Drawing dotted lines


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3 steps to show how to draw vertical and horizontal dotted lines(1 pixel on 2) using GDI calls. This code works under all Win32 platforms.

Step 1 (initialization)

A patterned brush is created during program (or view) initialization. This brush will be used to draw the dotted lines :

	// Create a dotted monochrome bitmap
	WORD b[8] = { 0xAAAA, 0x5555, 0xAAAA, 0x5555, 0xAAAA, 0x5555, 0xAAAA,
	0x5555 };
	bm.bmType = 0;
	bm.bmWidth = 16;
	bm.bmHeight = 8;
	bm.bmWidthBytes = 2;
	bm.bmPlanes = 1;
	bm.bmBitsPixel = 1;
	bm.bmBits = b;
	HBITMAP hbm = CreateBitmapIndirect(&bm);

	// Create the brush from the bitmap bits
	HBRUSH hPatternBrush = CreatePatternBrush(hbm);

	// Delete the useless bitmap


Step 2 (drawing)

Dotted lines are drawn using PatBlt() :

	// Select the patterned brush into the DC
	HBRUSH oldBrush = (HBRUSH)SelectObject(hDC, hPatternBrush);

	// Draw an horizontal line
	PatBlt(hDC, 10, 10, 300, 1, PATCOPY);

	// Invert a vertical line 2 pixels wide
	PatBlt(hDC, 10, 10, 2, 300, PATINVERT);

	// Clean up
	SelectObject(hDC, oldBrush);


If drawing occurs in a "scrollable view", don't forget to align the brush origin into the DC BEFORE to select the brush :


	// We are in a CScrollView, the patterned brush must be aligned
	CPoint sp = GetDeviceScrollPosition();
	SetBrushOrgEx(hDC, -sp.x & 7, -sp.y & 7, NULL);

	// Select the patterned brush into the DC
	HBRUSH oldBrush = (HBRUSH)SelectObject(hDC, hPatternBrush);


Step 3 (destruction)

When the patterned brush is useless, it must be destroyed :

	// Delete the patterned brush



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