Printable View
Hi
I am trying to build a simple snake game.
I have pretty much done it. It works well but theres a little problem.
if i try to add a static variable over the code that i have written, i get a weird error... (the rectangles of my snake behave very odd, crashing into walls at the press of a button)..
Why is this happening? Any ideas ? Should I upload parts of my code?
:rolleyes:
don't be so harsh. get your crystal ball out damnit!Quote:
Originally Posted by GCDEF
My car keeps refusing to start on Wednesdays. What could be wrong??? :D
Yes of course you'll need to upload some code - but not the full program. Upload the smallest sample that reproduces the problem.
What was that??? Do you believe your yelling helps somehow to solve the original issue?Quote:
Originally Posted by Amleto
The general idea is: you do that wrong way, or in wrong place, or for wrong reason.Quote:
Originally Posted by vinayak4gargya
If I were you, I would debug my app step by step and see what happens to my program variables. Sounds kinda trivial, but it really works most of the times. :)Quote:
Should I upload parts of my code?
not sure if serious.Quote:
Originally Posted by Igor Vartanov
http://media.photobucket.com/image/n...if-serious.jpg
I think you should look up, cos I think something just went over your head.
No, I think Igor just got mixed up, maybe thinking you were the original poster! It's an easy mistake to make when you're busy. He's probably still opening his Christmas presents! :DQuote:
Originally Posted by Amleto
Okay, in case that was some sort of humor, I didn't get that. Sorry, it happens time to time.
Vinayak4gargya, hi...
Don't know what it could be. Mine is just fine...
Albeit a bit ugly...
LOLCode:+----------------------------+
|Lives: 1 Score: 410|
+----------------------------+
| |
| |
| |
| o >-------+ |
| | |
|--+ | +------|
| | | | |
| | +----+ | |
| | | | |
| | | |
| +-----------+ |
| |
| |
| |
+----------------------------+
P.S. Use the [code][/code] tags when you post your code.
Heres WM_PAINT
And here is MoveSnakeCode:case WM_PAINT:
hdc = BeginPaint(hwnd,&ps);
SetIso(hdc,cxClient,cyClient); //Mapping mode
hPen = CreatePen(PS_SOLID,5,RGB(255,255,255));
hBrush = CreateSolidBrush(RGB(rand()%255,rand()%255,rand()%255));
//Draw Boundaries
SelectObject(hdc,hPen);
MoveToEx(hdc, -100, 100 , NULL);
LineTo(hdc,-100,-100);
MoveToEx(hdc, 100, 100, NULL);
LineTo(hdc, 100, -100);
SelectObject(hdc,hBrush);
TextOut(hdc,-180,0,szBuffer,wsprintf(szBuffer,"Your Score %i",(int)iScore));
SelectObject(hdc,(HPEN)GetStockObject(WHITE_PEN));
if(iDirect == 4)
TextOut(hdc,0,0,TEXT("Press Enter to start a New Game...."),36);
//Draw Snake's body rectangles
for(i = 0 ; i < iSnakeSize; i++)
Rectangle(hdc,pt[i][0].x,pt[i][0].y,pt[i][1].x,pt[i][1].y);
DeleteObject(hBrush);
hBrush = CreateSolidBrush(RGB(rand()%255,rand()%255,rand()%255));
//Draw Food
if(!bFoodOnScreen)
{
rectFood = CreateFood(pt,iSnakeSize);
bFoodOnScreen = TRUE;
}
SelectObject(hdc,hBrush);
Ellipse(hdc,rectFood.left,rectFood.top,rectFood.right,rectFood.bottom);
//Check if food has been eaten
if(EatFood(pt[0],rectFood))
{
iSnakeSize++;
iScore += 10;
bFoodOnScreen = FALSE;
}
SelectObject(hdc,(HPEN)GetStockObject(WHITE_PEN));
EndPaint(hwnd,&ps);
DeleteObject(hBrush);
DeleteObject(hPen);
return 0;
I DID try debugging only to get harrowing results!Code:void MoveSnake(POINT pt[500][2],int iDirect,int iLength)
