Hasch question, cheking to see if key pressed

[lordroba]

I'm making a racing game and I want the car speed up while the UP key is being pressed(i know how to do this), and I want the speed to slowly go down while no key is pressed.

How do I check if no key is being pressed and put this into an 'IF' condition so that it lowers the value of the speed variable when this is true?

[MihaiG]

heres a small example

code:

if not hasch then speed := speed - 1 %speed -= 1 end if

[lordroba]

thank you very much

[Cervantes]

Use Input.KeyDown, not hasch and getch. It will allow you to get multiple keystrokes at once.

You probably don't want to slow your car down when no key is pressed. Think about it: the user could press "h" and he would go at a constant speed and not use any fuel or anything. Instead, you want the car to slow down when the up arrow is not pressed.

code:

if keys (KEY_UP_ARROW) then     car.speed += car.acceleration else     car.speed *= car.deceleration end if

car.deceleration should be slightly less than 1. 0.99 is a good value to test.

Of course, you could use some physics to determine accelerations with regard to mass, applied force, and frictional forces.

Turing:

View.Set ("offscreenonly") var car :     record         x, y : real         mass : real         internal_friction, net_force : real         current_vert_angle : real         speed, applied_engine_force : real         current_surface_material, tire_material : string     end record := init (100, 100, 800, 200, 0, 0, 0, 10000, "dry asphault", "rubber") type Friction_Coefficient :     record         surface1, surface2 : string         value : real     end record fcn friction_coeffecient_init (surface1, surface2 : string, value : real) : Friction_Coefficient     var temp_coeff : Friction_Coefficient     temp_coeff.surface1 := surface1     temp_coeff.surface2 := surface2     temp_coeff.value := value     result temp_coeff end friction_coeffecient_init var coefficients : array 1 .. 2 of Friction_Coefficient coefficients (1) := friction_coeffecient_init ("rubber", "dry asphault", 0.6) coefficients (2) := friction_coeffecient_init ("rubber", "wet asphault", 1.2) fcn friction_force (surface1, surface2 : string, N : real) : real     for i : lower (coefficients) .. upper (coefficients)         if Str.Lower (coefficients (i).surface1) = Str.Lower (surface1) and                 Str.Lower (coefficients (i).surface2) = Str.Lower (surface2) then             %Force of friction = mew (coefficient of friction) * Normal force             result coefficients (i).value * N         end if     end for end friction_force var keys : array char of boolean loop     car.net_force := -car.internal_friction - friction_force (car.tire_material, car.current_surface_material, cosd (car.current_vert_angle) * car.mass * 9.8) %- car.speed     % the last bit, - car.speed is an approximation for wind resistance.  I'm not sure how wind resistance works.  Anyone know the formula?     Input.KeyDown (keys)     if keys (KEY_UP_ARROW) then         car.net_force += car.applied_engine_force     end if     car.speed += car.net_force / car.mass     car.speed := max (0, car.speed)     car.x += car.speed     car.x mod= maxx     cls     Draw.FillOval (round (car.x), round (car.y), 10, 10, black)     locate (1, 1)     put car.speed     View.Update     delay (10) end loop

I think this is all correct, except for the fact that the coefficient of friction changes depending upon your speed. This also does not take into account air resistance, which is greater than the friction between the tires and the road.

[lordroba]

Alright now i'm really pissed, I spent all day yesterday trying to figure this out but I'm having no success. As you can see in the attached program, the car moves fine, and it turns and everything, but I can't figure out how to make it keep going for a while when you let go of the acceleration(UP) button! It just stops right where you let go of the key.

can someone plz help me.

I not only want the car to move a fair bit and eventually stop after you let go of the gas, but I also want it so that the user still has ability to steer the car thru the corner when its moving.

Any help greatly appreciated!

[Cervantes]

There are two tutorials you should look at:
First, check out zylum's spaceship movement tutorial.
Second, check out Asian's rotation and movement tutorial. It explains how to store the rotated pictures in an array, so you don't have to Pic.Rotate each time through you're loop. That will speed your program up a lot.

The reason it stops immediately after letting go of the up arrow is because you've got this part inside your if keys (KEY_UP_ARROW) statement:

code:

player.x += cosd (player.dir) * player.forward_speed         player.y += sind (player.dir) * player.forward_speed

You want that to happen all the time. He won't move if his speed is 0, remember.

Here's the modified code.

