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DX11 Using multiple constant buffer

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Hi,
I've started to learn dx11 with the slimdx framework.
Currently i tried to use two constant buffer to update informations more frequent then other.

But with my current shader code I get some strange behaviour using the two constant buffers:
// cbuffer definition
struct ShaderLightBuffer
{
public Vector3 Ambient;
public float Alpha;
public Vector3 Diffuse;
public float Shininess;
public Vector3 Specular;
public float padding;
public Vector2 SpecularTextured;
public Vector2 padding2;
}

struct ShaderMatrixBuffer
{
public Matrix World;
public Matrix WorldViewProjection;
public Vector3 CameraPosition;
public float padding1;
}

// buffer initialization
_light_constant_buffer = new Buffer(Device, Marshal.SizeOf(typeof(ShaderLightBuffer)), ResourceUsage.Default, BindFlags.ConstantBuffer, CpuAccessFlags.None, ResourceOptionFlags.None, 0);
_matrix_constant_buffer = new Buffer(Device, Marshal.SizeOf(typeof(ShaderMatrixBuffer)), ResourceUsage.Default, BindFlags.ConstantBuffer, CpuAccessFlags.None, ResourceOptionFlags.None, 0);

// render logic
ImmediateContext.InputAssembler.InputLayout = _input_layout;
ImmediateContext.InputAssembler.PrimitiveTopology = PrimitiveTopology.TriangleList;

ImmediateContext.InputAssembler.SetVertexBuffers(0, _buffer_bindings.ToArray());
ImmediateContext.VertexShader.Set(_vertex_shader);

ImmediateContext.VertexShader.SetConstantBuffer(_matrix_constant_buffer, 0);
ImmediateContext.VertexShader.SetConstantBuffer(_light_constant_buffer, 1);

ImmediateContext.Rasterizer.SetViewports(Engine.DeviceManager.Viewport);

ImmediateContext.PixelShader.Set(_pixel_shader);
ImmediateContext.PixelShader.SetConstantBuffer(_light_constant_buffer, 2);

ImmediateContext.OutputMerger.SetTargets(DepthBuffer, RenderTarget);

// .. set wvp, world, camera position to matrix buffer..
ShaderMatrixBuffer matrix_buffer = new ShaderMatrixBuffer();
matrix_buffer.WorldViewProjection = view_proj;
matrix_buffer.World = world_matrix;
matrix_buffer.CameraPosition = Engine.Camera.Eye;

// update matrix constant buffer
var matrix_stream = new DataStream(Marshal.SizeOf(typeof(ShaderMatrixBuffer)), true, true);
matrix_stream.Write(matrix_buffer);
matrix_stream.Position = 0;

ImmediateContext.UpdateSubresource(new DataBox(0, 0, matrix_stream), _matrix_constant_buffer, 0);
ImmediateContext.VertexShader.SetConstantBuffer(_matrix_constant_buffer, 0);

foreach (var material in Materials)
{
ShaderLightBuffer light_buffer = new ShaderLightBuffer();
light_buffer.Alpha = 1f;
light_buffer.Ambient = material.Ambient;
light_buffer.Diffuse = material.Diffuse;
light_buffer.Specular = material.Specular;
light_buffer.Shininess = (int)material.Shininess;
light_buffer.SpecularTextured = new Vector2 (0);

if (!string.IsNullOrEmpty(material.TextureFilename))
{
light_buffer.SpecularTextured = new Vector2(1);
if (_shader_resource == null)
{
var texture = Texture2D.FromFile(Device, Path.Combine(material.Path, material.TextureFilename));
_shader_resource = new ShaderResourceView(Device, texture);
}

ImmediateContext.PixelShader.SetShaderResource(_shader_resource, 0);
}

ImmediateContext.PixelShader.SetSampler(_sampler_state, 0);

var light_stream = new DataStream(Marshal.SizeOf(typeof(ShaderLightBuffer)), true, true);
light_stream.Write(light_buffer);
light_stream.Position = 0;

ImmediateContext.UpdateSubresource(new DataBox(0, 0, light_stream), _light_constant_buffer, 0);

ImmediateContext.VertexShader.SetConstantBuffer(_light_constant_buffer, 1);
ImmediateContext.VertexShader.SetConstantBuffer(_light_constant_buffer, 2);

ImmediateContext.Draw(_vertices_count[i], 0);
}
// end render logic
Alright, I hope this code is straight forward, just setting all infos for the pipeline stages, updating the general constant buffer and the cbuffer
for each material used for the geometry.

