Ive been working on this all day, Im stumped! For some reason whenever I start the engine, my model, a car, starts to move backwards very slowly. Everything else works as normal. I cant figure out the reason for this strange backwards movement, any help would be appreciated.

Code:

---

var video_mode = 7; // 800x600 pixels
var video_depth = 32; // 32 bit mode

////////////////////////////////////////////////////////////////////////////////////

string homework18_wmb = <homework18.wmb>; 

ENTITY* car;

bmap bmpSpeed = "speedometer.bmp";

////////////////////////////////////////////////////////////////////////////////////

var accel = 1; //acceleration
var reverse = -1; //reverse acceleration
var absSpeed = 1; //universal speed, to be displayed by the speedometer negative numbers are reverse for now

function main()
{
	fps_max = 30;
	level_load (homework18_wmb);
	wait (3);
	while(1) //set up the camera
	{
		camera.x = car.x; 
		camera.y = car.y - 300;
		camera.z = car.z + 1000;
		camera.pan = 90; // set the correct orientation for the camera
		camera.tilt = -68; // using its pan and tilt angles
		
		wait(1);
	}
}

panel speedometer
{
	pos_x = 0;
	pos_y = 0;
	layer = 1;
	bmap =  bmpSpeed;
	digits(35,45,3,_a4font,1,absSpeed);
	flags = overlay, visible;
}

action my_car
{
	car = me;
	my.fat = on; 
	my.narrow = on; 
	c_setminmax(my); 
	while (1)
	{
		// move the car using relative_speed
		if (key_a == on)  //pans the car, but only if moving
		{	
			if(accel != 0)
			{
				my.pan += 5; // increase the pan angle of the car
			}
			if(reverse != 0)
			{
				my.pan += 5; // decrease the pan angle of the car
			}
		}
		
		if (key_d == on) //pans the car, but only if moving 
		{	
			if(accel != 0)
			{
				my.pan -= 5; // decrease the pan angle of the car
			}
			if(reverse != 0)
			{
				my.pan -= 5; // decrease the pan angle of the car
			}
		}
		
		if (key_w == on) //while pressing w...
		{	
			accel += 1;	  //accelerate by increasing the x value...
			c_move (my, vector(accel,0, 0), nullvector, glide); //in this vector
			if(accel >= 40)        //car cannot exceed 40 speed
			{
				accel = 40;
			}
			if(accel >= 1)			  //set up the value for the speedometer to display
			{
				absSpeed = accel;   //speedometer value == accel
			}
		}
		
		if(key_w == off)          //if you let off on the gas...
		{
			accel -= .5;           //decelerate
			c_move(my,vector(accel,0,0),nullvector,glide);
			if(accel <= 1)         //stop decelerating when not moving
			{
				accel = 0;
			}
			if(accel >= 1)				//set up values for speedometer
			{
				absSpeed = accel;
			}
		}
		
		if(key_s == on)           //when hitting reverse
		{
			c_move(my,vector(reverse,0,0), nullvector, glide); //decrease x value	
			reverse -= 1;          		 							   //in this vector to back up
			if(reverse < -18)
			{
				reverse = -18;
			}
			if(accel <= 1)						//set up values for speedometer
			{
				absSpeed = reverse;	
			}
		}
		
		if(key_s == off)             //when you let off on the gas
		{
			c_move(my,vector(reverse,0,0),nullvector,glide);  //slow down
			reverse += 1;
			if(reverse >= -1)
			{
				reverse = 0;
			}
			if(accel <= 1)				//set up values for speedometer
			{
				absSpeed = reverse;
			}
		}
		
		if(key_space == on) //brakes
		{
			if(accel > 0)
			{
				accel -= 2.5;
			}
			if(reverse < 0)
			{
				reverse += 2.5;
			}
		}
		
		
		wait (1);
		
	}
}

---

This is some modified and reworked code from the c-script tutorial, Im new to Gamestudio. Im using Gamestudio trial version 6.40.5. Thanks

I haven't done that tutorial, but from looking at your car action, you have two places that look like the problem:

Code:

---

if(key_w == off)
{
     ...
     ...
}

if(key_s == off)
{
     ...
     ...
}

---

These are both within a while loop that is constantly checking to see if keys are pressed. But you have these two set up so that if keys AREN'T pressed, then they do something. So when you start up your level, they instantly go into effect.