{
int i;
//Move all rectangular blocks one position up in the array
for(i = iLength-1 ; i > 0 ; i--)
{
pt[i][0] = pt[i-1][0];
pt[i][1] = pt[i-1][1];
}
//Move the first block (i.e. head)
switch(iDirect)
{
case 0:
pt[0][0].y = pt[1][0].y + BLOCK;
pt[0][1].y = pt[1][1].y + BLOCK;
break;
case 1:
pt[0][0].x = pt[1][0].x - BLOCK;
pt[0][1].x = pt[1][1].x - BLOCK;
break;
case 2:
pt[0][0].x = pt[1][0].x + BLOCK;
pt[0][1].x = pt[1][1].x + BLOCK;
break;
case 3:
pt[0][0].y = pt[1][0].y - BLOCK;
pt[0][1].y = pt[1][1].y - BLOCK;
break;
}
}
After the MoveSnake function call the topmost elements of the array remain unchanged!(if i add another static variable to the code)
Otherwise it works normally.
Do more debugging. I don't see what's difficult in seeeing why values in an array are not correct.Quote:
Originally Posted by vinayak4gargya
We don't know what the original values are before the function call, or the values you are sending to the MoveSnake function, so there is no way for us to tell you what you're doing wrong. If you took that MoveSnake function by itself, called the function with known arguments, what do you get?Quote:
After the MoveSnake function call the topmost elements of the array remain unchanged!
Also, I see no relation between the WM_PAINT code and the MoveSnake code.
You are adding static variables in the hope that it fixes the problem?Quote:
if i add another static variable to the code)
First, make a simple program -- it doesn't have to be a full blown Windows program. Then take that MoveSnake() function and call it with known parameters. Start off with a smaller two dimensional array:
So, where does this go wrong? What values are sent to MoveSnake in this simple piece of code that causes the problem? If you don't see the problem here, then the issue is not MoveSnake() -- it is something else going on in your program that is overwriting the array with bogus values.Code:#include <windows.h>
#define BLOCK 1 // or whatever it is in your code
void MoveSnake(POINT pt[10][2],int iDirect,int iLength)
{
int i;
for(i = iLength-1 ; i > 0 ; i--)
{
pt[i][0] = pt[i-1][0];
pt[i][1] = pt[i-1][1];
}
//Move the first block (i.e. head)
switch(iDirect)
{
case 0:
pt[0][0].y = pt[1][0].y + BLOCK;
pt[0][1].y = pt[1][1].y + BLOCK;
break;
case 1:
pt[0][0].x = pt[1][0].x - BLOCK;
pt[0][1].x = pt[1][1].x - BLOCK;
break;
case 2:
pt[0][0].x = pt[1][0].x + BLOCK;
pt[0][1].x = pt[1][1].x + BLOCK;
break;
case 3:
pt[0][0].y = pt[1][0].y - BLOCK;
pt[0][1].y = pt[1][1].y - BLOCK;
break;
}
}
int main()
{
POINT p[10][2] = { fill in with values };
MoveSnake(p, /* supply the rest of the parameters*/ );
}
Regards,
Paul McKenzie
Could this function be a problem?
OK here's the deal...Code:void NewGame(BOOL *bFoodOnScreen,int *iDirect, int *iSnakeSize,POINT pt[500][2],int *iScore)
{
int i;
*bFoodOnScreen = FALSE;
*iDirect = 4;
*iScore = 0;
*iSnakeSize = 4;
//Initialize the first four rectangles
for(i = 0; i< *iSnakeSize ; i++)
{
pt[i][0].x = 0;
pt[i][0].y = (3-i)*BLOCK;
pt[i][1].x = BLOCK;
pt[i][1].y = (3-i+1)*BLOCK;
}
//Fill the rest of the array with 0
for(i = *iSnakeSize; i < 500; i++)
{
pt[i][0].x = 0;
pt[i][0].y = 0;
pt[i][1].x = 0;
pt[i][1].y = 0;
}
}
As soon as I press Enter to start the Game this is what happens
http://www.freeimagehosting.net/imag...19a0213629.png
the movesnake function is called after every iteration , thats all..
