On Fri, 18 Sep 2026 18:57:28 GMT, Martin Fox <[email protected]> wrote:
>> This PR attempts to improve LCD text rendering on Windows and Linux. Changes >> include: >> >> - (Windows only) When setting up DirectWrite the code now uses the >> NATURAL_SYMMETRIC rendering mode except for very small glyphs where it uses >> NATURAL. Using NATURAL_SYMMETRIC avoids distorted glyphs at specific pixel >> sizes (see [JDK-8389632](https://bugs.openjdk.org/browse/JDK-8389632)) and >> retains the curves along the top and bottom of the glyphs. Using NATURAL at >> small sizes avoids glyphs turning very fuzzy and light. >> >> - The code is now consistently converts the colors from sRGB to a linear >> space (more or less), composites them, and then converts the result back to >> sRGB. >> >> - The shader applies a contrast equation to the LCD glyph mask which helps >> emphasize the stems. The same equation is used by Skia and probably added by >> Microsoft when they cleaned up text rendering for Chromium. BTW it’s just >> the equation for a parabola that goes through points (0, 0) and (1, 1). >> >> My testing was mostly done on a 27 inch display with a resolution of >> 2560x1440 and a screen scale of 150%. This was low enough to notice a >> difference. Resolutions higher than that (like full-on Retina) tend to hide >> a lot of sins. >> >> I recommend reading “The Raster Tragedy in Skia” which is concise but covers >> a lot of ground. It contains a section on the challenges of compositing text >> in sRGB space and also the issues getting LCD text to look dark enough >> without inflating the stems. I wish I had found this earlier in the process. >> >> --------- >> - [x] I confirm that I make this contribution in accordance with the >> [OpenJDK Interim AI Policy](https://openjdk.org/legal/ai). > > Martin Fox has updated the pull request with a new target base due to a merge > or a rebase. The incremental webrev excludes the unrelated changes brought in > by the merge/rebase. The pull request contains eight additional commits since > the last revision: > > - Merge remote-tracking branch 'upstream/master' into fontwork > - Glyph shaping and LCD rendering changes require system properties > - Added Swing version of the cascade > - Added manual text rendering test > - Upped contrast and adjusted it for white-on-black text > - Merge remote-tracking branch 'upstream/master' into fontwork > - Slight tweak to natural/symmetric choice > - LCD text rendering is sharper and on Windows less likely to create > distorted glyphs The font rendering changes now require system properties. To turn on SYMMETRIC mode use glyphshaping=symmetric. This affects both the LCD and grayscale paths on Windows (all other platforms ignore it). I'm not sure this is necessary for grayscale since it currently uses the DEFAULT rendering mode which uses NATURAL at small sizes and SYMMETRIC at larger sizes (the cutoff and how this is determined aren't documented). We can't use DEFAULT in the LCD path so if we wanted to reproduce that behavior we would need to do it ourselves. (There was talk some time ago about tweaking some metric-preserving flags in Freetype on Linux. Perhaps that could be added to the glyph shaping options as an experiment.) To turn on the new LCD rendering code use lcdrendering=new. That affects both Windows and Linux. ------------- PR Comment: https://git.openjdk.org/jfx/pull/2284#issuecomment-5734893150
