Collision done directly with OnCollision ( don't understand it, help me understand)

[robert83]

[I'm just experimenting... tried 3 different methods for now, this one got my atention because it's a built-in thing]


So about the improved code (I've found this inside an example from Asphyre 2d , the SpriteEngineRPGMap one to be exact)

Every time I move my character I write the following values into it's property...

Attachment 579

Left := Round(X); 
Top := Round(Y); 
Right := Round(X + Image.Width);
Bottom := Round(Y + Image.Height);

When my character collides with the PlatForm Sprite I do this :

1. Get same coordinates from Sprite I've just hit

procedure TBlurp.DoCollision(Sprite:TSprite; var Done:boolean);
var
TileLeft, TileRight,
TileTop, TileBottom: Integer;
begin
if Sprite is TPlatform then
begin
TileLeft := Trunc(TPlatform(Sprite).X);
TileTop := Trunc(TPlatform(Sprite).Y);
TileRight := Trunc(TPlatform(Sprite).X) + TPlatform(Sprite).Image.Width;
TileBottom := Trunc(TPlatform(Sprite).Y) + TPlatform(Sprite).Image.Height;
// up
if (GetKeyState(VK_UP) < 0) then
begin
if (Self.Top+3 > TileBottom) and
(Self.Right > TileLeft) and
(Self.Left < TileRight) then
begin
Y := TileBottom;
end;
end;

Attachment 580

Now that I drew it down... checking the logic +1 or -1 depending on direction should also be enough... maybe I'll look into my rounding... maybe I don't need it...

And I think I also understand why it does it like this ... in this case if I'm touching a wall from left or right... but Not touching a wall from TOP... it won't place me right bellow an incorrect tile...

I'll try to clean the code a bit more...

Greetings
Rob

[robert83]

unit Main;
interface
uses
  Windows,Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, AdDraws, AdClasses, AdTypes, AdPerformanceCounter, AdDevIL,AdSprites,Math;
  const
  TileW = 32; // tile width
  TileH = 32; // tile height
  PlayerH = 60; // Player Height
  PlayerW = 30; // Player Width
  type
  TPlatform = class(TImageSprite)
    private
    protected
      procedure DoMove(TimeGap: Double); override;
      procedure DoCollision(Sprite:TSprite; var Done:boolean); override;
    public
      constructor Create(AParent:TSprite);override;
    end;
  TBlurp = class(TImageSprite)
    private
    vx,vy : Single;  //current velocity in pixels/second
    FLeft, FTop, FRight, FBottom: double;
    nextv,v : double;
    jumping : boolean;
    protected
      procedure DoMove(TimeGap: Double);override;
      procedure DoCollision(Sprite:TSprite; var Done:boolean);override;
    public
      constructor Create(AParent:Tsprite);override;
      property Left: double read FLeft write FLeft;
      property Top: double read FTop write FTop;
      property Right: double read FRight write FRight;
      property Bottom: double read FBottom write FBottom;
    end;
  TForm1 = class(TForm)
    procedure FormCreate(Sender: TObject);
    procedure FormDestroy(Sender: TObject);
    procedure FormKeyDown(Sender: TObject; var Key: Word;
      Shift: TShiftState);
  private
    { Private declarations }
  public
    { Public declarations }
    AdDraw:TAdDraw;
    AdSpriteEngine:TSpriteEngine;
    AdImageList:TAdImageList;
    AdPerCounter:TAdPerformanceCounter;
    AdPixelCollisionTester: TAdSpritePixelCollisionTester;
    Blurp:TBlurp;
    procedure Idle(Sender:TObject; var Done:boolean);
    procedure LoadLevel;
  end;
var
  Form1: TForm1;
  ActTime : double;
  // camera positions
  camera_x : double;
  camera_y : double;

implementation
{$R *.dfm}
procedure TForm1.LoadLevel;
var
  level:TStringList;
  ax,ay:integer;
begin
  level := TStringList.Create;
  level.LoadFromFile(ExtractFilePath(Application.ExeName)+'level2.txt');
  for ay := 0 to level.Count-1  do
  begin
    for ax := 1 to length(level[ay]) do
    begin
      case level[ay][ax] of
        'x':
        begin
          with TPlatform.Create(AdSpriteEngine) do
          begin
            Image := AdImageList.Find('WALL');
            x := ax*TileW;
            y := ay*TileH;
            z := 0;
            CollisionTester := AdPixelCollisionTester;
          end;
        end;
        'X':
        begin
          with TPlatForm.Create(AdSpriteEngine) do
          begin
            Image := AdImageList.Find('WALL');
            x := ax*TileW;
            y := ay*TileH;
            z := 0;
            CollisionTester := AdPixelCollisionTester;
          end;
        end;
      end;
    end;
  end;
  level.Free;
end;

