[SOLVED] How to update (parts of the) Dynamic Vertex Buffers?

Graphics
1

Hi guys,

I hope someone has experience with this.

How does vertexBuffer.SetData work?

To be more accurate: How do I update parts of the vertexBuffer only?

vertexBuffer.SetData(vertices) gives me no problem.

But let’s say I want to change the 3 and 4th vertex element only.

vertexBuffer.SetData(2, vertices, 2, 2, stride);

somehow results in some broken mess. I am fairly certain my stride size is calculated correctly (sizeof(float)*6 for vector3, vector2, single).

Can anyone with experience enlighten me or provide examples of how he dealt with that?

thanks :slight_smile:

2

The first parameter is offsetInBytes. A value of 2 bytes does not look right to me.

3

You probably want to keep the first parameter as 0. The startIndex and elementCount look ok.

4

ah yes, I realized that later, I only used 0 and elements*stride as an offset in the actual code for the first parameter.

Either way,

vertexBuffer.SetData(0, vertices, 0, 4, stride);

doesn’t work for me either, is it possible that i somehow got my bytesize wrong?

public struct TrailVertex
    {
        // Stores the starting position of the particle.
        public Vector3 Position;

        // Stores TexCoords
        public Vector2 TextureCoordinate;

        // Visibility term
        public float Visibility;

        public static readonly VertexDeclaration VertexDeclaration = new VertexDeclaration
            (
            new VertexElement(0, VertexElementFormat.Vector3,
                VertexElementUsage.Position, 0),
            new VertexElement(sizeof(float) * 3, VertexElementFormat.Vector2,
                VertexElementUsage.TextureCoordinate, 0),
            new VertexElement(sizeof(float) * 3 + sizeof(float) * 2, VertexElementFormat.Single,
                VertexElementUsage.TextureCoordinate, 1)
            );

        public const int SizeInBytes = sizeof(float)*6; //24
    }

plus later on in the implementation

int stride = TrailVertex.SizeInBytes;
_vBuffer.SetData(0,vertices,0,4,stride,SetDataOptions.None);

or

_vBuffer.SetData(stride*4,vertices,4,4,stride,SetDataOptions.None);

both have heavy artifacts, so I guess it must be the stride size right?

5

Does TrailVertex.VertexDeclaration.VertexStride agree with your calculation? From what it looks like, it should work. There are some unit tests for this. Perhaps they’re missing something?

6

Yep, TrailVertex.VertexDeclaration.VertexStride is also 24.

I’ll try to check out some more cases tomorrow, but I think this is a problem specific to me and my implementation, because as far as I am aware the particle systems, which I just copied from the MS XNA samples, work without problems.

Note:
If I use this to basically copy the whole array like so
int stride = TrailVertex.SizeInBytes;
_vBuffer.SetData(0, vertices, 0, vertices.Length, stride, SetDataOptions.None);

it works without problems. Only when I use smaller parts do these crop up.

EDIT:
Ok I checked and rechecked and I got the bug - you were right, I missed the offsetInBytes in one function, but I also had a different problem where I rendered vertices that had an index but were not initialized yet.
Thanks :slight_smile: