Snake Game: Collision with apple (object)
lazarus / 31-LCL

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Danzino.Akz · 2019-02-14 15:06

Hey,
I am trying to make a maths game in Free Pascal for my A level
coursework. I have written code for a collision between the snake
(which is just a box for now) and the apples. I have also written some
code that randomizes the apples' positions after a collision. The
randomisation works, however, I have realised that the collisions are
very off and sometimes do not happen when the snake is touching the
object. I think it might have something to do with the coordinates
(.left and .width). Thanks for your help

This is my code for the collision:

begin

  if (
       (Image1.Left > Shape1.Left)
       and (Image1.Left + Image1.Width <= Shape1.Left + Shape1.Width)
       and (Image1.Top + Image1.Height >= Shape1.top)
       and (DirectionTop = False)
     )
    or
      ((Image2.Left > Shape1.Left)
       and (Image2.Left + Image2.Width <=Shape1.Left + Shape1.Width)
       and (Image2.Top + Image2.Height >= Shape1.top)
       and (DirectionTop = False))
     or
       ((Image2.Left > Shape1.Left)
       and (Image2.Left + Image2.Width <= Shape1.Left + Shape1.Width)
       and (Image2.Top + Image2.Height >= Shape1.top)
       and (DirectionTop = False)
     )
     or
       ((Image3.Left > Shape1.Left)
       and (Image3.Left + Image3.Width <= Shape1.Left + Shape1.Width)
       and (Image3.Top + Image3.Height >= Shape1.top)
       and (DirectionTop = False)
     )
     or
       ((Image4.Left > Shape1.Left)
       and (Image4.Left + Image4.Width <= Shape1.Left + Shape1.Width)
       and (Image4.Top + Image4.Height >= Shape1.top)
       and (DirectionTop = False)
       )
    then begin

       randomize();
       h1:=random(642);
       w1:=random(1050);
       h2:=random(642);
       w2:=random(1050);
       h3:=random(642);
       w3:=random(1050);
       h4:=random(642);
       w4:=random(1050);
       image1.top:=h1;
       image1.Left:=w1;
       image2.top:=h2;
       image2.Left:=w2;
       image3.top:=h3;
       image3.Left:=w3;
       image4.top:=h4;
       image4.Left:=w4;
       //include code to increase speed of snake
       score:= score + 1;

       Label1.caption:= IntToStr(score);
     end;
end;

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Handoko · 2019-02-14 15:19

Hello Danzino.Akz,
Welcome to the forum.

If you have problem with your source code, you should provide the
whole source code and all the necessary files. So we can inspect it,
tell you where you did it wrong and give you some advices.

To do it:
Create a new folder, copy and paste all the necessary files except:
the binary (exe file), *.bak, lib and backup folders. Compress the
folder and send the zip here.

Here has a detailed tutorial for writing a computer snake game:
https://forum.lazarus.freepascal.org/index.php/topic,38136.msg258381.h
tml#msg258381

The thread in the link above is very long and I guarantee it is
boriiiiiiiing. But if you follow the tutorial, you will learn:
- Game loop
- User input detection
- Using array to represent the the game world
- Collision detection
- How to use TList (to replace array)
- Using buffer for keyboard input
- Using buffer to reduce flickering

Have fun!

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Ñuño_Martínez · 2019-02-19 10:02

Collision is quite simple, actually.  Just take a piece of paper and a
pen or pencil and draw some rectangles, some of them colliding and
others that doesn't.  Then figure out what coordinates and sizes they
have and you'll get it.

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Thaddy · 2019-02-19 11:43

PointInRect comes to mind....

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User137 · 2019-02-19 17:58

2D collision in pseudo:

IF |object1.X - object2.X| < (object1Radius+object2Radius) THEN
   Collides in X axis

But doing it like that requires that visual representation of the
objects are separated from ones that are moving. You would be moving
the visuals to a centered position like:
image1.Left:=Snake.head.X - image1.Width div 2;

Is this confusing enough?    But truthfully it is always easiest to
calculate these things from objects center points. You can think of
snake as snake that it is, not something that is dragged from its
corner.

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Handoko · 2019-02-19 20:18

Actually, collision detection in snake game is much simpler than you
all have suggested.

Because each snake movement, each segment of the snake, each apple
occupies only exactly 1 space, the collision detection is simply
checking and comparing the target location (in the array).

Checking the target location is easy if you done these:

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i     type  
  TItem = (Empty, Snake, Fruit);
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i     var   
 GameWorld: array[1..WorldWidth, 1..WorldHeight] of TItem;
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i function
TForm1.GetItem(X, Y: Integer): TItem;begin  Result := Empty;  if (X <
1) or (X > WorldWidth) then Exit;  if (Y < 1) or (Y > WorldHeight)
then Exit;  Result := GameWorld[X, Y];end;
Again, I recommend OP to read the link I suggested.

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Danzino.Akz · 2019-02-23 20:15

Quote from: Handoko on February 14, 2019, 04:19:09 pmHello
Danzino.Akz,
Welcome to the forum.

If you have problem with your source code, you should provide the
whole source code and all the necessary files. So we can inspect it,
tell you where you did it wrong and give you some advices.

To do it:
Create a new folder, copy and paste all the necessary files except:
the binary (exe file), *.bak, lib and backup folders. Compress the
folder and send the zip here.

Here has a detailed tutorial for writing a computer snake game:
https://forum.lazarus.freepascal.org/index.php/topic,38136.msg258381.h
tml#msg258381

The thread in the link above is very long and I guarantee it is
boriiiiiiiing. But if you follow the tutorial, you will learn:
- Game loop
- User input detection
- Using array to represent the the game world
- Collision detection
- How to use TList (to replace array)
- Using buffer for keyboard input
- Using buffer to reduce flickering

Have fun!



Thank you very much, I really do appreciate it.