[Git][freetype/freetype][1100-sdf-precision-improvement] * include/freet

Anuj Verma pushed to branch 1100-sdf-precision-improvement at FreeType / FreeType

Commits:

8ffa9545

by Anuj Verma at 2021-10-09T10:53:39+05:30

* include/freetype/freetype.h (FT_RENDER_MODE_SDF): Improve documentation.

* include/freetype/freetype.h (FT_RENDER_MODE_SDF): Added more
  documentation for the render mode regarding the stability and point
  where artifacts are expected to occur.  Also added more information
  for both `sdf`, `bsdf` and when they are used.

1 changed file:

include/freetype/freetype.h

Changes:

include/freetype/freetype.h

@@ -3368,6 +3368,40 @@ FT_BEGIN_HEADER
     *   }
+    *
     *   ```
 +   *
 +   *   FreeType has two rasterizers for generating SDF, namely:
 +   *
 +   *   1. `sdf`  - For generating SDF directly from glyph's outline.
 +   *
 +   *   2. `bsdf` - For generating SDF from rasterized bitmaps.
 +   *
 +   *   Depending on the glyph type (i.e. outline or bitmap), one of the two
 +   *   rasterizer is chosen at runtime and used for generating SDF.  To
 +   *   force use `bsdf` you can simply render the glyph using any of the
 +   *   FreeType's other rendering modes (e.g. `FT_RENDER_MODE_NORMAL`) and
 +   *   then re-render using `FT_RENDER_MODE_SDF`.
 +   *
 +   *   Now, a few notes on the stability and point of failures for the SDF
 +   *   renderers (specifically `sdf`):
 +   *
 +   *   1. The `sdf` rasterizer is sensitive to really small features (e.g.
 +   *      sharp turns which are less than 1 pixel) and imperfections in the
 +   *      glyph's outline.  Having these in the outline can cause artifats
 +   *      in the final output.
 +   *
 +   *   2. The `sdf` rasterizer has limited support for handling intersecting
 +   *      contours and *cannot* handle self-intersecting contours whatsoever.
 +   *      Self intersection happens when a single connected contour intersect
 +   *      itself at some point and having these in your font will definately
 +   *      pose a problem to the rasterizer and cause artifacts.
 +   *
 +   *   3. Generating SDF for really small glyphs may result in undesirable
 +   *      output due to limited availability of pixel grid to store distance
 +   *      information.
 +   *
 +   *   Point (1) and (2) can be avoided by using `bsdf` and overall it is
 +   *   more stable than the `sdf` rasterizer.
 +   *
     */
    typedef enum  FT_Render_Mode_
+   {

From:	Anuj Verma (@anujv)
Subject:	[Git][freetype/freetype][1100-sdf-precision-improvement] * include/freetype/freetype.h (FT_RENDER_MODE_SDF): Improve documentation.
Date:	Sat, 09 Oct 2021 05:23:44 +0000