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Hi everyone! Today we're going to make a natural science educational project to explain light

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and the creation of shadows when light interacts with opaque objects. We're basically going to have

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a source of light which will be the sun and an opaque object, for example this apple,

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and another sprite which will actually create the light rays and will stop either when touching the

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edge or when touching the opaque object. And finally we will code it so that it

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runs instantly and we don't have to wait to see the shadow and I will give you

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some more ideas to improve your project as I usually do. Alright, so if you are

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ready let's get started.

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so let's begin adding the sprites first of all the Sun and then an opaque object

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I'm gonna take the Apple but you can take any object let me make the Sun a

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little bit smaller and this time I'm not gonna get rid of the cat because I'm

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gonna use the cat to draw the light rays well in fact you can use any sprite to

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draw the light rays. I'm gonna make the cat as small as possible, I'm gonna set

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size to one and as you see the minimum size is five and I'm gonna go to

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backdrops to convert it to bitmap and with the paint bucket I'm gonna make it

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black. So let's go back to the code and basically the program is gonna be this

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the cat is going to start from the Sun and it's going to move pen down I will

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explain to you what that is later and it's going to trace a yellow line it

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will stop when it touches the edge it will go back turn one degree and another

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line go back another line go back another line and when it is touching the

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apple it will also stop because if it continues we are not creating the shadow

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so when touching the apple it will stop we'll go back we'll turn make another

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ray stop when touching the Apple go back and so on so first of all I'm gonna go

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here and I'm going to add the pen which is what we need what I was saying well

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I'm gonna do it with the Apple so that you see it clearly look if pennies up

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and I move the Apple it doesn't paint anything but well pen up basically is

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when you move the pen up you are not touching the piece of paper so if you

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are not touching the piece of paper you cannot paint pen down means that I move

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the pen down and I'm touching the piece of paper so if I move the Apple with the

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pen down it traces a line alright so I'm gonna erase all I'm gonna take the apple

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here and let's begin coding I'm gonna go to scratch and in event well we could do

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one green flag clicked or when space key pressed when space key pressed first of

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all I'm gonna make sure I move the pen up so that I'm not touching the paper

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let's say the cat is over here so pen up so that I'm not touching the paper and

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now with the pen up I'm gonna move the cat to the Sun so go to Sun and I press

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space so now the cat is here and I can put the pen down I think before that at

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the beginning I'm going to do some things which could be this look when

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green flag clicked I'm going to set paint color to yellow because I don't

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want to have blue light rays set pen size this is how big how not how big how

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wide these lines are we can leave this number and later we will change the pen

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size and you will see the different results that we can obtain and finally

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what is the direction the cat is gonna be pointing in at the beginning let's

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say for example 45 which is this and when we're moving the direction of the

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cat we will reach okay other numbers so that could be so as we were saying when

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space key pressed the cat goes to the sun and moves the pen down. With the pen

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down and pointing in this direction now we can move the cat. As we have to move

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the cat a lot we're going to repeat this movement. So let's put repeat until. So

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cat is moving and when does the cat have to stop okay it has to stop when it is touching the edge

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or when touching the apple so the cat is going to repeat this until and i put an or until touching

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the edge or touching the apple. After this it's going to turn one degree and

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again go to the Sun to repeat the process. So it will turn one degree and

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then repeat this process I'm gonna do one thing when space key pressed the

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first thing we're going to do is erase all so that I press and it draws it has

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stopped so now basically it has to repeat this and this and this many times

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I'm gonna put the apple here so that you see what happens as you see when it

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touches the apple it stops and now that is not touching the apple anymore it

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completes and and paints the rest of the screen logically I don't want to be

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clicking here whenever I want to repeat this so I have a loop which is gonna be

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repeat 100 times for example place it here and now green flag oh well maybe

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this point in direction could be here let's begin as you see it works but it

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takes a long time and I don't want you to fall asleep so maybe you are

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wondering Diego is there way to do it instantly and the answer is yes of

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course look I'm gonna go to my blogs and I'm gonna make a blog called light up

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and I'm gonna select this run without screen refresh I'm gonna pass it here

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and all this this repetition is what has to be done instantly so I put the block

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light up here which is the same as all this which is run instantly and now only

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by pressing space this is done I'm gonna move the Apple I press space and as you

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this works very well so what you have here is the basic project this is very good but probably you

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want to make an excellent project and to make an excellent project i'm going to give you some ideas

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to make it better for example probably you know that a complete circumference has 360 degrees

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so if I repeat this 360 times as I'm turning one degree every time I'm gonna

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complete all this so I can put this anywhere spacebar and look I complete it

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other things we were saying if I change this which could be here as well all

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this could be here okay and we would get rid of the green flag if i set pen size to three

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as you see this is quite different because these lines are three pixels wide and not one

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if i set this to 10 i basically complete the whole the whole screen all right more things we can do

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probably you're wondering if we can add more objects obviously we can

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i'm going to add for example a bat and i'm going to put it here but look when i press spacebar

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the light race or the cat the sprite stops when touching the apple but it doesn't stop when

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touching the bat why because we haven't coded it yet okay in the cat we said that it has to

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move until touching it or apple but not until touching the bat so we need an or all this

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is going to be here and in this space we add touching bat now spacebar and that works

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another thing we can do here in the edition uh screen obviously we can move the object

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but if i am trying my game i can't so to be able to move the object here when i am actually playing

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i'm gonna go to uh the sun and i could put when green flag clicked

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it's here set drag mode to draggable okay so that you can drag the sun look now i can drag it

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but i can't drag these two so i'm gonna pass this to the apple and i'm gonna pass this to the bat

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green flag and now these three are draggable and i can drag them all right and with this you have

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an excellent project if you want to make it brilliant um you could add some uh variables

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for example if i want to control the pen size if i want to control

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this from the game i can create a variable called pen size in this variable with right click slider

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i make it into slider and with right click change slider range the minimum could be one

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and the maximum 10. so i'm going to set pen size to this variable so i put this here

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now if i put here an 8 we are setting pen size to 8. so

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before you press spacebar make sure you click on the screen and as you see i'm going to move

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the objects and I'm gonna set pen size to six okay so that works and another

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thing that you could add for example I'm just gonna do it in one of the objects

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but you could do it in both of them is that we can control the size of the

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Apple from the game or the size of the bat as well it's quite similar I'm gonna

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make a variable which is going to be apple size again right click slider

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right click change slider range and the size could go from 5 to 300 for example

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now in the Apple after this I could put forever set size to what I have here so

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variables Apple size so you will see now Apple size is tiny because this is zero

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but if I increase it it sets pen size so it says Apple size to this number so now

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I can move the Apple I can move the bat you could create another variable for

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the bat size and do the same as I've done in the apple and spacebar and I

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create the shadow so this is the project guys to study shadows and light and how

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light interacts with opaque objects I hope you liked it and please do not

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forget to send me a project when you have them done alright see you guys bye

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bye