use std::clog instead of std::cerr to log scanline progress (#935)
• Change - Updated figures throughout for improved clarity when possible
• Change - Generated images are now output gamma-corrected rather than in linear space
  (#980, #1033)
• Change - The camera class now handles images with width or height of one (#682, #1040)
• New - Introduce new interval class used throughout codebase (#777)
• New - rtw_image class for easier image data loading, better texture file search (#807)
• New - 2D quad primitive of arbitrary orientation (#756)
• New - box() utility function returns hittable_list of new quad primitives (#780)
• Delete - box, xy_rect, yz_rect, xz_rect classes. These are replaced with new quad
  primitive (#292, #780, #681)

In One Weekend

• Change - Updated all rendered images in text
• Change - Significant update to the diffuse reflection section (#696, #992)
• Change - Updated and clarified text around ray generation and the camera model
• New - More commentary about the choice between double and float (#752)
• New - Software context around the shadow acne listing

The Next Week

• Fix - Fixed bvh_node constructor definition signature (#872)
• Fix - Fixed scaling for final Perlin noise texture (#896).
• Change - Rearranged the texture-mapping presentation. The three types (solid, spatial, image)
  are now sequenced in that order, and the checker texture presented more explicitly as
  an illustration of a spatial texture.
• Change - Broad rewrite of time management for moving objects, primarily camera and
  sphere, but also impacting the API for hittable::bounding_box() (#799)
• Change - The sphere class now includes animation capability originally in moving_sphere
  (#1125)
• New - Add listing to use new bvh_node class in the random_spheres scene (#715).
• Delete - The moving_sphere class is deprecated, and functionality moved to sphere (#1125)

The Rest of Your Life

• Fix - Added missing functionality for isotropic (#664)
• Fix - Variable direction was used without being defined in listing 11 (#831)
• Fix - Fixed uniform sampling (#934)

v3.2.3 (2020-12-07)

A small patch release.

Common

• Change: Markdeep library URL updated to new location

The Next Week

• Fix: Correct parameter name typo for bvh_node constructor parameter src_objects

v3.2.2 (2020-10-31)

Common

• Fix: Added fmin to book text for cos_theta of refract (#732)
• Fix: Standardized naming for ray-t and time parameters (#746)
• Fix: random_unit_vector() was incorrect (#697)
• Fix: Synchronize text and copies of hittable.h
• Fix: Synchronize copies of hittable_list.h, material.h, sphere.h
• Change: refactor sphere::hit() method to reuse common blocks of code.
• Change: Improved the explanation and calculation of sphere UV coordinates (#533)

In One Weekend

• Fix: Catch cases where lambertian::scatter() yields degenerate scatter rays (#619)
• Fix: Syntax error in listing 58 (Dielectric material class with reflection) (#768)
• Fix: Correct wording for ray traversal text (#766)
• Change: Wrote brief explanation waving away negative t values in initial normal sphere

The Next Week

• Fix: Catch cases where lambertian::scatter() yields degenerate scatter rays (#619)

The Rest of Your Life

• Fix: Missing override keyword for xz_rect::pdf_value() and xz_rect::random() methods
  (#748)
• Fix: Synchronize book and source for cornell_box() function.
• Fix: Introduction of light code was introduced out of sequence (#738, #740)
• Fix: ray_color() was creating a new light for every ray bounce (#759)

v3.2.1 (2020-10-03)

Common

• Change: Refactored dielectric class for clarity
• Fix: Update local Markdeep library (for offline reading) to v1.11. The prior version had
  incorrect content (#712)
• Fix: Image texture destructor should call STBI_FREE instead of delete (#734)

In One Weekend

• Delete: Remove premature cstdlib include; not needed until we use rand() (#687)
• Fix: Replace old anti-alias result image with before-and-after image (#679)
• Fix: Listing 29: Added missing rtweekend.h include (#691)
• Fix: Undefined vup variable in camera definition (#686)
• Fix: Listing 51: Add missing hittable.h, rtweekend.h includes (#693)
• Fix: Listing 59: ["Full glass material"] Diverged from source
• Fix: Fix error in citation section (#721)
• Fix: Listings 33, 39: Add consistent function signature for trilinear_interp (#722)

The Next Week

• Change: bvh_node no longer reorders the source vector of scene objects; uses local copy
  instead (#701)
• Delete: Remove unused u,v,w variables in initial perlin::noise() function (#684)
• Fix: Listing 5: Neglected to add ray time for metal and dielectric materials (#133)
• Fix: Listing 15: In bvh.h, add missing hittable_list.h include (#690)
• Fix: Listing 33, 34, 38: Change implicit casts to explicit ones (#692)
• Fix: Listing 40: Change perlin.h in the caption to texture.h (#698)
• Fix: Listing 70: Add missing bvh.h (#694)
• Fix: Listing 70 and main.cc: Change a fuzz value of a metal sphere to 1.0 which is the maximum
  value (#694)
• Fix: Fix error in citation section (#721)

The Rest of Your Life

• Fix: Fix errors in citation section (#721)
• Fix: Area equation in section 3.3 Constructing a PDF and nearby text (#735)
• Add: Listing 36: Add missing updates to dielectric class for updating specular in scatter record

v3.2.0 (2020-07-18)

We're still chasing that elusive stable project state where we're mostly done with large changes,
yet we keep finding more and more to tweak and improve. Besides the usual batch of corrections and
small improvements, for this change we plodded through the complete code progression for both books
one and two (In One Weekend and The Next Week). This caught a lot of issues (to our dismay),
and allowed us to generate a complete set of new render images for both books, to catch up with all
of the changes we've been making. The end result is that readers should find a significantly better
agreement between the book and their code as they progress, and their renders should also generally
match.

Besides the new rendered images, we also much improved the image parameters, which were frequently
missing from the previous version, leaving readers to guess at their values, or go to the code to
try to figure out how we created some of the images. In general, our working renders are now 400
pixels wide, usually 16:9 aspect ratio. We now use an explicit aspect ratio and deduce the image
height and other camera values, so you can tweak your render size just by changing the image width
(instead of updating a bunch of dependent parameters).

One interesting late change we made was adding explicit C++ override labels to subclass methods.
We did this mostly to aid code readers, but were surprised to find that it actually caught a pretty
significant bug hiding in our code (see entry in common changes below).

You'll also see a new citation section at the end of the books, to encourage uniform citations out
in the world, making it easier for people to refer to and track these books.

As is typical, though we roughly follow semantic versioning, we're
considering this release a minor change instead of a major one. It's a common reflex, because people
generally have a (misguided) aversion to bumping the major version a lot. We consider it minor
because most of the changes are quite local, some classes get new constructors and any variances
should be quite simple and easy to fix up. Still, one might consider this more properly a major
version bump.

For our next larger-than-patch release, we're beginning a large revisit of book 3,
Ray Tracing: The Rest of Your Life. There's a lot of work to do, and this will likely be a
significant change and improvement. We're hoping that changes to books one and two will be small,
but that's never worked out for us before. Ah, dreams.

Common

• Bug: Found a bug in book 3 source isotropic::scatter() method. Commented out, using default
  (as it was previously). (#669)
• Delete: vestigial vec3::write_color() method (now in color.h)
• Change: All images and figures renamed to follow more logical convention, using the following
  pattern: {fig,img}-<book>.<sequence>-<title>.<filetype> (#495)
• Change: main() function gets organized into image, world, camera, and render chunks
• Change: Added header guards to the text of all three books whenever a new header file was
  introduced, consistent with source code (#645)
• New: Added constructors that take color arguments in addition to the constructors
  taking shared_ptr<texture> arguments, simplifying calling code. Applies to checker_texture,
  constant_medium, diffuse_light, lambertian, and isotropic (#516, #644)
• Change: Added override keywords throughout. This keyword marks a subclass method as one that
  is intended to override a superclass method. It makes the code a bit easier to understand, and
  ensures that your function is actually overriding the method you think it is. Which is good,
  because it already caught an existing bug in The Rest of Your Life source. This change
  includes commenting out the book 3 isotropic::scatter() method, which was accidentally ignored
  anyway. (#639, #669)
• New: each book gets a section of recommended citation examples (#500)

