adding

Author: mpinner

src/particle_trail.h

@@ -0,0 +1,54 @@
+// Simple particle system example for C++.
+
+#pragma once
+
+#include <math.h>
+#include "lib/color.h"
+#include "lib/effect.h"
+#include "lib/particle.h"
+
+class ParticleTrailEffect : public ParticleEffect
+{
+public:
+    ParticleTrailEffect()
+        : angle1(0), angle2(0), baseHue(0)
+    {}
+
+    float angle1;
+    float angle2;
+    float baseHue;
+
+    virtual void beginFrame(const FrameInfo &f)
+    {
+        const float tailLength = 8.0f;
+        const float speed = 9.0f;
+        const float lfoRatio = 0.15f;
+        const float hueRate = 0.01f;
+        const float brightness = 40.0f;
+        const unsigned numParticles = 200;
+
+        // Low frequency oscillators
+        angle1 = fmodf(angle1 + f.timeDelta * speed, 2 * M_PI);
+        angle2 = fmodf(angle2 + f.timeDelta * speed * lfoRatio, 2 * M_PI);
+        baseHue = fmodf(baseHue + f.timeDelta * speed * hueRate, 1.0f);
+
+        appearance.resize(numParticles);
+        for (unsigned i = 0; i < numParticles; i++) {
+            float s = float(i) / numParticles;
+            float tail = s * tailLength;
+
+            float radius = 0.2 + 1.5 * s;
+            float x = radius * cos(angle1 + tail);
+            float y = radius * sin(angle1 + tail + 10.0 * sin(angle2 + tail * lfoRatio));
+            float hue = baseHue + s * 0.4;
+
+            ParticleAppearance& p = appearance[i];
+            p.point = Vec3(x, 0, y);
+            p.intensity = (brightness / numParticles) * s;
+            p.radius = 0.1 + 0.4f * s;
+            hsv2rgb(p.color, hue, 0.5, 0.8);
+        }
+
+        ParticleEffect::beginFrame(f);
+    }
+};