Now the odd part - shader code
PS_INPUT VS( VS_INPUT input )
{
PS_INPUT output;

// Transform the position into world space for lighting, and projected space
float4 vPosWorld = mul( float4(input.position,1), World );
output.position = mul( float4(input.position,1), WorldViewProjection );

// pass texture coordinate
output.texcoord = input.texcoord;

// transform normal into world space for lighting
float3 normal_world = mul( input.normal, (float3x3) World);
float3 light_vector = normalize( LightPosition - vPosWorld.xyz );

// compute the ambient and diffuse components of illumination
output.color.rgb = LightColor * MaterialAmbient;
output.color.rgb += LightColor * MaterialDiffuse * saturate( dot( light_vector, normal_world ) );

if( SpecularTextured.x > 0)
{
float3 camera = normalize( vPosWorld.xyz - CameraPosition );
float3 reflection = reflect ( light_vector, normal_world );
float phone_value = saturate( dot( reflection, camera ) );
output.color.rgb += MaterialSpecular * pow( phone_value, MaterialShininess );
}

// odd things happens if i comment the next line -> [7480] D3D11: WARNING: ID3D11DeviceContext::Draw: The size of the Constant Buffer at slot 1 of the Vertex Shader unit is too small (64 bytes provided, 144 bytes, at least, expected). This is OK, as out-of-bounds reads are defined to return 0. It is also possible the developer knows the missing data will not be used anyway. This is only a problem if the developer actually intended to bind a sufficiently large Constant Buffer for what the shader expects. [ EXECUTION WARNING #351: DEVICE_DRAW_CONSTANT_BUFFER_TOO_SMALL ]
output.color.rgb = MaterialDiffuse;
output.color.a = MaterialShininess;

return output;
}

float4 PS( PS_INPUT input ) : SV_Target
{
float4 output = input.color;
//// Sample and modulate the texture
if ( SpecularTextured.y > 0 )
output.rgb *= MeshTexture.Sample( samLinear, input.texcoord );
return output;
}
If I set the color values to diffuse the in the vertex shader it draws my geometry correctly with the defined color.
But commenting out the color assignment (since this line was used for debugging), will give me the following warning:
[7480] D3D11: WARNING: ID3D11DeviceContext::Draw: The size of the Constant Buffer at slot 1 of the Vertex Shader unit is too small (64 bytes provided, 144 bytes, at least, expected). This is OK, as out-of-bounds reads are defined to return 0. It is also possible the developer knows the missing data will not be used anyway. This is only a problem if the developer actually intended to bind a sufficiently large Constant Buffer for what the shader expects. [ EXECUTION WARNING #351: DEVICE_DRAW_CONSTANT_BUFFER_TOO_SMALL ]

This happens also if I use UpdateSubResource method to update both constant buffers.
It seems that the second constant buffer update overwrites also the first constant buffer.

I wanted to ask how to handle multiple constant buffer updates? Am I missing something?

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When you have multiple constant buffers, you have to put them in separate slots. i don't know how to use slimdx, but in regular dx11, you can set the vertex's constant buffer by calling VSSetConstantBuffers of the device context, and setting the second parameter as 0 for the first constant buffer, and 1 for the second. If the vertex and pixel shader share a constant buffer, you will have to bind the same constant buffer separately to each shader, using VSSetConstantBuffers and VSSetConstantBuffers.

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Thanks for the quick response!
I think you meant VSSetConstantBuffer and PSSetConstantBuffer in the last sentence.