constructor TPlatform.Create(AParent: TSprite);
begin
  inherited;
end;
constructor TBlurp.Create(AParent: TSprite);
begin
  inherited;
  vx:=128;
  vy:=128;
  V := 10; // starting velocity, used for calculating gravity effect on our little hero
  jumping:=true; // cause our character is not jumping right now
end;
 
procedure TBlurp.DoMove(TimeGap: Double);
begin
  inherited;
     Left :=   X;
     Top :=    Y;
     Right :=  X + Image.Width;
     Bottom := Y + Image.Height;
  // setting the camera to follow our HERO
  if (X > 320) and (X < (40*TileW)-320-TileW) then
    begin
      // - 64 , because when loading the level my entire background is starting from 64 instead of 0
      // looks better if there is no black line at the edge of the level...
      camera_x:=(X*-1)+320-TileW;
    end;
  if (Y > 240) and (Y < (29*TileH)-240) then
    begin
      // 29 tiles down * 64 tile.height -240 half of the screen, only moving when at center of the screen
      // well not really the center...but close anyway :)
      camera_y:=(Y*-1)+240;
    end;
  // jump

 { if (jumping = true) then
    begin
      Y:=Y-5;   // the kick in the but
    end;  }
  // gravity done here
 { if jumping = true then
    begin
      if nextv < 15 then nextv:=nextv+(v*TimeGap);
      Y:=Y+nextv;
    end
  else
    begin
      nextV:=0;
      jumping:=true;
    end; }

    if GetKeyState(VK_LEFT) < 0 then
      begin
        x := x - vx * TimeGap;
      end;
    if GetKeyState(VK_RIGHT) < 0 then
      begin
        x := x + vx * TimeGap;
      end;
    if GetKeyState(VK_UP) < 0 then
      begin
        y := y - vy * TimeGap;
      end;
    if GetKeyState(VK_DOWN) < 0 then
      begin
        y := y + vy * TimeGap;
      end;
 
  Collision;
end;

procedure TPlatform.DoMove(TimeGap : Double);
begin
  inherited;
end;

procedure TBlurp.DoCollision(Sprite:TSprite; var Done:boolean);
var
   TileLeft, TileRight,
   TileTop, TileBottom: double;
begin
  if Sprite is TPlatform then
    begin
      TileLeft := TPlatform(Sprite).X;
      TileTop := TPlatform(Sprite).Y;
      TileRight := TPlatform(Sprite).X + TPlatform(Sprite).Image.Width;
      TileBottom := TPlatform(Sprite).Y + TPlatform(Sprite).Image.Height;

      // up
      if (GetKeyState(VK_UP) < 0) then
        begin
          if (Self.Top+1  > TileBottom) and
             (Self.Right  > TileLeft) and
             (Self.Left  < TileRight) then
              begin
                 Y := TileBottom;
              end;
        end;
      // down
      if (GetKeyState(VK_DOWN) < 0) then
        begin
          if (Self.Bottom -1  < TileTop )  and
             (Self.Right  > TileLeft)  and
             (Self.Left  < TileRight) then
              begin
                 Y := TileTop-PlayerH;
              end;
        end;
      // left
      if GetKeyState(VK_LEFT) < 0 then
        begin
          if (Self.Left+1 > TileRight) and
          (Self.Top< TileBottom) and
          (Self.Bottom>TileTop)  then
            begin
              X := TileRight;
            end;
        end;
      // right
      if GetKeyState(VK_RIGHT) < 0 then
        begin
          if (Self.Right-1 < TileLeft )and
          (Self.Top< TileBottom) and
          (Self.Bottom>TileTop)  then
            begin
              X := TileLeft -PlayerW;
            end;
        end;
    end;
end;
procedure TPlatform.DoCollision(Sprite:TSprite; var Done:boolean);
begin
end;
 

procedure TForm1.FormCreate(Sender: TObject);
begin
  AdPerCounter := TAdPerformanceCounter.Create;
  AdDraw := TAdDraw.Create(self);
  AdDraw.DllName := 'AndorraDX93D.dll';

if AdDraw.Initialize then
  begin
    Application.OnIdle := Idle;
    AdImageList := TAdImageList.Create(AdDraw);
    AdImageList.LoadFromFile('BackGround.ail');

    //create the SpriteEngine
     AdSpriteEngine := TSpriteEngine.Create(nil);
     AdSpriteEngine.Surface := AdDraw;
    //Create the collision tester
    AdPixelCollisionTester := TAdSpritePixelCollisionTester.Create(AdDraw);
    LoadLevel;
    //create TImageSprite
    Randomize;
        Blurp := TBlurp.Create(AdSpriteEngine);
        with Blurp.Create(AdSpriteEngine) do
          begin
            Image := AdImageList.Find('TallHero2');
            X := 144;
            Y := 144;
            Z := 0;
            CollisionTester := AdPixelCollisionTester;
          end;
 
