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hpl2:tutorials:script:disable_gravity_tutorial

Beginner Scripting Tutorial 1

This is an easy tutorial for beginners. It is not intended to teach you new techniques but more to show you all the neat stuff you can do with the functions and the HPL2 engine.

In this tutorial you will learn how to make entities 'float' or rather make them seem to be very very light. Possible uses could be for some strange sanity effects or even simulating an underwater environment!

Getting started

Start by creating a new level in the level editor and then saving the map. There are no real limits, but keep it simple and include some movable entities you can use the script on. In my little room they are the skull and two books. You should include another entity you do not use the effect on, so you can compare their characteristics!

My room looks like this:

Link

After you have saved your map, create a .hps file with the same name. This is where we will do all the scripting, add the default script there. I have removed the if-clause in my example, it is not needed.

////////////////////////////
// Run first time starting map
void OnStart()
{   
   GiveItemFromFile("lantern", "lantern.ent");
 
   for(int i=0;i< 10;i++) GiveItemFromFile("tinderbox_"+i, "tinderbox.ent");    
}
 
////////////////////////////
// Run when entering map
void OnEnter()
{
 
}
 
////////////////////////////
// Run when leaving map
void OnLeave()
{
 
}

The scripting

Now we will do the actual scripting! The floating effect is based on timer functions, and one of these we will add in OnStart() so it is immediately called when the level loads! The syntax for timer function looks like this:

//Function syntax: Func(string &in asTimer)
void  AddTimer(string& asName, float afTime, string& asFunction);

The first string asName is the name of our timer, afTime is the time when the timer will call the function in asFunction after the timer is executed. Adding our timer in OnStart() will make our code look like this:

////////////////////////////
// Run first time starting map
void OnStart()
{
    GiveItemFromFile("lantern", "lantern.ent");
    for(int i=0;i< 10;i++) GiveItemFromFile("tinderbox_"+i, "tinderbox.ent");  
 
    AddTimer("FloatTime", 0.01, "FloatObjects");
}

As you can see, FloatTime is the name of our timer which calls the function FloatObjects after a very short time, exactly 0.01 seconds. The purpose of this will be explained after we created FloatObjects!

For actually making the objects float, we will add this function in FloatObjects:

AddPropImpulse(string& asName, float afX, float afY, float afZ, string& asCoordSystem);

AddPropImpulse gives a specified entity an impulse, which means pushing it in a certain way with certain force. asName is the name of the entitity, The floats afX, afY and afZ are the direction coordinates the push has to follow and asCoordSystem specifies the coordinate system the game refers to. You can leave it empty, but valid strings would be “World” for using the XYZ planes you can see in the editor or “local” if it should use the XYZ axis of the object you are adressing.
AddPropImpulse has to be created for every object you want to float, which makes three of them in my case! The last thing we add in FloatObjects is a timer function that practically calls itself so we can create a loop that will continually execute FloatObjects and give our entities a little push every 0.01 seconds! Our function should look like this:

void FloatObjects(string &in asTimer)
{
    AddPropImpulse("human_skull_1", 0, 0.15, 0, "");
    AddPropImpulse("book01_1", 0, 0.15, 0, "");
    AddPropImpulse("book01_2", 0, 0.15, 0, "");
    AddTimer("FloatTime", 0.01, "FloatObjects");
}

So now I have added an impulse for every object I want to float (the skull and the two books) and a timer that calls itself, repeating FloatObjects over and over.

You may have noticed that I have only put in a value for the afY float. That means the impulse only goes in the Y direction or UP! 0.15 is a very weak impulse, but it is applied every 0.01 seconds so all the little pushes ca not be noticed by the player which creates the effect of the objects floating or falling very slowly. You can now save the .hps file and load your level. Have fun and thanks for reading!

Additional information

Here you can put the little things you have noticed while playing around and testing my script. Stuff I have already found out:

  • Different entities need different afY values! For small objects like books 0.15 is enough, but everything bigger than 2 will make them float upwards like a helium balloon.
  • Play around with afTime! Bigger values like 0.5 combined with larger impulses like 5 can create some crazy bouncing effect!
hpl2/tutorials/script/disable_gravity_tutorial.txt · Last modified: 2011/02/15 21:17 by l1ght5h0w