I've replaced setting both cbuffer at the same time

[color=#660066]ImmediateContext[color=#666600].[color=#660066]VertexShader[color=#666600].[color=#660066]SetConstantBuffers[color=#666600]([color=#000088]new[color=#666600][][color=#000000] [color=#666600]{[color=#000000] _matrix_constant_buffer[color=#666600],[color=#000000] _light_constant_buffer [color=#666600]},[color=#000000] [color=#006666]0[color=#666600],[color=#006666]2[color=#666600]);

with

ImmediateContext.VertexShader.SetConstantBuffer(_matrix_constant_buffer, 0);
ImmediateContext.VertexShader.SetConstantBuffer(_light_constant_buffer, 1);

and also set the cbuffer to the pixel shader
ImmediateContext.PixelShader.SetConstantBuffer(_light_constant_buffer, 1);

I also tried to attach - : register(cbx) to the cbuffer declaration in the shader code.
but the result is the same error message sad.png

Alright, I tried the same code with the sharpdx framework with the same ouput.. Edited by caballero

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sorry it didn't work for you, but one other thing, iis (as far as i know) you have to put each buffer in it's own slot, even if two shaders use the same buffer, they should go into separate slots, so when you bind your pixel shaders buffer, you should try changing the '1' to a '2'

also, can you show the structure of your constant buffers?

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The structure of the constant buffer is


cbuffer Matrixbuffer : register(cb0)
{
matrix World;
matrix WorldViewProjection;
float3 CameraPosition;
float padding;
};

and

cbuffer LightBuffer : register(cb1)
{
float3 MaterialAmbient; // Material's ambient color
float MaterialAlpha;
float3 MaterialDiffuse; // Material's diffuse color
float MaterialShininess;
float3 MaterialSpecular; // Material's specular color
float padding2;
float2 SpecularTextured;
float2 padding3;
};


It seems to me that updating the constant buffer in the foreach loop overwrites the first "global" constant buffer.
Could there be something that I am missing?

Would a pix run file help you to get more information out of it?

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actually, could you post the constant buffers in your main app?

This might not be the problem, but just check it out. Are you making sure you are packaging your constant buffers correctly in your app? the shader takes 16 byte chunks for the constant buffer, so if you have a variable that's split between two chunks, it will cause problems. float variables are 4 bytes, float3's are 12 bytes, matrices are 16 bytes. I see you have it aligned correctly in the shader, so i'm guessing it's probably the same for your app, but double check.

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I just noticed you are not setting your constant buffers after you change them. I think you have to reset them every time they change. also, try using update subresource instead:
ImmediateContext->UpdateSubresource( light_buffer, 0, NULL, &_light_constant_buffer, 0, 0 );
Somethng like that anyway

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[7480] D3D11: WARNING: ID3D11DeviceContext::Draw: The size of the Constant Buffer at slot 1 of the Vertex Shader unit is too small (64 bytes provided, 144 bytes, at least, expected). This is OK, as out-of-bounds reads are defined to return 0. It is also possible the developer knows the missing data will not be used anyway. This is only a problem if the developer actually intended to bind a sufficiently large Constant Buffer for what the shader expects. [ EXECUTION WARNING #351: DEVICE_DRAW_CONSTANT_BUFFER_TOO_SMALL ]


The error message has all the information about the problem. Your constant buffer bound at slot 1 has size of 64 bytes, but the shader is reading data from area outside of the 64 bytes area.

This means that you have the light buffer bound to slot 1, but on the shader expects the matrix buffer to be at slot 1. You have to have same registers at the program side and at the shader side. Remember that the register indices are 0-based.



Cheers!

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Hi, I've updated all code parts in my previous posts.

Thx kauna for the hint since after changing the slots in the code no warnings or errors occur.

// I've set the following for slots for the buffers to be comprehensible
vs.setconstantbuffer(matrix_buffer, 1);
vs.setconstantbuffer(light_buffer, 0);
ps.setconstantbuffer(light_buffer, 2);

I thought that the cbuffers in the shader will be declared in sequential order since I'm defining first the Matrix cbuffer then the Light cbuffer. I tried to fixate that by setting : register(cb#).

Obviously i was wrong with this assumption.

Now it's all black (of course it is black, I think I am really learning dx the hard way) without any warnings thanks for your help!

Theoretically, if I define more cbuffers, how can I find out which slots they were assigned to?

