Convert vector to angle?
OneSadCookie Wrote:On a modern processor, a sin/cos lookup table with any accuracy is almost certainly more expensive than just calculating the sin or cosine directly.
Cache coherency?
Scott Lembcke  Howling Moon Software
Author of Chipmunk Physics  A fast and simple rigid body physics library in C.
Nevada Wrote:Whoa there. Why are we squaring everything? The square of a ratio is not identical to the ratio itself. I realize we're trying to avoid the overhead of the expensive sqrt call, but if you square the ratio, you'll have to take the square root anyway. Hog had it right...
Oh yeah. Sin, cos, and atan2 are all very expensive (performancewise) function calls and are very prone to rounding errors. So if we can avoid all that with one call to sqrt, the routine should perform better.
correct a/b is not equal to (a*a)/(b*b)... but no one said it was.
Sir, e^iÏ€ + 1 = 0, hence God exists; reply!
Skorche Wrote:Cache coherency?
Memory access latency (if your lookup isn't in L1 you're going to pay as much in stall cycles as you would in just calculating the thing).
Possibly particularly true on x86 where there is an fsincos instruction that can be used.
unknown Wrote:Code:
#define SPRITE_SPEED2 SPRITE_SPEED*SPRITE_SPEED
...
vector.x = new_world_dst.x  player.x;
vector.y = new_world_dst.y  player.y;
float sqd = vector.x * vector.x + vector.y * vector.y;
if(sqd > 0.00001f) {
float scale = SPRITE_SPEED2/sqd;
position.x += vector.x*vector.x*scale;
position.y += vector.y*vector.y*scale;
}
Correct me if I'm wrong, but it seems this translates to:
x = x + (dx*dx)*(speed*speed)/(dx*dx+dy*dy) = x + [dx*speed/sqrt(dx^2 + dy^2)]^2
It should simply be:
x = x + dx*speed/sqrt(dx^2 + dy^2)
Unfortunately, the former wouldn't work even if you added it to x^2 instead, because of it's inherent nonlinearity.
I think he was joking due to the incorrectness of the previous post.
No it wasn't a joke but it mistake.
Sir, e^iÏ€ + 1 = 0, hence God exists; reply!
Possibly Related Threads...
Thread:  Author  Replies:  Views:  Last Post  
Formula for converting angle to vector?  komirad  2  10,639 
Jul 29, 2011 07:29 AM Last Post: ThemsAllTook 

Question Regarding the Reflect Angle of a Transition  iBaby  3  3,738 
Apr 27, 2010 03:15 PM Last Post: JustinFic 

ending location from angle and speed  Kazooless  5  4,762 
Apr 3, 2009 02:40 PM Last Post: Gillissie 

Angle between two points?  Graphic Ace  6  5,703 
Nov 8, 2008 12:11 PM Last Post: macnib 

calculating X and Y coordinates w/ an angle and distance  ferum  13  15,772 
Jun 25, 2008 10:53 PM Last Post: rosenth 