git.s-ol.nu forks/DiligentFX / gltf-multiview Components
gltf-multiview

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Rendering Components

Rendering components are designed to be plug-and-play blocks of functionaliy that can be used by applications.

Shadows

The shadowing component implements the following BKMs:

  • Cascaded shadow maps with cascade stabilization
  • PCF
  • Variance shadow maps
  • Two and four-component exponential variance shadow maps
  • Optimized fixed-size or world-sized filter kernels
  • Best cascade search based on projection into light space
  • Filtering across cascades
  • Various artifact removal techniques

Integrating shadows into application

The component is implemented by the following source files:

Initialization

The shadow map manager is responsible for creating required textures and views, cascade partitioning, converting shadow map to filterable representations (VSM/EVSM) etc.

To initialize the manager, prepare ShadowMapManager::InitInfo structure that defines initialization parameters and call ShadowMapManager::Initialize, for example:

ShadowMapManager::InitInfo SMMgrInitInfo;
SMMgrInitInfo.Format               = TEX_FORMAT_D16_UNORM;
SMMgrInitInfo.Resolution           = 1024;
SMMgrInitInfo.NumCascades          = 4;
SMMgrInitInfo.ShadowMode           = SHADOW_MODE_PCF;
SMMgrInitInfo.pComparisonSampler   = m_pComparisonSampler;
m_ShadowMapMgr.Initialize(m_pDevice, SMMgrInitInfo);

Most of the fields of ShadowMapManager::InitInfo structure are self-explanatory. pComparisonSampler defines optional texture sampler to be set in the shadow map resource view. If the sampler is null, the application is responsible for setting appropriate sampler before using the shadow map in the shader.

Cascade Partitioning

To distribute shadow map cascades, populate ShadowMapManager::DistributeCascadeInfo that defines partitioning parameters and call ShadowMapManager::DistributeCascades:

ShadowMapManager::DistributeCascadeInfo DistrInfo;
DistrInfo.pCameraView         = &m_Camera.GetViewMatrix();
DistrInfo.pCameraProj         = &m_Camera.GetProjMatrix();
DistrInfo.pLightDir           = &m_f3LightDirection;
DistrInfo.fPartitioningFactor = 0.95f;
m_ShadowMapMgr.DistributeCascades(DistrInfo, m_LightAttribs.ShadowAttribs);

fPartitioningFactor member defines the ratio between fully linear (0.0) and fully logarithmic (1.0) partitioning. The method populates the ShadowMapAttribs structure that is part of the LightAttribs structure and should be made available to a shader via constant buffer.

Rendering Shadow Cascades

After cascades are distributed, use ShadowMapManager::GetCascadeTranform method to access transform matrices and render every cascade:

auto iNumShadowCascades = m_LightAttribs.ShadowAttribs.iNumCascades;
for(int iCascade = 0; iCascade < iNumShadowCascades; ++iCascade)
{
    const auto CascadeProjMatr = m_ShadowMapMgr.GetCascadeTranform(iCascade).Proj;

    auto WorldToLightViewSpaceMatr = m_LightAttribs.ShadowAttribs.mWorldToLightViewT.Transpose();
    auto WorldToLightProjSpaceMatr = WorldToLightViewSpaceMatr * CascadeProjMatr;
    CameraAttribs ShadowCameraAttribs = {};
    ShadowCameraAttribs.mViewT     = m_LightAttribs.ShadowAttribs.mWorldToLightViewT;
    ShadowCameraAttribs.mProjT     = CascadeProjMatr.Transpose();
    ShadowCameraAttribs.mViewProjT = WorldToLightProjSpaceMatr.Transpose();

    {
        MapHelper<CameraAttribs> CameraData(m_pImmediateContext, m_CameraAttribsCB, MAP_WRITE, MAP_FLAG_DISCARD);
        *CameraData = ShadowCameraAttribs;
    }

    auto* pCascadeDSV = m_ShadowMapMgr.GetCascadeDSV(iCascade);
    m_pImmediateContext->SetRenderTargets(0, nullptr, pCascadeDSV,
                                          RESOURCE_STATE_TRANSITION_MODE_TRANSITION);
    m_pImmediateContext->ClearDepthStencil(pCascadeDSV, CLEAR_DEPTH_FLAG, 1.f, 0,
                                           RESOURCE_STATE_TRANSITION_MODE_TRANSITION);

    DrawMesh(m_pImmediateContext);
}

When using filterable representations, the shadow map must be post-processed before it can be used in a shader: 

if (m_ShadowSettings.iShadowMode > SHADOW_MODE_PCF)
    m_ShadowMapMgr.ConvertToFilterable(m_pImmediateContext, m_LightAttribs.ShadowAttribs);

Rendering with Shadows

To use shadowing functionality in the shader, include BasicStructures.fxh and Shadows.fxh files and depending on the shadowing mode, define shadow map or filterable shadow map textures and corresponding samplers (note that the names must be different to allow HLSL to GLSL conversion):

#include "BasicStructures.fxh"
#include "Shadows.fxh"

#if SHADOW_MODE == SHADOW_MODE_PCF
    Texture2DArray<float>  g_tex2DShadowMap;
    SamplerComparisonState g_tex2DShadowMap_sampler;
#else
    Texture2DArray<float4> g_tex2DFilterableShadowMap;
    SamplerState           g_tex2DFilterableShadowMap_sampler;
#endif

To filter shadow map, call FilterShadowMap or SampleFilterableShadowMap function:

FilteredShadow Shadow;
#if SHADOW_MODE == SHADOW_MODE_PCF
    Shadow = FilterShadowMap(g_LightAttribs.ShadowAttribs, g_tex2DShadowMap, g_tex2DShadowMap_sampler,
                             VSOut.PosInLightViewSpace, VSOut.CameraSpaceZ);
#else
    Shadow = SampleFilterableShadowMap(g_LightAttribs.ShadowAttribs, g_tex2DFilterableShadowMap,
                                       g_tex2DFilterableShadowMap_sampler, VSOut.PosInLightViewSpace,
                                       VSOut.CameraSpaceZ);
#endif
DiffuseIllumination *= Shadow.fLightAmount;

Shadow filtering mode is controlled by a number of macros that should be defined when creating the shader:

ShaderCreateInfo ShaderCI;
ShaderMacroHelper Macros;
Macros.AddShaderMacro( "SHADOW_MODE",            m_ShadowSettings.iShadowMode);
Macros.AddShaderMacro( "SHADOW_FILTER_SIZE",     m_LightAttribs.ShadowAttribs.iFixedFilterSize);
Macros.AddShaderMacro( "FILTER_ACROSS_CASCADES", m_ShadowSettings.FilterAcrossCascades);
Macros.AddShaderMacro( "BEST_CASCADE_SEARCH",    m_ShadowSettings.SearchBestCascade );
ShaderCI.Macros = Macros;

Shadows sample gives an example of using the shadowing component.

References

History of Components @gltf-multiview git clone https://git.s-ol.nu/forks/DiligentFX.git