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// I've set the following for slots for the buffers to be comprehensible
vs.setconstantbuffer(matrix_buffer, 1);
vs.setconstantbuffer(light_buffer, 0);
ps.setconstantbuffer(light_buffer, 2);


Hi, you may set the light_buffer to slot 0 for vertex shader and pixel shader. I assume that in the shader code you have probably slot 0 (both vs and ps) for the light_buffer?

You may use shader reflection API to extract information from the shaders (including which constant buffer is expected at which register ...)

Best regards!

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Thanks for info!

Additionally some further gamedev redirections:
how to find the constant buffer slots via shader reflection
http://www.gamedev.net/topic/607104-d3d11shaderreflection-and-constant-buffer-slot/

some thoughts about UpdateSubResource vs Map/Unmap
http://www.gamedev.net/topic/616350-dx11-fastest-way-to-update-a-constant-buffer-per-draw-call/

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      Another important thing that pipeline state object encompasses is the input layout description that defines how inputs to the vertex shader, which is the very first shader stage, should be read from the memory. Input layout may define several vertex streams that contain values of different formats and sizes:
      // Define input layout InputLayoutDesc &Layout = PSODesc.GraphicsPipeline.InputLayout; LayoutElement TextLayoutElems[] = {     LayoutElement( 0, 0, 3, VT_FLOAT32, False ),     LayoutElement( 1, 0, 4, VT_UINT8, True ),     LayoutElement( 2, 0, 2, VT_FLOAT32, False ), }; Layout.LayoutElements = TextLayoutElems; Layout.NumElements = _countof( TextLayoutElems ); Finally, pipeline state defines primitive topology type. When all required members are initialized, a pipeline state object can be created by IRenderDevice::CreatePipelineState() method:
      // Define shader and primitive topology PSODesc.GraphicsPipeline.PrimitiveTopologyType = PRIMITIVE_TOPOLOGY_TYPE_TRIANGLE; PSODesc.GraphicsPipeline.pVS = pVertexShader; PSODesc.GraphicsPipeline.pPS = pPixelShader; PSODesc.Name = "My pipeline state"; m_pDev->CreatePipelineState(PSODesc, &m_pPSO); When PSO object is bound to the pipeline, the engine invokes all API-specific commands to set all states specified by the object. In case of Direct3D12 this maps directly to setting the D3D12 PSO object. In case of Direct3D11, this involves setting individual state objects (such as rasterizer and blend states), shaders, input layout etc. In case of OpenGL, this requires a number of fine-grain state tweaking calls. Diligent Engine keeps track of currently bound states and only calls functions to update these states that have actually changed.
      Binding Shader Resources
      Direct3D11 and OpenGL utilize fine-grain resource binding models, where an application binds individual buffers and textures to certain shader or program resource binding slots. Direct3D12 uses a very different approach, where resource descriptors are grouped into tables, and an application can bind all resources in the table at once by setting the table in the command list. Resource binding model in Diligent Engine is designed to leverage this new method. It introduces a new object called shader resource binding that encapsulates all resource bindings required for all shaders in a certain pipeline state. It also introduces the classification of shader variables based on the frequency of expected change that helps the engine group them into tables under the hood:
      Static variables (SHADER_VARIABLE_TYPE_STATIC) are variables that are expected to be set only once. They may not be changed once a resource is bound to the variable. Such variables are intended to hold global constants such as camera attributes or global light attributes constant buffers. Mutable variables (SHADER_VARIABLE_TYPE_MUTABLE) define resources that are expected to change on a per-material frequency. Examples may include diffuse textures, normal maps etc. Dynamic variables (SHADER_VARIABLE_TYPE_DYNAMIC) are expected to change frequently and randomly. Shader variable type must be specified during shader creation by populating an array of ShaderVariableDesc structures and initializing ShaderCreationAttribs::Desc::VariableDesc and ShaderCreationAttribs::Desc::NumVariables members (see example of shader creation above).
      Static variables cannot be changed once a resource is bound to the variable. They are bound directly to the shader object. For instance, a shadow map texture is not expected to change after it is created, so it can be bound directly to the shader:
      PixelShader->GetShaderVariable( "g_tex2DShadowMap" )->Set( pShadowMapSRV ); Mutable and dynamic variables are bound via a new Shader Resource Binding object (SRB) that is created by the pipeline state (IPipelineState::CreateShaderResourceBinding()):
      m_pPSO->CreateShaderResourceBinding(&m_pSRB); Note that an SRB is only compatible with the pipeline state it was created from. SRB object inherits all static bindings from shaders in the pipeline, but is not allowed to change them.
      Mutable resources can only be set once for every instance of a shader resource binding. Such resources are intended to define specific material properties. For instance, a diffuse texture for a specific material is not expected to change once the material is defined and can be set right after the SRB object has been created:
