Re Integer Combine2 and Combine3

[dicepd]

Jerome,

I am proposing the following changes to the pascal Combine2 & 3 for integer vectors.

function TGLZVector4b.Combine2(constref V2: TGLZVector4b; const F1, F2: Single): TGLZVector4b;
//Var
//  va, vb : TGLZVector4b;
//  ws : Byte;
begin
  //ws:=Self.W;               // doing it this way is both inefficient and
  //va := Self * F1;          // inaccurate with 12 calls to clampbyte
  //vb := v2 * F2;            // reducing the precision. Also more conversions
  //result := va + vb;        // from int to float and float to int.
  result.X := ClampByte(Round(Self.X * F1 + V2.X * F2));
  result.Y := ClampByte(Round(Self.Y * F1 + V2.Y * F2));
  result.Z := ClampByte(Round(Self.Z * F1 + V2.Z * F2));
  result.W := Self.W;
end;              

Benefits:

• It is what I think a routine like this should be doing, providing a more accurate integer multiple operations at scale. It does not throw away intermediate partials when calculating the result.
• For asm routines we would no longer have to do the trunc.
• It is faster in pure pascal with fewer calls to lower routines.

Disadvantage

• none that I can see.

I am basing this on the presumption that this in its int form is used in areas like scaling and offsetting a scene object at a distance, Hit tests etc.

[jdelauney]

Yes calling "self" for doing calculs with decrease perf and reduce accuracy. You're right. I don't think about about those calls to clampbyte