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This abstract interface allows setting rendering matrices typically communicated to the shader via a dynamic constant buffer. This interface is implemented by all built-in effects, but is not required for all effects (i.e. a valid effect can implement IEffect and not implement IEffectMatrices).

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<BasicEffect> effect;

...

effect->SetWorld( world );
effect->SetView( view );
effect->SetProjection( projection );

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 RTTI to obtain the interface.

std::shared_ptr<IEffect> effect;

...

auto imatrices = dynamic_cast<IEffectMatrices*>( part->effect.get() );
if ( imatrices )
{
    imatrices->SetWorld( world );
    imatrices->SetView( view );
    imatrices->SetProjection( projection );
}

Note For the specific case of IEffectMatrices, you could try to make the assumption that all effects in use implement IEffectMatrices and make use of a reinterpret_cast<> or old-school C-style cast instead of dynamic_cast<>, however this will not work since IEffectMatrices is not derived from IEffect. You would have to assume a specific class of effect instead.

Setting matrices

The matrices used by effects can be left-handed or right-handed coordinates, but are always in row-major form.

As an optimization, most shaders actually consume matrices in column-major form, so effects implementations will transpose them as needed when setting them into the constant buffer.

The effects implementations will lazily update various computations (such as inverses and concatenations of matrices), so that changing only one of the three matrices can be less computationally expensive than changing all three.

Most BasicEffect shaders make no particular distinction between the view, and projection matrices. You can, for example, provide the combined view*projection matrix with SetProjection and leave the others identity with the same results.

The BasicEffect shaders require the world matrix to be distinct from the view and projection matrices for doing proper transforms of normals into world coordinates.

Some complex shaders such as DGSLEffect where the HLSL shader is given access to both local->world and local->projected transforms could make a distinction between view and projection as well, which requires the three matrices to be set independently to get correct results.

Last edited Jul 28, 2015 at 8:07 PM by walbourn, version 16