Thread: Getting a Bitmap's Buffer

Is there a way to get the buffer from an HBITMAP object? I don't want to write my own bitmap loading function if there's a couple functions I can call. I start search. (I know. Search the forums first. Post code. I'm working on it) [edit]Actually I don't really have any forums to search so I don't feel to bad[/edit]

Ok, I found this function:

Code:

LONG GetBitmapBits(
  HBITMAP hbmp,      // handle to bitmap
  LONG cbBuffer,     // number of bytes to copy
  LPVOID lpvBits     // pointer to buffer to receive bits
);

I can't find a function to get the size of the bitmaps. I know there should be something about the bitmap header.

[edit]Found it (I think)

Code:

BOOL GetBitmapDimensionEx(
  HBITMAP hBitmap,     // handle to bitmap
  LPSIZE lpDimension   // address of structure receiving dimensions
);

[/edit]

I'm either using it wrong or it doesn't work like I expect it to.

Code:

#define STRICT
#include <windows.h>
#include <stdio.h>


int pascal WinMain(HINSTANCE hInst, HINSTANCE hPrevInstance,
				   LPSTR lpszCmdParam, int nCmdShow)
{
	HBITMAP bmp;
	SIZE bmp_size;
	char string[100];

	bmp = LoadBitmap(hInst, "TestBmp");
	if (!bmp)
	{
		MessageBox(0, "Failure to load bitmap", "Fatal Error", MB_OK | MB_ICONEXCLAMATION);
		return 0;
	}

	if (!GetBitmapDimensionEx(bmp, &bmp_size))
	{
		MessageBox(0, "Failure to get bitmap dimensions", "Fatal Error", MB_OK | MB_ICONEXCLAMATION);
		return 0;
	}

	sprintf(string, "Width: %d\nHeight:%d", bmp_size.cx, bmp_size.cy);

	MessageBox(0, string, "Info", MB_OK | MB_ICONINFORMATION);

	return 0;
}

[edit]Actually, I already know the dimensions cause I'm the one who made the bitmap. :-D. Hopefully the pitch isn't different than the width.[/edit]

Three things:
1. GetBitmapDimensionEx says that

The GetBitmapDimensionEx function retrieves the dimensions of a compatible bitmap. The retrieved dimensions must have been set by the SetBitmapDimensionEx function.

2. You must delete the HBITMAP handle with DeleteObject.
3. If you want to get the bitmap dimmensions, you can try GetObject:

Code:

BITMAP tagbmp;
GetObject(bmp, sizeof(BITMAP), &tagbmp);

wsprintf(string, "W: %i\nH: %i", tagbmp.bmWidth, tagbmp.bmHeight);
MessageBox(0, string, 0, 0);
DeleteObject(bmp);

Of course! I knew there was something like that I just could remember what it was. Thank you.

tagbmp.bmBits is 0. Any ideas?

ok, I've got this code. It gets the job done, but it's a little sloppy. Oh well:

Code:

#define STRICT
#include <windows.h>
#include <windowsx.h>
#include <stdio.h>


int pascal WinMain(HINSTANCE hInst, HINSTANCE hPrevInstance,
				   LPSTR lpszCmdParam, int nCmdShow)
{
	HBITMAP bmp;
	BITMAP tagbmp;
	HDC main_dc, bitmap_dc;
	UINT color;
	UCHAR r, g, b;
	char string[100];

	bmp = LoadBitmap(hInst, "TestBmp");
	if (!bmp)
	{
		MessageBox(0, "Failure to load bitmap", "Fatal Error", MB_OK | MB_ICONEXCLAMATION);
		return 0;
	}

	GetObject(bmp, sizeof(BITMAP), &tagbmp);

	main_dc = GetDC(0);

	bitmap_dc = CreateCompatibleDC(main_dc);
	HBITMAP old_bmp = SelectBitmap(bitmap_dc, bmp);

	color = GetPixel(bitmap_dc, 0, 0);

	SelectBitmap(bitmap_dc, old_bmp);
	DeleteDC(bitmap_dc);
	DeleteObject(bmp);

	r = (color >> 0) & 0xFF;
	g = (color >> 8) & 0xFF;
	b = (color >> 16) & 0xFF;
	sprintf(string, "r: %d\ng: %d\nb: %d", r, g, b);
	MessageBox(0, string, 0, 0);

	return 0;
}

Given this structure:

Code:

typedef struct TAGIMAGE
{
	int m_width;
	int m_height;
	UINT *m_buffer;
} IMAGE, *LPIMAGE;

These two functions should give me the same result, correct?

Code:

bool CreateImage(LPIMAGE image, HINSTANCE hInst, char *res)
{
	HBITMAP hbmp;
	BITMAP bmp;

	hbmp = LoadBitmap(hInst, res);
	if (!hbmp)
		return false;

	GetObject(hbmp, sizeof(BITMAP), &bmp);
	
	image->m_width = bmp.bmWidth;
	image->m_height = bmp.bmHeight;

	image->m_buffer = (UINT*)GetBitmapPixels(hbmp, GetDC(0));
	if (image->m_buffer == NULL)
		return false;
	return true;
}

Code:

bool CreateImage(LPIMAGE image, HINSTANCE hInst, char *res)
{
	HBITMAP hbmp;
	BITMAP bmp;
	HDC main_dc, bitmap_dc;
	
	hbmp = LoadBitmap(hInst, res);
	if (!hbmp)
		return false;

	GetObject(hbmp, sizeof(BITMAP), &bmp);
	
	image->m_width = bmp.bmWidth;
	image->m_height = bmp.bmHeight;

	main_dc = GetDC(0);
	bitmap_dc = CreateCompatibleDC(main_dc);
	HBITMAP old_bmp = SelectBitmap(bitmap_dc, hbmp);

	image->m_buffer = new UINT[image->m_width * image->m_height];
	for (int y = 0; y < image->m_height; y++)
		for (int x = 0; x < image->m_width; x++)
			image->m_buffer[y * image->m_width + x] = GetPixel(bitmap_dc, x, y);

	SelectBitmap(bitmap_dc, old_bmp);
	DeleteDC(bitmap_dc);
	DeleteObject(hbmp);

	return true;
}

The second works but the first doesn't.