Platform collision using whatdotcolor (based off of the movement tutorial)

[rcbhs]

Ok so we are trying to make collision for this movement system based off of whatdotcolor. We used the movement from the movement tutorial...however, when I reach the platform during my fall it will jump up from that platform, however I can't make the box actually land on the platform. If I take out the code I used to make it able to jump he will land, but, then he can't jump...any help would be appreciated.

code:

const GROUND_HEIGHT := 120 const RUN_SPEED := 10 const JUMP_SPEED := 30 const GRAVITY := 2.7 var win := Window.Open ("graphics:640;480,offscreenonly") var chars : array char of boolean % player position and velocity var posx, posy : int var velx, vely : real posx := 20 velx := 0 posy := 400 vely := 0 loop     Input.KeyDown (chars)     if chars ('q') then         exit     end if     % to make the player move     if chars (KEY_LEFT_ARROW) then         velx := -RUN_SPEED     elsif chars (KEY_RIGHT_ARROW) then         velx := RUN_SPEED     else         velx := 0     end if     % remember, in order to jump you MUST be on the ground when pressing UP     if chars (KEY_UP_ARROW) and posy = GROUND_HEIGHT or posy = 220 then         vely := JUMP_SPEED     end if     % subtract your "gravity" constant from the velocity EACH frame     vely -= GRAVITY     posx += round (velx)     posy += round (vely)     % simple "collision" check. just makes sure the player stays above ground     if posy < GROUND_HEIGHT then         posy := GROUND_HEIGHT         vely := 0     elsif posy = 220 then         posy := 220         vely := 0     end if     % different colours just to illustrate whether or not you may jump     if posy = GROUND_HEIGHT then         drawfillbox (posx - 10, posy, posx + 10, posy + 20, green)     else         drawfillbox (posx - 10, posy, posx + 10, posy + 20, red)     end if     drawfillbox (200, 200, 300, 220, 3)     drawline (0, GROUND_HEIGHT, maxx, GROUND_HEIGHT, blue)     %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%     if whatdotcolor (posx, posy) = 3 then         posy := 220         vely := 1     end if     %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%     View.Update     delay (25)     cls end loop Window.Close (win)

[mirhagk]

for something like falling and jumping you shouldn't be using whatdotcolour, you should probably be using linear collision detection. (if you don't know how to use it, I can write a tutorial for you!)

[rcbhs]

We will look into linear collisio, if you write a tutorial So umm yeah, write one up.

[mirhagk]

alright I'll start working on it right now. Have you done/ do you remember linear math (like intersection of lines and stuff). If you don't, you might want to brush up on some of that because you'll be using intersections for linear collision

[rcbhs]

Now my question is, if we are going to have upwards of 50 platforms per level, won't linear platform collision be nothing but a TON of code? We figured with whatdotcolor we can just kinda draw a bunch of boxes throughout the level in paint and do our collision that way.

[TheGuardian001]

This is where the magic of arrays comes into play.
Basically, instead of defining each box with its own variable, you define the lot of them under an array, then iterate through them with a for loop. You'll need to know these at some point if you want to get anywhere, so you might as well pick them up now. We have a tutorial on arrays right over here.

[mirhagk]

the thing is that linear collision detection is actually very cheap in terms of speed (especially if you calculate the character's "line" first then use arrays and for loops to compare it to every other one)

Whatdotcolour is extremely ineffiecient and only allows objects to be a specific colour (or a picture with a two step drawing[not very fast at all])

I'm about half done the tutorial btw, when I'm done I'll post a link to it here k.

[rcbhs]

TheGuardian001 @ Thu Dec 10, 2009 1:04 am wrote:

This is where the magic of arrays comes into play.
Basically, instead of defining each box with its own variable, you define the lot of them under an array, then iterate through them with a for loop. You'll need to know these at some point if you want to get anywhere, so you might as well pick them up now. We have a tutorial on arrays right over here.

So basically your saying we will still have to hard code every single platform somewhere? Unless I am thinking of liner collision differently then it actually is, we will still have to tell the program exactly what the left x and right x coordinates are...My thought of using whatdotcolo is that 1, we dont care what color the platforms are (lol), this way we can just work on other concepts of our game as opposed to platform collision.