      m_pSRB->GetVariable(SHADER_TYPE_PIXEL, "tex2DDiffuse")->Set(pDiffuseTexSRV); In some cases it is necessary to bind a new resource to a variable every time a draw command is invoked. Such variables should be labeled as dynamic, which will allow setting them multiple times through the same SRB object:
      m_pSRB->GetVariable(SHADER_TYPE_VERTEX, "cbRandomAttribs")->Set(pRandomAttrsCB); Under the hood, the engine pre-allocates descriptor tables for static and mutable resources when an SRB objcet is created. Space for dynamic resources is dynamically allocated at run time. Static and mutable resources are thus more efficient and should be used whenever possible.
      As you can see, Diligent Engine does not expose low-level details of how resources are bound to shader variables. One reason for this is that these details are very different for various APIs. The other reason is that using low-level binding methods is extremely error-prone: it is very easy to forget to bind some resource, or bind incorrect resource such as bind a buffer to the variable that is in fact a texture, especially during shader development when everything changes fast. Diligent Engine instead relies on shader reflection system to automatically query the list of all shader variables. Grouping variables based on three types mentioned above allows the engine to create optimized layout and take heavy lifting of matching resources to API-specific resource location, register or descriptor in the table.
      This post gives more details about the resource binding model in Diligent Engine.
      Setting the Pipeline State and Committing Shader Resources
      Before any draw or compute command can be invoked, the pipeline state needs to be bound to the context:
      m_pContext->SetPipelineState(m_pPSO); Under the hood, the engine sets the internal PSO object in the command list or calls all the required native API functions to properly configure all pipeline stages.
      The next step is to bind all required shader resources to the GPU pipeline, which is accomplished by IDeviceContext::CommitShaderResources() method:
      m_pContext->CommitShaderResources(m_pSRB, COMMIT_SHADER_RESOURCES_FLAG_TRANSITION_RESOURCES); The method takes a pointer to the shader resource binding object and makes all resources the object holds available for the shaders. In the case of D3D12, this only requires setting appropriate descriptor tables in the command list. For older APIs, this typically requires setting all resources individually.
      Next-generation APIs require the application to track the state of every resource and explicitly inform the system about all state transitions. For instance, if a texture was used as render target before, while the next draw command is going to use it as shader resource, a transition barrier needs to be executed. Diligent Engine does the heavy lifting of state tracking.  When CommitShaderResources() method is called with COMMIT_SHADER_RESOURCES_FLAG_TRANSITION_RESOURCES flag, the engine commits and transitions resources to correct states at the same time. Note that transitioning resources does introduce some overhead. The engine tracks state of every resource and it will not issue the barrier if the state is already correct. But checking resource state is an overhead that can sometimes be avoided. The engine provides IDeviceContext::TransitionShaderResources() method that only transitions resources:
      m_pContext->TransitionShaderResources(m_pPSO, m_pSRB); In some scenarios it is more efficient to transition resources once and then only commit them.
      Invoking Draw Command
      The final step is to set states that are not part of the PSO, such as render targets, vertex and index buffers. Diligent Engine uses Direct3D11-syle API that is translated to other native API calls under the hood:
      ITextureView *pRTVs[] = {m_pRTV}; m_pContext->SetRenderTargets(_countof( pRTVs ), pRTVs, m_pDSV); // Clear render target and depth buffer const float zero[4] = {0, 0, 0, 0}; m_pContext->ClearRenderTarget(nullptr, zero); m_pContext->ClearDepthStencil(nullptr, CLEAR_DEPTH_FLAG, 1.f); // Set vertex and index buffers IBuffer *buffer[] = {m_pVertexBuffer}; Uint32 offsets[] = {0}; Uint32 strides[] = {sizeof(MyVertex)}; m_pContext->SetVertexBuffers(0, 1, buffer, strides, offsets, SET_VERTEX_BUFFERS_FLAG_RESET); m_pContext->SetIndexBuffer(m_pIndexBuffer, 0); Different native APIs use various set of function to execute draw commands depending on command details (if the command is indexed, instanced or both, what offsets in the source buffers are used etc.). For instance, there are 5 draw commands in Direct3D11 and more than 9 commands in OpenGL with something like glDrawElementsInstancedBaseVertexBaseInstance not uncommon. Diligent Engine hides all details with single IDeviceContext::Draw() method that takes takes DrawAttribs structure as an argument. The structure members define all attributes required to perform the command (primitive topology, number of vertices or indices, if draw call is indexed or not, if draw call is instanced or not, if draw call is indirect or not, etc.). For example:
      DrawAttribs attrs; attrs.IsIndexed = true; attrs.IndexType = VT_UINT16; attrs.NumIndices = 36; attrs.Topology = PRIMITIVE_TOPOLOGY_TRIANGLE_LIST; pContext->Draw(attrs); For compute commands, there is IDeviceContext::DispatchCompute() method that takes DispatchComputeAttribs structure that defines compute grid dimension.
      Source Code
      Full engine source code is available on GitHub and is free to use. The repository contains two samples, asteroids performance benchmark and example Unity project that uses Diligent Engine in native plugin.
      AntTweakBar sample is Diligent Engine’s “Hello World” example.

