Waypoint generator between 2 points on 2d map - c++

Question

I'm now trying to generate straight sync points on my 2D map path.
In other words I want to spilt distance between point A on map for example X : 301 Y : 679 to point B X : 360 Y : 630, every 8 unit of distance is passed.
Every 8 distance unit calculated by sqrt(pow(a_x - b_x, 2), pow(a_y - b_y, 2)). I want to obtain next coordinates on map, like by a a_x + distance and b_y + distance.
I tried to do it but it didn't work, x axis doesnt change propertly.
Here is my code :
float base_x = active->getX();
float base_y = active->getY();
float destx = incoming_packet.get()->getFloat(4);
float desty = incoming_packet.get()->getFloat(8);
float distance = active->distance(destx, desty); // calculated by sqrt(pow(curent character x pos - destx, 2), pow(current character y pos - desty, 2))
float delta_X = active->vDistance(base_x, destx); // calculated by sqrt(pow(base_x - destx, 2))
float delta_Y = active->vDistance(base_y, desty); // calculated by sqrt(pow(base_y - desty, 2))
float cosa = delta_X / distance;
float sina = delta_Y / distance;
int mapx = 1;
int mapy = 1;
if(distance > 8)///active sync
{
for(float dist = 8; dist < distance;dist+=8)
{
base_x += mapx * (cosa * 8);
base_y += mapy * (sina * 8);
BOOST_LOG_TRIVIAL(debug) << "[ACTIVESYNC]NEXT SYNC ACK X : " << base_x << " Y : " << base_y;
}
}
What I'm doing here wrong ?

Answer 1

"cosa" (and cosb) are apparently dimensionless. (i.e. meters / meters)
"mapx" (and "mapy") are also dimensionless.
Note that in your for loop, base_x, base_y describe a point on the map.
And the 2 interesting computations in that loop
base_x += mapx * (cosa * 8);
base_y += mapy * (sina * 8);
become meaningless by attempting to add dimensionless numbers to a point. It might be ok to multiply by dimensionless numbers, but it is unreasonable to add dimensionless numbers to map points.
I suggest cosa and cosb be changed to represent the distance (i.e. meters) for each step.
float cosa = delta_X / 8; // size of steps in x direction
float sina = delta_Y / 8; // size of steps in y direction
Now the for loop can add 8 steps of cosa and sina appropriately to describe the path way points, and cosa and sina both have appropriate dimensions for the next computation.
The for loop can simplify to :
for(int step = 0; step < 8; step += 1)
{
base_x += (mapx * cosa);
base_y += (mapy * sina);
// remove or adapt the following
std::cout << std::setw(10) << std::left << (step+1) << std::setw(10)
<< base_x << std::setw(10) << base_y << std::endl;
// you were using:
//BOOST_LOG_TRIVIAL(debug) << "[ACTIVESYNC]NEXT SYNC ACK X : "
// << base_x << " Y : " << base_y;
}
My dummy code outputs:
base x/y 301 679
dest x/y 360 630
delta x/y 59 -49
step_x = 7.375
step_y = -6.125
step base_x base_y
0 301 679
1 308.375 672.875
2 315.75 666.75
3 323.125 660.625
4 330.5 654.5
5 337.875 648.375
6 345.25 642.25
7 352.625 636.125
8 360 630
Do these way points look more what you are looking for?