feat: add support for drawing velocity vectors

include/screen.hpp

@@ -51,8 +51,11 @@ struct Screen {
     ~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

@@ -53,6 +53,10 @@ 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();
@@ -178,7 +182,8 @@ main(int argc, char **argv) {
 	    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

@@ -57,6 +57,32 @@ 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};