How-to-detect-simple-collision-and-transparency


            Title: How to detect simple collision and transparency
function CheckBoundryCollision( R1, R2 : TRect; pR : PRect = nil; OffSetY : LongInt = 0; OffSetX : LongInt = 0): boolean; {overload;}
 // Simple collision test based on rectangles.
begin
 // Rectangle R1 can be the rectangle of the character (player)
 // Rectangle R2 can be the rectangle of the enemy
 if( pR nil ) then
 begin
 // Simple collision test based on rectangles. We use here the
 // API function IntersectRect() which returns the intersection rectangle.
 with( R1 ) do
 R1:=Rect( Left+OffSetX, Top+OffSetY, Right-(OffSetX * 2), Bottom-(OffSetY * 2));
 with( R2 ) do
 R2:=Rect( Left+OffSetX, Top+OffSetY, Right-(OffSetX * 2), Bottom-(OffSetY * 2));
 Result:=IntersectRect( pR^, R1, R2 );
 end
 else begin
 // Simple collision test based on rectangles. We can also use the
 // API function IntersectRect() but i believe this is much faster.
 Result:=( NOT ((R1.Bottom - (OffSetY * 2) .Top + OffSetY)
 or(R1.Top + OffSetY R2.Bottom - (OffSetY * 2))
 or( R1.Right - (OffSetX * 2) .Left + OffSetX)
 or( R1.Left + OffSetX R2.Right - (OffSetX * 2))));
 end;
end;
(*
 Also you can make an overloaded function with the same name based on handles (to make it easier).
*)
function CheckBoundryCollision( h1, h2 : Hwnd; pR : PRect = nil; OffSetY : LongInt = 0; OffSetX : LongInt = 0): boolean; {overload;}
var
 R1 : TRect;
 R2 : TRect;
begin
 FillChar( R1, SizeOf( R1 ), 0 );
 FillChar( R2, SizeOf( R2 ), 0 );
 // Note: You will get here the REAL screen coordinates.
 // It doesn't matter if a control is placed inside a panel or something.
 GetWindowRect( h1, R1 );
 GetWindowRect( h2, R2 );
 Result:=CheckBoundryCollision( R1, R2, pR, OffsetY, OffSetX );
end;
As an example, the above function may be used in a (threated timer) loop like this to check the player against multiple enemies:
 for i := 0 to Length( Enemies ) - 1 do
 if( CheckCollision( Player.Handle, Enemies[i].Handle, nil, 4, 4 )) then
 GameOver;
(*
Bottom line is that usually it's enough if it "looks" real, and less important that
it "is" real. It's a balance between how exact we want it, and how fast we need it to perform.
I have used this methods in a simple game and it just works fine. Let's talk about transparency.
You can use Regions to create special shaped Wincontrols. For example: A TPanel with a TImage
on it (Panel1 and Image1). You can shape the panel to the image using the following examples:
*)
function CreateRegion( Bitmap : TBitmap; Rect : TRect; TransColor : TColor ) : hRgn;
var
 i1, Count : LongInt;
 x,y : LongInt;
 c1 : Cardinal;
 c,t : TColor;
 Msg : TMsg;
begin
 Result:=0;
 if( NOT Assigned( Bitmap )) then
 Exit;
 Count :=0;
 {if( TransColor = clAutomatic ) then
 }t:=Bitmap.Canvas.Pixels[ Rect.Left, Rect.Top ]
 {else t:=TransColor};
 with( Bitmap.canvas ) do
 for y := Rect.Top to Rect.Bottom do
 begin
 // Sort of the same like Application.ProcessMessages but doesn't require
 // the bulky Forms unit.
 PeekMessage( Msg, 0, 0, 0, PM_REMOVE );
 x:=Rect.Left;
 while( x = Rect.Right ) do
 begin
 C:=Pixels[ x, y ];
 if( C t ) then
 begin
 i1 := x;
 while( C t ) do
 begin
 Inc(i1);
 C:=Pixels[ i1, y ];
 if( i1 = Rect.Right ) then
 Break;
 end;
 c1:=CreateRectRgn( x-Rect.Left,y-Rect.Top, i1-Rect.Left, (y-Rect.Top) + 1 );
 if( count = 0 ) then
 Result:=c1
 else begin
 CombineRgn( Result, Result, c1, RGN_OR );
 DeleteObject( c1 );
 end;
 Inc( Count );
 x := i1;
 Continue;
 end;
 Inc(x);
 end;
 end;
 if( Count = 0 ) and ( Result 0 ) then
 begin
 DeleteObject( Result );
 Result:=0;
 end;
end;
 // Put this somewhere in your code (for example in the FormCreate event)
 begin
 Image1.Left:=0;
 Image1.Top:=0;
 Image1.AutoSize:=TRUE;
 Panel1.BevelInner:=bvNone;
 Panel1.BevelOuter:=bvNone;
 Panel1.Width:=Image1.Width;
 Panel1.Height:=Image1.Height;
 // Create a region of the bitmap that is inside the image and set the region for the window.
 // Note: In this example the transparent color is black. Make sure the transparent (background) color is
 // black! To be sure that you using the right color, you can also try this: Image1.Picture.Bitmap.Pixels[ 0, 0 ]
 with( Panel1 ) do
 SetWindowRgn( Handle, CreateRegion( Image1.Picture.Bitmap, Rect( 1, 1, Width, Height ), clBlack ));
 end;
 
(*
Note: When you move the panel it is possible that the bitmap starts to flicker. You can create an
 Message handler for the message WN_EREASEBKGND to avoid the flicker. See the help of Delphi how to
 create new components and/or message handlers if do not know. Here is an example:
 procedure TMyPanel.WMEraseBkgnd(var Message: TWmEraseBkgnd);
 begin
 if( csDesigning in ComponentState ) then
 inherited
 else Message.Result:=1; // Fake erase
 end;
*)
(*
NOTE: Absolutly no warranty to this code. This is just an example. It is possible that you need to make some
improvements to the code to give it a more proffesional behaviour.
This article was aimed towards beginners wanting get into game programming, I??ll hope it was helpful.
Regards and good luck,
Erwin Haantjes.
*)
Hardware Delphi
