libui/windows/areautil.c

// 18 december 2015
#include "uipriv_windows.h"
#include "area.h"

// I love COM interfaces that actually only work on C++
// ID2D1RenderTarget::GetSize is defined as returninig a structure
// with stdcall, this means it's an extra last argument
// the compiler tries to return it directly, and crashes
// I originally thought this was a bug in MinGW-w64, but it turns out it also affects MSVC! https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64384
// So we have to work around it.
// TODO is the return type correct? or should we just use C++?
void renderTargetGetSize(ID2D1RenderTarget *rt, D2D1_SIZE_F *size)
{
	typedef void (STDMETHODCALLTYPE *fptr)(ID2D1RenderTarget *, D2D1_SIZE_F *);
	fptr f;

	f = (fptr) (rt->lpVtbl->GetSize);
	(*f)(rt, size);
}

void loadAreaSize(uiArea *a, ID2D1RenderTarget *rt, double *width, double *height)
{
	D2D1_SIZE_F size;

	*width = 0;
	*height = 0;
	if (!a->scrolling) {
		if (rt == NULL)
			rt = (ID2D1RenderTarget *) (a->rt);
		renderTargetGetSize(rt, &size);
		*width = size.width;
		*height = size.height;
	}
}

void pixelsToDIP(uiArea *a, double *x, double *y)
{
	FLOAT dpix, dpiy;

	ID2D1HwndRenderTarget_GetDpi(a->rt, &dpix, &dpiy);
	// see https://msdn.microsoft.com/en-us/library/windows/desktop/dd756649%28v=vs.85%29.aspx (and others; search "direct2d mouse")
	*x = (*x * 96) / dpix;
	*y = (*y * 96) / dpiy;
}

void dipToPixels(uiArea *a, double *x, double *y)
{
	FLOAT dpix, dpiy;

	ID2D1HwndRenderTarget_GetDpi(a->rt, &dpix, &dpiy);
	*x = (*x * dpix) / 96;
	*y = (*y * dpiy) / 96;
}