Posted on by cambalinho

VB6 – why the ‘for’ loop is so slow?

see these 'for' loop:

Public Function SetTransparentColor(color As Long)
    Dim X As Integer
    Dim Y As Integer
    Dim c As Long
    Dim h As Long
    Dim w As Long
    Dim temp As BGRAQUAD ' substitua BGRColor pelo tipo de dado correto usado em bDibBGRA


    h = Height - 1
    w = Width - 1


    For c = 0 To h * w ' movendo as operaes fora do loop for
        X = c Mod (w + 1)
        Y = Int(c / (w + 1))
        temp = bDibBGRA(c)


        ' modificando apenas a propriedade necessria
        If (RGB(temp.B, temp.G, temp.R) = color) Then
            temp.B = 255
            bDibBGRA(c) = temp
        End If


Next c


End Function

even i comment all the code, inside the 'for', i lose more than 50% of performance\optimization :(
in these case the image is 330X330.