IEffectSkinning

This abstract interface controls skinning animation matrices.

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

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(device, EffectFlags::None, pd);

...

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, and/or SkinnedEffect), use Run-Time Type Information (RTTI) to obtain the interface.

std::shared_ptr<SkinnedEffect> effect(device, EffectFlags::None, pd);

...

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.

Built-in Effect Notes

BasicEffect, AlphaTestEffect, DualTextureEffect, EnvironmentMapEffect, NormalMapEffect

These built-in effects do not implement skinning animation.

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)