2D Side Scroller - Terrain and AI questions - DBC

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Garfield1983

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Posted: 7th Feb 2007 23:59

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Hi folks,

I'm trying to create a 2D side-scrolling game where the player controls a ship that flies along shooting down waves of enemies. It's in the early stages but after reading up alot on the db forums i've managed to get the ship moving and firing.

- Scrolling -

I've read various tutorials on scrolling the background - I currently have an image of some terrain as a sprite with the X position changed until a certain point using an IF THEN statement and the DEC command.

The terrain image is currently not very large (2048 pixels in diameter) and since I want the player to have to fly for a considerable time before the end of the level, I am looking for the best way to scroll the terrain - I don't think making the image larger would work as it's already slightly jittery.

Q - 1) Is it best to 'loop' this sprite and how would this be acheived?

Q - 2) How would I go about having an efficient but large varied landscape? ie not a looping image

I may be answering my own questions but i've been considering (1) tiling the background and updating the edge tile as in rpgs (not really my strong point atm!), (2) texturing a plain and scrolling the texture (3) Having a looping background with additonal sprites for the individual foreground graphics to make the terrain appear varied.

I'm not sure which of the above is the norm?

- Artificial Intelligence -

Again I've been reading up on AI in games - I'm still looking into waypoints as a way to have enemies follow a pattern, but the tutorials I've found are for 3D games - However, my main question is how to display these enemies?

I'm planning on having the player encounter enemies as they progress through the level - a bit like Cloud Master on the Master System if anyone remembers?

Q - 3) How would I space these enemies out so that the player encounters them at specific points throughout the level? This would also apply to any foreground clutter that the player might crash into

Any help would be greatly appreciated and I apologise if this has been covered elsewhere - I did look but I may have missed it

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TDK

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Posted: 8th Feb 2007 01:31 Edited at: 8th Feb 2007 01:41

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With regards to the scrolling, tiling is by far the most efficient (and fastest) way to do it.

The tiles used to make up the screen would be placed in an array and as such a screen could be hundreds of thousands of tiles wide before repeating.

I've not done it myself, but I would imagine that if your screen was 800x600 and made up from a 25x18 grid of 32x32 pixel tiles and you were scrolling the screen left (ship is moving right) then it would be a case of:

* Using the array/tiles to build the screen on a second bitmap
* Grabbing part of that screen into an image
* Pasting the image 1 pixel to the left on the main screen
* Updating the rightmost column of tiles from the array when required
* Doing the Sync

This shouldn't cause jittering even in DBC. This interests me, so I'm experimenting with this at the moment!

AI:

I'm not familiar with Cloud Master so I'll leave it to someone who has to comment on that aspect.

Q3:

This would be tied into the tiling aspect. You would be advised to create a separate program (level editor) for generating the data which goes into the screen tile array.

This same program would also allow you to have a second object array the same size as the tile array. You give it the ability to drop a tile onto the grid or an object.

In your program, when you update the tiles from the tile array, you also update from the objects array before doing the Sync.

TDK_Man

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TDK

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Posted: 8th Feb 2007 03:11

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Here's a small scrolling example I came up with.

Rem Side Scrolling Demo Using Tiles & Arrays
Rem (c) TDK_Man Feb 2007

Gosub Setup
Gosub Create_Tiles
Gosub Build_Screen

Do
  If LeftKey() Then Gosub Scroll_Left
  If RightKey() Then Gosub Scroll_Right
  Sync
Loop
End

Scroll_Left:
  If XTileOffset > 0
    Set Current Bitmap 1
    Dec XPixelOffset,ScrollSpeed
    If XPixelOffset <= 0
      XPixelOffset=32
      Dec XTileOffset
      CLS
      For Nx=0 To 25
        For Ny=0 To 17
          Paste Image Tiles(NX+XTileOffset,NY),Nx*32,Ny*32
        Next Nx
      Next Ny
    Endif
    Get Image 1000,XPixelOffset,0,806+XPixelOffset,576
    Set Current Bitmap 0
    Paste Image 1000,0,0
  Endif
Return

Scroll_Right:
  If XTileOffset < ScrnTileWidth
    Set Current Bitmap 1
    Inc XPixelOffset,ScrollSpeed
    If XPixelOffset >= 32
      XPixelOffset=0
      Inc XTileOffset
      CLS
      For Nx=0 To 25
        For Ny=0 To 17
          Paste Image Tiles(NX+XTileOffset,NY),Nx*32,Ny*32
        Next Nx
      Next Ny
    Endif
    Get Image 1000,XPixelOffset,0,806+XPixelOffset,576
    Set Current Bitmap 0
    Paste Image 1000,0,0
  Endif
Return

