## Thrusting in different directions

When you press the control key, the player’s ship will accelerate in whatever direction (0-23) it is facing. To make this possible, I pre-populated a couple of float arrays with values x and y for thrust in any of the 24 directions.

This function populate the two arrays. These are declared as

``````float thrustx[24];
float thrusty[24];

void InitThrustAngles() {
const float pi = 3.14159265f;
const float degreeToRad = pi / 180.0f;
float degree = 0.0f;
for (int i = 0; i<24; i++) {
degree += 15;
}
}``````

It uses trigonometry to calculate the horizontal and vertical amounts for any of the angles 0,15,30..345 degrees. As sin and cos functions work in radians rather than degrees, the variable radianValue is calculated from the degree angle by multiplying by the value degreesToRad. If you remember your school trigonometry, one radian = 180/pi degrees. So the code divides by this value (or multiplies by its inverse in this case).

Then when you press the control key, it just adds the appropriate thrustx and thrusty value to the vx and vy variables. Simple and fast.

## How to find files in Ubuntu

In this I’m looking for the SDL2 header files. These are installed when you install libsdl2-dev as we saw yesterday.

While you can do it from a terminal with the find command, I find it easier to do it from the GUI. We need the Files utility which you get by clicking on this icon on the left toolbar. Now click Other Locations on the left and you should see something like this.

Click Computer. This will let you search through the entire Linux file tree.

Click on the magnifying glass icon and in the text box that appears type in sdl2 and press enter. It will spend a few seconds or minutes searching and then find a number of files/folders.

The first result was SDL2 and the usr/include is a big clue. Double-click on this and it will open on a folder full of header files!That’s what we want.

When you are configuring gcc/clang and want to add paths for include files like SDL2, it’s important to know where those files are located.