[PATCH 0/1] MR140: vkd3d-shader/hlsl: Handle SV_IsFrontFace semantic.

[PATCH 1/1] vkd3d-shader/hlsl: Handle SV_IsFrontFace semantic.

[Nikolay Sivov]

From: Nikolay Sivov

---
 libs/vkd3d-shader/hlsl_sm4.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/libs/vkd3d-shader/hlsl_sm4.c b/libs/vkd3d-shader/hlsl_sm4.c
index f81be3e9..3fa18c53 100644
--- a/libs/vkd3d-shader/hlsl_sm4.c
+++ b/libs/vkd3d-shader/hlsl_sm4.c
@@ -115,6 +115,7 @@ bool hlsl_sm4_usage_from_semantic(struct hlsl_ctx *ctx, const struct hlsl_semant

{"position",                    false, VKD3D_SHADER_TYPE_PIXEL,     D3D_NAME_POSITION},
         {"sv_position",                 false, VKD3D_SHADER_TYPE_PIXEL,     D3D_NAME_POSITION},
+        {"sv_isfrontface",              false, VKD3D_SHADER_TYPE_PIXEL,     D3D_NAME_IS_FRONT_FACE},

{"color",                       true,  VKD3D_SHADER_TYPE_PIXEL,     D3D_NAME_TARGET},
         {"depth",                       true,  VKD3D_SHADER_TYPE_PIXEL,     D3D_NAME_DEPTH},

[Zebediah Figura (＠zfigura)]

This should be simple to test; we already have support in the shader runner for manual vertex buffers.

[Nikolay Sivov (＠nsivov)]

I think I found an example in hlsl-struct-semantics.shader_test of what you're talking about regarding manually filled vertex buffers. I couldn't make it work for purposes of this semantic, because I don't fully understand how it works. I did try to specify 3 vertices, and use draw triangle strip 3. With SV_IsFrontFace I was going to switch between returned target colors. Flipping vertices order did not make any difference in shader output. I'm sure I screwed up something.

Is there a good tutorial for this front face flag?

For the patch itself, I'm sure having a test would be better and I'm going to look at adding one, but the change is very straightforward and generates what it should, according to disassembly.

[Zebediah Figura (＠zfigura)]

> I think I found an example in hlsl-struct-semantics.shader_test of what you're talking about regarding manually filled vertex buffers. I couldn't make it work for purposes of this semantic, because I don't fully understand how it works. I did try to specify 3 vertices, and use draw triangle strip 3. With SV_IsFrontFace I was going to switch between returned target colors. Flipping vertices order did not make any difference in shader output. I'm sure I screwed up something.

Changing the vertex order doesn't change anything at all?

I do realize now that the shader runners all have default (i.e. back face) culling, so it won't render anything at all if the triangle is back-facing. We can probably just disable culling unconditionally.

That doesn't explain why you're getting the same face by changing the order, though.

[Nikolay Sivov (＠nsivov)]

Test shader I used returned different color depending on this flag. Changing order gave me zeroes I believe, that shader never returns. I'll need to try again.