#Greenfoot draw line code#

#Greenfoot draw line code#

Our code for moving at an angle is:ĭouble radians = Math.toRadians(getRotation()) ĭouble moveX = (int)(s(radians) * moveSpeed) ĭouble moveY = (int)(Math.sin(radians) * moveSpeed) For this, we use Java’s standard maths libraries. That’s the calculation for our specific example, but we need to put it in our code. You can always sanity check those figures using good old pythagoras: it should be the case that (or near enough, given that we’ve rounded). You can bang that into your calculator right now (being wary of degrees vs radians), to get moveX=4.70 (to 2dp) and moveY=1.71 (to 2dp). The tiniest bit of re-arrangement in each equation gives: The cosine equation is similar, but rather than opposite divided by hypotenuse, it’s adjacent divided by hypotenuse, which in our setting is: We can adapt the equation from wikipedia to our setting: We want to know the length of the adjacent side (the horizontal line, labelled moveX) and the opposite side (the vertical line, labelled moveY). We can see that the hypotenuse is 5, and alpha is 20 degrees. Of the other two sides, the adjacent is the one that is adjacent to the angle you’re interested in (labelled with the greek letter alpha,, above), and the opposite is the one opposite the angle you’re interested in. The hypotenuse is always the side that is opposite the right-angle: in all our diagrams, this is the slanted diagonal line between the two points we’re interested in. Here is the relevant sidebox from the current wikipedia article:Ī few notes. Nowadays you can google it, or just go straight to wikipedia (score one for computing!). This is key for much of the use of trigonometry in games and simulations.īack in maths class, you might have tried to memorise which sides sine and cosine refer to, using an acronym for the letter jumble SOHCAHTOA. No matter which two points you are interested in on an X-Y grid system, you can always form a right-angled triangle by drawing connecting lines parallel to the X and Y axes. Sine and cosine are functions that take an angle, and give back a ratio between two sides of the corresponding right-angle triangle. What we need to know are the amounts to move: moveX and moveY.Ĭalculating the X and Y distances when moving at an angle is where sine and cosine come in useful. We know the angle (20 degrees in this example) and the distance in a straight line (5, our movement speed). (NB: one thing computing does much better than mathematics is use meaningful variable names, and we will do the same.) So we have a starting position for the spaceship labelled (oldX, oldY) in the bottom left, and a position we want to move to, which will be (oldX + moveX, oldY + moveY). First, let’s draw a little diagram of our problem: This problem is a common application of sine and cosine (which fall under the umbrella of trigonometry). See this note.) But what if the spaceship is pointing at a diagonal angle somewhere between right and upwards, let’s say 20 degrees from horizontal. (Remember that while in maths, positive values on the Y-axis are upwards, in computing they are generally downwards. Similarly, if the spaceship is pointing upwards, the code is simple: setLocation(getX(), getY() - 5) In Greenfoot, this is: setLocation(getX() + 5, getY()) You just move 5 units to the right, which means adding 5 to its X coordinate. If it’s pointing exactly to the right, that’s really easy to implement. Let’s say that the spaceship has a fixed speed of 5 units per frame. Positions on the screen in a 2D system use X and Y coordinates, so any movement on the screen is simply an alteration of the X and/or Y coordinates. Imagine you have a game where you control a spaceship in 2D, flying it around the screen. This post is about moving at a given angle, or: what use are sine and cosine anyway?