And i am not fixing this problem with static variables, they are CAUSING this problem.
I need the static variable to implement a functionality in the game.
The direction changes on keystrokes.
These are the values of the Snakes body after the first few iterations:
>1st iteration
- pt 0x013481a0 pt tagPOINT [500][2]
- [0] 0x013481a0 pt {x=-10 y=30} tagPOINT [2]
+ [0] {x=-10 y=30} tagPOINT
+ [1] {x=0 y=40} tagPOINT
- [1] 0x013481b0 {x=0 y=30} tagPOINT [2]
+ [0] {x=0 y=30} tagPOINT
+ [1] {x=10 y=40} tagPOINT
- [2] 0x013481c0 {x=0 y=20} tagPOINT [2]
+ [0] {x=0 y=20} tagPOINT
+ [1] {x=10 y=30} tagPOINT
- [3] 0x013481d0 {x=0 y=10} tagPOINT [2]
+ [0] { x=0 y=10} tagPOINT
+ [1] {x=10 y=20} tagPOINT
>2nd
- pt 0x013481a0 pt tagPOINT [500][2]
- [0] 0x013481a0 pt {x=-266 y=30} tagPOINT [2]
+ [0] {x=-266 y=30} tagPOINT
+ [1] {x=-10 y=40} tagPOINT
- [1] 0x013481b0 {x=-256 y=30} tagPOINT [2]
+ [0] {x=-256 y=30} tagPOINT
+ [1] {x=0 y=40} tagPOINT
- [2] 0x013481c0 {x=0 y=30} tagPOINT [2]
+ [0] {x=0 y=30} tagPOINT
+ [1] {x=10 y=40} tagPOINT
- [3] 0x013481d0 {x=0 y=20} tagPOINT [2]
+ [0] {x=0 y=20} tagPOINT
+ [1] {x=10 y=30} tagPOINT
As you can see, the value of x is -266 ?????
I say it again .. it works fine unless i introduce one more static variable to the code after that all i get is a -256 on the x and a weird scoreline...
HELPP!!!
These are the values passed to MoveSnake
- pt 0x00bd81a0 pt tagPOINT [2]*
+ [0] {x=0 y=30} tagPOINT
+ [1] {x=10 y=40} tagPOINT
iDirect 1 int
iLength 4 int
after the function finishes , every value is incremented (normal)
I just tried out a data breakpoint(its a new thing for me) and i set it to view any change in the value of the array after this function..
It does report a breakpoint but then shows a "theres no source code available" thing.
Something is changing the value of the snakes head but i cannot figure out where!!
Again, you just say it, but don't show how/where you introduce it (at least I cannot see any in your code). As long as this badly affects your program behavior, you do that wrong way, or in wrong place, or for wrong reason. You know, there are lots of ways how you could break your program which currently works fine.Quote:
I say it again .. it works fine unless i introduce one more static variable to the code after that all i get is a -256 on the x and a weird scoreline...
Besides, this prototype looks really dangerous:
In case you cross the array bounds somehow, you spoil the stack with unpredictable behavior.Code:void MoveSnake(POINT pt[500][2],int iDirect,int iLength)
Ok heres some more detail...
