Snow ADSR (bug 221)

This has the same ideas as the patch but is implemented slightly differently. Tweaks to various constants/timings welcome.

git-svn-id: http://supertux.lethargik.org/svn/supertux/trunk/supertux@6261 837edb03-e0f3-0310-88ca-d4d4e8b29345

diff --git a/src/object/particlesystem.cpp b/src/object/particlesystem.cpp
index 7684696..ae15ba0 100644 (file)
--- a/src/object/particlesystem.cpp
+++ b/src/object/particlesystem.cpp
@@ -66,7 +66,7 @@ void ParticleSystem::draw(DrawingContext& context)
     //if(pos.x > virtual_width) pos.x -= virtual_width;
     //if(pos.y > virtual_height) pos.y -= virtual_height;
 
-    context.draw_surface(particle->texture, pos, z_pos);
+    context.draw_surface(particle->texture, pos, particle->angle, Color(1.0f, 1.0f, 1.0f), Blend(), z_pos);
   }
 
   context.pop_transform();

diff --git a/src/object/particlesystem.hpp b/src/object/particlesystem.hpp
index 0e72620..78e3616 100644 (file)
--- a/src/object/particlesystem.hpp
+++ b/src/object/particlesystem.hpp
@@ -55,6 +55,7 @@ protected:
   public:
     Particle() :
       pos(),
+      angle(),
       texture()
     {}
    
@@ -62,6 +63,8 @@ protected:
     {}
 
     Vector pos;
+    // angle at which to draw particle
+    float angle;
     SurfacePtr texture;
 
   private:

diff --git a/src/object/snow_particle_system.cpp b/src/object/snow_particle_system.cpp
index cc02ffc..a0efa35 100644 (file)
--- a/src/object/snow_particle_system.cpp
+++ b/src/object/snow_particle_system.cpp
@@ -22,7 +22,22 @@
 #include "supertux/globals.hpp"
 #include "video/drawing_context.hpp"
 
-SnowParticleSystem::SnowParticleSystem()
+// TODO: tweak values
+namespace SNOW {
+static const float SPIN_SPEED = 60.0f;
+static const float WIND_SPEED = 30.0f; // max speed of wind will be randf(WIND_SPEED) * randf(STATE_LENGTH)
+static const float STATE_LENGTH = 5.0f;
+static const float DECAY_RATIO = 0.2f; // ratio of attack speed to decay speed
+static const float EPSILON = 0.5f; //velocity changes by up to this much each tick
+static const float WOBBLE_DECAY = 0.99f; //wobble decays exponentially by this much each tick
+static const float WOBBLE_FACTOR = 4 * .005f; //wobble approaches drift_speed by this much each tick
+}
+
+SnowParticleSystem::SnowParticleSystem() :
+  state(RELEASING),
+  timer(),
+  gust_onset(0),
+  gust_current_velocity(0)
 {
   snowimages[0] = Surface::create("images/objects/particles/snow2.png");
   snowimages[1] = Surface::create("images/objects/particles/snow1.png");
@@ -30,6 +45,8 @@ SnowParticleSystem::SnowParticleSystem()
 
   virtual_width = SCREEN_WIDTH * 2;
 
+  timer.start(.01);
+
   // create some random snowflakes
   size_t snowflakecount = size_t(virtual_width/10.0);
   for(size_t i=0; i<snowflakecount; ++i) {
@@ -39,13 +56,18 @@ SnowParticleSystem::SnowParticleSystem()
     particle->pos.x = systemRandom.randf(virtual_width);
     particle->pos.y = systemRandom.randf(SCREEN_HEIGHT);
     particle->anchorx = particle->pos.x + (systemRandom.randf(-0.5, 0.5) * 16);
+    // drift will change with wind gusts
     particle->drift_speed = systemRandom.randf(-0.5, 0.5) * 0.3;
     particle->wobble = 0.0;
 
     particle->texture = snowimages[snowsize];
+    particle->flake_size = powf(snowsize+3,4); // since it ranges from 0 to 2
 
-    particle->speed = 1 + (2 - snowsize)/2 + systemRandom.randf(1.8);
-    particle->speed *= 20; // gravity
+    particle->speed = 2 * (1 + (2 - snowsize)/2 + systemRandom.randf(1.8)) * 10; // gravity
+
+    // Spinning
+    particle->angle = systemRandom.randf(360.0);
+    particle->spin_speed = systemRandom.randf(-SNOW::SPIN_SPEED,SNOW::SPIN_SPEED);
 
     particles.push_back(particle);
   }
@@ -63,19 +85,60 @@ SnowParticleSystem::~SnowParticleSystem()
 
 void SnowParticleSystem::update(float elapsed_time)
 {
+  // Simple ADSR wind gusts
+
+  if (timer.check()) {
+    // Change state
+    state = (State) ((state + 1) % MAX_STATE);
+
+    if(state == RESTING) {
+      // stop wind
+      gust_current_velocity = 0;
+      // new wind strength
+      gust_onset   = systemRandom.randf(-SNOW::WIND_SPEED, SNOW::WIND_SPEED);
+    }
+    timer.start(systemRandom.randf(SNOW::STATE_LENGTH));
+  }
+
+  // Update velocities
+  switch(state) {
+    case ATTACKING:
+      gust_current_velocity += gust_onset * elapsed_time;
+      break;
+    case DECAYING:
+      gust_current_velocity -= gust_onset * elapsed_time * SNOW::DECAY_RATIO;
+      break;
+    case RELEASING:
+      // uses current time/velocity instead of constants
+      gust_current_velocity -= gust_current_velocity * elapsed_time / timer.get_timeleft();
+      break;
+    case SUSTAINING:
+    case RESTING:
+      //do nothing
+      break;
+    default:
+      assert(false);
+  }
+
   std::vector<Particle*>::iterator i;
 
   for(i = particles.begin(); i != particles.end(); ++i) {
     SnowParticle* particle = (SnowParticle*) *i;
     float anchor_delta;
 
+    // Falling
     particle->pos.y += particle->speed * elapsed_time;
-    particle->pos.x += particle->wobble * elapsed_time /* * particle->speed * 0.125*/;
-
-    anchor_delta = (particle->anchorx - particle->pos.x);
-    particle->wobble += (4 * anchor_delta * 0.05) + systemRandom.randf(-0.5, 0.5);
-    particle->wobble *= 0.99f;
+    // Drifting (speed approaches wind at a rate dependent on flake size)
+    particle->drift_speed += (gust_current_velocity - particle->drift_speed) / particle->flake_size + systemRandom.randf(-SNOW::EPSILON,SNOW::EPSILON);
     particle->anchorx += particle->drift_speed * elapsed_time;
+    // Wobbling (particle approaches anchorx)
+    particle->pos.x += particle->wobble * elapsed_time;
+    anchor_delta = (particle->anchorx - particle->pos.x);
+    particle->wobble += (SNOW::WOBBLE_FACTOR * anchor_delta) + systemRandom.randf(-SNOW::EPSILON, SNOW::EPSILON);
+    particle->wobble *= SNOW::WOBBLE_DECAY;
+    // Spinning
+    particle->angle += particle->spin_speed * elapsed_time;
+    particle->angle = fmodf(particle->angle, 360.0);
   }
 }
 

diff --git a/src/object/snow_particle_system.hpp b/src/object/snow_particle_system.hpp
index f66e923..682eb48 100644 (file)
--- a/src/object/snow_particle_system.hpp
+++ b/src/object/snow_particle_system.hpp
@@ -18,6 +18,7 @@
 #define HEADER_SUPERTUX_OBJECT_SNOW_PARTICLE_SYSTEM_HPP
 
 #include "object/particlesystem.hpp"
+#include "supertux/timer.hpp"
 
 class SnowParticleSystem : public ParticleSystem
 {
@@ -41,14 +42,44 @@ private:
     float anchorx;
     float drift_speed;
 
+    // Turning speed
+    float spin_speed;
+
+    // for inertia
+    unsigned int flake_size;
+
     SnowParticle() :
       speed(),
       wobble(),
       anchorx(),
-      drift_speed()
+      drift_speed(),
+      spin_speed(),
+      flake_size()
     {}
   };
 
+  // Wind is simulated in discrete "gusts"
+
+  // Gust state
+  enum State {
+    ATTACKING,
+    DECAYING,
+    SUSTAINING,
+    RELEASING,
+    RESTING,
+    MAX_STATE
+  };
+  State state;
+
+
+  // Gust state delay timer
+  Timer timer;
+
+  // Peak magnitude of gust is gust_onset * randf(5)
+  float gust_onset,
+  // Current blowing velocity of gust
+        gust_current_velocity;
+
   SurfacePtr snowimages[3];
 
 private: