add starfield rendering

assets/shader/starfield.fs

@@ -2,6 +2,59 @@
 
 out vec4 frag_color;
 
+uniform vec2 resolution;
+uniform vec2 inverse_resolution;
+uniform vec3 origin;
+uniform mat2 rotation;
+uniform float zoom;
+
+#define iterations 15
+#define volsteps 6
+#define sparsity 0.5f
+#define stepsize 0.3f
+#define frequency_variation 1.3f
+#define brightness 0.0018f
+#define distfading 0.68f
+
 void main() {
-	frag_color = vec4(1.f);
+	vec2 uv = gl_FragCoord.xy * inverse_resolution - 0.5f;
+	uv.y *= resolution.y * inverse_resolution.x;
+
+	vec3 direction = vec3(uv * zoom, 1.f);
+	direction.xy *= rotation;
+
+	float s = 0.1f;
+	float fade = 0.01f;
+	frag_color = vec4(0.f);
+
+	for (int r = 0; r < volsteps; ++r) {
+		vec3 p = origin + direction * (s * 0.5f);
+		p = abs(vec3(frequency_variation) - mod(p, vec3(frequency_variation * 2.f)));
+
+		float prevlen = 0.f;
+		float a = 0.f;
+		for (int i = 0; i < iterations; ++i) {
+			p = abs(p);
+			p = p * (1.f / dot(p, p)) + (-sparsity);
+			float len = length(p);
+			a += abs(len - prevlen);
+			prevlen = len;
+		}
+
+		a *= a * a;
+
+		frag_color.rgb += (vec3(s, s * s, s * s * s) * a * brightness + 1.f) * fade;
+		fade *= distfading;
+		s += stepsize;
+	}
+
+	frag_color.rgb = min(frag_color.rgb, vec3(1.2f));
+
+	float intensity = min(frag_color.r + frag_color.g + frag_color.b, 0.7f);
+
+	ivec2 sgn = (ivec2(gl_FragCoord.xy) & 1) * 2 - 1;
+	vec2 gradient = vec2(dFdx(intensity) * sgn.x, dFdy(intensity) * sgn.y);
+	float cutoff = max(max(gradient.x, gradient.y) - 0.1f, 0.f);
+	frag_color.rgb *= max(1.f - cutoff * 0.6f, 0.3f);
+	frag_color.a = 1.f;
 }

src/rendering/rendering_system.cpp

@@ -835,6 +835,19 @@ namespace gdw {
 
 	void rendering_system::render_starfield(float delta_time, camera_component& camera) {
 		const static auto model = glm::scale(glm::mat4(1.f), glm::vec3(500.f));
+		const static auto width = static_cast<float>(engine_.graphics_system().width());
+		const static auto height = static_cast<float>(engine_.graphics_system().height());
+
+		static auto origin = glm::vec3(width / 2.f, height / 2.f, -100.f);
+		origin.x += delta_time / 1000.f;
+
+		static auto alpha = 0.f;
+		alpha += delta_time / 100.f;
+		if (alpha >= 2.f * glm::pi<float>()) {
+			alpha = 0.f;
+		}
+		auto rotation = glm::mat2(glm::cos(alpha), -glm::sin(alpha), glm::sin(alpha), glm::cos(alpha));
+
 
 		composition_buffer_.bind();
 
@@ -847,6 +860,11 @@ namespace gdw {
 		starfield_program_.uniform("projection", false, camera.projection());
 		starfield_program_.uniform("view", false, camera.view());
 		starfield_program_.uniform("model", false, model);
+		starfield_program_.uniform("resolution", glm::vec2(width, height));
+		starfield_program_.uniform("inverse_resolution", 1.f / glm::vec2(width, height));
+		starfield_program_.uniform("origin", origin);
+		starfield_program_.uniform("rotation", false, rotation);
+		starfield_program_.uniform("zoom", 1.f);
 		starfield_->draw(starfield_program_);
 
 		glDisable(GL_CULL_FACE);