Posts Tagged ‘C++11’

July 2018 Development Update

Sunday, August 26th, 2018 by fireclaw

Despite the vacation period, the developers have not remained idle in July. Here is an update on some of the new developments.

Collision shapes

While the internal collision system provides many useful tests between various collision solids, the CollisionTube solid (representing a capsule shape) in particular was only really useful as an “into” collision shape. Many of you have requested for more tests to be added so that it can also be used as a “from” shape, since many see it as a good fit for use with character bodies. Earlier, we had already added tube-into-plane and tube-into-sphere tests. We have now also extended this to include tube-into-tube tests and tube-into-box tests. We have also added a line-into-box test to complete the suite of CollisionBox tests.

For those who are using Bullet physics instead of the internal collision system, we have also extended the ability to convert collision solids from the Panda3D representation to the Bullet representation to include CollisionTube and CollisionPlane as well. These solids can now be easily converted to a BulletCapsuleShape and BulletPlaneShape, respectively. This way you can add these shapes directly to your .egg models and load them into your application without needing custom code to convert them to Bullet shapes.

Depth buffer precision

As most Panda3D programmers will know, two important variables to define when configuring a camera in any game are the “near” and “far” distances. These determine the range of the depth buffer; objects at the near distance have a value in the depth buffer of 0.0, whereas objects at the far plane have a value of 1.0. As such, they also determine the drawing range: objects that fall outside this range cannot be rendered. This is fundamental to how perspective rendering works in graphics APIs.

As it happens, because of the way the projection matrix is defined, it is actually possible to set the “far” distance to infinity. Panda3D added support for this a while ago already. Because of the reciprocal relationship between the distance to the camera and the generated depth value, the near distance is far more critical to the depth precision than the far distance. If it is too low, then objects in the distance will start to flicker as the differences in depth values between different objects becomes 0; the video card can no longer tell the difference between their respective distances and gets confused about which surface to render in front of the other. This is usually known as “Z-fighting”.

This is a real problem in games that require a very large drawing distance, while still needing to render objects close to the camera. There are a few ways to deal with this.

One way people usually try to resolve this is by increasing the precision of the depth buffer. Instead of the default 24 bits of depth precision, we can request a floating-point depth buffer, which has 32 bits of depth precision. However, since 32-bit floating-point numbers still have a 24-bit mantissa, this does not actually improve the precision by that much. Furthermore, due to the exponential nature of floating-point numbers, most precision is actually concentrated near 0.0, whereas we actually need precision in the distance.

As it turns out, there is a really easy way to solve this: just invert the depth range! By setting the near distance to infinity, and the far distance to our desired near distance, we get an inverted depth range whereby a value of 1.0 is close to the camera and 0.0 is infinitely far away. This turns out to radically improve the precision of the depth buffer, as further explained by this NVIDIA article, since the exponential precision curve of the floating-point numbers now complements the inverse precision curve of the depth buffer. We also need to swap the depth comparison function so that objects that are behind other objects won’t appear in front of them instead.

There is one snag, though. While the technique above works quite well in DirectX and Vulkan, where the depth is defined to range from 0.0 to 1.0, OpenGL actually uses a depth range of -1.0 to 1.0. Since floating-point numbers are most precise near 0.0, this actually puts all our precision uselessly in the middle of the depth range:

This is not very helpful, since we want to improve depth precision in the distance. Fortunately, the OpenGL authors have remedied this in OpenGL 4.5 (and with the GL_ARB_clip_control extension for earlier versions), where it is possible to configure OpenGL to use a depth range of 0.0 to 1.0. This is accomplished by setting the gl-depth-zero-to-one configuration variable to `true`. There are plans to make this the default Panda3D convention in order to improve the precision of projection matrix calculation inside Panda3D as well.

All the functionality needed to accomplish this is now available in the development builds. If you wish to play with this technique, check out this forum thread to see what you need to do.