You need to take into account here, we have like 2 more weeks to get this game going and well, we don't want to spend that time on hard coding the locations we want our platforms when we could just make identical colored platforms and use whatdotcolor...

[DemonWasp]

No hard coding would be required. The magic of arrays is such that you can read the locations of all of your platforms from a file really, really easily. You would then draw platform "tiles" at those locations, instead of having them imprinted on your background images.

[mirhagk]

alright sorry I've been kinda busy lately with other stuff so I haven't been able to write that tutorial. I'll explain the basics here though. Basically what you want is an array that stores the x and y as well as the height and width of the box. Read the above tutorial on arrays so you understand it but something like this is what you want:

Turing:

type box: record x,y:int h,w:int end record var boxes:array 1..50 of box

now to draw these boxes you'd simply do the following

Turing:

for i:1..50 drawfillbox(boxes(i).x,boxes(i).y,boxes(i).x+boxes(i).w,boxes(i).y+boxes(i).h,red) end for

that way you can draw as many boxes as you want in just 3 lines. You can already see arrays are much more effecient.

[rcbhs]

mirhagk @ Mon Dec 14, 2009 10:46 am wrote:

alright sorry I've been kinda busy lately with other stuff so I haven't been able to write that tutorial. I'll explain the basics here though. Basically what you want is an array that stores the x and y as well as the height and width of the box. Read the above tutorial on arrays so you understand it but something like this is what you want:

Turing:

type box: record x,y:int h,w:int end record var boxes:array 1..50 of box

now to draw these boxes you'd simply do the following

Turing:

for i:1..50 drawfillbox(boxes(i).x,boxes(i).y,boxes(i).x+boxes(i).w,boxes(i).y+boxes(i).h,red) end for

that way you can draw as many boxes as you want in just 3 lines. You can already see arrays are much more effecient.

Now I'm not sure if its just me (I do have this problem often) not understanding what your saying again lol. I understand how that code works (least I understand exactly what that code does), however at some point we need to set the locations of those platforms, correct? If at any point we need to set the positions of all 50+ platforms we have PER LEVEL, its not worth the time imho. We don't want random platforms, I could have made random platforms in the very beginning. Our platforms are going to be in specific positions.

Again, sorry for any confusion, I hate trying to figure stuff out via typing cause, I tend tomisunderstand what people are saying.

[DemonWasp]

How do you want to specify the locations of platforms? You have two basic ways: some sort of bitmap or image, or else a data file. The second option is simpler, while the first option may make it easier to design the map.

[mirhagk]

you should put the locations of the platforms into a map file. You can even create a program that lets you draw the locations on-screen and then places that location in the map file. That way you can easily design the map, while having an effecient system of drawing the platforms and checking for collisions.

Also putting the locations into map files and having them created with another program makes it very simple to add new levels, freeing up your time to do more important things.

If you don't understand how to do this, I'd be glad to help you (I'll do anything to stop a programmer from using the whatdotcolour command)

[rcbhs]

mirhagk @ Tue Dec 15, 2009 11:52 am wrote:

you should put the locations of the platforms into a map file. You can even create a program that lets you draw the locations on-screen and then places that location in the map file. That way you can easily design the map, while having an effecient system of drawing the platforms and checking for collisions.

Also putting the locations into map files and having them created with another program makes it very simple to add new levels, freeing up your time to do more important things.

If you don't understand how to do this, I'd be glad to help you (I'll do anything to stop a programmer from using the whatdotcolour command)

So it would be easier in the long run to make a map file to place the locations (not 100% sure what you mean by mapfile btw lol)? Did you just mean I make one program to place the platform locations and one program to run the rest of my game?

[DemonWasp]

You make one program to run your game. It includes a (relatively tiny) bit of code to read the positions of your platforms from a file. The position of each platform is nothing more than a rectangle with (x1,y1,x2,y2) coordinates. This means you can have a map file as follows:

code:

100 100 300 110 0 0 10000 10

Which would define a rectangle up in the air, near the start of the level (assuming you start at 0) and another platform (the floor) starting at the start of the map and continuing considerably past the end of the screen.

You should be able to figure out how to read this with your program.