From c72893637cc722b478bf90fd55c87c8ff3964931 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Daniel=20Ekl=C3=B6f?= <daniel@ekloef.se>
Date: Wed, 27 Nov 2019 21:41:29 +0100
Subject: [PATCH] font: force a pixel fixup factor for scalable bitmap fonts

That is, for color bitmap fonts (typically emoji fonts). Use the same
calculation used by fontconfig's 10-scale-bitmap-fonts.conf.

Note: if the user has enabled bitmap font scaling in general, we'll
pick it up and scale the final glyph image, regardless of whether the
font is a regular bitmap font, or a color bitmap font.

But, if the user has disabled bitmap font scaling, we only force a
fixup factor on color bitmap fonts.
---
 font.c | 34 ++++++++++++++++++++++++++++++----
 1 file changed, 30 insertions(+), 4 deletions(-)

diff --git a/font.c b/font.c
index 4951113..ec4eba2 100644
--- a/font.c
+++ b/font.c
@@ -177,8 +177,11 @@ from_font_set(FcPattern *pattern, FcFontSet *fonts, int start_idx,
     if (FcPatternGetDouble(final_pattern, FC_DPI, 0, &dpi) != FcResultMatch)
         dpi = 96;
 
+    double size;
     double pixel_size;
-    if (FcPatternGetDouble(final_pattern, FC_PIXEL_SIZE, 0, &pixel_size)) {
+    if (FcPatternGetDouble(final_pattern, FC_SIZE, 0, &size) != FcResultMatch ||
+        FcPatternGetDouble(final_pattern, FC_PIXEL_SIZE, 0, &pixel_size) != FcResultMatch)
+    {
         LOG_ERR("%s: failed to get size", face_file);
         FcPatternDestroy(final_pattern);
         return false;
@@ -188,9 +191,32 @@ from_font_set(FcPattern *pattern, FcFontSet *fonts, int start_idx,
     if (FcPatternGetBool(final_pattern, FC_SCALABLE, 0, &scalable) != FcResultMatch)
         scalable = FcTrue;
 
+    FcBool outline;
+    if (FcPatternGetBool(final_pattern, FC_OUTLINE, 0, &outline) != FcResultMatch)
+        outline = FcTrue;
+
     double pixel_fixup;
-    if (FcPatternGetDouble(final_pattern, "pixelsizefixupfactor", 0, &pixel_fixup) != FcResultMatch)
-        pixel_fixup = 1.;
+    if (FcPatternGetDouble(final_pattern, "pixelsizefixupfactor", 0, &pixel_fixup) != FcResultMatch) {
+        /*
+         * Force a fixup factor on scalable bitmap fonts (typically
+         * emoji fonts). The fixup factor is
+         *   requested-pixel-size / actual-pixels-size
+         */
+        if (scalable && !outline) {
+            double original_pixel_size;
+            if (FcPatternGetDouble(pattern, FC_PIXEL_SIZE, 0, &original_pixel_size) != FcResultMatch) {
+                double original_size;
+                if (FcPatternGetDouble(pattern, FC_SIZE, 0, &original_size) != FcResultMatch)
+                    original_size = size;
+                original_pixel_size = original_size * dpi / 72;
+            }
+            pixel_fixup = original_pixel_size / pixel_size;
+
+            LOG_DBG("estimated fixup factor to %f (requested pixel size: %f, actual: %f)",
+                    pixel_fixup, original_pixel_size, pixel_size);
+        } else
+            pixel_fixup = 1.;
+    }
 
     LOG_DBG("loading: %s", face_file);
 
@@ -285,7 +311,7 @@ from_font_set(FcPattern *pattern, FcFontSet *fonts, int start_idx,
     font->face = ft_face;
     font->load_flags = load_flags | FT_LOAD_COLOR;
     font->render_flags = render_flags;
-    font->pixel_size_fixup = scalable ? pixel_fixup : 1.;
+    font->pixel_size_fixup = pixel_fixup;
     font->bgr = fc_rgba == FC_RGBA_BGR || fc_rgba == FC_RGBA_VBGR;
     font->fc_idx = font_idx;
     font->is_fallback = is_fallback;