Some test programs, particularly the shader runner, are built from
many different files nowadays, and a line number is relatively
cumbersome to use if you don't know which file that line comes from.
These system values are bound to the same allocation rules as other
semantics: they can share registers with other semantics with the same
interpolation mode and they prefer forming shorter writemasks. However,
for some reason, these don't allow further semantics to share the same
register once allocated, except among themselves.
Default value initializers behave differently than regular initializers
for matrices on SM4 profiles.
While regular initializers assign the rhs elements in reading-order
(completing one row at the time), default initializers assing the rhs
elements in Chinese reading-order (completing one column at the time).
So after lowering a default value to a constant, the index of the
component to which this default value is stored is computed to meet
this expectation. This can be done because the default values.
For reference, compiling this shader:
row_major int2x3 m = {1, 2, 3, 4, 5, 6};
float4 main() : sv_target
{
return float4(m[0][0], 99, 99, 99);
}
gives the following buffer definition:
// cbuffer $Globals
// {
//
// row_major int2x3 m; // Offset: 0 Size: 28
// = 0x00000001 0x00000003 0x00000005 0x00000000
// 0x00000002 0x00000004 0x00000006
//
// }
Given that the matrix is column-major, m's default value is actually
{{1, 3, 5}, {2, 4, 6}}, unlike the {{1, 2, 3}, {4, 5, 6}} one would
expect in a regular initializer.
SM1 profiles assign the elements in regular reading order.
