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vkd3d-shader/tpf: Don't pass 0x4 as mask for vec4 constant src registers.

Francisco Casas requested to merge fcasas/vkd3d:evan_bug into master

Evan Tang reported that new fixmes appeared on the shader_runner when running some of his tests after f50d0ae2.

vkd3d:652593:fixme:shader_sm4_read_src_param Unhandled mask 0x4.

The change to blame seems to be this added line in sm4_src_from_constant_value().

+    src->swizzle = VKD3D_SHADER_NO_SWIZZLE;

On tpf binaries the last 12 bytes of each src register in an instruction specify the swizzle, and there are 5 possible combinations:

Dimension NONE
-------- 00

Dimension SCALAR
-------- 01

Dimension VEC4, with a 4 bit writemask:
---- xxxx 00 01

Dimension VEC4, with an 8 bit swizzle:
xx xx xx xx 01 01

Dimension VEC4, with a 2bit scalar dimension number:
------ xx 10 01

So far, we have only seen src registers use 4 bit writemasks in a single case: for vec4 constants, and it is always zero.

So we expect this:

---- 0000 00 01

Now, I probably wanted to initialize src->swizzle to zero when writing constants, but VKD3D_SHADER_NO_SWIZZLE is not zero, it is actually the default swizzle:

11 10 01 00

And the last 4 bits (0x4) get written in the mask part, which causes the reader to complain.

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