Set alpha on colored subpixels

I can't seem to find good info on what this should be.

src/FreeType.cake

@@ -404,12 +404,20 @@
       (when pixel-set
         (if (> num-components-per-freetype-pixel 1)
             (scope
+             (var component-max-brightness (unsigned char) 0)
              (each-in-range 3 component
-               (set (at component current-pixel-out) (at component current-pixel))))
+               (set (at component current-pixel-out) (at component current-pixel))
+               (when (> (at component current-pixel) component-max-brightness)
+                 (set component-max-brightness (at component current-pixel))))
+             ;; Set the alpha based on the brightest component, where components are likely max
+             ;; brightness unless part of the color fringe for subpixel anti-aliasing. I'm not sure
+             ;; what this value is actually supposed to be, partially because it depends on the
+             ;; renderer's blending algorithm.
+             (set (at 3 current-pixel-out) component-max-brightness))
             (scope
              (each-in-range 3 component
-               (set (at component current-pixel-out) (deref current-pixel)))))
-        (set (at 3 current-pixel-out) 255))))
+               (set (at component current-pixel-out) (deref current-pixel)))
+             (set (at 3 current-pixel-out) 255))))))
 
   ;; Wrapping happens after we know what the next glyph's dimensions are
   (set (path font > write-state . atlas-write-x) (+ (path font > write-state . atlas-write-x) num-columns))