Starting from this site: http://www.petercollingridge.co.uk/book/export/html/6

I get to the part where he defines:

def move(self): self.x += math.sin(self.angle) * self.speed self.y -= math.cos(self.angle) * self.speed

I am working on my own little project at the same time and my issue is finding a way to make a circle of enemies close in on the player at their fixed angles. (Like in the first level of Axley for snes!)

On my way home from the library my idea was that the x1-x2/y1-y2 would give a ratio, and then I can subtract a fixed amount from I guess x, and then multiply y by the ratio so that x and y keep the same ratio which should mean the same angle.

However, I want to get this trig stuff cause I feel it will keep being important and in my face. So I wiki’d it and found, „And for a given angle, cos and sin give the respective x, y coordinates on a unit circle.“

Then I wiki’d „unit circle“ and found out that it is like a circle generalized to a radius of one and the angle is at the 0,0 in Cartesian format so the middle of an x,y axis. So sine(self.angle) gives the x value out of a radius of 1, and cos(self.angle) the same, for a given angle. This means that the self.x and self.y that result will be…I can’t think of the word but it’s like generalized lol. It’s that it’s based on a standardized value and has nothing to do with the size of your grid or screen or anything. It’s x and y values based on a unit circle with radius 1.

This might help. So the max y value is 1, the min y value is also 1. Any other values are somewhere in between including the values calculated in our example.

ok, so self.angle is in radians. So with a fixed angle being initialized, the x and y values, will also be fixed as generalized x and y values. Then incrementing by the sin(self.angle) and cos(self.angle) will result in movement along the fixed angle (self.angle) because incrementing the x and y based on their ratio to a fixed angle maintains that angle.

self.angle = math.pi/2

Make the angle pi/2 = 90 degrees , and you will have a (y) value of zero because 90 degrees is completely horizontal. Oh, and hear I based on how the angle is drawn here startingat the y line and going down. From there 90 degrees is hitting the x line and 180 is hitting the y line at the bottom.

The picture above this one has 90 degrees as the y line which is different I guess.