Using OpenGL and Assimp in a Qt Widget application to render 3D models / practice writing GLSL shaders

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README.md

Qtk

Qtk is a Qt OpenGL graphics library created primarily for my own learning purposes. The library wraps some QOpenGL functionality in convenience classes that allow rendering geometry in 2D and 3D using custom GLSL shader programs.

The long-term goal for this project is to create a tool that I can use to practice shader coding or graphics programming techniques. In doing this I hope to also learn more about the Qt UI framework, and the CMake build system.

Key features that are planned:

Runtime loading of .obj or similar 3D models.
Drag-and-drop interaction for adding objects to the scene.
Runtime reloading of modified GLSL shaders attached to objects within scenes.
Multiple views of a scene at one time.
Camera control modes such as panning, orbiting, or following objects.
Save / load for scene data. The current inheritance model is temporary.
Basic text editor for quickly modifying shaders attached to objects.
Shader / object properties panel to modify related settings.
Reduce size of application resources and git references.

The Qtk desktop application provides a model loader using Assimp within a Qt widget application.

For examples of using the Qtk API, see the example-app project in the root of this repository.

To get textures loading on models look into material files and see some examples in the resources/models/ directory.

Source Builds

Qtk was developed and tested using CLion and Qt Creator. Simply open the root CMakeLists.txt with either of these editors and configurations will be loaded.

This project has been ported to Qt 6.6.0, which is not yet available in Ubuntu apt repositories. To run this project, you will need to install Qt6 Open Source Binaries for your system, version 6.6.0 or later. Be sure to take note of the Qt6 installation directory, as we will need it to correctly set our CMAKE_PREFIX_PATH in the next steps.

If you are building on Windows / Mac, consider setting the -DQTK_ASSIMP_NEW_INTERFACE cmake build option.

If the build is configured with all options enabled, we can subsequently install individual components as needed with cmake.

sudo apt update -y && sudo apt install libassimp-dev cmake build-essential git ccache libgl1-mesa-dev libglvnd-dev zlib1g-dev -y
git clone https://github.com/shaunrd0/qtk
cd qtk
# Configure the build with all components enabled
cmake -B build-all -DQTK_GUI=ON -DQTK_PLUGINS=ON -DQTK_EXAMPLE=ON -DCMAKE_PREFIX_PATH=$HOME/Qt/6.6.0/gcc_64
# Build all targets
cmake --build build-all/

By default, the build will not initialize Assimp as a git submodule and build from source. We can turn this on by setting the -DQTK_SUBMODULES=ON flag when running CMake. Building using this option will fetch and build Assimp for us, but builds will take longer as a result. Using -DQTK_SUBMODULES=ON supports providing assimp on cross-platform builds ( Windows / Mac / Linux) and may be easier to configure.

cmake -B build-all -DQTK_GUI=ON -DQTK_PLUGINS=ON -DQTK_EXAMPLE=ON -DQTK_SUBMODULES=ON -DCMAKE_PREFIX_PATH=$HOME/Qt/6.6.0/gcc_64

Qtk GUI

cmake --build build-all/ --target qtk_gui -- -j $(nproc)
# Install Qtk desktop application (output removed)
# Installation prefix path must be absolute, since Qtk uses Qt deploy tools.
cmake --install build-all/ --component qtk_gui --prefix=$(pwd)/install
./install/bin/qtk_gui

If any errors are encountered loading plugins, we can debug plugin loading by setting the following environment variable -

QT_DEBUG_PLUGINS=1 ./install/bin/qtk_gui

Qtk Library

Qtk provides a simple library for working with QOpenGL. We can install this library on a system path or a custom path and then set CMAKE_PREFIX_PATH to point to this location when building an application using libqtk.