Your problem is that you're trying to make these things happen when the user "lets off" the gas, but the code executes whenever the key is not being pressed. You need to make these things happen after the key has already been pressed, and THEN the user releases. Give it a shot for a little while and if you can't figure it out, I'll help.

I see! Your explanation makes perfect sense, however...I cant seem to figure out how to apply it. I tried replacing (key_s == off) and (key_w == off) with (key_lastpressed == 31) and (key_lastpressed == 17), but this didnt work too well. Are there any other functions that can do the job better?

Thanks again

Hmm, after a second look, there might be an easier fix. Change:

Code:

---

if(key_w == off)          //if you let off on the gas...
{
	accel -= .5;           //decelerate
	c_move(my,vector(accel,0,0),nullvector,glide);
	if(accel <= 1)         //stop decelerating when not moving
	{
		accel = 0;
	}
	if(accel >= 1)				//set up values for speedometer
	{
		absSpeed = accel;
	}
}

---

to this:

Code:

---

if(key_w == off)          //if you let off on the gas...
{
	accel -= .5;           //decelerate	
	if(accel <= 1)         //stop decelerating when not moving
	{
		accel = 0;
	}
	if(accel >= 1)				//set up values for speedometer
	{
		absSpeed = accel;
	}
        c_move(my,vector(accel,0,0),nullvector,glide);

}

---

See what changed? This way, the updated acceleration isn't applied until after the check to make sure it doesn't go negative. That should keep your car from going backwards at the start.

There are other ways to approach it too. You could do something like:

Code:

---

if(key_w == off && accel > 0)
{
     ...
}

---

So that it's only executed if the car is already accelerating forward when key_w is off.

Your code for slowing down the reverse speed when the user lets up the key might be a little awkward since you're switching between the accel and reverse variable.

It worked! But now I have another problem. When I start the engine, my speedometer correctly reads a speed of zero. But after moving the car and slowing back down to a complete stop, the speedometer reads 1. Once again, Ive got no idea whats causing this.

Thanks for your help, the fix was brilliant!

I forgot...heres the updated code:

Code:

---

var video_mode = 7; // 800x600 pixels
var video_depth = 32; // 32 bit mode

////////////////////////////////////////////////////////////////////////////////////

string homework18_wmb = <homework18.wmb>; 

ENTITY* car;

bmap bmpSpeed = "speedometer.bmp";

////////////////////////////////////////////////////////////////////////////////////

var accel; //acceleration
var reverse; //reverse acceleration
var absSpeed; //universal speed, to be displayed by the speedometer negative numbers are reverse for now

function main()
{
	fps_max = 30;
	level_load (homework18_wmb);
	wait (3);
	while(1) //set up the camera
	{
		camera.x = car.x; 
		camera.y = car.y - 300;
		camera.z = car.z + 1000;
		camera.pan = 90; // set the correct orientation for the camera
		camera.tilt = -68; // using its pan and tilt angles
		
		wait(1);
	}
}

panel speedometer
{
	pos_x = 0;
	pos_y = 0;
	layer = 1;
	bmap =  bmpSpeed;
	digits(35,45,3,_a4font,1,absSpeed);
	flags = overlay, visible;
}

action my_car
{
	car = me;
	my.fat = on; // the first 3 lines of code
	my.narrow = on; // enable the new 
	c_setminmax(my); // collision detection system used by A6.2 or newer versions
	while (1)
	{
		// move the car using relative_speed
		if (key_a == on)  //pans the car, but only if moving
		{	
			if(accel != 0)
			{
				my.pan += 5; // increase the pan angle of the car
			}
			if(reverse != 0)
			{
				my.pan += 5; // decrease the pan angle of the car
			}
		}
		
		if (key_d == on) //pans the car, but only if moving 
		{	
			if(accel != 0)
			{
				my.pan -= 5; // decrease the pan angle of the car
			}
			if(reverse != 0)
			{
				my.pan -= 5; // decrease the pan angle of the car
			}
		}
		
		if(key_w == on) //while pressing w...
		{	
			accel += 1;	  //accelerate by increasing the x value...
			
