Can't display bitmap in win32

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This is how i'm creating the bitmap

C++

Bitmap bmp(100, 100, PixelFormat32bppARGB);

Then I use LockBits to change a portion of the bitmap's pixels

C++

void Example_LockBits2()
{
	UINT* pixels;
	// Lock a 50xs30 rectangular portion of the bitmap for writing.
	BitmapData bitmapData;
	Rect rect(20, 10, 50, 30);

	bmp.LockBits(
		&rect,
		ImageLockModeWrite,
		PixelFormat32bppARGB,
		&bitmapData);

	// Write to the temporary buffer provided by LockBits.
	pixels = (UINT*)bitmapData.Scan0;

	for (UINT row = 0; row < 30; ++row)
	{
		for (UINT col = 0; col < 50; ++col)
		{
			pixels[row * bitmapData.Stride / 4 + col] = 0xff00ff00;
		}
	}

	// Commit the changes, and unlock the 50x30 portion of the bitmap.  
	bmp.UnlockBits(&bitmapData);
}

And finally try to display it in WM_PAINT

C++

case WM_PAINT:
	{
		Example_LockBits2();
		Graphics grap(GetDC(hwnd));
		grap.DrawImage(&bmp, 150, 100);
		break;
	}

Since i'm new to GDI+ i think it could be anything, especially on the creation of the Bitmap, any help appreciated

Posted 12-Dec-14 3:26am

Member 11287295

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Comments

Richard MacCutchan 12-Dec-14 10:02am

What happens if you try without calling Example_LockBits2? Does it then work successfully? You also need to check that your call to DrawImage conforms to the rules in the documentation.

Member 11287295 12-Dec-14 11:23am

Doesn't work either way, that's why I'm thinking you cannot create a bitmap with that constructor, but I can't see no example online on how to create a gdi+ bitmap on runtime

Richard MacCutchan 12-Dec-14 11:35am

I have:


Graphics    myGraphics(GetDC(hWnd));
PointF      point(0., 0.);
Image*      image = new Image(L"BACK12.BMP");
myGraphics.DrawImage(image, point);

which works fine. You need to use your debugger to find out what is happening in your code.

Member 11287295 12-Dec-14 11:49am

I assume you're loading a picture from a file, which is not what i'm trying to do. I need to create variable in size bitmaps on runtime

Richard MacCutchan 12-Dec-14 11:57am

You have not shown where your bitmap comes from or how you created it. I would suggest you focus on getting a basic bitmap displayed, before trying to modify it. See http://msdn.microsoft.com/en-us/library/ms533815(v=vs.85).aspx for more information.

Member 11287295 12-Dec-14 12:02pm

It's the first line of code of the question :

Bitmap bmp(100, 100, PixelFormat32bppARGB);

Actually I know the procedure to display bitmaps the whole purpose of the question is why this particular case doesn't work

Richard MacCutchan 12-Dec-14 13:12pm

That is a 100x100 bitmap, but you are only adding data to a small part of it. I think you need to start with a fully initialised bitmap.

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bling · Accepted Answer · 2014-12-22T07:08:00

Solution 1

You need to assign bitmapData to the return value for Lockbits.

BitmapData bitmapData = bmp.LockBits(
    &rect,
    ImageLockModeWrite,
    PixelFormat32bppARGB,
    &bitmapData);

Posted 22-Dec-14 7:08am

bling