## Using Qt3D today

Qt3D is an amazing library for Qt that gives you the ability to render your own 3D stuff together with your existing widget or QML based GUI. The library was started by the Qt developers a few years back, but has not yet been released with the official Qt SDK. It was announced that it would be bundled with Qt5.0, but because of the state of the library at the time, its release was postponed. Even so, the library is still very mature and appears to work very well in my opinion. So I would urge you to test it out.

## Simple install on Ubuntu

To use the library you have a couple of different choices. If you are running Ubuntu, you may just run the following commands:

sudo apt-get install qt3d5-dev qtdeclarative5-qt3d-plugin

And you should be good to go. Look for examples in the Qt3D documentation.

Note that Ubuntu currently doesn’t have QtQuick.Controls available, so you will have to follow the instructions below to combine Qt3D with QtQuick.Controls.

## Install Qt3D into the newest Qt release

Currently Qt5.1.1 is the newest stable release of Qt and is the version I’d recommend that you use with Qt3D.

2. Clone Qt3D from Gitorious:
git clone git://gitorious.org/qt/qt3d.git qt3d
3. Open QtCreator from your new Qt installation.
4. Open the qt3d.pro file from the cloned repository and configure it to use the platforms on which you want to use Qt3D (desktop, Android, etc.).
5. Build for each platform you want to use. Set the build to Release instead of Debug mode while building. You should receive about one hundred warnings if you are building for Android. As always, ignore these.
6. Open the build folder in a terminal and run
make install

This will not install to your system, but to your Qt installation, so that it gets the ability to do awesome 3D stuff.

You should now have Qt3D installed in your Qt installation and be ready to run projects that are using Qt3D.

## Speeding up compilation on Ubuntu with Qt Creator

Are you reading random stuff on the web while waiting for your C++ compilation to finish? Then you have come to the right place. In this post I will tell you about two really nice tweaks you may do to speed up your compilations, namely ccache and the make -j flag, and how you may set these up in Qt Creator.

## ccache

ccache is a clever tool that wraps you compiler (g++ or mpicxx) and understands whether the file you are compiling has been compiled before with exactly the same contents and settings. If it has, it just returns a cached result.

Unlike regular make, ccache is extremely good at detecting the true state of what you are compiling. I have never had any trouble with ccache.

This really speeds up the compilation when you are using make clean, especially if you are switching git branches. In other words, it is a much simpler solution to achieve fast compilation with git branches than to create separate build folders for each branch.

To enable ccache, install it with

sudo apt-get install ccache

QMAKE_CXX = ccache g++

Replace g++ with mpicxx if you are using MPI.

## The make -j flag

I realized when compiling the Qt source that make has a -j flag that enables threaded compilation on all available processors on the machine. This also speeds up compilation significantly, and I made a 3.55x performance gain on a 4 core CPU. To enable this flag, go to the Projects view in Qt Creator and add the following arguments to the make build step:

-j

This should look something like this afterwards:

If you prefer not to use all available processors for compilation, you may add a number after -j to set the number of processors. For instance make -j 3 would compile with 3 processors.