Double precision vertices in shaders

For those who need the greatest level of numerical precision in their simulations, it has been possible to compile Panda3D with double-precision support. This makes Panda3D perform all transformation calculations with 64-bit precision instead of the default 32-bit precision at a slight performance cost. However, by default, all the vertex information of the models are still uploaded as 32-bit single-precision numbers, since only recent video cards natively support operations on 64-bit precision numbers. By setting the vertices-float64 variable, the vertex information is uploaded to the GPU as double-precision.

This worked well for the fixed-function pipeline, but was not supported when using shaders, or when using an OpenGL 3.2+ core-only profile. This has now been remedied; it is possible to use double-precision vertex inputs in your shaders, and Panda3D will happily support this in the default shaders when vertices-float64 is set.

Interrogate additions

The system we use to provide Python bindings for Panda3D’s C++ codebase now has limited support for exposing C++11 enum classes to Python 2 as well by emulating support for Python 3 enums. This enables Panda3D developers (and any other users of Interrogate) to use C++11 enum classes in order to better wrap enumerations in the Panda3D API.

Multi-threading

We have continued to improve the thread safety of the engine in order to make it easier to use the multi-threaded rendering pipeline. Mutex lock have been added to the X11 window code, which enables certain window calls to be safely made from the App thread. Furthermore, a bug was fixed that caused a crash when taking a screenshot from a thread other than the draw thread.

May 2018 Development Update

Sunday, June 24th, 2018 by rdb

With the work on the new input system and the new deployment system coming to a close, it is high time we shift gears and focus our efforts on bundling all this into a shiny new release. So with an eye toward a final release of Panda3D 1.10, most of the work in May has centered around improving the engine’s stability and cleaning up the codebase.

As such, many bugs and regressions have been fixed that are too numerous to name. I’m particularly proud to declare the multithreaded render pipeline significantly more stable than it was in 1.9. We have also begun to make better use of compiler warnings and code-checking tools. This has led us find bugs in the code that we did not even know existed!

We announced two months ago that we were switching the minimum version of the Microsoft Visual C++ compiler from 2010 to 2015. No objections to this have come in, so this move has been fully implemented in the past month. This has cleared the way for us to make use of C++11 to the fullest extent, allowing us to write more robust code and spend less of our time writing compiler-specific code or maintaining our own threading library, which ultimately results in a better engine for you.

Thinking ahead

Behind the scenes, many design discussions have been taking place regarding our plans for the Panda3D release that will follow 1.10. In particular, I’d like to highlight a proposed new abstraction for describing multi-pass rendering that has begun to take shape.

Multi-pass rendering is a technique to render a scene in multiple ways before compositing it back together into a single rendered image. The current way to do this in Panda3D hinges on the idea of a “graphics buffer” being similar to a regular on-screen window, except of course that it does not appear on screen. At the time this feature was added, this matched the abstractions of the underlying graphics APIs quite well. However, it is overly cumbersome to set up for some of the most common use cases, such as adding a simple post-processing effect to the final rendered image. More recent additions like FilterManager and the RenderPipeline’s RenderTarget system have made this much easier, but these are high-level abstractions that simply wrap around the same underlying low-level C++ API, which still does not have an ideal level of control over the rendering pipeline.

That last point is particularly relevant in our efforts to provide the most optimal level of support for Oculus Rift and for the Vulkan rendering API. For reasons that go beyond the scope of this post, implementing these in the most optimal fashion will require Panda3D to have more complete knowledge of how all the graphics buffers in the application fit together to produce the final render result, which the current API makes difficult.

To remedy this, the proposed approach is to let the application simply describe all the rendering passes up-front in a high-level manner. You would graph out how the scene is rendered by connecting the inputs and outputs of all the filters and shaders that should affect it, similar to Blender’s compositing nodes. You would no longer need to worry about setting up all the low-level buffers, attachments, cameras and display regions. This would all be handled under the hood, enabling Panda3D to optimize the setup to make better use of hardware resources. We could even create a file format to allow storing such a “render blueprint” in a file, so something like loading and enabling a deferred rendering pipeline would be possible in only a few lines of code!

This is still in the early design stages, so we will talk about these things in more detail as we continue to iron out the design. If you have ideas of your own to contribute, please feel free to share them with us!

