libplacebo is essentially the core rendering algorithms and ideas of mpv turned into a library. This grew out of an interest to accomplish the following goals:
- Clean up mpv's internal RA API and make it reusable for other projects.
- Provide a standard library of useful GPU-accelerated image processing
primitives based on GLSL, so projects like VLC or Firefox can use them
without incurring a heavy dependency on
libmpv. - Rewrite core parts of mpv's GPU-accelerated video renderer on top of
redesigned abstractions. (Basically, I wanted to eliminate code smell like
shader_cache.cand totally redesigngpu/video.c)
libplacebo's main developer is Niklas Haas (@haasn), but the project would not be possible without the development of mpv, which was done primarily by Vincent Lang (@wm4).
For a full list of past contributors to mpv, see the mpv authorship page.
This project exists thanks to all the people who contribute.
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Since the code derives from several LGPLv2.1+-licensed parts of mpv, there's little choice but to license libplacebo the same way. It's worth pointing out that, except for some minor exceptions (e.g. filters.c and colorspace.c), most of the code is either original work or can be attributed to only a small number of developers, so a relicensing to a more permissive license might be possible in principle.
The public API of libplacebo is currently split up into the following
components, the header files (and documentation) for which are available
inside the src/include/libplacebo directory. The
API is available in different "tiers", representing levels of abstraction
inside libplacebo. The APIs in higher tiers depend on those in lower tiers.
Which tier is used by a user depends on how much power/control they want over
the actual rendering. The low-level tiers are more suitable for big projects
that need strong control over the entire rendering pipeline; whereas the
high-level tiers are more suitable for smaller or simpler projects that want
libplacebo to take care of everything.
colorspace.h: A collection of enums and structs for describing color spaces, as well as a collection of helper functions for computing various color space transformation matrices.common.h: A collection of miscellaneous utility types and macros that are shared among multiple subsystems. Usually does not need to be included directly.context.h: The main entry-point into the library. Controls memory allocation, logging. and guards ABI/thread safety.config.h: Macros defining information about the way libplacebo was built, including the version strings and compiled-in features/dependencies. Usually does not need to be included directly. May be useful for feature tests.dither.h: Some helper functions for generating various noise and dithering matrices. Might be useful for somebody else.filters.h: A collection of reusable reconstruction filter kernels, which can be used for scaling. The generated weights arrays are semi-tailored to the needs of libplacebo, but may be useful to somebody else regardless. Also contains the structs needed to define a filter kernel for the purposes of libplacebo's upscaling routines.
The API functions in this tier are either used throughout the program (context, common etc.) or are low-level implementations of filter kernels, color space conversion logic etc.; which are entirely independent of GLSL and even the GPU in general.
gpu.h: Exports the GPU abstraction API used by libplacebo internally.swapchain.h: Exports an API for wrapping platform-specific swapchains and other display APIs. This is the API used to actually queue up rendered frames for presentation (e.g. to a window or display device).vulkan.h: GPU API implementation based on Vulkan.
As part of the public API, libplacebo exports a middle-level abstraction for dealing with GPU objects and state. Basically, this is the API libplacebo uses internally to wrap OpenGL, Vulkan, Direct3D etc. into a single unifying API subset that abstracts away state, messy details, synchronization etc. into a fairly high-level API suitable for libplacebo's image processing tasks.
It's made public both because it constitutes part of the public API of various image processing functions, but also in the hopes that it will be useful for other developers of GPU-accelerated image processing software.
shaders.h: The low-level interface to shader generation. This can be used to generate GLSL stubs suitable for inclusion in other programs, as part of larger shaders. For example, a program might use this interface to generate a specialized tone-mapping function for performing color space conversions, then call that from their own fragment shader code. This abstraction has an optional dependency ongpu.h, but can also be used independently from it.
