Jump to content
  • Advertisement
Sign in to follow this  

[SlimDX-11] updating a constant buffer each frame

This topic is 2152 days old which is more than the 365 day threshold we allow for new replies. Please post a new topic.

If you intended to correct an error in the post then please contact us.

Recommended Posts

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
int size = Marshal.SizeOf(Matrix.Identity) * 3 + Marshal.SizeOf(Vector4.Zero);
return size;
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.Position = 0;

Game.GraphicsDevice.ImmediateContext.UpdateSubresource(new DataBox(0, 0, data), worldViewCBuffer, 0);
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?

Share this post

Link to post
Share on other sites
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

Share this post

Link to post
Share on other sites
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.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));

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

Share this post

Link to post
Share on other sites
Sign in to follow this  

  • Advertisement

Important Information

By using GameDev.net, you agree to our community Guidelines, Terms of Use, and Privacy Policy.

We are the game development community.

Whether you are an indie, hobbyist, AAA developer, or just trying to learn, GameDev.net is the place for you to learn, share, and connect with the games industry. Learn more About Us or sign up!

Sign me up!