			if(accel >= 40)        //car cannot exceed 40 speed
			{
				accel = 40;
			}
			if(accel >= 0)			  //set up the value for the speedometer to display
			{
				absSpeed = accel;   //speedometer value == accel
			}
			c_move (my, vector(accel,0, 0), nullvector, glide); //in this vector
		}
		
		if(key_w == off && accel > 0)          //if you let off on the gas...
			{
				accel -= .5;           //decelerate
				if(accel > 0)
				{
					absSpeed = accel;
				}
				if(accel <= 1)         //make sure you cannot go backwards when accelerating
				{
					accel = 0;
				}
				c_move(my,vector(accel,0,0),nullvector,glide);
			}
		
		if(key_s == on)           //when hitting reverse
		{
			c_move(my,vector(reverse,0,0), nullvector, glide); //decrease x value	
			reverse -= 1;          		 							   //in this vector to back up
			if(reverse < -18)
			{
				reverse = -18;
			}
			if(accel <= 1)						//set up values for speedometer
			{
				absSpeed = reverse;	
			}
			
		}
		
		if(key_s == off && reverse < 0)             //when you let off on the gas
			{
				c_move(my,vector(reverse,0,0),nullvector,glide);  //slow down
				reverse += 1;
				if(reverse >= -1)
				{
					reverse = 0;
				}
				if(accel <= 1)				//set up values for speedometer
				{
					absSpeed = reverse;
				}
			}
		
		if(key_space == on)
		{
			if(accel > 0)
			{
				accel -= 2.5;
			}
			if(reverse < 0)
			{
				reverse += 2.5;
			}
		}
		
		
		wait (1);
		
	}
}

---

Well, just try to imagine what's going on in your head, step by step. You have a panel called speedometer, that displays your speed via a variable called absSpeed. So we know that absSpeed must not be getting set correctly.

We also know that absSpeed is incorrect when the car slows down to a stop, so we should probably look at our code for when we release the w key.

Code:

---

if(key_w == off && accel > 0)
{
	accel -= .5;
	if(accel > 0)
	{
		absSpeed = accel;
	}
	if(accel <= 1) 
	{
		accel = 0;
	}
	c_move(my,vector(accel,0,0),nullvector,glide);
}

---

Now work through this part step by step, that's the same way the computer reads it. First, it checks if accel is above 0, then sets the absSpeed variable to whatever accel is. But right after that, it sets accel to 0 whenever it's less than or equal to 1. You should update the absSpeed variable after accel is set to 0.

My friend, you are a genius! Here's how I fixed it:

Code:

---

if(key_w == off && accel > 0)          //if you let off on the gas...
			{
				accel -= .5;           //decelerate
				if(accel <= 1)         //make sure you cannot go backwards when accelerating
				{
					accel = 0;
					absSpeed = accel;
				}
				if(accel > 0)
				{
					absSpeed = accel;
				}
				c_move(my,vector(accel,0,0),nullvector,glide);
			}

---

thank you very much

Multiply your movement vectors with time or time_step


Code:

---

c_move(my,vector(accel.x * time,0,0),nullvector,glide);  

---

or

Code:

---

c_move(my,vector(accel.x * time_step,0,0),nullvector,glide);

---

you dont really need to set absSpeed twice:

Code:

---

	absSpeed = accel;
}
	if(accel > 0)
	{
		absSpeed = accel;
	}

---

just:

Code:

---

if(accel <= 1)
{
    accel=0;
}

absSpeed=accel;  

---

This should work to but correct me when im wrong



nipx