I would like to write a programme that can demonstrate how gravity work by showing bouncing balls on the screen- the idea is that the user can set the strength of the gravity, and then see how the balls react and bounce differently depending on how strong gravity is.

I know how to create objects and draw circles on the screen (to represent the balls) but I have no idea how to make them move around- or how to move them around in real time.

Could anyone please help me and give me some tips?

first thing, you must learn a lot of physics, until your be able to calculate on paper how a ball is bouncing.
after that chapter is completed then you take the delphi and learn about canvas(which is the base of graphics in delphi) and from there how to draw a circle at a specific position on the screen.

best regards,

Thanks for the help- I've been told that if I want to have the balls bouncing around in real time, a 'thread' is best- I've done this sort of thing in Gamemaker before, and its easy to do, as bouncing is calculated for you, and the screen would update the balls position every frame- Could anyone please help explain how threads work in Delpih?

i'm not sure how complex is this "ball bouncing" but i don't think you need a thread for that. anyway if you want to learn about threads in delphi search on google. also take a look here: http://delphi.about.com/sitesearch.h...de=3176&type=1

best regards,

Thank you for your help- I have figured out how to make a ball bounce, there was no thread needed- It was possible with a while loop.

now, is the moment to help the others:cheesy:. if you can, please post your code, in this way if somebody search the same thing, he can find it here

best regards,

Ok right- here is my code:




unit frm_main;
interface
uses
Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
Dialogs, ExtCtrls, StdCtrls, ComCtrls, Math;
type
TForm1 = class(TForm)
Backround_pnl: TPanel;
Bouncing_ball_image: TShape;
Go_btn: TButton;
EnergyLost_bar: TTrackBar;
Gravity_strength_bar: TTrackBar;
Label1: TLabel;
Label2: TLabel;
Horizontal_Movement_bar: TTrackBar;
Label3: TLabel;
Reset_btn: TButton;
procedure Go_btnClick(Sender: TObject);
procedure FormCreate(Sender: TObject);
procedure Reset_btnClick(Sender: TObject);
private
{ Private declarations }
public
{ Public declarations }
end;
var
Form1: TForm1;
StartingHeight : Integer; //saves how high the ball starts
StartingLeft : Integer; //saves where the ball's left position is
implementation
{$R *.dfm}
procedure TForm1.Go_btnClick(Sender: TObject); //when clicking on the go button
var
BallMoving : Boolean; //checks to see if the ball is moving- to end the loop
Velocity : Real; //speed in pixels per loop
LastTop : Integer; //Specifies the position of the ball's last position (the top of the ball's x value)
AddonVelocity : Real; //speed in pixels per loop one loop ahead
EnergyLost : Real; //Energy Lost makes the ball bounce less high each time
LastLeft : Integer;// the last position of the ball's y value
Sideways_Velocity : Real; //Sideways speed in pixels per loop- a - speed makes it go to the left, + to the right
Addon_Sideways_Velocity : Real; //Sideways Speed one loop ahead
Horizontal_Component : Real; //controls sideways speed (- is to the left, + is to the right)
//top, left, width, height, tag are properties of the ball- thus not set as variables here

begin
Bouncing_ball_image.Top := StartingHeight;
Velocity := 0;
BallMoving := true;
tag := 0; //-----------setting starting values-----------------------
lasttop := 0;
Sideways_Velocity := 0;
LastLeft := 0;

with Bouncing_ball_image do //--------------------------Starting repeat loop with the ball's position------------------------
repeat
AddonVelocity := Velocity + 1; //Adds one pixel per loop onto the speed each loop, simulating acceleration
if Velocity >= 0 then //means the ball is going down
Begin //only starts next statement if velocity is bigger or equal to 0 (Ball going down)
//------------------ball going down code--------------------------
If (top + AddonVelocity) >= (Backround_pnl.Height - height)//checks if ball hits floor( if ball's x + speed (distance moved
//next loop) > = the panel's height - ball height, it'll be on the floor
then
begin
LastTop := top;
Top := Backround_pnl.Height - height; //so that the ball cannot go throught the floor- it bounces right on the surface
//Makes the ball's x = panel hegith - ball's height, therefore won't go through bottom of panel
EnergyLost := (EnergyLost_bar.Position / EnergyLost_bar.Max); //Works out energy lost- has to be > 1 else the ball stops at once.
AddonVelocity := ((AddonVelocity * EnergyLost)* -1); //this makes the ball turn around (reverses vertical speed, therefore it goes up)

