README.md
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 # [`gltest`][]
 
 A [C++11][]/[OpenGL][] \>=[1.0][] [testing][] library.
 
 [`gltest`]: https://git.rcrnstn.net/rcrnstn/gltest
 [C++11]: https://en.wikipedia.org/wiki/C++11
 [OpenGL]: https://en.wikipedia.org/wiki/OpenGL
 [1.0]: https://en.wikipedia.org/wiki/OpenGL#Version_history
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 ## Usage
 
 ```cpp
 #include <cerrno>
 #include <cstring>
 #include <fstream>
 #include <stdexcept>
 #include <string>
 
 #include <GL/glew.h>
 
 #include <glbackend.hpp>
 #include <gltest.hpp>
 
 
 // Function that throws with a system-supplied message.
 void file_open(std::string const & filename)
 {
     auto file = std::ifstream{"nonexistent"};
     if (!file)
         throw std::runtime_error(std::string{} +
             "Could not open file '" + filename + "':\n" +
             std::strerror(errno) + "." // NOLINT
         );
 }
 
 
 GLTEST(gltest, 640, 480, 2, 0)
 {
     backend.prefix("assets/tests");
 
     GLTEST_EXPECT_VALUE(
         GL_FALSE,
         glIsEnabled(GL_DEPTH_TEST)
     )
     GLTEST_EXPECT_EXCEPTION(false,
         "Expected exception",
         throw std::runtime_error("Expected exception")
     )
     GLTEST_EXPECT_EXCEPTION(true,
         "Could not open file 'nonexistent':\n",
         // "No such file or directory"
         file_open("nonexistent")
     )
 
     constexpr auto size = 0.5;
     glBegin(GL_TRIANGLE_STRIP);
     glVertex3f(-size, -size, 0);
     glVertex3f(-size, +size, 0);
     glVertex3f(+size, -size, 0);
     glVertex3f(+size, +size, 0);
     glEnd();
     backend.tga_compare("GLTest.tga");
 }
 ```
 
 A `main()` entry point is provided which calls each test declared with the
 macro `GLTEST(VERSION_MAJOR, VERSION_MINOR, WIDTH, HEIGHT, NAME)`. A double
 buffered OpenGL debug context compatible with the specified version and with a
 window of the specified width and height is set up prior to each test run and
 teared down afterwards.
 
 If OpenGL \>=4.3 or the extension [`KHR_debug`][] is available,
 non-notification debug messages throw errors unless disabled by calling `bool
 gltest_debug(false)` (which returns the old value). The root directory for
 reading and writing files is set with `void gltest_root(std::string)`. Timing
 can be manipulated with `void gltest_set_time(float)` and `float
 gltest_get_time()`. Swapping buffers is performed with `void
 gltest_swap_buffers()`.
 
 The macro `GLTEST_EXPECT_VALUE(EXPR, VALUE)` runs `EXPR`, compares the result
 to `VALUE` and throws an error if they do not match.
 
 The macro `GLTEST_EXPECT_EXCEPTION(PREFIX, EXPR, WHAT)` catches any
 [`std::exception`][]-derived exception thrown by `EXPR`, compares its
 [`what()`][] to `WHAT` and throws an error if they do not match. If `PREFIX` is
 true it is only required that `WHAT` is a prefix of `what()`, to allow trailing
 external messages of unknown format. An error is also thrown if `EXPR` throws
 no exception at all. `gltest_debug(false)` is automatically called before
 `EXPR` is run, the previous value is restored afterwards.
 
 The macro `GLTEST_EXPECT_FRAME(PATH)` reads `PATH` from disk, compares it to
 the current (back) framebuffer and throws an error if they do not match. If
 `PATH` does not exist, the current framebuffer is instead written to it and a
 warning is printed.
 
 If a `GLTEST_EXPECT_*` fails, the values of `GL_VENDOR`, `GL_RENDERER`,
 `GL_VERSION` and `GL_SHADING_LANGUAGE_VERSION` is printed to standard error. In
 addition, `GLTEST_EXPECT_VALUE` or `GLTEST_EXPECT_EXCEPTION` print something in
 the style of:
 
 ```
 >>> Expression:
 glIsEnabled(GL_DEPTH_TEST)
 >>> Expected value:
 GL_TRUE = 1
 >>> Got:
 0
 ```
 
 [`std::exception`]: https://en.cppreference.com/w/cpp/error/exception
 [`what()`]: https://en.cppreference.com/w/cpp/error/exception/what
 [`KHR_debug`]: https://www.khronos.org/registry/OpenGL/extensions/KHR/KHR_debug.txt
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 ## Build system
 
 This project supports [CMake][] and uses [`cmake-common`][]. There are several
 ways to use it in other CMake-based projects:
 
 -   With [`find_package`][]: ([Package][] and) [install][] it on the system.
 
 -   With [`add_subdirectory`][]: Bundle it.
 
 -   With [`FetchContent`][]: Download it as part of the CMake configure step.
 
 -   With [`cmake-common`][]: Use any of the above methods through a simplified
     interface.
 
 As usual, use [`add_dependencies`][] or [`target_link_libraries`][] (or
 `cmake-common`'s `DEPENDENCIES_*`) to declare the dependency.
 
 [CMake]: https://cmake.org
 [`cmake-common`]: https://git.rcrnstn.net/rcrnstn/cmake-common
 [`FetchContent`]: https://cmake.org/cmake/help/v3.14/module/FetchContent.html
 [`add_subdirectory`]: https://cmake.org/cmake/help/v3.14/command/add_subdirectory.html
 [`find_package`]: https://cmake.org/cmake/help/v3.14/command/find_package.html
 [Package]: #Package
 [Install]: #Install
 [`add_dependencies`]: https://cmake.org/cmake/help/v3.14/command/add_dependencies.html
 [`target_link_libraries`]: https://cmake.org/cmake/help/v3.14/command/target_link_libraries.html
 
 ### Configure and generate
 
 To configure and generate a build tree, use `cmake`:
 
 ```sh
 cmake -B _build
 ```
 
 To set the build type, pass e.g. `-D`[`CMAKE_BUILD_TYPE`][]`=Release`.
 
 [`cmake`]: https://cmake.org/cmake/help/v3.14/manual/cmake.1.html#generate-a-project-buildsystem
 [`CMAKE_BUILD_TYPE`]: https://cmake.org/cmake/help/v3.14/variable/CMAKE_BUILD_TYPE.html
 
 ### Build
 
 To build, use [`cmake --build`][]:
 
 ```sh
 cmake --build _build
 ```
 
 To disable building tests, pass `-D`[`BUILD_TESTING`][]`=OFF`.
 
 [`cmake --build`]: https://cmake.org/cmake/help/v3.14/manual/cmake.1.html#build-a-project
 [`BUILD_TESTING`]: https://cmake.org/cmake/help/v3.14/module/CTest.html
 
 ### Test
 
 To run tests, use [`ctest`][]:
 
 ```sh
 (cd _build && ctest)
 ```
 
 To show output from failing tests, pass `--output-on-failure`. To show output
 from all tests, pass `--verbose`.
 
 [`ctest`]: https://cmake.org/cmake/help/v3.14/manual/ctest.1.html
 
 ### Package
 
 To package, use [`cpack`][]:
 
 ```sh
 (cd _build && cpack)
 ```
 
 [`cpack`]: https://cmake.org/cmake/help/v3.14/manual/cpack.1.html
 
 ### Install
 
 To install onto the current system, use [`cmake --install`][]:
 
 ```sh
 cmake --install _build
 ```
 
 To set the prefix, pass e.g. `-D`[`CMAKE_INSTALL_PREFIX`][]`="$HOME/.local"`.
 
 [`cmake --install`]: https://cmake.org/cmake/help/v3.14/manual/cmake.1.html#install-a-project
 [`CMAKE_INSTALL_PREFIX`]: https://cmake.org/cmake/help/v3.14/variable/CMAKE_INSTALL_PREFIX.html
 
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 ## License
 
 Licensed under the [ISC License][] unless otherwise noted, see the
 [`LICENSE`][] file.
 
 [ISC License]: https://choosealicense.com/licenses/isc
 [`LICENSE`]: LICENSE