分配TImage组件的位图句柄中的内存泄漏

Question

Assuming I have a TImage component placed on a form along with a TButton. When I click the button I run the code that follows. Ignoring the palette (I know how to create a grayscale palette and assign it) the following code works:

BYTE bBits[] = { 0x00, 0x22, 0x44, 0x88, 0x00, 0x22, 0x44, 0x88,
         0x22, 0x44, 0x88, 0x00, 0x22, 0x44, 0x88, 0x00,
         0x44, 0x88, 0x00, 0x22, 0x44, 0x88, 0x00, 0x22,
         0x88, 0x00, 0x22, 0x44, 0x88, 0x00, 0x22, 0x44 };

Image1->Picture->Bitmap->Width=32;
Image1->Picture->Bitmap->Height=32;
Image1->Picture->Bitmap->PixelFormat = pf8bit;
SetBitmapBits(Image1->Picture->Bitmap->Handle,32*32,&bBits);

Now if I try this:

BYTE bBits[] = { 0x00, 0x22, 0x44, 0x88, 0x00, 0x22, 0x44, 0x88,
         0x22, 0x44, 0x88, 0x00, 0x22, 0x44, 0x88, 0x00,
         0x44, 0x88, 0x00, 0x22, 0x44, 0x88, 0x00, 0x22,
         0x88, 0x00, 0x22, 0x44, 0x88, 0x00, 0x22, 0x44 };


HBITMAP HBmp = CreateBitmap(32, 32, 1, 8, bBits);
Image1->Picture->Bitmap->Handle=HBmp;

It does not work - it displays nothing. But if I change the CreateBitmap code to:

HBITMAP HBmp = CreateBitmap(32, 32, 1, 8, bBits);

it displays however a monochrome image which is incorrect anyway.

The real "weirdness" though is this:

BYTE bBits[] = { 0x00, 0x22, 0x44, 0x88, 0x00, 0x22, 0x44, 0x88,
         0x22, 0x44, 0x88, 0x00, 0x22, 0x44, 0x88, 0x00,
         0x44, 0x88, 0x00, 0x22, 0x44, 0x88, 0x00, 0x22,
         0x88, 0x00, 0x22, 0x44, 0x88, 0x00, 0x22, 0x44 };
Image1->Picture->Bitmap->Width=32;
Image1->Picture->Bitmap->Height=32;
Image1->Picture->Bitmap->PixelFormat = pf8bit;
HBITMAP HBmp = CreateBitmap(32, 32, 1, 8, bBits);
Image1->Picture->Bitmap->Handle=HBmp;

Again nothing displays but if I click the button twice, I get an out of resources exception so it appears there is a memory leak.

Finally if I change the order:

HBITMAP HBmp = CreateBitmap(32, 32, 1, 8, bBits);
Image1->Picture->Bitmap->Handle=HBmp;
Image1->Picture->Bitmap->Width=32;
Image1->Picture->Bitmap->Height=32;
Image1->Picture->Bitmap->PixelFormat = pf8bit;

results in an instant exception (ie only need click the button once).

Note this memory leak has nothing to do with the original bitmap handle of the TImage ie Image1->Picture->Bitmap->Handle is NULL to begin with so there is no exisitng HBITMAP to release and DeleteObject etc. I am assuming when HBITMAP is assigned to TImage1's handle that TImage takes ownership.

Any explanation? Thank you in advance.

PS: For reference sake this is how I did it with SetBitmapBits which worked:

BYTE bBits[] = { 128, 128, 128, 128, 0x00, 0x22, 0x44, 0x88,
         0x22, 0x44, 0x88, 0x00, 0x22, 0x44, 0x88, 0x00,
         0x44, 0x88, 0x00, 0x22, 0x44, 0x88, 0x00, 0x22,
         0x88, 0x00, 0x22, 0x44, 0x88, 0x00, 0x22, 0x44 };

TMaxLogPalette lp;
lp.palVersion = 0x0300;
lp.palNumEntries = 256;

for (int i = 0; i < 256; i++) {
    lp.palPalEntry[i].peRed   = i;
    lp.palPalEntry[i].peGreen = i;
    lp.palPalEntry[i].peBlue  = i;
    lp.palPalEntry[i].peFlags = PC_RESERVED;
}

HPALETTE pal= CreatePalette((LOGPALETTE*)&lp);

Image1->Picture->Bitmap->Width=32;
Image1->Picture->Bitmap->Height=32;
Image1->Picture->Bitmap->PixelFormat = pf8bit;
Image1->Picture->Bitmap->Palette = pal;
SetBitmapBits(Image1->Picture->Bitmap->Handle,32*32,&bBits);

Answer 1

Ok figured part of it out:

As soon as you do this:

Image1->Picture->Bitmap->Width=32;
Image1->Picture->Bitmap->Height=32;
Image1->Picture->Bitmap->PixelFormat = pf8bit;

Image1 creates a new HBITMAP so the reference to the bitmap:

HBITMAP HBmp = CreateBitmap(32, 32, 1, 8, bBits);

gets lost without memory cleanup - hence a memory leak.

However I still don't get why:

HBITMAP HBmp = CreateBitmap(32, 32, 1, 8, bBits);
Image1->Picture->Bitmap->Handle=HBmp;

doesn't work.

To clarify the following code works without leaking:

BYTE bBits[] = { 0x00, 0x22, 0x44, 0x88, 0x00, 0x22, 0x44, 0x88,
     0x22, 0x44, 0x88, 0x00, 0x22, 0x44, 0x88, 0x00,
     0x44, 0x88, 0x00, 0x22, 0x44, 0x88, 0x00, 0x22,
     0x88, 0x00, 0x22, 0x44, 0x88, 0x00, 0x22, 0x44 };


HBITMAP h= Image1->Picture->Bitmap->Handle;

if (h) {
Image1->Picture->Bitmap->ReleaseHandle();
DeleteObject(h);
}
Image1->Picture->Bitmap->Width=32;
Image1->Picture->Bitmap->Height=32;
Image1->Picture->Bitmap->PixelFormat = pf8bit;
h= Image1->Picture->Bitmap->Handle;
Image1->Picture->Bitmap->ReleaseHandle();
DeleteObject(h);

HBITMAP HBmp = CreateBitmap(32, 32, 1, 8, bBits);
Image1->Picture->Bitmap->Handle=HBmp;

Note that

Image1->Picture->Bitmap->ReleaseHandle();
DeleteObject(h);

is necessary before and after. The first time the button is clicked the before is unnecessary since h will be null, however on subsequent clicks it is.