if AddonVelocity > (-5) then BallMoving := false; //if the ball bounces less than 5 pixels it'll stop-
end //to avoid the ball bouncing- but not high enough to be noticed.
else
top := top + round(AddonVelocity); //If its not hitting the ground...ball's x = ball's x + speed. (rounded else you get incompatible types error- float with integer)
end
else //----------if the ball is going up--------------------------
Begin
If top + round(AddonVelocity) < 0 then //If ball's x + speed (how many pixels it'll move next loop) < 0 then it'd go through the top of the panel
begin
Top := 0 //would prevent the ball going through the top of the form

end
else
If LastTop > 0 then //if the ball's x > 0...
Begin
Top := LastTop;
LastTop := 0;
AddonVelocity := AddonVelocity - 1; //now each loop u take away speed (one less pixel per loop)- to simulate deacceleration
end
else
Begin
Top := top + round(AddonVelocity); //else ball's x = ball's x + speed
end;
end;

//the sideways bouncing code
//--------------------------------------------Code below works out bouncing on the right wall---------------------------
Horizontal_Component := Horizontal_Movement_bar.Position; //Horizonal bar thingy
Addon_Sideways_Velocity := Horizontal_Component; //Adds one pixel per loop onto the speed each loop, simulating acceleration
if Sideways_Velocity >= 0 then //means the ball is going right
Begin //only starts next statement if Sideways_Velocity is bigger or equal to 0 (Ball going right)
//if y + pixels/loop >= 1009 - 65 then...
If (left + Addon_Sideways_Velocity) >= (Backround_pnl.Width - width) //the next loop would put the ball through the walls-
then // if statement below is to stop that happening
begin
//LastLeft := left;
Left := Backround_pnl.Width - Width; //so that the ball cannot go throught the wall- it bounces right on the surface
Horizontal_Movement_bar.Position := (Horizontal_Movement_bar.Position*-1); //the horizontal bar position is made negative as that is what controls sideways bouncing
Addon_Sideways_Velocity := ((Addon_Sideways_Velocity * Horizontal_Component)* -1); //this makes the ball reverse direction

if Addon_Sideways_Velocity > (-5) then Sideways_Velocity := 0; //if the ball bounces less than 5 pixels it'll stop- and just fall
end
else
left := left + round(Addon_Sideways_Velocity);
end
else
// -----------------------------Code Below works out bouncing on left wall---------------------------------
Begin //y + Pixels/loop < 0 then...
If left + round(Addon_Sideways_Velocity) < 0 then //Code is for when it hits left wall
begin
left := 0; //prevents the ball going through the walls of the form
Horizontal_Movement_bar.Position := Horizontal_Movement_bar.Position * -1; //reverses direction
end
else
If LastLeft > 0 then
//ball going left
Begin
LastLeft := 0;
Left := LastLeft;
Addon_Sideways_Velocity := Addon_Sideways_Velocity -1;
//Addon_Sideways_Velocity := Horizontal_Component;
Horizontal_Movement_bar.Position := Horizontal_Movement_bar.Position * -1;
Addon_Sideways_Velocity := Horizontal_Component * -1 ;
end
else
Begin
Left := Left + round(Addon_Sideways_Velocity);
end; //--------------end of left wall bouncing---------------------
end;
If Bouncing_ball_image.Tag > 0 then
Begin
BallMoving := false;
end;

Sideways_Velocity := Addon_Sideways_Velocity ;
Velocity := AddonVelocity;
Application.processmessages;
sleep(Gravity_strength_bar.Max - Gravity_strength_bar.position);
If Bouncing_ball_image.Left > Backround_pnl.Width then
Begin
Bouncing_ball_image.Left := Backround_pnl.Width -1;
end;


until BallMoving = false; //while loop ends when the ball is not moving

end;
procedure TForm1.FormCreate(Sender: TObject); //when form is created
begin
Bouncing_ball_image.Brush.Color := clRed; //Makes the ball red
Backround_pnl.DoubleBuffered := true; //a function to make the moving look smoother
StartingHeight := Bouncing_ball_image.Top; //Sets the default hieght (x)
StartingLeft := Bouncing_ball_image.Left; //sets default starting left (y)
end;
procedure TForm1.Reset_btnClick(Sender: TObject); //resetting button
begin
//Tag := 1;
Bouncing_ball_image.Left := StartingLeft;
Bouncing_ball_image.Top := StartingHeight;
Horizontal_Movement_bar.Position := 0;
Gravity_strength_bar.Position := 10;
EnergyLost_bar.Position := 20;
end;
end.