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shaders/instancing/glsl/starfield.frag

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+#version 450
+/* Copyright (c) 2019-2024, Sascha Willems
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * Licensed under the Apache License, Version 2.0 the "License";
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+layout (location = 0) in vec3 inUVW;
+
+layout (location = 0) out vec4 outFragColor;
+
+#define HASHSCALE3 vec3(443.897, 441.423, 437.195)
+#define STARFREQUENCY 0.01
+
+// Hash function by Dave Hoskins (https://www.shadertoy.com/view/4djSRW)
+float hash33(vec3 p3)
+{
+	p3 = fract(p3 * HASHSCALE3);
+	p3 += dot(p3, p3.yxz+vec3(19.19));
+	return fract((p3.x + p3.y)*p3.z + (p3.x+p3.z)*p3.y + (p3.y+p3.z)*p3.x);
+}
+
+vec3 starField(vec3 pos)
+{
+	vec3 color = vec3(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 += vec3(starCol);
+	}	
+	return color;
+}
+
+void main() 
+{
+	outFragColor = vec4(starField(inUVW), 1.0);
+}