Turing:

var winID := Window.Open ("graphics:1200;800,nobuttonbar,offscreenonly") colourback (2) var player :     record         x, y : real         angle : real         speed : real         rotation_speed : real         forward_accel : real         backward_accel : real         max_forward_speed : real         max_backward_speed : real     end record player.x := 100 player.y := 100 player.angle := 90 player.speed := 0 player.rotation_speed := 5 player.forward_accel := 1 player.backward_accel := 0.5 player.max_forward_speed := 10 player.max_backward_speed := -5 var picCar := Pic.FileNew ("Trueno.bmp") var picCarRotated := Pic.Rotate (picCar, round (player.angle), Pic.Width (picCar) div 2, Pic.Height (picCar) div 2) var picRoad := Pic.FileNew ("Road1.jpg") procedure playerControls     var keys : array char of boolean     Input.KeyDown (keys)     if keys (KEY_RIGHT_ARROW) & player.speed ~= 0 then         player.angle := (player.angle - player.rotation_speed) mod 360     end if     if keys (KEY_LEFT_ARROW) & player.speed ~= 0 then         player.angle := (player.angle + player.rotation_speed) mod 360     end if     if not keys (KEY_UP_ARROW) & not keys (KEY_DOWN_ARROW) then         if player.speed <= 0.5 & player.speed >= -0.5 then             player.speed := 0         end if         player.speed *= 0.97     else         if keys (KEY_UP_ARROW) then             player.speed := min (player.max_forward_speed, player.speed + player.forward_accel)         end if         if keys (KEY_DOWN_ARROW) then             player.speed := max (player.max_backward_speed, player.speed - player.backward_accel)         end if     end if end playerControls procedure updatePlayer     playerControls     player.x += cosd (player.angle) * player.speed     player.y += sind (player.angle) * player.speed     picCarRotated := Pic.Rotate (picCar, round (player.angle), Pic.Width (picCar) div 2, Pic.Height (picCar) div 2)     Pic.Draw (picCarRotated, 600, 400, picMerge)     Pic.Free (picCarRotated)     put player.x, " ", player.y, " ", player.speed end updatePlayer loop     cls     Pic.Draw (picRoad, -round (player.x), -round (player.y), picCopy)     updatePlayer     View.Update end loop Window.Close (winID)

I also rotated the picture by 90°, so you don't have to bother with the Pic.Rotate in the initialization stages.

[[Gandalf]]

I was wondering how would you check if the user hit any key at all, not everything (including having no key pressed at all) except some certain keys. Can't think of anything right now ... Thanks.

[Cervantes]

Could you restate that?

[[Gandalf]]

Yeah, I knew it was a bit unclear...

When you have an Input.Keydown statment, like if keys ('a') then ... and then you add an else, that else will include when no keys are pressed at all. I only want to do something when an actual key is pressed (when a key is pressed that is not 'b' for example).

Basically, I want to do an 'else' like statement but without a null key - I can't think of how to detect that. Probably a pretty simple solution, but I've been wondering for a while and decided to ask.

[Cervantes]

code:

if hasch and not keys ('b') then

[Gandalf] wrote:

When you have an Input.Keydown statment, like if keys ('a') then ... and then you add an else, that else will include when no keys are pressed at all.

The else would be entered only if 'a' is not pressed. Other conditions, such as if 'b' is pressed, are irrelevent.

[[Gandalf]]

Ok, thanks. I wasn't thinking about hasch/getch, trying to avoid it. Is there a way of doing it without them? Still, it's a pretty good use of hasch (as opposed to using it as a replacement of Input.Keydown).

I know about the else statment, I was just trying to explain the problem that I can't detect if keys(nothingatall).

[Cervantes]

I agree: I try to avoid using hasch & getch with Input.KeyDown, because of problems with one catching keystrokes that I want the other to catch.

Here's another way to do it. There's some need tricks in here, particularly the range of the for loop.

Turing:

var keys : array char of boolean fcn key_pressed_other_than (key : char, keyboard : array char of boolean) : boolean     if keyboard (key) then         result false     end if     for i : char         if keyboard (i) then             result true         end if     end for     result false end key_pressed_other_than loop     Input.KeyDown (keys)     locate (1, 1)     if key_pressed_other_than ('b', keys) then         put "A key has been pressed other than 'b'"     else         put "'b' has been pressed, or no key has been pressed"     end if     exit when keys (KEY_ESC) end loop

[[Gandalf]]

Nice. I'll try it out later on, thanks again .
Interesting way of doing it, I was wondering about different for loops, now I have something to think about.