Challenge: PointInRect and RectInRect

[grudzio]

All right. Here is another version that works for all cases including JSoftware's one.
[pascal]
function RectInRect(R1,R2 : TRect) : boolean;
var
w,h : integer;
x1,x2,y1,y2 : integer;
begin
w := (R1.Right - R1.Left) + (R2.Right - R2.Left);
h := (R1.Bottom - R1.Top) + (R2.Bottom - R2.Top);

x1 := min(R1.Left, R2.Left);
x2 := max(R1.Right, R2.Right);
y1 := min(R1.Top, R2.Top);
y2 := max(R1.Bottom, R2.Bottom);

Result := ((x2-x1) < w) and ((y2-y1) < h);
end;
[/pascal]

This function uses the fact that if two rects overlap then the difference
between smallest left and biggest right coordinate must be smaller then the sum of their widths. Same with Top and Bottom values.
What is your opinion? Any thoughts on improving?

[Nitrogen]

You could have early-outs so the function doesnt have to compute needless information:

[pascal]function RectInRect(R1,R2 : TRect) : boolean;
var
w,h : integer;
x1,x2,y1,y2 : integer;
begin
w := (R1.Right - R1.Left) + (R2.Right - R2.Left);

x1 := min(R1.Left, R2.Left);
x2 := max(R1.Right, R2.Right);

if ((x2-x1) < w) then begin result := false; exit; end;

h := (R1.Bottom - R1.Top) + (R2.Bottom - R2.Top);

y1 := min(R1.Top, R2.Top);
y2 := max(R1.Bottom, R2.Bottom);

Result := ((y2-y1) < h);
end;[/pascal]

[jdarling]

Well, JSoftware points out a situation that should work. I have to admit that my code doesn't work in that situation . Course, the idea is to post a common problem and hopefully find a fast solution for anyone to use, idealy the sample code I provide would work, but in this case, seems I goofed.

[User137]

Here's my versions:

Makes check for rectangle first and turn it around if needed... reading above solutions this may not be fastest :s

// Switches 2 any variables
procedure SwitchVar(p1,p2: Pointer; Size: Integer);
var temp: pointer;
begin
getmem(temp,size);
try
movememory(temp,p1,Size);
movememory(p1,p2,Size);
movememory(p2,temp,Size);
finally
freemem(temp);
end;
end;

function PointInRect2(p: TPoint; r: TRect): boolean;
begin
if r.Left>r.Right then switchvar(@r.left,@r.right,4);
if r.Top>r.Bottom then switchvar(@r.top,@r.bottom,4);
result:=(p.x>=r.Left) and (p.x<=r.Right) and
(p.y>=r.Top) and (p.y<=r.Bottom);
end;


I found this function in other language who knows where.. anyway i just tested every possible situation with it to success. Only exception for fail is if rectangles are not made normally; top left to bottom right.

function RectCollide(x0,y0,x1,y1,x2,y2,x3,y3: single): boolean;
begin
result:=not( ((x0<x2) and (x1<x2)) or
((x0>x3) and (x1>x3)) or
((y0<y2) and (y1<y2)) or
((y0>y3) and (y1>y3)) );
end;

Edit: Had to remove all BBCode etc. because they removed parts of code...