In the C++ code, do
__declspec( align( 16 ) ) struct ConstantBuffer
{
/*...*/
};

Ok, i never saw that function, but ill research it... thanks!

It's not going to matter because when you map it you're getting a pointer to a different chunk of memory that has already been properly aligned/sized/etc when the cbuffer was created.

Aligning a struct to 16-bytes will affect the alignment and size of that structure, but not the members within it. The reason it's useful this case is because it will round up your structure size to the next multiple of 16-bytes (which is a requirement for constant buffers), but you could also do that just by rounding it up yourself. What you really need to be careful about with constant buffers is the alignment of the individual variables within the constant buffer. HLSL has its own particular rules for this that differ from the defaults for 32-bit and 64-bit C++, which means if you want to use a C++ struct to fill a constant buffer then you need to pay attention to member alignment. One way to do this will be to use __declspec(align(16)) to align individual members to the next 16-byte boundary. Here's a simple example:


struct ConstantBuffer
{
float3 position;
__declspec(align(16)) float3 color;
};


Without the alignment on the "color" member, it will be placed 12-bytes from the start of the constant buffer while HLSL requires it to be placed at the next 16-byte boundary.