    // The Entire Engine is moved left by -64 , this is because of the Level Loader ...
    Camera_X:=-TileW;
    Camera_Y:=0;
    AdSpriteEngine.X:=camera_x;
    AdSpriteEngine.Y:=camera_y;

    // ************* hater *********************************
  end
 else
  begin
     ShowMessage('Error while initializing Andorra 2D. Try to use another display'+
               'mode or use another video adapter.');
    halt; //<-- Completely shuts down the application
  end;
end;
procedure TForm1.Idle(Sender: TObject; var Done: boolean);
 begin
   if AdDraw.CanDraw then // Only continue, if drawing is possible
   begin
    AdPerCounter.Calculate;
    AdPerCounter.MaximumFrameRate:=60;

    AdDraw.ClearSurface(clBlack); // Fill the surface with black color
    AdDraw.BeginScene;
    // Here you need to perform all drawing operations later
    ActTime := ActTime + AdPerCounter.TimeGap;
    if ActTime > 10 then
    begin
      AdSpriteEngine.X:=camera_x;
      AdSpriteEngine.Y:=camera_y;
      ActTime := ActTime-10;
    end;

    AdSpriteEngine.Draw;
    AdSpriteEngine.Move(AdPerCounter.TimeGap/1000);
    AdSpriteEngine.Dead;
    // debug
 
    AdDraw.EndScene;
    AdDraw.Flip; // Draws you result on the screen. Otherwise, you would not see anything
   end;
  Done := false; // Important, otherwise the function will not be called in every loop
 end;
procedure TForm1.FormDestroy(Sender: TObject);
begin
   AdSpriteEngine.Free;
   AdImageList.Free;
   AdPerCounter.Free;
   AdDraw.Free;
end;
procedure TForm1.FormKeyDown(Sender: TObject; var Key: Word;
  Shift: TShiftState);
begin
  if Key = VK_ESCAPE then Close;
end;
 
end.

Works like a charm, round trunc was my problem, and now I understand why I need +1 or -1 for x or y. Only needed to draw it down.

Greetings
Robert

[User137]

Your main problem is that you are not identifying which side you are hitting, and code you posted above has values after VK_UP all illogical.

Maybe something like this. I'm turning the logics upside down, by assuming that DoCollision is called only when and with sprite that it collides with. So all i do is check which side the block is in relation to player and move (untested):

procedure TBlurp.DoCollision(Sprite:TSprite; var Done:boolean);
var
  TileLeft, TileRight, TileTop, TileBottom: Integer;
begin
  if Sprite is TPlatform then begin
    TileLeft := Trunc(TPlatform(Sprite).X);
    TileTop := Trunc(TPlatform(Sprite).Y);
    TileRight := TileLeft + TPlatform(Sprite).Image.Width;
    TileBottom := TileTop + TPlatform(Sprite).Image.Height;
    
    if TileLeft div TileW = trunc(X+Width/2) div TileW then 
      if TileTop div TileH < trunc(Y+Height/2) div TileH then begin
        Y := TileBottom;
      end else if TileTop div TileH > trunc(Y+Height/2) div TileH then begin
        Y := TileTop - Height;
      end;
    if TileTop div TileH = trunc(Y+Height/2) div TileH then
      if TileLeft div TileW < trunc(X+Width/2) div TileW then begin
        X := TileRight;
      end else if TileLeft div TileW > trunc(X+Width/2) div TileW then begin
        X := TileLeft - Width;
      end;
  end;
end;

Edited. Noticed it might have acted wrong without extra if's. And another major error hopefully fixed. Now i notice this could use more precalculation to vars... The code blew up in hands.

Also wanted to mention this earlier. By math logics this can be simplified:

camera_x:=(X*-1)+320-TileW;

camera_x:=320-X-TileW;

Last edit: Realising that this code of mine will not cause collision when moving towards corners, it's almost as good as nothing. So i'll stick to what i said earlier, you need something really different kind of collision method for this problem.

The versions you showed earlier with gravity seemed to work almost fine. Just a few fixable bugs but they had overall more potential to work. One thing for example, when the jumping state is on and player hits block above, you must set the vertical velocity 0 and make player start dropping. This caused player to stick to the roof for small time.

Last edit2 (lol i'm just bored): I think it might work with this kind of doCollision too if instead of just checking player position, use the player movement direction (vx, vy) as help to determine what wall to collide with. What mainly boggles my mind is situation where there is 3 roof blocks above, and player holds keys Left and Up. First collision test will be to the top left block which will same time cause player to stop vertical and horizontal movement in corner. That is why in above code i ignore corner blocks, but that causes another issue when there is only corner and nothing above, it wouldn't collide.