Why can't DirectX/DirectWrite/Direct2D text rendering be as sharp as GDI?
directx, gdi, smoothing, text-rendering, winapi
Solution
You aren't comparing like with like. Your Direct2D samples are all rendered in grayscale, whereas the GDI and Linux samples are using sub-pixel anti-aliasing (aka ClearType on Windows).
This page describes what you need to do to enable cleartype: http://msdn.microsoft.com/en-us/library/windows/desktop/dd368170%28v=vs.85%29.aspx
N.B. When testing rendering like this, it's always worth using Windows Magnifier or similar to check that you are actually getting what you think you are getting.
Problem
I already know that sub-pixel positioning causes DirectWrite text rendering to be blurry compared to GDI. However, my question is a bit more fundamental: Why can't DirectWrite (and related methods) be made to render text as sharply as GDI? In other words: What prevents DirectWrite from being able to snap text to the nearest pixel, the way GDI can? Is it, for example, a hardware issue? A driver architecture issue? Is it simply not implemented? Or something else? Smaller sample: Larger samples: Direct2D, aliased: Direct2D, default: Direct2D ("classic GDI"): Direct2D ("natural GDI"): Actual classic GDI: Actual ClearType GDI: Note: If all of these look blurry to you, run ``` document.body.style.zoom = 1 / window.devicePixelRatio ``` in Chrome's console and view it afterward.