When creating games, you will often want to animate your sprites.  In KPL, to animate sprites, you use the ‘MoveSpriteToPoint’ command, which we looked at earlier in conjunction with an iteration loop.

To make it look at though a sprite is moving smoothly across the screen, we actually move the sprite by a few co-ordinates, stop the program for a few milliseconds and then move the sprite again.  By doing this at a rate of approximately 30hz (30 movements every second), the brain thinks the sprite is moving smoothly.

Setup a for loop, using the variable ‘Count’ with initial value 0 and final value 400.
Inside the loop, move the a preloaded sprite to co-ordinate (Count, Count) and set a delay of 5ms. Eg

Define Count As Int
LoadSprite("SpaceShip", "UFO.gif")
ShowSprite("SpaceShip")
For Count = 1 To 400
            MoveSpriteToPoint("SpaceShip", Count, Count)
            Delay(5)
Next

Now, when you run your program, a UFO will move diagonally down the screen!  By using iteration and moving the sprite so that a co-ordinate is the iterated variable, we have got our sprite to move.  The same could be down with a while loop.

By changing the delay, we can change the speed.  By changing the parameter of the for loop, we can change the starting and ending positions.

Exercises

• Make a sprite ‘fly’ horizontally across the screen
• Make a sprite ‘fall’ straight down the screen, with x co-ordinate 200.

Some sprites in KPL are made in ‘Graphics Interchange Format’ (GIF).  This means they are made up of more than one picture.  For example, in KPL, go to the list of sprites and double click on missile1.gif.  You will see that it says ‘Frame 1 of 6’

This means it has 6 ‘frames’ which make up the picture.  If you scroll the bar along, you will see the different frames and notice that the missile appears to be spinning.

KPL has a built in procedure which will make a sprite repeatedly cycle through all the different frames.  First, you need to make a mental note of how many frames there are on this screen.  Next, go into your code and use the following code, replacing ‘NumberOfFrames’ with the relevant number:

Define Count As Int
Define Timeline As Int[NumberOfFrames]
LoadSprite("MainSprite", "UFO.gif")
MoveSpriteToPoint("MainSprite", 20, 200)
ShowSprite("MainSprite")
For Count = 1 To NumberOfFrames
            Timeline[Count] = 100
Next

SetSpriteAnimationTimeline("MainSprite", True, Timeline)
In this example, we have loaded a sprite, along with a variable of type Int[6] (the square brackets are important!).  We have then set the time which each frame should be displayed for to 100.  We used a for loop in the above code, because it is easier than copying and pasting code.  For example, if we had used Earth.gif, which has 15 frames, we would have to copy and paste 15 times, which is silly.

Remember that the sprite will only animate whilst the program is running, therefore in the above example, nothing would happen as the program stops as soon as the animation starts.  You can use the following code to keep the sprite going.

While True=True
            Delay(1)
End While

This works, because True is always going to equal True, therefore the program never exists the loop, yet the loop doesn’t really do anything, so you just see your sprite being animated.

Exercises

• Use a for loop to set the animation timeline for ‘Earth.gif’
• Use a for loop to set the animation timeline for ‘EnemyShip1.gif’