Fix MaterialX compilation on M1 Macs

[JGamache-autodesk]

Fixes #2267 ?

Removes a global struct that was used to pass vertex data around.

This is an educated guess based on the GLSL compilation error message I received:

ERROR: 0:338: Missing initializer for const variable ‘g_mxVertexData’
ERROR: 0:1557: Use of undeclared identifier ‘g_mxVertexData’
ERROR: 0:1558: Use of undeclared identifier ‘g_mxVertexData’
ERROR: 0:1559: Use of undeclared identifier ‘g_mxVertexData’

[JGamache-autodesk]

Confirmed to work by @hodoulp on his M1 machine. Ready for review.

[JGamache-autodesk]

To be further replaced later so we get the familiar Nw( PIX_IN.Nw ) that can be observed in the shader main function if looking with APITrace.

[JGamache-autodesk]

These are captured in the shader main and passed as parameters, so they do not require the PIX_IN treatment.

[JGamache-autodesk]

Here is the final change in shader code so we see the result in a less abstract form:

--- /d/fragment1.glsl	2022-09-06 14:03:14.386810800 -0400
+++ /d/fragment2.glsl	2022-09-06 14:06:13.377655600 -0400
@@ -1,9 +1,3 @@
-struct
-{
-    vec3 Nw;
-    vec3 Pw;
-} g_mxVertexData;
-
 #define MAX_LIGHT_SOURCES 1
 
 struct BSDF { vec3 response; vec3 throughput; float thickness; float ior; };
@@ -1329,9 +1323,9 @@
     vec3 coat_affected_diffuse_color_out = pow(base_color, vec3(coat_gamma_out));
     surfaceshader shader_constructor_out = surfaceshader(vec3(0.0),vec3(0.0));
     {
-        vec3 N = normalize(g_mxVertexData.Nw);
-        vec3 V = normalize(u_viewPosition - g_mxVertexData.Pw);
-        vec3 P = g_mxVertexData.Pw;
+        vec3 N = normalize(Nw( PIX_IN.Nw ));
+        vec3 V = normalize(u_viewPosition - Pw( PIX_IN.Pw ));
+        vec3 P = Pw( PIX_IN.Pw );
 
         float surfaceOpacity = opacity_luminance_out.x;
 
@@ -1550,13 +1544,11 @@
     vec3 emission_color,
     vec3 opacity,
     bool thin_walled,
-    vec3 Nw,
-    vec3 Pw)
+    vec3 unused_normalWorld,
+    vec3 unused_positionWorld)
 {
-    g_mxVertexData.Nw = Nw;
-    g_mxVertexData.Pw = Pw;
-    vec3 geomprop_Nworld_out = normalize(g_mxVertexData.Nw);
-    vec3 geomprop_Pworld_out = g_mxVertexData.Pw;
+    vec3 geomprop_Nworld_out = normalize(Nw( PIX_IN.Nw ));
+    vec3 geomprop_Pworld_out = Pw( PIX_IN.Pw );
     vec3 Tw_reader_out = vec3(0.0);
     mx_arbitrarytangents_vector3(geomprop_Pworld_out, geomprop_Nworld_out, Tw_reader_out);
     surfaceshader SR_USD_Mtlx_VP2_Material_out = surfaceshader(vec3(0.0),vec3(0.0));

[vlasovi]

Looks good

[JGamache-autodesk]

Timeout glitch on preflight. Ready for merge.