Build_Screen:
  Create Bitmap 1,1024,768
  For Nx=0 To 25
    For Ny=0 To 17
      Paste Image Tiles(NX+XTileOffset,NY),Nx*32,Ny*32
    Next Nx
  Next Ny
  Get Image 1000,XPixelOffset,0,806+XPixelOffset,576
  Set Current Bitmap 0
  Paste Image 1000,0,0
  Ink RGB(255,255,255),0
  Set Text Font "Tahoma"
  Set Text Size 16
  Center Text 400,580,"Use Cursor Left/Right To Scroll"
Return

Create_Tiles:
  Create Bitmap 1,800,600
  Rem Create 20 different random shaded tiles
  For N=1 To 20
    CLS RGB(255,255,255)
    Ink RGB(0,0,0),0: Box 1,1,31,31
    C=Rnd(155)+100
    Ink RGB(C,C,C),0: Box 1,1,30,30
    Get Image N,0,0,32,32: Rem Store tiles in images 1 to 20
  Next N
  Set Current Bitmap 0
  Delete Bitmap 1

Rem Place Random Tiles Into The Tiles Array. This would normally be done manually
  Rem with a level editor for a game.
  Rem For This Example, We'll Also Limit The Landscape To Being 10,000 Tiles Wide
  For LandscapeX=0 To ScrnTileWidth-1
    For LandscapeY=0 To 17
      Tiles(LandscapeX,LandscapeY)=Rnd(19)+1
    Next LandscapeY
  Next LandscapeX
Return

Setup:
  Set Display Mode 800,600,16
  Sync On: Sync Rate 60: CLS 0
  Randomize Timer()
  Dim Tiles(50000,17)
  XTileOffset=0
  XPixelOffset=0
  ScrollSpeed=2
  ScrnTileWidth=10000: Rem Number of tiles across on this level
Return

+ Code Snippet

Rem Side Scrolling Demo Using Tiles & Arrays
Rem (c) TDK_Man Feb 2007

Gosub Setup
Gosub Create_Tiles
Gosub Build_Screen

Do
  If LeftKey() Then Gosub Scroll_Left
  If RightKey() Then Gosub Scroll_Right
  Sync
Loop
End

Scroll_Left:
  If XTileOffset > 0
    Set Current Bitmap 1
    Dec XPixelOffset,ScrollSpeed
    If XPixelOffset <= 0
      XPixelOffset=32
      Dec XTileOffset
      CLS
      For Nx=0 To 25
        For Ny=0 To 17
          Paste Image Tiles(NX+XTileOffset,NY),Nx*32,Ny*32
        Next Nx
      Next Ny
    Endif
    Get Image 1000,XPixelOffset,0,806+XPixelOffset,576
    Set Current Bitmap 0
    Paste Image 1000,0,0
  Endif
Return

Scroll_Right:
  If XTileOffset < ScrnTileWidth
    Set Current Bitmap 1
    Inc XPixelOffset,ScrollSpeed
    If XPixelOffset >= 32
      XPixelOffset=0
      Inc XTileOffset
      CLS
      For Nx=0 To 25
        For Ny=0 To 17
          Paste Image Tiles(NX+XTileOffset,NY),Nx*32,Ny*32
        Next Nx
      Next Ny
    Endif
    Get Image 1000,XPixelOffset,0,806+XPixelOffset,576
    Set Current Bitmap 0
    Paste Image 1000,0,0
  Endif
Return

Build_Screen:
  Create Bitmap 1,1024,768
  For Nx=0 To 25
    For Ny=0 To 17
      Paste Image Tiles(NX+XTileOffset,NY),Nx*32,Ny*32
    Next Nx
  Next Ny
  Get Image 1000,XPixelOffset,0,806+XPixelOffset,576
  Set Current Bitmap 0
  Paste Image 1000,0,0
  Ink RGB(255,255,255),0
  Set Text Font "Tahoma"
  Set Text Size 16
  Center Text 400,580,"Use Cursor Left/Right To Scroll"
Return

Create_Tiles:
  Create Bitmap 1,800,600
  Rem Create 20 different random shaded tiles
  For N=1 To 20
    CLS RGB(255,255,255)
    Ink RGB(0,0,0),0: Box 1,1,31,31
    C=Rnd(155)+100
    Ink RGB(C,C,C),0: Box 1,1,30,30
    Get Image N,0,0,32,32: Rem Store tiles in images 1 to 20
  Next N
  Set Current Bitmap 0
  Delete Bitmap 1

