Pixel perfect GUI text, DPI awareness font scaling

[iaomw]

GUI text is blurred because not considering DPI while loading the TTF font.

DPI blind	DPI awareness

Pilot is using AddFontFromFileTTF to load font. It should also consider DPI because the second parameter is measured in pixel.

ImFont* ImFontAtlas::AddFontFromFileTTF(const char* filename, float size_pixels, const ImFontConfig* font_cfg_template, const ImWchar* glyph_ranges)

Reference: ocornut/imgui#2956

Then, how to get correct DPI?

Through my experiment ImGui::GetMainViewport()->DpiScale is not good enough to get DPI. It's buggy and always return 0 before ImGui::NewFrame(). That's a bit too late for fonts loading with DPI info.