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Crash Course 2: Invaders - Part 9
by Hectate (Updated on 2015-02-01)
Part 9: Keeping the Ship On Screen
You probably played around with the game so far and noticed something; the ship can go off the screen (and doesn't come back!). Let's fix that, we need to restrict the Ship’s position so it can’t go past the screen’s edge.
Step 66: Create a new When Updating Event for the Ship. We need to add an If and an Otherwise If block inside.
We will use the first to check if the Ship’s position on screen is beyond the left-most edge of the screen (an X position of 0). The second will check if it’s past the right-most edge (a value equal to the screen’s width) of the screen.
Note that it will need to take into account the Ship’s width. Stencyl measures an Actor’s x position from the left-most edge of the graphic; if we didn't account for the Ship's width, the right side of the ship could go further than the right side of the screen.
Step 67: For our conditions, we need to compare two numbers; the Ship's position and the left or right edge of the screen. Let's grab the Greater Than and the Less Than blocks from palette. You can find them in the Flow category, Conditions sub-category, in the Equality section.
Put the Less Than (shaped like < ) block in the top If block's empty space. Put the Greater Than (shaped like > ) in the second, Otherwise If block's empty space.
Step 68: As mentioned previously, one of the numbers we want to compare is the Ship's position. We need a block that tells us that, and we can find it under the Actor category, Position sub-category, Position section; visible as x of Self.
We want to drag two of these blocks out; one for each of our comparison blocks (the < and > blocks). We need one in the left side for both. We need one more change for these two blocks, we want them to say "x (on screen)" instead of just "x". We can click on each one and change them easily with the drop-down menus that appear.
Step 69: Now that we have our first value to compare, we need a second value to compare it against. For our first comparison, we are just going to compare to 0; since an X value of zero is the left side of the screen. All we have to do is type a 0 into the right half of the Less Than block.
The second, Greater Than, comparison will be slightly more complex, however. As previously noted, we have to account for the width of the actor on the right side. Let's get the following blocks and drop them side-by-side in the workspace.
- Minus (found in Numbers & Text > Math > Arithmetic)
- Screen Width (found in Scene > View > Screen Bounds)
- Width of Self (found in Actor > Properties > Size)
We then need to drag the Screen Width into the left side of the Minus block, and the Width of Self into the right side. The result will be a stack of blocks that looks like the below image.
We need to drag this set of blocks into the other half of our second condition. Be sure to grab the Minus block to move them in, or we might only get one of the blocks inside of it instead.
Here's a image of what we should have so far.
Step 70: The goal of setting up these two conditions is to identify when the Ship has gone too far and has reached the edge of the screen. Since we now have those conditions set up, we can have something happen when they are true.
Given that our goal is to keep the Ship on the screen, we want to reset the position of our Ship Actor so that it is back on-screen anytime these conditions are met. To do so, we need two of the Set X to [ ] for Self blocks; one for each condition. Let's drag a couple out and put them where they belong.
Step 71: Just like with the comparison for our condition, the first value is rather easy. We just need to put a 1 into the block so it reads Set X to 1 for Self. Simply put, if our Ship is ever at 0 or less X position (further left than the left edge of the screen), we are going to force it back to 1 instead. This will prevent it from ever going off the left side of the screen.
Again, like our second comparison for our condition, the second value requires a few more blocks to do what we want it to. In this case, let's get the following blocks. Remember that you can ALT-drag on our existing blocks to duplicate them; you should do this to grab the entire stack out of the comparison.
- Minus
- Screen Width
- Width of Self
- Minus (yes, we need a second one)
Again, we need the same math to subtract the width of the Ship from the width of the Screen. This time though, we put that stack of blocks inside the left side of the second Minus block. On the right side, we enter a value of 1 so our Ship gets replaced 1 pixel inside of the right edge of the screen.
Step 72: Now we just need to take the above stack of blocks and insert it into the second Set X to [ ] for Self block in our conditionals. The complete set should look just like the image below.
Once you’ve got this new Event set up, test your game. If it’s working, and your Ship stays on screen, it’s time to move on to our next major Event, enabling our Ship to fire the Bullets we created earlier.
97 Comments
Well. This is garbage. Its like the guy who was writing the tutorial just decided to cash it in and go have lunch when he got to this step...
1
Hey Guys, i need a little bit help here.
I cant choose "Self" anywhere, I can just choose "Actor".
Maybe thats the reason why the flash player error #1009 appears. =D
1
@lize, "screen(width)" is located under Scene, and then View.
It's a shame how detailed every step has been up until this page. You want to use "screen(width)" for something like this because in other projects your scene may be bigger than what is shown.
0
The solution to step 66 was posted here in the comments section some time ago by patdi85
Just follow the instructions below and it will work.
patdi85
Here is step by step to getting the ship on screen to work:
1: Add event updated.
2: From flow, conditionals: drag on if
3: From if dropdown, select comparison, inequality , 0 < 0. there should two dropdowns.
4: 1st drop down, select actor, basics: select x of self
5: Enter 0 in second dropdown
6: From Actor, position box on right, select set x to 0 for self. Override 0 with a 1
7: From flow, conditionals select otherwise if and drag under existing if just created.
8: In otherwise if dropdown select comparison, inequalties, select 0 > 0
9: In the 1st dropdown of the 0 > 0, select actor, basics: select x of self
10: in 2nd dropdown if the 0 > 0, select math, Arithmetic, 0 - 0. You should now have 2 dropdowns.
11: In 1st unfilled dropdown for the 0 - 0, select scene, screen width
.
12: In the 2nd unfilled dropdown for the 0 - 0, select Actor, Basics, width of self.
13: From right, under Actor, Position, select set x to 0 for self under the otherwise if.
14: select math, Arithmetic, 0 - 0. You should now have 2 dropdowns.
15: In the Math 0 - 0, in the first dropdown, again select Math, Arithmetic, 0 - 0. this will give 3 dropdowns to create the second part of the otherwise if.
16: In 1st unfilled dropdown, select scene, screen width
17: In 2nd unfulled dropdown, select Actor, Basics, width of self.
18: In 3rd dropdown, enter 1. Ath this point it should match pitcure above Step 67.
19: Test and verify everything works.
9
Dear Flava621.
It seems these instructions are for the old 2.0 version of Stencyl. In 3.0 'Self' isn't an option. The option that seems to work is to 'choose actor'. This prompts a screen shot of the scene to pop up and you can then click directly on the actor you wish to apply these behaviors to.
I got the above tutorial to work, by selecting the players ship directly from that prompt window.
0
@Gamerlocke117 when you drag in your IF conditional (from FLOW > CONDITIONAL), in the IF drop down select COMPARISON > INEQUALITY AND SELECT THE 0 < 0. For the left side of the comparison use the palette on the right of screen to drag via the Actor button > position category > x of self . (and then click the drop down to make it say (x on screen)
0
I can't seem to find "X(On Screen)of self >0" Please PLEASE Help
I'm 13 year old boy and all i want to be since i was 3 and played Halo was make games for big companies and this is my chance to make games. make my dream come true!
-1
