[fpc-pascal] Syntax to select constant or variable with function call

[Michael Van Canneyt]

On Mon, 25 Sep 2017, James Richters wrote:

>
>> See what I wrote yesterday :)
> Sorry I had a duplicate message, I was having difficulty with my email and accidentally sent a mail with an alias, I thought it was rejected but it was just delayed.
>
> Here is what I have now, and it's working great, thanks for the help.
>
> Function Find_Color(ColorArray : Array of VGARGBRec; R ,G ,B : Word) : Byte;
> Var
>   Dist,Closest:Double;
>   i,BestChoice:Byte;
> Begin
>   Closest:=200000;
>   For i:= Low(ColorArray) to High(ColorArray) do
>      Begin
>         Dist := ((R-ColorArray[i].R)*(R-ColorArray[i].R))
>               + ((G-ColorArray[i].G)*(G-ColorArray[i].G))
>               + ((B-ColorArray[i].B)*(B-ColorArray[i].B));
>         If Dist <= Closest Then
>            Begin
>               Closest:=Dist;
>               BestChoice:=i;
>            End;
>      End;
>   Find_Color:=BestChoice;
> end;
>
> Call with:
> Find_Color(Arrayname, Red, Green, Blue);
>
>
>> The loop can still be optimized, but that is another topic.
>
> Please elaborate, I would be very interested in how this could be optimized.

1. Use a pointer to the element in the array.
2. Use SQR instead of x*x
2. Use With to calculate your distance

     With ColorArray[i] do
       Dist :=Sqr(aR-R)+Sqr(aG-G)+Sqr(aB-B);

I would think that something like the following is the most optimal:

  Function Find_Color(ColorArray : Array of VGARGBRec; aR ,aG ,aB : Word) : Byte;

  Var
    Dist,Closest:Double;
    i,BestChoice:Byte;
    P : ^VGARGBRec;

  Begin
    BestChoice:=255;
    Closest:=200000;
    P:=@ColoyArray[Low(ColorArray)];
    For i:= Low(ColorArray) to High(ColorArray) do
      begin
      With P^ do
        Dist:=Sqr(aR-R)+Sqr(aG-G)+Sqr(aB-B);
      If Dist<=Closest Then
        Begin
        Closest:=Dist;
        BestChoice:=i;
        End;
      Inc(P);
      end;
    Find_Color:=BestChoice;
  end;

I didn't test the code, but you catch my drift, I suppose...

Michael.