Add slang shaders for additional samples

shaders/slang/pbrtexture/irradiancecube.slang

@@ -0,0 +1,39 @@
+/* Copyright (c) 2025, Sascha Willems
+ *
+ * SPDX-License-Identifier: MIT
+ *
+ */
+
+SamplerCube samplerEnv;
+
+struct PushConsts {
+	[[vk::offset(64)]] float deltaPhi;
+	[[vk::offset(68)]] float deltaTheta;
+};
+[[vk::push_constant]] PushConsts consts;
+
+#define PI 3.1415926535897932384626433832795
+
+[shader("fragment")]
+float4 fragmentMain(float3 inPos)
+{
+    float3 N = normalize(inPos.xyz);
+	float3 up = float3(0.0, 1.0, 0.0);
+	float3 right = normalize(cross(up, N));
+	up = cross(N, right);
+
+	const float TWO_PI = PI * 2.0;
+	const float HALF_PI = PI * 0.5;
+
+	float3 color = float3(0.0, 0.0, 0.0);
+	uint sampleCount = 0u;
+	for (float phi = 0.0; phi < TWO_PI; phi += consts.deltaPhi) {
+		for (float theta = 0.0; theta < HALF_PI; theta += consts.deltaTheta) {
+			float3 tempVec = cos(phi) * right + sin(phi) * up;
+			float3 sampleVector = cos(theta) * N + sin(theta) * tempVec;
+			color += samplerEnv.Sample(sampleVector).rgb * cos(theta) * sin(theta);
+			sampleCount++;
+		}
+	}
+	return float4(PI * color / float(sampleCount), 1.0);
+}