Helping out

In the meantime, we will continue to work towards a final release of 1.10. And this is the time when you can shine! If you wish to help, you are encouraged to check out a development build of Panda3D from the download page (or installed via our custom pip index) and try it with your projects. If you encounter an issue, please go to the issue tracker on GitHub and let us know!

March 2018 Development Update

Friday, April 20th, 2018 by fireclaw

Winter is over and it’s time for a spring-cleaning. Many issues have been fixed this month and we’ve also completely refreshed the forum system. Also, changes have been made towards cleaning up the codebase and removing obsolete code. Keep an eye open for the awesome things our developers have in store for later this year!

Forum

The forums got a complete overhaul and has been moved over to Discourse, a 100% free and open source discussion board with plenty of neat features and a modern look. It has become quite a popular system of late, so it may appear familiar to some. The new software is considerably better at preventing spam and the increased mobile usability, code highlighting support and better notifications are welcome features as well. However, due to the conversion to Markdown, some formatting in old forum posts may not have been converted correctly.
If you have any trouble or concerns using the new forum, let us know! We’ll do our best to make the transition as smooth as possible.

Adjacency Geometry

Silhoutte rendering using a geometry shader. Model by Christophe Seux.

Silhoutte rendering using a geometry shader (click to enlarge). Model by Christophe Seux.

Support has been added to the OpenGL renderer for adjacency information. This is primarily useful for geometry shaders that need to access information about vertices connected to the primitive that is being processed, which is useful when implementing effects such as silhouette rendering (as seen in the screenshot to the right). Panda3D can automatically generate adjacency information for existing meshes, but can also take precomputed adjacency information.

Logging in deploy-ng

A new addition to deploy-ng which could help with debugging deployed apps—especially on Windows—is the possibility to provide a path to a log file to which a packaged app will automatically write all of its output. As GUI applications on Windows can’t write to the console, this new way of logging can be used to easily reroute the output to a log file without having to write an extra logging mechanism in your application.
To enable this feature for your application, you simply have to set the log_filename variable in your setup.py script. For an example, take a look at the setup script in the asteroids example in the deploy-ng branch. By default the log file will be rewritten every time, but with a simple switch of the log_append variable, you can preserve the previous content.

Dropping support for MSVC 2010

Since we are continuing to take greater advantage of C++11 features in the Panda3D codebase, we can no longer support the Microsoft Visual C++ 2010 compiler. The 2015 version has been made the new default for building Panda3D from source on Windows systems, and we intend to cease supporting 2010 very soon. If this is causing issues for you or your team, please make your voice heard as soon as possible on the corresponding GitHub issue!

Dropping Mac OS X 10.6 “Snow Leopard” support

Furthermore, we also intend to stop supporting Mac OS X 10.6 “Snow Leopard” due to the limits it imposes on how much of the C++11 standard can be used in the Panda3D codebase. However, if your application is still targeting this version of macOS, please give your opinion on the corresponding GitHub issue.

Video4Linux

Panda3D now supports the grayscale pixel format on Linux which is used for example by some infrared (IR) cameras. Additionally, the reading of video frames from the camera is now done asynchronously, meaning that the framerate of the application is no longer locked to the framerate of the camera in Augmented Reality applications. The previous behaviour can be restored by enabling the v4l-blocking configuration variable.

Better Python 3 Support

Support for Python 3 has been enhanced by replacing usage of the C++ string type with vector_uchar where it is used to refer to binary data. Since all strings are seen as UTF-8 now, this avoids exceptions which were raised due to confusion about whether buffers contained UTF-8 strings or binary data. Convenience functions have been added for efficiently dealing with the new way of representing binary buffers.

Media decoding and playing

CFSworks, who regularly contributes to the project, has done some work on various parts of the audio system, among many other changes. Firstly, he implemented workarounds for some rare OpenAL implementation bugs which are particularly prevalent on the Apple implementation. He also helped to clean up use of deprecated APIs in the FFMpeg integration and implemented features available to newer versions of this library. We are very grateful to him for his continued contributions.