[RESOLVED] Memory leak GdipCreateBitmapFromScan0

[LeandroA]

hello does anyone know why GdipCreateBitmapFromScan0 causes memory leak, next a very simple example with a timer calling the function and removing the image.

In the task manager you can see how VB6.exe gradually increases its memory

Option Explicit
Private Declare Sub GdiplusShutdown Lib "gdiplus" (ByVal Token As Long)
Private Declare Function GdiplusStartup Lib "gdiplus" (Token As Long, inputbuf As GdiplusStartupInput, Optional ByVal outputbuf As Long = 0) As Long
Private Declare Function GdipDisposeImage Lib "gdiplus" (ByVal Image As Long) As Long
Private Declare Function GdipCreateBitmapFromScan0 Lib "GdiPlus.dll" (ByVal Width As Long, ByVal Height As Long, ByVal stride As Long, ByVal PixelFormat As Long, scan0 As Any, BITMAP As Long) As Long

Private Type GdiplusStartupInput
    GdiplusVersion              As Long
    DebugEventCallback          As Long
    SuppressBackgroundThread    As Long
    SuppressExternalCodecs      As Long
End Type
Private Const PixelFormat32bppPARGB     As Long = &HE200B
Private Const GDIP_OK As Long = 0&
Dim GdipToken As Long

Private Sub Form_Load()
    Dim GdipStartupInput As GdiplusStartupInput
    GdipStartupInput.GdiplusVersion = 1&
    Call GdiplusStartup(GdipToken, GdipStartupInput, ByVal 0&)
    Timer1.Interval = 100
End Sub

Private Sub Timer1_Timer()
    Dim hImage As Long
    If GdipCreateBitmapFromScan0(16&, 16&, 0&, PixelFormat32bppPARGB, ByVal 0&, hImage) = GDIP_OK Then
        Debug.Print hImage
        GdipDisposeImage hImage
    End If
End Sub

Private Sub Form_Unload(Cancel As Integer)
    Call GdiplusShutdown(GdipToken)
End Sub

[LeandroA]

Well, it seems, according to the example, the first minutes the memory is increasing but after a few minutes it stabilizes

[wqweto]

Well, it seems, according to the example, the first minutes the memory is increasing but after a few minutes it stabilizes

It can stabilize even faster if instead of on a timer the image allocation/free is done repeatedly in an infinite loop, optionally with a single DoEvents to make UI responsive.

cheers,
</wqw>

[LeandroA]

It can stabilize even faster if instead of on a timer the image allocation/free is done repeatedly in an infinite loop, optionally with a single DoEvents to make UI responsive.

cheers,
</wqw>

If it is just an example to show that calling GdipCreateBitmapFromScan0 leaves some kind of memory leaks, but it reassures me to know that at some point it stops increasing and stabilizes

[[citation-needed]]

Do the results change if you pass valid parameters? The .NET equivalent constructor Bitmap::Bitmap(INT,INT,INT,PixelFormat,BYTE*) requires both a valid stride and a non-null pointer, neither of which is supplied in the sample code above.

[wqweto]

Do the results change if you pass valid parameters? The .NET equivalent constructor Bitmap::Bitmap(INT,INT,INT,PixelFormat,BYTE*) requires both a valid stride and a non-null pointer, neither of which is supplied in the sample code above.

Passing both stride = 0 and scan0 = NULL is supported use-case for creating empty images. This is what the oridinary Bitmap::Bitmap (int width, int height) constructor uses to create a blank bitmap.

Check out this line as implemented in libgdiplus by mono

status = GdipCreateBitmapFromScan0 (width, height, 0, PixelFormat32bppPARGB, NULL, &result);

If you follow their GdipCreateBitmapFromScan0 they bail out early only on

if (scan0 && (stride == 0 || stride % 4))

return InvalidParameter;

. . . but passing both scan0 and stridy empty is handled.

cheers,
</wqw>

[[citation-needed]]

Excellent information, @wqweto. Thank you for correcting my wrong information!