IEffectSkinning

DirectXTK	Effects

This abstract interface controls skinning animation matrices. Settings for this interface can influence the choice of shader permutation.

Effects that implement this interface typically require BLENDINDICES and BLENDWEIGHT semantic data in the vertex input layout.

Related tutorial: Using skinned models

Obtaining the interface

There are two methods used in DirectX Tool Kit. For simple cases, just maintain a reference directly to the desired effect class:

std::shared_ptr<SkinnedEffect> effect;

...

effect->SetBoneTransforms( bones.get(), boneCount );

For more general cases where a number of effect classes can be in use (such as Model which uses a mix of BasicEffect, DualTextureEffect, SkinnedEffect, and/or DGSLEffect), use Run-Time Type Information (RTTI) to obtain the interface.

std::shared_ptr<IEffect> effect;

...

auto iskin = dynamic_cast<IEffectSkinning*>( effect.get() );
if ( iskin )
{
    iskin->SetBoneTransforms( bones.get(), boneCount );
}

Skinning

The skinning interface is primarily used to set the per-bone transformation matrices for rendering. This is accomplished through the SetBoneTransforms method. Because the method takes a pointer to XMMATRIX, the memory buffer must be 16-byte aligned. While this is the default of new and malloc on 64-bit platforms, this is not true by default for 32-bit platforms. Use of _aligned_malloc is recommended.

struct aligned_deleter { void operator()(void* p) { _aligned_free(p); } };

std::unique_ptr<XMMATRIX[], aligned_deleter> bones(
        reinterpret_cast<XMMATRIX*>( _aligned_malloc(
            sizeof(XMMATRIX) * boneCount, 16 ) ) );

...

// Simple time-based uniform scaling
float s = 1 + sin(time * 1.7f) * 0.5f;
XMMATRIX scale = XMMatrixScaling(s,s,s);

for (size_t j=0; j < boneCount; ++j )
{
    bones[ j ] = scale;
}

effect->SetBoneTransforms(bones.get(), boneCount);

Note that the maximum bone count must be <= MaxBones (72).

You can call ResetBoneTransforms to reset all per-bone transforms to the identity, which is also the default when the effect is newly created.

Finally, the SetWeightsPerVertex method is used as a way to optimize performance of the vertex shader. By default, it assumes that all 4 bones listed in the per-vertex BLENDINDICES and BLENDWEIGHT are used by the model. You can use this method to set the value to 1 or 2 which will choose a lighter-weight shader permutation that ignores the extra 3 or 2 bones influences per vertex, or back to the default of 4. The choice of this value is driven entirely by the content.

Built-in Effect Notes

SkinnedDGSLEffect

This effect implements skinning for the DGSL pipeline.

In older versions of DirectX Tool Kit, skinning was directly implemented by DGSLEffect with a ctor parameter. In the current library, the DGSL effect only supports skinning if it's a SkinnedDGSLEffect instance.

SkinnedEffect

See Built-in effects, permutations, and performance for performance costs of the various shader permutations.

SkinnedNormalMapEffect, SkinnedPBREffect

These built-in effects also support skinning.

Remark

As an optimization, the skinning effects assume that all the matrices are affine transformations, and that the final column is (0 0 0 1). This means that the value of the last column is effectively ignored when set into the constant buffer containing the bone transformations (i.e. the shaders use float4x3)