# DX11 [D3D11] Constant buffers and textures...

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I'm trying to get my head around textures, but I think I'm coming to the realisation that I don't understand constant buffers entirely, either. My biggest trouble is finding how to link access a texture from a shader.

I have created a ID3D11ShaderResourceView via D3DX11CreateShaderResourceViewFromFile and everything has worked fine up to here. I've heard that constant buffers and textures are completely different, and that I have to link it to a shader using CSSetShaderResources. Is this right? How am I then supposed to access this particular texture from the shader?

On a similar note, how do constant buffers work in terms of accessing it from the shader? The way I understand it is the constant buffer is treated as an array (or memory block), and you access a particular part of it by using register( c# ) where # is the start of the memory you want to use. Is this correct?

Thanks.

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A constant buffer is bound to the pipeline directly instead of needing a resource view like the texture. Using both of these resource types from within HLSL requires the declaration of an appropriate resource object in the HLSL code. For example, here is a sample shader that has a constant buffer declared in it:

cbuffer Transforms{	matrix WorldViewProjMatrix;		matrix WorldViewMatrix;};struct VS_INPUT{	float3 position : POSITION;	float2 tex		: TEXCOORDS0;	float3 normal	: NORMAL;};struct VS_OUTPUT{	float4 position : SV_Position;	float2 tex    : TEXCOORDS0;	float3 normal : NORMAL;};VS_OUTPUT VSMAIN( in VS_INPUT input ){	VS_OUTPUT output;		output.position = mul( float4( input.position, 1.0f ), WorldViewProjMatrix );	output.tex = input.tex;	float3 ViewSpaceNormals = mul( float4( input.normal, 0.0f ), WorldViewMatrix ).xyz;	output.normal = ViewSpaceNormals * 0.5f + 0.5f;	return output;}

And here is the matching pixel shader with a texture declared in it:

Texture2D       ColorTexture : register( t0 );           SamplerState    LinearSampler : register( s0 );struct VS_OUTPUT{	float4 position : SV_Position;	float2 tex      : TEXCOORD0;	float3 normal   : NORMAL;};float4 PSMAIN( in VS_OUTPUT input ) : SV_Target{	float4 vValues = ColorTexture.Sample( LinearSampler, input.tex );	return( vValues );}

You have the option of either sampling a texture or directly loading its memory, both of which are performed with the methods of the resource object that is declared (as shown above).

The constant buffer contents are globally visible within the scope of the file taht they are declared in. So from the first snippet above, the named parameters WorldViewProjMatrix and WorldViewMatrix are both visible as if they weren't declared inside the cbuffer. This means that the names within all of your cbuffers need to unique as well, so watch out for that.

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You bind a texture by setting its shader resource view onto the pipeline for whichever stage you want to access it. So PSSetShaderResources for the pixel shader, VSSetShaderResources for the vertex shader, etc. Constant buffers on the other hand are bound with PSSetConstantBuffers or the equivalent for the stage you want to use them in.

Constant buffers in shaders provide a very simple way to access a small number of individual constants in your shader. You access individual constants as if they were global variables. It looks like this:
cbuffer VSConstants : register(cb0){    float4x4 World;    float4x4 WorldViewProjection;}// Vertex shaderVSOutput VSMain(in VSInput input){    float3 worldPos = mul(input.Position, World).xyz;    ...}

Textures are accessed using a Texture object. There's a few types of texture objects (Texture2D, Texture3D, TextureCube, Texture2DMS) depending on the type and MSAA settings for the texture. See the documentation for the methods you can call on a texture object. "Sample" is the most standard, where you provide texture coordinates and a sampler state. This allows you to do your standard texture fetch with linear/aniso filtering + mipmapping. The other methods are useful for more specialized cases.

I would suggest that you have a look through the samples that come with the SDK. Almost all of them use textures and constant buffers.

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Ah, yes, I get it now. And I've finally got textures now! Thankyou.

