Use atan2 for LIGH angle calculations

atan2 gives the actual angle (in the range -pi to pi). acos and asin just
give the principal value (in the range 0 to pi, or -pi/2 to pi/2)

2 files changed, 9 insertions, 7 deletions

diff --git a/src/elements/ligh.c b/src/elements/ligh.c
index a17954f..31f53b3 100644
--- a/src/elements/ligh.c
+++ b/src/elements/ligh.c
@@ -217,15 +217,19 @@ int update_LIGH(UPDATE_FUNC_ARGS)
 	{
 		int t=parts[near].type;
 		float n_angle; // angle to nearest part
+		float angle_diff;
 		rx=parts[near].x-x;
 		ry=parts[near].y-y;
-		if (rx*rx+ry*ry!=0)
-			n_angle = asin(-ry/sqrt(rx*rx+ry*ry));
+		if (rx!=0 || ry!=0)
+			n_angle = atan2f(-ry, rx);
 		else
 			n_angle = 0;
 		if (n_angle<0)
 			n_angle+=M_PI*2;
-		if (parts[i].life<5 || fabs(n_angle-parts[i].tmp*M_PI/180)<M_PI*0.8) // lightning strike
+		angle_diff = fabsf(n_angle-parts[i].tmp*M_PI/180);
+		if (angle_diff>M_PI)
+			angle_diff = M_PI*2 - angle_diff;
+		if (parts[i].life<5 || angle_diff<M_PI*0.8) // lightning strike
 		{
 			create_line_par(x, y, x+rx, y+ry, PT_LIGH, parts[i].temp, parts[i].life, parts[i].tmp-90, 0);
 
diff --git a/src/elements/sprk.c b/src/elements/sprk.c
index 11a12ad..4f95565 100644
--- a/src/elements/sprk.c
+++ b/src/elements/sprk.c
@@ -78,19 +78,17 @@ int update_SPRK(UPDATE_FUNC_ARGS) {
 					r = pmap[y+ry][x+rx];
 					if (r)
 						continue;
-					if (rand()%(parts[i].tmp*parts[i].tmp/20+6)==0)
+					if (parts[i].tmp>4 && rand()%(parts[i].tmp*parts[i].tmp/20+6)==0)
 					{
 						int p=create_part(-1, x+rx*2, y+ry*2, PT_LIGH);
 						if (p!=-1)
 						{
-							if(parts[i].tmp<=4) //Prevent Arithmetic errors with zero values
-								continue;
 							parts[p].life=rand()%(2+parts[i].tmp/15)+parts[i].tmp/7;
 							if (parts[i].life>60)
 								parts[i].life=60;
 							parts[p].temp=parts[p].life*parts[i].tmp/2.5;
 							parts[p].tmp2=1;
-							parts[p].tmp=acos(1.0*rx/sqrt(rx*rx+ry*ry))/M_PI*360;
+							parts[p].tmp=atan2(-ry, rx)/M_PI*360;
 							parts[i].temp-=parts[i].tmp*2+parts[i].temp/5; // slight self-cooling
 							if (fabs(pv[y/CELL][x/CELL])!=0.0f)
 							{