In One Weekend

• Change: Updated all rendered images except for 1.13, 1.14 (#179, #547, #548, #549, #550, #551,
  #552, #553, #554, #555, #556, #557, #560, #561, #562, #563, #564, #565, #566)
• Change: Standard working render width changed to 400 pixels
• Change: Image 6 is now a before-and-after pair to illustrate antialiasing
• Change: Listing 48: Refactored material and geometry declarations
• Change: Listing 52: Refactored assignment of etai_over_etat
• Change: Listing 56: Refactored material declarations
• Change: Listing 61: Refactored material and geometry declarations
• Fix: Corrected various missed change highlights in code listings
• Fix: Listing 7: Added missing color.h, vec3.h includes
• Fix: Listing 18: Add missing double t member of struct hit_record (#428)
• Fix: Listing 24: Add missing color.h include
• Fix: Listing 30: Add missing camera.h include
• Fix: Listing 42: Don't need to include ray.h when using rtweekend.h
• Fix: Listing 48: Add missing material.h include
• Fix: Listing 51: refract() function was missing fabs() on sqrt() argument (#559)
• Fix: Listing 61: Include updated cam declaration, show context w/highlighting
• Fix: Listing 62: Highlight rename of camera::get_ray() parameters to s, t (#616)
• Fix: Listing 63: Show reverted scene declarations
• Fix: Listing 68: Show final scene render parameters with highlighting
• Fix: Rewrote refracted ray perpendicular and parallel components for correctness (#526)
• New: Listing 50: Show the updated material definitions

The Next Week

• Delete: Deleted the section covering the old flip_face class, renumbered images as this
  eliminated the rendering with missing Cornell box faces (#270, #482, #661)
• Delete: scenes 7 & 9 from the original (cornell_balls and cornell_final), as these were not
  covered in the book. Made the source and book consistent with each other. There are now a total
  of eight scenes for the second book (#653, #620)
• Change: Listing 10: Separate out world & camera definitions in main (#646)
• Change: Updated most rendered images for book 2: 2.01-2.03, 2.07-2.13, 2.15-2.22.
• Change: Scenes get custom image parameters (#650)
• Fix: Reduced code duplication in dielectric::scatter() function
• Fix: "Intance" typo in Chapter 8.1 to "Instance" (#629)
• Fix: Listing 7: Show reverted viewing parameters from book 1 final scene
• Fix: Typo in listing caption for filename moving-sphere.h

The Rest of Your Life

• Change: use vup for camera, as in other two books
• Fix: world and camera setup in main(), and include full body in book listing (#646)
• New: flip_face moved to book 3, where it's needed for the light source (#661)

v3.1.2 (2020-06-03)

In One Weekend

• Fix: Correct typo: "Intance Translation" -> "Instance Translation"
• Fix: Corrected geometry type when computing distance between two points, final scene (#609)

The Rest of Your Life

• Fix: Missing closing parenthesis in listing 10 (#603)
• Fix: Tiny improvements to the lambertian::scatter() development (#604)
• Fix: Correct geometry type and unit vector method in ray_color(), listing 20 (#606)
• Fix: Listing 26: alternate random_double() switched distribution, generator (#621)
• Fix: Listing 28, 30: light_shape should have default material, not 0 (#607)
• Fix: Listing 30: mixture_pdf needs shared_ptr arguments (#608)

v3.1.1 (2020-05-16)

Common

• Fix: Refactoring the camera code in v3.1.0 missed updating the viewport to match, resulting in
  distorted renders (#536)
• Change: Camera code improvements to make it more robust when any particular value changes. Also,
  the code develops in a smoother series of iterations as the book progresses. (#536)

In One Weekend

• Fix: Camera initialization with explicit up vector (#537)
• Fix: Changed some text around the camera model and the camera defocus blur model (#536)
• Change: The C++ <random> version of random_double() no longer depends on <functional>
  header.
• Change: Refactored random_scene(). More named intermediate values, sync'ed with source.
  (#489)

The Next Week

• Fix: Added clarification about updating lambertian variables from color to solid_color.
• Fix: Corrected for-loop indices (they differed from the version in book 1) in random_scene().
• Fix: Introduce "Texture Coordinates for Spheres" in Chapter 4 to support (u,v) coordinates in
  hit_record (#496)
• Fix: Small correction: we now use std::sort instead of qsort (#490)
• Change: Refactored random_scene(). More named intermediate values, sync'ed with version in
  In One Weekend and with source. Added highlight for update from last version in book 1. (#489)
• Change: The C++ <random> version of random_double() no longer depends on <functional>
  header