I break at MoveSnake;Code:case WM_TIMER:
InvalidateRect(hwnd,NULL,TRUE);
SetRect(&rect,pt[0][0].x,pt[0][0].y,pt[0][1].x,pt[0][1].y);
int check;
check = CheckHit(pt,iSnakeSize,rect);
MoveSnake(pt,iDirect,iSnakeSize);
if((check==0) | WallHit(pt[0] ))
{
KillTimer(hwnd,1);
MessageBox(hwnd,szBuffer,szAppName,MB_OK|MB_ICONINFORMATION);
iDirect = 4;
NewGame(&bFoodOnScreen,&iDirect,&iSnakeSize,pt,&iScore);
}
return 0;
Everythings normal;
Everything normal upto return 0;
"No source code available"
Breakpoint at switch (msg) of WndProc
Step Into;
Takes me to WM_PAINT:
Step Into : hdc = BeginPaint(hwnd,&ps);
Step Into again : I am returned back to switch(msg) (??) (The rest of the code of WM_PAINT is not executed)(??)
Step Into again : msg = 20;
Step Into : DefWindowProc();
Step Into again : At this time pt[0][0].x is -256
are the two variables I want in my code.Code:static BOOL bKeyPressed;
static HBITMAP hBitmap;
If I compile it with them I have a problem.
If I compile without them I dont have a problem
Both these variables are put along with all other variables at the top of the WndProc Code
So what should the correct prototype be?Quote:
Originally Posted by Igor Vartanov
remove the array size... just put.. POINT pt[][].. so that it takes enough memory by itself..
Make sure are these system defined variables or user defined.. if not . rename them to some other name... to avoid the clash..Code:static BOOL bKeyPressed;
static HBITMAP hBitmap;
You must be careful when debugging WM_PAINT messages.Quote:
Originally Posted by vinayak4gargya
You cannot debug them if you have the debugger popup over your window. The reason is obvious -- each time the debugger is closed, your app window has to be repainted, causing another WM_PAINT message to be generated and the breakpoint is hit again. Then you continue the program, causing the app window to be exposed, meaning another WM_PAINT message is generated, which hits the breakpoint, then etc. etc. etc. You are basically in a "debugging" infinite loop of breakpoint, WM_PAINT, show app window, breakpoint, WM_PAINT, show app window, ...
The way you debug WM_PAINT messages is either
1) Make sure your Visual Studio debugger window does not intersect anyway with your main app window. This means that you have to resize your app and/or Visual Studio IDE window so that they do not overlap each other.
OR
2) You have a dual monitor setup, where your app is on one monitor, and your Visual Studio IDE is on the other monitor.
Regards,
Paul McKenzie
This is much more flexible:Quote:
Originally Posted by vinayak4gargya
If you decide to use a different type, different dimensions, etc. all you need to do is change the typedef.Code:typedef double SnakeBoard[500][10];
void MoveSnake(SnakeBoard& myGameBoard,int iDirect,int iLength);
int main()
{
SnakeBoard sb;
MoveSnake(sb, 1, 1);
}
Regards,
Paul McKenzie
This is just a guess but is it possible that MoveSnake() is somehow getting called recursively? Since you pass the address of an array I can imagine all kinds of problems if something is trying to modify the array whilst a previous call is still in the midst of modifying it.
I'd check for something like that before you start blaming the static variables. I can pretty much assure you that if your app breaks after you add those statics, it's just a coincidence.
In any case (forgive me if you already explained this) but is the problem seen after the mere fact of adding the static variables? Or does it only happen after your program modifies them?
Done it!!!!!
There was definitely something overwriting the snake head!
Of course the weird scoreline!
See I print the scoreline --"Your Score __"
Well I had declared this to be a static char[10]...THAT was the problem.So everytime I wsprintf to update the score, it overwrote the snakes head.Now ive made it static char[15]
How Silly!! How so very silly!
Thanks a lot guyz I wouldnt have come back at this program without your help!
As is now obvious, you'd introduced an error that was completely outside of the code samples you posted. I hope you understand now why you should never provide incomplete code fragments that only tell part of the story. For problems like this one you should always provide a minimal (but buildable) sample program that actually exhibits the problem.