DialogFontFix.hpp

#pragma once
// DLGTEMPLATEEX structure
// https://docs.microsoft.com/en-us/windows/desktop/dlgbox/dlgtemplateex

const uint8_t* SkipIDorString(const uint8_t* p)
{
	if (*reinterpret_cast<const uint16_t*>(p) == 0xFFFF)
		return p + sizeof(uint16_t) * 2;

	while (*reinterpret_cast<const uint16_t*>(p))
		p += sizeof(uint16_t);

	return p += sizeof(uint16_t);
}

const uint8_t* SkipString(const uint8_t* p)
{
	while (*reinterpret_cast<const uint16_t*>(p))
		p += sizeof(uint16_t);

	return p += sizeof(uint16_t);
}

WORD MapFontHeightToPointSize(LONG height)
{
	if (height < 0)
	{
		HDC hdc = GetDC(nullptr);
		if (hdc)
		{
			auto dpi = GetDeviceCaps(hdc, LOGPIXELSY);
			ReleaseDC(0, hdc);
			return MulDiv(-height, 72, dpi);
		}
	}
	return static_cast<WORD>(height);
}

INT_PTR DialogBoxIndirectParamFixFontWithSize(HINSTANCE hInstance, LPCDLGTEMPLATEW hDialogTemplate, size_t templateSize,  HWND hWndParent, DLGPROC lpDialogFunc, LPARAM dwInitParam)
{
	auto dlgVerAndSignature = reinterpret_cast<const WORD*>(hDialogTemplate);
	// is an extended dialog box and version is 1
	if (dlgVerAndSignature[1] == 0xFFFF && *dlgVerAndSignature == 1)
	{
		auto dlgTemplate = reinterpret_cast<const uint8_t*>(hDialogTemplate);
		dlgTemplate += sizeof(WORD); // dlgVer
		dlgTemplate += sizeof(WORD); // signature
		dlgTemplate += sizeof(DWORD); // helpID
		dlgTemplate += sizeof(DWORD); // exStyle
		dlgTemplate += sizeof(DWORD); // style
		dlgTemplate += sizeof(WORD); // cDlgItems
		dlgTemplate += sizeof(short); // x
		dlgTemplate += sizeof(short); // y
		dlgTemplate += sizeof(short); // cx
		dlgTemplate += sizeof(short); // cy
		dlgTemplate = SkipIDorString(dlgTemplate); // menu
		dlgTemplate = SkipIDorString(dlgTemplate); // windowClass
		dlgTemplate = SkipString(dlgTemplate); // title

		NONCLIENTMETRICSW ncm = { sizeof(ncm) };
		if (SystemParametersInfoW(SPI_GETNONCLIENTMETRICS, sizeof(ncm), &ncm, 0))
		{
			size_t fontSize = (wcslen(ncm.lfMessageFont.lfFaceName) + 1) * sizeof(wchar_t);
			size_t origTemplateSize = dlgTemplate - reinterpret_cast<const uint8_t*>(hDialogTemplate);
			size_t newTemplateSize = origTemplateSize;
			newTemplateSize += sizeof(WORD); // pointsize
			newTemplateSize += sizeof(WORD); // weight
			newTemplateSize += sizeof(BYTE); // italic
			newTemplateSize += sizeof(BYTE); // charset
			newTemplateSize += fontSize; // typeface

			dlgTemplate += sizeof(WORD); // pointsize
			dlgTemplate += sizeof(WORD); // weight
			dlgTemplate += sizeof(BYTE); // italic
			dlgTemplate += sizeof(BYTE); // charset
			dlgTemplate = SkipString(dlgTemplate); // typeface
			size_t remainSize = templateSize - (dlgTemplate - reinterpret_cast<const uint8_t*>(hDialogTemplate));
			newTemplateSize += remainSize;

			auto newTemplate = new uint8_t[newTemplateSize];
			memcpy(newTemplate, hDialogTemplate, origTemplateSize);

			auto newTemplateFont = newTemplate + origTemplateSize;
			*reinterpret_cast<WORD*>(newTemplateFont) = static_cast<WORD>(MapFontHeightToPointSize(ncm.lfMessageFont.lfHeight)); // pointsize
			newTemplateFont += sizeof(WORD);
			*reinterpret_cast<WORD*>(newTemplateFont) = static_cast<WORD>(ncm.lfMessageFont.lfWeight); // weight
			newTemplateFont += sizeof(WORD);
			*reinterpret_cast<BYTE*>(newTemplateFont) = ncm.lfMessageFont.lfItalic; // italic
			newTemplateFont += sizeof(BYTE);
			*reinterpret_cast<BYTE*>(newTemplateFont) = ncm.lfMessageFont.lfCharSet; // charset
			newTemplateFont += sizeof(BYTE);

			memcpy(newTemplateFont, ncm.lfMessageFont.lfFaceName, fontSize);
			newTemplateFont += fontSize;
			memcpy(newTemplateFont, dlgTemplate, remainSize);

			auto ret = DialogBoxIndirectParamW(hInstance, reinterpret_cast<LPCDLGTEMPLATEW>(newTemplate), hWndParent, lpDialogFunc, dwInitParam);

			delete[] newTemplate;
			return ret;
		}
	}
	return DialogBoxIndirectParamW(hInstance, hDialogTemplate, hWndParent, lpDialogFunc, dwInitParam);
}

INT_PTR DialogBoxParamFixFont(HINSTANCE hInstance, LPCWSTR lpTemplateName, HWND hWndParent, DLGPROC lpDialogFunc, LPARAM dwInitParam)
{
	auto hResInfo = FindResourceW(hInstance, lpTemplateName, RT_DIALOG);
	if (hResInfo)
	{
		auto hDialogTemplate = reinterpret_cast<LPCDLGTEMPLATEW>(LoadResource(hInstance, hResInfo));
		if (hDialogTemplate)
		{
			auto size = SizeofResource(hInstance, hResInfo);
			return DialogBoxIndirectParamFixFontWithSize(hInstance, hDialogTemplate, size, hWndParent, lpDialogFunc, dwInitParam);
		}
	}
	return -1;
}