Qt Graphics and Performance – OpenGL

Introduction

Here’s the next instalment of the graphics performance blog series. We’ll begin by looking at some background about how OpenGL and QPainter work. We’ll then dive into how the two are married together in OpenGL 2 Paint Engine and finish off with some advice about how to get the best out of the engine. Enjoy!

Why OpenGL?

Before I dive into the OpenGL paint engine, I want to make sure we all understand the motivation for the OpenGL 2.0 paint engine. I’ve talked about this before in my article about hardware acceleration, but we still frequently get questions like “Why not implement a Direct2D paint engine?”.

Everyone knows OpenGL means fast graphics right? Well, this is actually a bit of a misconception. What makes graphics fast is a bit of hardware dedicated to computer graphics called a GPU (Graphics Processing Unit). OpenGL 2.x is a software library which often (but not always) uses a particular class of GPU to help satisfy drawing operations (Note: OpenGL 1.x used a different class of GPU). A modern programmable GPU (e.g. nVidia GTX 295) can usually be programmed via both OpenGL, Direct3D and OpenCL. The only difference then is that Direct3D is only available on the Windows platform and OpenCL is not universally supported.

So the reason we are investing our time and effort into OpenGL, rather than Direct3D or OpenCL, is that OpenGL 2.0 is sufficient to give us access to all the GPU features we currently want to use. It is also available on more platforms, especially if you limit yourself to the ES sub-set. We are also looking into restricting ourselves further to only use APIs in OpenGL 3.2 Core Profile.

This might change in the future if we see a new class of GPU, like ones designed for 2D vector graphics which can’t be abstracted by OpenGL 2.0 very well (enter OpenVG), or, if we want to start using GPU features which OpenGL (ES) 2.0 doesn’t give us access to. Having said that, OpenGL is very good at exposing new GPU features through extensions.

History

Qt has had an OpenGL paint engine since early Qt 4.0 days. This engine was designed for the fixed-function hardware available at the time. As time went on and manufacturers added newer bits of hardware to their GPUs, the OpenGL paint engine was adapted to use those features through OpenGL extensions. Over the last 4 years, lots of people have hacked on the engine and added support for things like ARB fragment programs and even adapted the engine to work on OpenGL ES 1.1. The engine is pretty stable and has lots of fall-backs (or original code-paths, depending on how you look at them) for old hardware missing GL extensions the engine can utilise. But, fundamentally, it is an OpenGL 1.x engine. Continue reading.

Related Posts

Free Software PDF readers Linux and BSD desktop distributions have several PDF readers in their repository that any user may download and use. PDF, an acronym for Portable Docu...
Gnome and Mozilla Foundations to Join Forces The Gnome Foundation, which is responsible for the Gnome project, and the Mozilla Foundation, a non-profit organization responsible for overseeing the...
Elisa 0.5.15 Released "The Elisa team is happy to announce the release of Elisa Media Center 0.5.15, code-named "Through Her Eyes". The focus during this release cycle has ...
Theora 1.0 Released The Xiph.Org Foundation has announced the release of Theora 1.0. "Theora is a video codec with a small CPU footprint that offers easy portability and ...
Lightworks Goes Open Source? The makers of the powerful video editing suite Lightworks have announced plans to “open source” the project. Lightworks is an award winning editor wit...
Ask YouTube for Ogg support! People are voting for Google to offer HTML5/Ogg video support on YouTube, in Google's own product ideas voting space. This piece of Ogg activism is...

We Recommend These Vendors and Free Offers

Launch an SSD VPS in Europe, USA, Asia & Australia on Vultr's KVM-based Cloud platform starting at $5:00/month (15 GB SSD, 768 MB of RAM).

Deploy an SSD Cloud server in 55 seconds on DigitalOcean. Built for developers and starting at $5:00/month (20 GB SSD, 512 MB of RAM).

Want to become an expert ethical hacker and penetration tester? Request your free video training course of Online Penetration Testing and Ethical Hacking

Whether you're new to Linux or are a Linux guru, you can learn a lot more about the Linux kernel by requesting your free ebook of Linux Kernel In A Nutshell.


Leave a Comment

Your email address will not be published. Required fields are marked *

*