  Rem Place Random Tiles Into The Tiles Array. This would normally be done manually
  Rem with a level editor for a game.
  Rem For This Example, We'll Also Limit The Landscape To Being 10,000 Tiles Wide
  For LandscapeX=0 To ScrnTileWidth-1
    For LandscapeY=0 To 17
      Tiles(LandscapeX,LandscapeY)=Rnd(19)+1
    Next LandscapeY
  Next LandscapeX
Return

Setup:
  Set Display Mode 800,600,16
  Sync On: Sync Rate 60: CLS 0
  Randomize Timer()
  Dim Tiles(50000,17)
  XTileOffset=0
  XPixelOffset=0
  ScrollSpeed=2
  ScrnTileWidth=10000: Rem Number of tiles across on this level
Return

It creates it's own media randomly and you use the left and right cursor keys to scroll.

It's not 100% glitch-free on my system because I have inexpensive TFT monitors with fairly slow refresh rates. It should be fine on a proper monitor. Try it and let me know.

It creates random coloured tiles and simply stores them randomly in an array. You would need to create a level editor so you decide where to place the tiles you create yourself, but the scrolling would be the same.

TDK_Man

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Garfield1983

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Posted: 10th Feb 2007 12:53

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Hi TDK, thanks for the help!!

Your code works perfectly on my system. I still need to go through it line by line to see how it works as i've only had a preliminary read (I've been ill with flu this week), i'll let you know if I get stuck. The theory behind it makes sense though.

I'm not sure I have the knowledge to take on such a big project as making a level editor, although this would be a good feature to include in the finished game itself.

I know there are already level editors out there but I want to create as much of this game as possible myself - I'm the kind of person who hates the idea of simply copying other peoples code and calling it my own, where's the learning in that?

I may use a 3rd party level editor, atleast to get something working and get some ideas for my own editor. I've been exploring the idea of creating a textured matrix in your exellent program MatEdit and pointing the camera at it to give the illusion of 2D, then moving the matrix or camera when the cursor keys are pressed. I'm not sure how I would place the enemy/player sprites etc - I need to look into if these can be put onto 3D plains, I think I read something about that. This would probably be quite taxing on system resources though.

Another idea i've explored before is data statements. I need to study these again as I never quite got the code working on my last attempt (admittedly some time ago!). I need to brush up on arrays in general but perhaps data statements will allow me to create 'levels' (possibly as external notepad files to allow additional levels to be added easily) and perhaps a seperate one for the starting points of the enemies.

Anyway, I need to go away and look into all this, as well as study your code in more detail, but I wanted to let you know I'm still around and say thank you for the detailed response - you are legendary around here for the help you so kindly give.

Cheers!

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TDK

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Posted: 11th Feb 2007 02:57

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Quote: "Another idea i've explored before is data statements"

They would work, but I'd advise against using them.

The main problem is that your levels are built into the final exe and adding more (or modifying existing ones) requires supplying a new exe - and re-writing the program to cater for the difference in levels.

No, the best way is to store the data for each level in the game as a separate data file.

Your program can look at these files and know how many there are in total, so adding more levels isn't a problem.

And, if you tweak a couple of levels, you only need to supply the new data files for those levels - not everything.

As for the level editor side of things, it sounds a lot more complicated than it actually is.

In the example code I posted above, all it does is create 20 random coloured 32x32 pixel tiles. They are all stored in images numbered 1 to 20. In your game, you would create your own tiles.

It creates an array (tile grid) of size 10001 tiles across and 18 tiles down (don't forget element 0). This equates to a screen playing area 320032 pixels wide and 576 pixels high. The array is actually dimensioned with Dim Tiles(50000,17), but you don't need to use all elements.

Likewise, use a number bigger than 50000 to create even bigger levels.

It then randomly fills the the array with the 20 tile numbers.

All a level editor needs to do is allow you to select which of your manually created tiles goes where on the grid, then write out the resulting numbers to a file.

Obviously this program can be as complicated or as basic as you want it to be, but essentially needs to be able to:

* display the tiles available
* show you a section of the grid
* select what section you want to work on
* Allow you to place the tiles
* save a data file
* load a data file
* test what you have already done

You could also give it the ability to add 'spawn points' for enemies, creatures or objects and save this data to the level data file.

It sounds like an interesting project and if you need any help with the editor side of things just shout.

TDK_Man

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DarkBASIC Discussion / 2D Side Scroller - Terrain and AI questions - DBC