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A texture footprint with 'width' characteristic size corresponds to texture
sampling rate with 1 sample per screen pixel. In order to satisfy the Nyquist
limit we need a filter of size '2*width' - and that's what we have in the original
code. This computation does not take into account though, that after computing
lod and selecting mip levels, we apply bilinear filtering to sample each mip.
This effectively increases filter size to '4*width' which results in too blurry images.

There could be at least two solutions here: the first one is to use '2*width' filter size
and then use point sampling when working with separate mip levels. Another solution
proposed here is to select the mip levels based on the 'width' filter size and then rely
on bilinear filtering to get correct result.

I didn't check this but the second method could provide better results because the last step
when we apply bilinear filtering takes into account specific use case and in the case of
point sampling the final result is baked into the mip level, so we don't have an opportunity
to select proper position between texels as we do with bilinear filtering.

The proposed solution also matched HW filtering results, for example, in this
project, the RTX raytracing code
computes texture lod using just 'width' and then applies bilinear filter. The result
closely matches rasterization version. Color encoding of lod levels used in that demo
allows to visualize differences in lod selection. By modifying the code to use '2*width' it
can be shown that is produces wrong result.

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pbrt, Version 3

Build Status Build status

This repository holds the source code to the version of pbrt that is described in the third edition of Physically Based Rendering: From Theory to Implementation, by Matt Pharr, Wenzel Jakob, and Greg Humphreys. As before, the code is available under the BSD license.

The pbrt website has general information about both the Physically Based Rendering book as well as many other resources for pbrt. As of October 2018, the full text of the book is now available online, for free.

Example scenes

Over 8GB of example scenes are available for download. (Many are new and weren't available with previous versions of pbrt.) See the pbrt-v3 scenes page on the pbrt website for information about how to download them.

After downloading them, see the file in the scene distribution for more information about the scenes and preview images.

Additional resources

  • There is a pbrt Google Groups mailing list that can be a helpful resource.
  • Please see the User's Guide for more information about how to check out and build the system as well as various additional information about working with pbrt.
  • Should you find a bug in pbrt, please report it in the bug tracker.
  • Please report any errors you find in the Physically Based Rendering book to

Note: we tend to let bug reports and book errata emails pile up for a few months for processing them in batches. Don't think we don't appreciate them. :-)

Building pbrt

To check out pbrt together with all dependencies, be sure to use the --recursive flag when cloning the repository, i.e.

$ git clone --recursive

If you accidentally already cloned pbrt without this flag (or to update an pbrt source tree after a new submodule has been added, run the following command to also fetch the dependencies:

$ git submodule update --init --recursive

pbrt uses cmake for its build system. On Linux and OS X, cmake is available via most package management systems. To get cmake for Windows, or to build it from source, see the cmake downloads page. Once you have cmake, the next step depends on your operating system.

Makefile builds (Linux, other Unixes, and Mac)

Create a new directory for the build, change to that directory, and run cmake [path to pbrt-v3]. A Makefile will be created in the current directory. Next, run make to build pbrt, the obj2pbrt and imgtool utilities, and an executable that runs pbrt's unit tests. Depending on the number of cores in your system, you will probably want to supply make with the -j parameter to specify the number of compilation jobs to run in parallel (e.g. make -j8).

By default, the makefiles that are created that will compile an optimized release build of pbrt. These builds give the highest performance when rendering, but many runtime checks are disabled in these builds and optimized builds are generally difficult to trace in a debugger.

To build a debug version of pbrt, set the CMAKE_BUILD_TYPE flag to Debug when you run cmake to create build files to make a debug build. To do so, provide cmake with the argument -DCMAKE_BUILD_TYPE=Debug and build pbrt using the resulting makefiles. (You may want to keep two build directories, one for release builds and one for debug builds, so that you don't need to switch back and forth.)

Debug versions of the system run much more slowly than release builds. Therefore, in order to avoid surprisingly slow renders when debugging support isn't desired, debug versions of pbrt print a banner message indicating that they were built for debugging at startup time.


To make an Xcode project on OS X, run cmake -G Xcode [path to pbrt-v3]. A PBRT-V3.xcodeproj project file that can be opened in Xcode. Note that the default build settings have an optimization level of "None"; you'll almost certainly want to choose "Faster" or "Fastest".

MSVC on Windows

On Windows, first point the cmake GUI at the directory with pbrt's source code. Create a separate directory to hold the result of the build (potentially just a directory named "build" inside the pbrt-v3 directory) and set that for "Where to build the binaries" in the GUI.

Next, click "Configure". Note that you will want to choose the "Win64" generator for your MSVC installation unless you have a clear reason to need a 32-bit build of pbrt. Once cmake has finished the configuration step, click "Generate"; when that's done, there will be a "PBRT-V3.sln" file in the build directory you specified. Open that up in MSVC and you're ready to go.

Build Configurations

There are two configuration settings that must be set when configuring the build. The first controls whether pbrt uses 32-bit or 64-bit values for floating-point computation, and the second controls whether tristimulus RGB values or sampled spectral values are used for rendering. (Both of these aren't amenable to being chosen at runtime, but must be determined at compile time for efficiency). The cmake configuration variables PBRT_FLOAT_AS_DOUBLE and PBRT_SAMPLED_SPECTRUM configure them, respectively.

If you're using a GUI version of cmake, those settings should be available in the list of configuration variables; set them as desired before choosing 'Generate'.

With command-line cmake, their values can be specified when you cmake via -DPBRT_FLOAT_AS_DOUBLE=1, for example.


Source code for pbrt, the renderer described in the third edition of "Physically Based Rendering: From Theory To Implementation", by Matt Pharr, Wenzel Jakob, and Greg Humphreys.







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