sfsim

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• Announcements·6 Sept 2026Official

  Shockwaves

  I am excited to share early results of shockwave rendering with the community!I would like to add visualization of a glowing shockwave during atmospheric reentry in the sfsim spaceflight simulator. I explored possible approaches by discussing the problem with Google Gemini. Popular approaches seem to use meshes with animated semi-transparent noise textures. However this still leaves the problem of determining the shape of the mesh.Also the shape of the single-stage-to-orbit spacecraft is complex and the shockwave will look different depending on the orientation of the spacecraft. In the end, Google Gemini pointed out the Jump Flooding Algorithm (JFA), published in 2006. This algorithm essentially enables a real-time distance transform on the GPU. In this case, it can instead be adapted to fit a shockwave to each wind-facing surface patch and determine, for each pixel, which shockwave candidate lies farthest upstream in the wind direction.Here is a depth image as seen from the direction the wind is coming from. JFA then expands this image into a depth image of the shock front. Billig’s formula is used (with a fixed nose curvature radius for this prototype) to create a shockwave emitter at each surface pixel. The following image visualizes the seed pixel coordinates for the image. JFA has to track seed pixel coordinates in order to properly propagate the dominant/nearest shockwave. The remaining step is to use this depth image for volumetric rendering of the shockwave. The next image shows a volumetric box used for rendering the shockwave. By limiting the fog to pixels behind the shockwave, one obtains the following image. One can instead apply exponential fall-off to create a more realistic image of a glowing shock front. Future work includes taking into account the surface slope and curvature to get more realistic shockwaves.Let me know any feedback and comments in the sfsim playtest discussion forum or one of the social channels.
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• Announcements·27 Aug 2026Official

  Deferred Rendering

  I have released version 0.30-1 of sfsim.This release introduces a major overhaul of the rendering code as well as a runway for the spacecraft. The rendering system is implemented using the Clojure programming language as well as GLSL. LWJGL3 is used to access the graphics card’s OpenGL bindings.The new rendering code uses deferred shading, which first computes and stores per-pixel geometry data in a geometry buffer (G-buffer), then calculates each pixel’s final lighting in a separate shader pass. Deferred shading makes it easy to render decals, which are essentially textures projected onto scene geometry. It also enables efficient real-time rendering of many localized light sources.Deferred rendering splits rendering into stages so geometry is processed first, lighting later.Step by step from the images:Geometry PassProjecting GeometryThe scene is made of triangles. A vertex shader is used to project the triangles which are passed to the rasterizer. For the planet mesh, the geometry is further refined through tessellation and geometry shaders. The geometry pass draws all visible geometry and stores per-pixel surface data into multiple buffers (textures) as shown below instead of computing final lighting immediately.Although the runway could be rendered as a decal in a separate pass, it was chosen to render it within the same shader as the planet. This will make it easier to later adopt runtime virtual texturing, for example to render airport ground surfaces with markings.Diffuse bufferThe diffuse buffer stores the base RGB color of the material at each pixel. There is also an emissive buffer for light-emitting surfaces which is not shown here.Material property bufferThe metallic buffer stores a scalar indicating how reflective the material at each pixel is. The buffer with specular strength (inverse roughness) is not shown here.Normal bufferThe normal buffer stores the surface normal vector at each pixel in the camera coordinate system. Normals are useful lateron in...
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• Patch Notes·7 Aug 2026Official

  Metallic and roughness factor

  I have released version 0.29-1 of sfsim.The Open Asset Import Library (assimp) which is shipped with the LWJGL3 library has been updated some time ago. I am now able to access the metallic value and the roughness value from the glTF exported by Blender. The metallic and roughness value are now used in the model shader programs so that the spacecraft has a more metallic surface.In the meantime I am still working on implementing deferred shading to facilitate rendering of a runway and localized light sources.Let me know any feedback and comments in the sfsim playtest discussion forum.Don’t forget to wishlist sfsim!
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• Announcements·16 Jul 2026Official

  Deferred shading

  Currently I am working on deferred shading. This requires me to separate rendering into two passes:Geometry pass: render data to a point buffer, normal buffer, and a color buffer, etc.Lighting pass: use the geometry buffers to compute lighting including shadows and volumetric clouds.The change is quite a bit of work, because I have to split up the graphics code and the shaders for rendering the space craft, the planet, and the atmosphere.However this will facilitate rendering of runway textures which are at the same height as the rest of the scene but have a higher texture resolution. Simply adding textured polygons to render a runway does not work, because extra geometry placed at the same elevation as the ground causes z-fighting. Z-fighting is a rendering artifact where two surfaces are so close together that the depth buffer can’t reliably tell which one is in front.Another nice feature of deferred shading is that it allows for multiple localized lights to be rendered at once. You can render the backfaces of a small cube around the light source and use the geometry buffers to light the scene additively, factoring in both the incident angle and the distance from the light source.I.e., deferred shading enables detailed nighttime runway rendering with dense, spatially localized illumination, while keeping performance manageable compared to forward rendering with many dynamic lights.Don’t forget to wishlist sfsim!Also you can catch me on the sfsim Discord.
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• Patch Notes·30 Jun 2026Official

  Github CI

  Hi,Here is release version 0.28-1 of sfsim.This release has a minor fix for time lapse limits. Also I have increased the coverage of the schemas used for checking correctness of the software.The bigger change which hopefully is not noticeable is that I am trialing Github CI builds. Github kindly provides free CI for public repositories. I was already using Github CI for running unit tests.Using an automated build process on a controlled environment has many advantages:less error prone than performing multiple manual build stepsconfiguration changes on developer machines do not affect software releasesbuilds for both Linux and Windows can be triggered from any computerthe complete build process including dependencies is capturedbuild logs are onlineit is easier for others to create modified buildsLet me know in the sfsim playtest discussion forum if there are any problems.Don’t forget to wishlist sfsim!Enjoy!
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