# Install libqtk only
cmake --build build-all/ --target qtk_library -- -j $(nproc)
cmake --install build-all/ --component qtk_library --prefix=/usr/local
-- Install configuration: "Release"
-- Installing: /usr/local/lib/cmake/Qtk/QtkConfig.cmake
-- Installing: /usr/local/lib/cmake/Qtk/QtkConfigVersion.cmake
-- Installing: /usr/local/lib/cmake/Qtk/QtkTargets.cmake
-- Installing: /usr/local/lib/cmake/Qtk/QtkTargets-release.cmake
-- Installing: /usr/local/lib/static/libqtk_library.a
-- Installing: /usr/local/include/qtk/camera3d.h
-- Installing: /usr/local/include/qtk/input.h
-- Installing: /usr/local/include/qtk/meshrenderer.h
-- Installing: /usr/local/include/qtk/model.h
-- Installing: /usr/local/include/qtk/modelmesh.h
-- Installing: /usr/local/include/qtk/object.h
-- Installing: /usr/local/include/qtk/qtkapi.h
-- Installing: /usr/local/include/qtk/qtkiostream.h
-- Installing: /usr/local/include/qtk/qtkiosystem.h
-- Installing: /usr/local/include/qtk/scene.h
-- Installing: /usr/local/include/qtk/shape.h
-- Installing: /usr/local/include/qtk/skybox.h
-- Installing: /usr/local/include/qtk/texture.h
-- Installing: /usr/local/include/qtk/transform3D.h

Qtk Plugin Collection

This project defines a collection of widget plugins for use with Qt Designer. These plugins were used to build the interface for the Qtk desktop application. Qt Designer will list Qtk widgets in the side panel when editing a UI file within the designer. Qtk widgets will also render and behave correctly within the UI preview in designer. The widgets in the Qtk collection were created by implementing the QDesignerCustomWidgetInterface and QDesignerCustomWidgetCollectionInterface interfaces.

To build and install the Qtk plugin collection -

cmake --build build-all/ --target qtk_plugins -- -j $(nproc)
# Install Qtk widget collection to use Qt Designer
# The path here should be initialized during build configuration, so no need for --prefix
cmake --install build-all/ --component qtk_plugins
-- Install configuration: "Release"
-- Up-to-date: /home/shaun/Qt/6.6.0/gcc_64/../../Tools/QtCreator/lib/Qt/lib/libqtk_library.a
-- Up-to-date: /home/shaun/Qt/6.6.0/gcc_64/../../Tools/QtCreator/lib/Qt/lib/libqtk_plugin_library.a
-- Up-to-date: /home/shaun/Qt/6.6.0/gcc_64/../../Tools/QtCreator/lib/Qt/plugins/designer/libqtk_collection.so

To uninstall after a previous installation, we can run the following command from the root of the repository.

xargs rm < build/install_manifest.txt

Qtk Example

There is a simple example of using libqtk in the example-app/ directory. The example can be built standalone using find_package or as a target within any qtk build.

# Build the example from a configured qtk build tree
cmake --build build-all/ --target qtk_example -- -j $(nproc)
cmake --install build-all/ --component qtk_example --prefix=install
./install/bin/qtk_example

See the README in the example-app/ subdirectory for instructions on standalone builds.

Controls

You can fly around the scene if you hold the right mouse button and use WASD. If you see a small triangle floating by a model it represents the light source that is being used for the shader rendering the model. These appear on models using phong, specular, and diffuse lighting techniques.

Object names can be double-clicked in the tree view panel for quick camera navigation. All panels and toolbars are dockable widgets that can be popped out and reorganized as needed. Panels can be stacked to create a docked widget with tabs. The central widget that provides the camera view into the scene cannot be detached from the main window in this way. See the View menu to enable debug console widgets for open scenes or reopen previously closed panels.

Spartan with no normals -

Spartan with normals -

Development

This project uses version 15.0.5 of clang-format. Before merging any branch we should run clang-tidy followed by clang-format.

git clone git@github.com:llvm/llvm-project.git -b llvmorg-15.0.5
cd llvm-project
cmake -B build -DLLVM_ENABLE_PROJECTS=clang -DLLVM_ENABLE_RUNTIMES="libcxx;libcxxabi" -DCMAKE_BUILD_TYPE=Release -G "Unix Makefiles" llvm
cmake --build build -j $(nproc --ignore=2)
sudo cmake --build build -j $(nproc --ignore=2) --target install

If the clang-format version is any earlier than 15.0.0, running clang-format will fail because this project uses configuration options made available since 15.0.0.

clang-format --version
clang-format version 15.0.5 (git@github.com:llvm/llvm-project.git 154e88af7ec97d9b9f389e55d45bf07108a9a097)

CLion has integration for IDE code reformatting actions with clang-format. If you're using CLion, the .clang-format configuration will be picked up by CLion automatically.

clang-tidy can be run with the following commands.

