fix: applied a workaround to fix a Microsoft HLSL compiler issue

close #131
https://fogbugz.unity3d.com/default.asp?934464_sjh4cs4ok77ne0cj&_ga=2.124069071.432066521.1640792064-45545210.1640792064

Shaders/SoftMask.cginc

@@ -7,6 +7,11 @@ float4x4 _GameVP;
 float4x4 _GameTVP;
 half4 _MaskInteraction;
 
+float CustomStep(float a, float x)
+{
+	return x >= a;
+}
+
 fixed Approximately(float4x4 a, float4x4 b)
 {
 	float4x4 d = abs(a - b);
@@ -30,16 +35,16 @@ float SoftMaskInternal(float4 clipPos)
 		float4 cpos = mul(_GameTVP, mul(UNITY_MATRIX_M, wpos));
 		view = lerp(view, cpos.xy / cpos.w * 0.5 + 0.5, isSceneView);
 		#if UNITY_UV_STARTS_AT_TOP
-			view.y = lerp(view.y, 1 - view.y, step(0, _ProjectionParams.x));
+			view.y = lerp(view.y, 1 - view.y, CustomStep(0, _ProjectionParams.x));
 		#endif
 	#elif UNITY_UV_STARTS_AT_TOP
-		view.y = lerp(view.y, 1 - view.y, step(0, _ProjectionParams.x));
+		view.y = lerp(view.y, 1 - view.y, CustomStep(0, _ProjectionParams.x));
 	#endif
 
 	fixed4 mask = tex2D(_SoftMaskTex, view);
 	half4 alpha = saturate(lerp(fixed4(1, 1, 1, 1), lerp(mask, 1 - mask, _MaskInteraction - 1), _MaskInteraction));
 	#if SOFTMASK_EDITOR
-	alpha *= step(0, view.x) * step(view.x, 1) * step(0, view.y) * step(view.y, 1);
+	alpha *= CustomStep(0, view.x) * CustomStep(view.x, 1) * CustomStep(0, view.y) * CustomStep(view.y, 1);
 	#endif
 
 	return alpha.x * alpha.y * alpha.z * alpha.w;
@@ -53,4 +58,4 @@ float SoftMaskInternal(float4 clipPos)
 	#define SoftMask(clipPos, worldPosition) SoftMaskInternal(clipPos)
 #endif
 
-#endif // UI_SOFTMASK_INCLUDED
+#endif // UI_SOFTMASK_INCLUDED