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## [SlimDX] Shader Constants and their registers

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### #1qorthos  Members

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Posted 28 January 2013 - 02:54 PM

Hi everyone.  I've just started transitioning from XNA to SlimDX (and DirectX11) and boy am I confused!  I have a deferred shader and a good way to instance primitives (cubes cones, spheres, etc) in XNA and I'm trying currently trying to learn enough of SlimDX and Directx11 to recreate those.

My brain already hurts.  I started off by trying to expand the 3rd SlimDX tutorial: simple triangle.  I modified the tutorial effect file to this:

cbuffer ColorBuffer : register(cb0)
{
float4	color;
}

cbuffer WorldBuffer : register(cb1)
{
float4x4	world;
}

struct VS_INPUT
{
float4 Position : POSITION;
};

struct VS_OUTPUT
{
float4 Position : SV_POSITION;
float4 Color	: COLOR0;
};

{
VS_OUTPUT output = (VS_OUTPUT)0;

output.Position = mul(input.Position, world);
output.Color = color;

return output;
}

{
return input.Color;
}


It's simple enough.

I then attempt to set the shader constants in the SlimDX MessagePump:

            MessagePump.Run(form, () =>
{
context.ClearRenderTargetView(renderTarget, new Color4(0.5f, 0.5f, 1.0f));

System.DateTime now = System.DateTime.Now;
System.TimeSpan span = System.TimeSpan.FromTicks(now.Ticks - start.Ticks);

world = Matrix.RotationZ((float)span.TotalSeconds);

worldStream.Position = 0;
worldStream.Write(world);
worldStream.Position = 0;

worldBuffer = new Buffer(
device,
worldStream,
64,
ResourceUsage.Dynamic,
BindFlags.ConstantBuffer,
CpuAccessFlags.Write,
ResourceOptionFlags.None,
4);

color = new Color4(1, 1, 1, 1);
colorStream.Position = 0;
colorStream.Write(color);
colorStream.Position = 0;

colorBuffer = new Buffer(
device,
colorStream,
16,
ResourceUsage.Dynamic,
BindFlags.ConstantBuffer,
CpuAccessFlags.Write,
ResourceOptionFlags.None,
4);

// draw the triangle
context.Draw(3, 0);
swapChain.Present(0, PresentFlags.None);
});


The world matrix is set correctly, but the output behaves as if the color constant was never set.  And to add to my puzzlement, I don't understand why context.VertexShader.SetConstantBuffer(worldBuffer, 0) sets the second ConstantBuffer in the shader file.

What am I doing wrong?

Edited by qorthos, 28 January 2013 - 03:08 PM.

### #2qorthos  Members

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Posted 28 January 2013 - 04:01 PM

Yea, I have no idea what I'm doing.  Calling Dispose() on my Buffers after setting them on the shader makes everything work right.

There's definitely some stuff going on under the hood that I'm completely unaware of.  Also, should I be disposing of these buffers every frame?  It seems like there would be a lot of overhead associated with that, but I don't see a way to re-use them.

### #3Mike.Popoloski  Members

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Posted 28 January 2013 - 08:50 PM

You should create the buffer once and just make updates to it each frame by calling DeviceContext.Map / UnmapSubresource.

Mike Popoloski | Journal | SlimDX

### #4qorthos  Members

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Posted 28 January 2013 - 11:37 PM

You should create the buffer once and just make updates to it each frame by calling DeviceContext.Map / UnmapSubresource.

Thanks for taking the time to respond.

I'm creating the worldBuffer like this:

            worldBuffer = new Buffer(
device,
worldStream,
64,
ResourceUsage.Dynamic,
BindFlags.ConstantBuffer,
CpuAccessFlags.Write,
ResourceOptionFlags.None,
4);


And then trying to map/unmap to set the data in the MessagePump and attempting to update the worldStream (and thus the worldBuffer, I hope):

                context.MapSubresource(worldBuffer, MapMode.Write, SlimDX.Direct3D11.MapFlags.None);

worldStream.Position = 0;
worldStream.Write(world);
worldStream.Position = 0;

context.UnmapSubresource(worldBuffer, 0);


When I run the program, I get the following error message: "E_INVALIDARG: An invalid parameter was passed to the returning function (-2147024809)" when trying to map the resource.

### #5MJP  Moderators

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Posted 29 January 2013 - 12:19 AM

To get more detailed error information, you'll want to create your device with the DeviceCreationFlags.Debug flag passed to the constructor. If you do this and enable native code debugging (it's a checkbox under the Debug section of your project properties) you'll get get descriptive error and warning messages in the debugger output window. In cases like these they will usually tell you exactly what you're doing wrong. In this particular case you probably just need to pass MapMode.WriteDiscard instead of MapMode.Write. WriteDiscard is the common pattern for dynamic resources, where you invalidate the previous contents and completely fill the buffer with new contents. Also you may know this already, but if you'd like you can put both your world matrix and your color in the same constant buffer.

### #6Mike.Popoloski  Members

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Posted 29 January 2013 - 12:26 AM

Also MapSubresource returns the data stream you should write to. Your old one is no good.

Mike Popoloski | Journal | SlimDX

### #7qorthos  Members

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Posted 29 January 2013 - 08:43 AM

Gentlemen, thank you for your time.

Also MapSubresource returns the data stream you should write to. Your old one is no good.

Ah geez, I didn't even see that the method had a return value.

To get more detailed error information, you'll want to create your device with the DeviceCreationFlags.Debug flag passed to the constructor. If you do this and enable native code debugging (it's a checkbox under the Debug section of your project properties) you'll get get descriptive error and warning messages in the debugger output window. In cases like these they will usually tell you exactly what you're doing wrong. In this particular case you probably just need to pass MapMode.WriteDiscard instead of MapMode.Write. WriteDiscard is the common pattern for dynamic resources, where you invalidate the previous contents and completely fill the buffer with new contents. Also you may know this already, but if you'd like you can put both your world matrix and your color in the same constant buffer.

The MapMode changed fixed the crashing problem (could have sworn I checked that before posting here, but it looks like I done missed it.  I checked for an option to enable native code debugging but didn't find it.  Is that an option available for Visual Studio Express?

Edited by qorthos, 29 January 2013 - 08:43 AM.

### #8MJP  Moderators

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Posted 29 January 2013 - 01:26 PM

Oh, I'm pretty sure that the express edition only supported managed debugging. To get around that, you can use DebugView.

### #9qorthos  Members

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Posted 30 January 2013 - 07:41 PM

Oh, I'm pretty sure that the express edition only supported managed debugging. To get around that, you can use DebugView.

DebugView doesn't appear to do much on my computer.  I think it might be an issue with the crapware that Asus installed on my Zenbook.  I might have to do a clean install.

Also: I've resolved all issues.  Thanks for the help you two.  I've attached the final sourcecode in the unlikely event someone has the same issue as I.  I also went a step further and added in a view/projection matrix and an indexbuffer for the triangle.

#### Attached Files

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