# Move to the root of the repo
cd qtk
# Build
cmake -B build && cmake --build build -- -j $(nproc)
clang-tidy -p build/ --fix --config-file=.clang-tidy src/*.cpp src/*.h app/*.cpp app/*.h

Last we need to run clang-format, this can be done with the command directly. This will reformat all the code in the repository.

clang-format -i --style=file:.clang-format src/app/*.cpp src/app/*.h src/qtk/*.cpp src/qtk/*.h example-app/*.cpp example-app/*.h

clang-format can be run with git integration (or CLion if you prefer). Git will only reformat the lines you modified, which can be useful.

# If we want to format the last N commits
# git clang-format HEAD~N
# 3 commits
git clang-format HEAD~3
changed files:
    app/examplescene.h
    app/mainwindow.h
    src/abstractscene.cpp
    src/skybox.h
    src/texture.cpp
    src/texture.h
    src/transform3D.h

Packaging

Packaging for Qtk is in early development. This section documents how to package Qtk, but only source builds have been verified on Windows / Mac / Linux. For this reason, it is recommended to install Qtk by strictly building from source at this time.

Below are the steps to package a Qtk release.

cd /path/to/qtk && cmake -B build
# Package Qtk
cmake --build build --target package
# Package Qtk including source files
cmake --build build --target package_source

Alternatively, we can use cpack directly -

cd /path/to/qtk && cmake -B build
# Generate all install packages
cpack -C Release
# Generate a specific archive package (ZIP)
cpack -C Release -G ZIP
# Generate a specific archive package (TGZ)
cpack -C Release -G TGZ
# Generate debian package (DEB)
cpack -C Release -G DEB
# Generate NSIS install package (NSIS)
cpack -C Release -G NSIS

Any of the above options can be appended with --trace-expand to debug package generation issues. The contents of all packages will depend on how the build was configured.

To generate packages for Qtk desktop application, we should set -DQTK_GUI=ON. If this option is not set we will only package libqtk.

The NSIS installer will allow component-specific path modification for all of these installation components through a GUI install application.

Resources

Some useful links and resources that I have found while working on this project.

Qt Designer UI file format

QtPlugin Import / Export plugins

KDAB

Model Artists

"Alien Hominid" (https://skfb.ly/onStx) by Nwilly_art is licensed under Creative Commons Attribution (http://creativecommons.org/licenses/by/4.0/).

"Scythe World Of Warcraft" (https://skfb.ly/6UooG) by Warcraft-3D-Models is licensed under Creative Commons Attribution (http://creativecommons.org/licenses/by/4.0/).

"Spartan Armour MKV - Halo Reach" (https://skfb.ly/6QVvM) by McCarthy3D is licensed under Creative Commons Attribution (http://creativecommons.org/licenses/by/4.0/).

"Survival Guitar Backpack (Low Poly)" (https://skfb.ly/6RnCB) by Berk Gedik is licensed under Creative Commons Attribution (http://creativecommons.org/licenses/by/4.0/). Model by Berk Gedik, from: https://sketchfab.com/3d-models/survival-guitar-backpack-low-poly-799f8c4511f84fab8c3f12887f7e6b36 Modified (learnopengl.com) material assignment (Joey de Vries) for easier load in OpenGL model loading chapter, and renamed albedo to diffuse and metallic to specular to match non-PBR lighting setup.

"Terror-bird (NHMW-Geo 2012/0007/0001)" (https://skfb.ly/onAWy) by Natural History Museum Vienna is licensed under Creative Commons Attribution-NonCommercial (http://creativecommons.org/licenses/by-nc/4.0/).

"Golden Lion Sitting OBJ Low Poly FREE" (https://skfb.ly/onZAH) by LordSamueliSolo is licensed under Creative Commons Attribution (http://creativecommons.org/licenses/by/4.0/).