Jump to content

View more

Image of the Day

The night is still, but the invasion brings chaos. #screenshotsaturday #hanako #indiegame #gameart #ue4 #samurai https://t.co/cgILXuokoS
IOTD | Top Screenshots

The latest, straight to your Inbox.

Subscribe to GameDev.net Direct to receive the latest updates and exclusive content.

Sign up now

[SlimDX-11] updating a constant buffer each frame

4: Adsense

Old topic!

Guest, the last post of this topic is over 60 days old and at this point you may not reply in this topic. If you wish to continue this conversation start a new topic.

  • You cannot reply to this topic
2 replies to this topic

#1 cephalo   Members   


Posted 27 November 2012 - 10:00 AM

I've been trying to google some SlimDX samples of updating a typical worldviewproj constant buffer, and I'm getting a lot of differences and performance, marshaling gotcha's from the internets that I don't fully understand.
Let's say I have this buffer:
[source lang="csharp"] struct WorldProjectionViewBuffer { public Matrix World { get; set; } public Matrix Projection { get; set; } public Matrix View { get; set; } public Vector4 VecEye { get; set; } public static int SizeOf { get { int size = Marshal.SizeOf(Matrix.Identity) * 3 + Marshal.SizeOf(Vector4.Zero); return size; } } }[/source]
Which I initialize with:
[source lang="csharp"] var cb = new WorldProjectionViewBuffer(); cb.World = Matrix.Identity; cb.Projection = Matrix.Identity; cb.View = Matrix.Identity; cb.VecEye = Vector4.Zero; worldViewCBuffer = new Buffer(Game.GraphicsDevice, new BufferDescription { Usage = ResourceUsage.Dynamic, SizeInBytes = WorldProjectionViewBuffer.SizeOf, BindFlags = SlimDX.Direct3D11.BindFlags.ConstantBuffer, CpuAccessFlags = CpuAccessFlags.Write }); var data = new DataStream(WorldProjectionViewBuffer.SizeOf, true, true); data.Write(cb); data.Position = 0; Game.GraphicsDevice.ImmediateContext.UpdateSubresource(new DataBox(0, 0, data), worldViewCBuffer, 0);[/source]
Now, what I have read is that UpdateSubresource is slow for every frame use, and that you want to Map/Unmap such a constant buffer each frame. I'm a little confused by that, as I don't have to read these constants, just update them every frame. I read in MJP's book that the buffer in this case should be write access only and dynamic. So when I use 'MapSubresource', isn't that reading? What is the best way to write a method for updating this buffer every frame?

#2 eppo   Members   


Posted 27 November 2012 - 12:16 PM

D3D11_CPU_ACCESS_READ (CpuAccessFlags.Read) implies allowing the cpu to read 'back' from gpu-memory, which in your case you don't need to do.

I'd say for a buffer that's updated every frame:

cpu access: D3D11_CPU_ACCESS_WRITE

...then Map() it with a D3D11_MAP_WRITE_DISCARD flag (unless you wan't to update part of the buffer (which b.t.w. isn't possible with UpdateSubresource()))

Edited by eppo, 27 November 2012 - 12:29 PM.

#3 cephalo   Members   


Posted 27 November 2012 - 01:09 PM

Ok, here is my first stab at this. I can't test it right now because I'm neck deep in converting this dx9 project to dx11, and I won't have anything runnable for a while. The commented out parts are what I used to do with dx9.

[source lang="csharp"] public void SetupLighting(Matrix world, Matrix view, Matrix projection, Vector3 vecEye) { DataBox box = Game.GraphicsDevice.ImmediateContext.MapSubresource(worldViewCBuffer, MapMode.WriteDiscard, SlimDX.Direct3D11.MapFlags.None); WorldProjectionViewBuffer viewBuffer = new WorldProjectionViewBuffer(); viewBuffer.World = world; viewBuffer.View = view; viewBuffer.Projection = projection; viewBuffer.VecEye = new Vector4(vecEye, 1); box.Data.Write<WorldProjectionViewBuffer>(viewBuffer); box.Data.Position = 0; Game.GraphicsDevice.ImmediateContext.UnmapSubresource(worldViewCBuffer, 0); //EffectHandle lightingHandle = effect.GetParameter(null, "World"); //effect.SetValue<Matrix>(lightingHandle, world); //lightingHandle = effect.GetParameter(null, "View"); //effect.SetValue<Matrix>(lightingHandle, view); //lightingHandle = effect.GetParameter(null, "Projection"); //effect.SetValue<Matrix>(lightingHandle, projection); //lightingHandle = effect.GetParameter(null, "vecEye"); //effect.SetValue<Vector4>(lightingHandle, new Vector4(vecEye, 1)); }[/source]

I'm not confident that I'm doing this right. Can I just write into the returned DataBox and have it stick?

Edited by cephalo, 27 November 2012 - 06:06 PM.

Old topic!

Guest, the last post of this topic is over 60 days old and at this point you may not reply in this topic. If you wish to continue this conversation start a new topic.