feat: add support for centering the screen around best/midpoint

Pressing 'c' will center the screen around the average position of the
particles. Pressing 'f' will center the screen on each frame.

Pressing 'b' will center the screen around the best found point.

include/screen.hpp

@@ -40,19 +40,23 @@ struct Screen {
     Symbol &at(int x, int y);
     Symbol &at(float x, float y);
 
-    void resize(std::size_t n);
     void resize(std::size_t x, std::size_t y);
 
+    void move_to(float x, float y);
+
     std::pair<float, float> screen_to_xy(int w, int h);
     std::pair<int, int> xy_to_screen(float x, float y);
 
-    Screen(std::size_t n) : buf(nullptr) { resize(n); }
-    Screen(std::size_t x, std::size_t y) : buf(nullptr) { resize(x, y); }
+    Screen(std::size_t x, std::size_t y) : buf(nullptr)
+    { resize(x, y); move_to(0, 0); }
     ~Screen() { delete[] buf; }
 
     std::vector<const vec<2>*> points;
+    std::vector<std::pair<const vec<2>*,const vec<2>*>> vecs;
     char_shader_t shader;
 
+    bool draw_vecs = true;
+
 private:
     Symbol *buf;
     Symbol _dummy;

include/swarm.hpp

@@ -132,6 +132,7 @@ struct Particle : public Agent<vec<N>> {
     }
 
     const vec<N> &get_position() const { return position; };
+    const vec<N> &get_velocity() const { return velocity; };
 
 private:
     A alg;

src/main.cpp

@@ -8,6 +8,7 @@ static constexpr int   kFPS = 60;
 static constexpr float kDT  = 1.0 / kFPS;
 
 float f(vec<2> x) {
+    // return std::pow(x.x, 2) + std::pow(x.y, 2);
     return  50 * (std::pow(std::sin((x.x - 10)/2),2) + std::pow(std::sin(x.y/2),2)) +
 	std::pow(std::abs(x.x - 3.141592653589), 1.2) + std::pow(std::abs(x.y), 1.2);
 }
@@ -53,6 +54,10 @@ main(int argc, char **argv) {
 
     for(const auto &p : swarm.get_particles()) {
 	scr.points.push_back(&p.get_position());
+	scr.vecs.push_back({
+		&p.get_position(),
+		&p.get_velocity(),
+	    });
     }
 
     enter_noncanonical_mode();
@@ -61,6 +66,7 @@ main(int argc, char **argv) {
 
     bool pause = false;
     bool frame_step = false;
+    bool auto_follow = false;
 
     // initialize colorizer scale/translate
     scr.draw();
@@ -75,6 +81,15 @@ main(int argc, char **argv) {
 	       255, 255, 255, x.x, x.y, y);
     };
 
+    auto center_screen = [&]() -> void {
+	vec<2> pos = 0;
+	for(const auto &p : swarm.get_particles()) {
+	    pos += p.get_position();
+	}
+	pos /= swarm.get_particles().size();
+	scr.move_to(pos.x, pos.y);
+    };
+
     // We draw to the screen at a rate of `kFPS', but step()ing the swarm at
     // this rate would be far too fast to be interesting to look at. On the
     // other hand, step()ing once a second is too slow.
@@ -98,6 +113,8 @@ main(int argc, char **argv) {
 	    printf("Current iteration: %d\nCurrent frame: %d\n", i * 4 / kFPS, i);
 	}
 
+	if(auto_follow) center_screen();
+
 	if(frame_step) {
 	    pause = true;
 	    frame_step = false;
@@ -174,11 +191,30 @@ main(int argc, char **argv) {
 	    update_and_draw();
 	    break;
 
+	case 'v':
+	    scr.draw_vecs = !scr.draw_vecs;
+	    break;
+
+	case 'b': {
+	    const auto [_, b] = swarm.best();
+	    scr.move_to(b.x, b.y);
+	    break;
+	}
+
+	case 'c':
+	    center_screen();
+	    break;
+
+	case 'f':
+	    auto_follow = !auto_follow;
+	    break;
+
 	case 'h':
 	    printf("  movement  zoom  coloring  pause step \n"
 		   "     W       io    IK LO     SPC   .,  \n"
 		   "    ASD                                \n"
-		   "                            quit:  q   \n");
+		   "   [%c] draw (v)elocities   quit:  q   \n",
+		   scr.draw_vecs ? 'x' : ' ');
 	    break;
 	}
 

src/screen.cpp

@@ -4,11 +4,6 @@
 
 /* Screen */
 
-void Screen::resize(std::size_t n) {
-    w = n; h = 1;
-    buf = (Symbol *)realloc(buf, n * sizeof(Symbol));
-}
-
 void Screen::resize(std::size_t x, std::size_t y) {
     w = x; h = y;
     buf = (Symbol *)realloc(buf, x * y * sizeof(Symbol));
@@ -41,6 +36,10 @@ std::pair<int, int> Screen::xy_to_screen(float x, float y) {
     };
 }
 
+void Screen::move_to(float x, float y) {
+    dx = x - w*sx/2;
+    dy = y - h*sy/2;
+}
 
 void Screen::clear() {
     static const Symbol s {' ', {0,0,0}};
@@ -57,6 +56,32 @@ void Screen::draw() {
 	}
     }
 
+    // draw lines for each velocity vector
+    if(draw_vecs) {
+	for(const auto &[start, vel] : vecs) {
+	    auto end = *start + (*vel) / 3;
+	    if(start->x == end.x) {
+		// TODO: draw horizontal/vertical lines
+		continue;
+	    }
+
+	    auto a = (end.y - start->y) / (end.x - start->x);
+	    auto b = start->y - a * start->x;
+
+	    for(int i = 0; i < w; ++i) {
+		const auto [x, _] = screen_to_xy(i, 0);
+		if(x < std::min(start->x, end.x)
+		   || x > std::max(start->x, end.x)) continue;
+
+		auto y = a*x + b;
+		at(x, y) = Symbol{
+		    .sym = '+',
+		    .color = { 0.75, 0, 0 },
+		};
+	    }
+	}
+    }
+
     // write out a '#' wherever we have a point registered
     for(const auto &p : points) {
 	at(p->x, p->y) = {.sym = '#', .color = 1};