Add slang shader for instancing sample

shaders/slang/instancing/starfield.slang

@@ -0,0 +1,50 @@
+/* Copyright (c) 2025, Sascha Willems
+ *
+ * SPDX-License-Identifier: MIT
+ *
+ */
+
+#define HASHSCALE3 float3(443.897, 441.423, 437.195)
+#define STARFREQUENCY 0.01
+
+// Hash function by Dave Hoskins (https://www.shadertoy.com/view/4djSRW)
+float hash33(float3 p3)
+{
+	p3 = frac(p3 * HASHSCALE3);
+	p3 += dot(p3, p3.yxz+float3(19.19, 19.19, 19.19));
+	return frac((p3.x + p3.y)*p3.z + (p3.x+p3.z)*p3.y + (p3.y+p3.z)*p3.x);
+}
+
+float3 starField(float3 pos)
+{
+	float3 color = float3(0.0, 0.0, 0.0);
+	float threshhold = (1.0 - STARFREQUENCY);
+	float rnd = hash33(pos);
+	if (rnd >= threshhold)
+	{
+		float starCol = pow((rnd - threshhold) / (1.0 - threshhold), 16.0);
+		color += starCol.xxx;
+	}
+	return color;
+}
+
+struct VSOutput
+{
+    float4 Pos : SV_POSITION;
+    float3 UVW;
+};
+
+[shader("vertex")]
+VSOutput vertexMain(uint VertexIndex: SV_VertexID)
+{
+    VSOutput output;
+    output.UVW = float3((VertexIndex << 1) & 2, VertexIndex & 2, VertexIndex & 2);
+    output.Pos = float4(output.UVW.xy * 2.0f - 1.0f, 0.0f, 1.0f);
+    return output;
+}
+
+[shader("fragment")]
+float4 fragmentMain(VSOutput input)
+{
+	return float4(starField(input.UVW), 1.0);
+}