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This is kind of an odd question, but what would be the best solution for rendering a 3D scene without a render window active? The end goal would be to simply render a 3D scene to an image file.

I have done similar things in the past with DirectX and XNA but both required me to have a render window running in-order for the API to initialize. Is there a way to render directly to a texture so that you could perform the rendering with a DLL file in other desktop applications?

The way I envision it working is you create a self contained DLL which has all the rendering logic, a user is using a standard windows application to customize his parameters, once he has them locked he sends a render request to the DLL and it responds with a PNG file of the rendered scene. Ideally this would be a CPU based render since performance is not a huge issue.

Are there APIs out there which one could use to accomplish this?

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It sounds to me like you are looking for a ray tracer. It has many benefits over rasterization but if you need something fast then it might not be for you.

Ray Tracing is a technique for generating an image by tracing the path of light through pixels in an image plane and simulating the effects of its encounters with virtual objects. The technique is capable of producing a very high degree of visual realism, usually higher than that of typical scanline rendering methods, but at a greater computational cost. This makes ray tracing best suited for applications where the image can be rendered slowly ahead of time, such as in still images and film and television special effects, and more poorly suited for real-time applications like computer games where speed is critical. Ray tracing is capable of simulating a wide variety of optical effects, such as reflection and refraction, scattering, and chromatic aberration.

I am not aware of any major ray tracing specifications or platforms other then openrt. However, it appears to be an outdated project now.

I would recommend visiting the "ray tracing" forums ( if you have more specific questions. Also, they have a tools section where you may find something that suits your needs. For example TinyRT is a good place to start.

Also, here are some articles to get you started:



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That's pretty easy to do with both DirectX and OpenGL: You initialize with an hidden window (for OpenGL and DX9) or no window at all (DX10+). Then you create FBO or RenderTargets of arbitrary size and do all your rendering into those. This also allows you to render images with higher than screen resolution without problems. In all that cases, no window will be visible to the user and no rendering is ever blitted on the screen. You can read back those buffers by simply mapping the underlying surface.

You might consider to write a renderer in CUDA/OpenCL, in that case, you can just create a buffer on the GPU to write to. The reason for using DX/GL/etc. is that you usually can get results on screen faster than writing your own ray-tracer :)

Of course, if you just want to render an image, a CPU only implementation is probably the easiest thing to do. As mentioned, look at Aqsis for a complete renderer which can be linked into your app. It basically boils down to providing some API to pass data from the app to the renderer and retrieve the image. Usually you don't want to send PNGs back though, but rather provide a callback so the calling application can provide progress output as well as store it in any format it wants.

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There are lots of software rendering programs out there. The most common model is just to execute the renderer as another process, rather than call into a DLL. (Though, that exists as well.) Depending on your needs you may find that Aqsis or LuxRender suits your needs. Another renderer to check out is PovRay.

Many such applications exist. Hopefully, those couple of examples will give you enough information to get you started.

Another way to go would be an OpenGL FBO. That's basically rendering to a texture in memory on the GPU. You can then use it for whatever you want, such as reading back to host memory, and writing it out as a PNG.

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