In addition to this low-level interface, there are several available shader routines which libplacebo exports:
shaders/av1.h: Helper shaders for AV1 decoding, currently only implements a film grain synthesis shader.shaders/colorspace.h: Shader routines for decoding and transforming colors, tone mapping, dithering, and so forth.shaders/sampling.h: Shader routines for various algorithms that sample from images, such as debanding and scaling.
dispatch.h: A higher-level interface to thepl_shadersystem, based ongpu.h. This dispatch mechanism generates+executes complete GLSL shaders, subject to the constraints and limitations of the underlying GPU.
This shader dispatch mechanism is designed to be combined with the shader
processing routines exported by shaders/*.h, but takes care of the low-level
translation of the resulting pl_shader_res objects into legal GLSL. It also
takes care of resource binding, shader input placement, as well as shader
caching and resource pooling; and makes sure all generated shaders have unique
identifiers (so they can be freely merged together).
renderer.h: A high-level renderer which combines the shader primitives and dispatch mechanism into a fully-fledged rendering pipeline that takes raw texture data and transforms it into the desired output image.utils/upload.h: A high-level helper for uploading generic data in some user-described format to a plane texture suitable for use withrenderer.h. These helpers essentially take care of picking/mapping a good image format supported by the GPU. (Note: Eventually, this function will also support on-CPU conversions to a different format where necessary, but for now, it will just fail)
This is the "primary" interface to libplacebo, and the one most users will be interested in. It takes care of internal details such as degrading to simpler algorithms depending on the hardware's capabilities, combining the correct sequence of colorspace transformations and shader passes in order to get the best overall image quality, and so forth.
An
ebuild
is available in the overlay gentoo-gpu. (Currently pending being merged into
upstream gentoo)
libplacebo is built using the meson build system. You can build the project using the following steps:
$ DIR=./build
$ meson $DIR
$ ninja -C$DIRTo rebuild the project on changes, re-run ninja -Cbuild. If you wish to
install the build products to the configured prefix (typically /usr/local/),
you can run ninja -Cbuild install. Note that this is normally ill-advised
except for developers who know what they're doing. Regular users should rely
on distro packages.
In principle, libplacebo has no mandatory dependencies - only optional ones.
However, to get a useful version of libplacebo. you most likely want to build
with support for both vulkan and at least one of shaderc (preferred) or
glslang (fallback/alternative).
libplacebo built without these can still be used (e.g. to generate GLSL shaders such as the ones used in VLC), but the usefulness is severely impacted since most components will be missing, impaired or otherwise not functional.
To get a list of configuration options supported by libplacebo, after running
meson $DIR you can run meson configure $DIR, e.g.:
$ meson $DIR
$ meson configure $DIRIf you want to disable a component, for example Vulkan support, you can
explicitly set it to false, i.e.:
$ meson configure $DIR -Dvulkan=disabled -Dshaderc=disabled
$ ninja -C$DIRTo enable building and executing the tests, you need to build with
tests enabled, i.e.:
$ meson configure $DIR -Dtests=true
$ ninja -C$DIR testA naive benchmark suite is provided as an extra test case, disabled by default
(due to the high execution time required). To enable it, use the bench
option:
$ meson configure $DIR -Dbench=true
$ meson test -C$DIR benchmark --verboseBuilding a trivial project using libplacebo is straightforward:
// build with -lplacebo
#include <libplacebo/context.h>
void main()
{
struct pl_context *ctx;
ctx = pl_context_create(PL_API_VER, &(struct pl_context_params) {
.log_cb = pl_log_color,
.log_level = PL_LOG_INFO,
});
// do something..
pl_context_destroy(&ctx);
}For a full documentation of the API, refer to the above API Overview as well as the public header files. You can find additional examples of how to use the various components in the demo programs as well as in the unit tests.
I will create more and expanded tutorials/examples once libplacebo is a bit more feature-complete.
If you like what I am doing with libplacebo, and would like to help see this project grow beyond its initial scope, feel free to support me via the links at the top of this file.