       
      Atmospheric scattering sample is a more advanced example. It demonstrates how Diligent Engine can be used to implement various rendering tasks: loading textures from files, using complex shaders, rendering to multiple render targets, using compute shaders and unordered access views, etc.

      Asteroids performance benchmark is based on this demo developed by Intel. It renders 50,000 unique textured asteroids and allows comparing performance of Direct3D11 and Direct3D12 implementations. Every asteroid is a combination of one of 1000 unique meshes and one of 10 unique textures.

      Finally, there is an example project that shows how Diligent Engine can be integrated with Unity.

      Future Work
      The engine is under active development. It currently supports Windows desktop, Universal Windows and Android platforms. Direct3D11, Direct3D12, OpenGL/GLES backends are now feature complete. Vulkan backend is coming next, and support for more platforms is planned.
    • By kan123
      Hello,
      DX9Ex. I have the problem with driver stability in time of serial renderings, which i try to use for image processing in memory with fragment shaders. For big bitmaps the video driver sometimes becomes unstable ("Display driver stopped responding and has recovered") and, for instance, if the media player runs video in background, it sometimes freezes and distorts. I tried to use next methods of IDirect3DDevice9Ex:
      SetGPUThreadPriority(-7);
      WaitForVBlank(0);
      EvictManagedResources();
      with purpose to give some time for GPU between scenes, but it seems to be has not notable effect in this case. I don't want to reinitilialize subsystem for every step to avoid performance loss.
      So, my question is next: does some common practice exists to avoid overloading of GPU by running tasks? Many thanks in advance.
       
    • By AxeGuywithanAxe
      I wanted to see how others are currently handling descriptor heap updates and management.
      I've read a few articles and there tends to be three major strategies :
      1 ) You split up descriptor heaps per shader stage ( i.e one for vertex shader , pixel , hull, etc)
      2) You have one descriptor heap for an entire pipeline
      3) You split up descriptor heaps for update each update frequency (i.e EResourceSet_PerInstance , EResourceSet_PerPass , EResourceSet_PerMaterial, etc)
      The benefits of the first two approaches is that it makes it easier to port current code, and descriptor / resource descriptor management and updating tends to be easier to manage, but it seems to be not as efficient.
      The benefits of the third approach seems to be that it's the most efficient because you only manage and update objects when they change.
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