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• By Baemz
Hello,
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float angle = CU::ToRadians(45.f); Plane<float> nearPlane(Vector3<float>(0, 0, aNear), Vector3<float>(0, 0, -1)); Plane<float> farPlane(Vector3<float>(0, 0, aFar), Vector3<float>(0, 0, 1)); Plane<float> right(Vector3<float>(0, 0, 0), Vector3<float>(angle, 0, -angle)); Plane<float> left(Vector3<float>(0, 0, 0), Vector3<float>(-angle, 0, -angle)); Plane<float> up(Vector3<float>(0, 0, 0), Vector3<float>(0, angle, -angle)); Plane<float> down(Vector3<float>(0, 0, 0), Vector3<float>(0, -angle, -angle)); myVolume.AddPlane(nearPlane); myVolume.AddPlane(farPlane); myVolume.AddPlane(right); myVolume.AddPlane(left); myVolume.AddPlane(up); myVolume.AddPlane(down); When checking the intersections I am using a BoundingSphere of my models, which is calculated by taking the average position of all vertices and then choosing the furthest distance to a vertex for radius. The actual intersection test looks like this, where the "myFrustum90" is the actual frustum described above.
The orientationInverse is the viewMatrix in this case.
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Please bare in mind that this code is not optimized nor well-written by any means. I am just looking to get it working.
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Thanks.

• hi,
i have read very much about the binding of a constantbuffer to a shader but something is still unclear to me.
e.g. when performing :   vertexshader.setConstantbuffer ( buffer,  slot )
is the buffer bound
or
b. to the VertexShader that is currently set as the active VertexShader
Is it possible to bind a constantBuffer to a VertexShader e.g. VS_A and keep this binding even after the active VertexShader has changed ?
I mean i want to bind constantbuffer_A  to VS_A, an Constantbuffer_B to VS_B  and  only use updateSubresource without using setConstantBuffer command every time.

Look at this example:
perform drawcall       ( buffer_A is used )

perform drawcall   ( buffer_B is used )
perform drawcall   (now which buffer is used ??? )

I ask this question because i have made a custom render engine an want to optimize to
the minimum  updateSubresource, and setConstantbuffer  calls

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If I change my lines to PCN and pass them to the 3D shader with my triangles, then the lighting screws them all up.  I only want the lighting for the 3D triangles, but no SpecularBlinnPhong/Lighting for the lines (just PC).
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I assume I somehow need to draw the 3D triangles using one shader, and then "switch" to another shader and draw the lines?  But I have no clue how to use two different shaders in the same scene.  And then are the lines just drawn on top of the triangles, or vice versa (maybe draw order dependent)?
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I'm also more than happy to post my simple test code if that helps as well!

• By Reitano
Hi,
I am writing a linear allocator of per-frame constants using the DirectX 11.1 API. My plan is to replace the traditional constant allocation strategy, where most of the work is done by the driver behind my back, with a manual one inspired by the DirectX 12 and Vulkan APIs.
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The new allocator appears to be working but I am not 100% confident it is actually correct. In particular:
1) it relies on queries which I am not too familiar with. Are they 100% reliable ?
2) it maps/unmaps the constant buffer of each page at the beginning of a new frame and then writes the mapped memory as the frame is built. In pseudo code:
BeginFrame:
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device.Unmap(page.buffer)
RenderFrame
Alloc(size, initData)
...
memcpy(page.data + page.start, initData, size)
Alloc(size, initData)
...
memcpy(page.data + page.start, initData, size)
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Is this valid ?
3) I don't fully understand how many frames I should keep in the history. My intuition says it should be equal to the maximum latency reported by IDXGIDevice1::GetMaximumFrameLatency, which is 3 on my machine. But, this value works fine in an unit test while on a more complex demo I need to manually set it to 5, otherwise the allocator starts overwriting previous frames that have not completed yet. Shouldn't the swap chain Present method block the CPU in this case ?
4) Should I expect this approach to be more efficient than the one managed by the driver ? I don't have meaningful profile data yet.
Is anybody familiar with the approach described above and can answer my questions and discuss the pros and cons of this technique based on his experience ?
For reference, I've uploaded the (WIP) allocator code at https://paste.ofcode.org/Bq98ujP6zaAuKyjv4X7HSv.  Feel free to adapt it in your engine and please let me know if you spot any mistakes
Thanks
Stefano Lanza

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