Mega Code Archive
How to detect simple collision and transparency
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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.
*)
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