bug 829523 - disable font hinting on b2g, but retain pixel-snapped metrics except in the browser app. r=cjones

gfx/thebes/gfxAndroidPlatform.cpp

@@ -247,20 +247,53 @@ gfxAndroidPlatform::FontHintingEnabled()
 {
     // In "mobile" builds, we sometimes use non-reflow-zoom, so we
     // might not want hinting.  Let's see.
+
 #ifdef MOZ_USING_ANDROID_JAVA_WIDGETS
     // On android-java, we currently only use gecko to render web
     // content that can always be be non-reflow-zoomed.  So turn off
     // hinting.
     // 
-    // XXX when gecko-android-java is used as an "app runtime", we'll
-    // want to re-enable hinting.
+    // XXX when gecko-android-java is used as an "app runtime", we may
+    // want to re-enable hinting for non-browser processes there.
+    return false;
+#endif
+
+#ifdef MOZ_B2G
+    // On B2G, the UX preference is currently to keep hinting disabled
+    // for all text (see bug 829523).
     return false;
-#else
-    // Otherwise, enable hinting unless we're in a content process
-    // that might be used for non-reflowing zoom.
-    return XRE_GetProcessType() != GeckoProcessType_Content ||
-           !ContentChild::GetSingleton()->IsForBrowser();
 #endif //  MOZ_USING_ANDROID_JAVA_WIDGETS
+
+    // Currently, we don't have any other targets, but if/when we do,
+    // decide how to handle them here.
+
+    NS_NOTREACHED("oops, what platform is this?");
+    return gfxPlatform::FontHintingEnabled();
+}
+
+bool
+gfxAndroidPlatform::RequiresLinearZoom()
+{
+#ifdef MOZ_USING_ANDROID_JAVA_WIDGETS
+    // On android-java, we currently only use gecko to render web
+    // content that can always be be non-reflow-zoomed.
+    //
+    // XXX when gecko-android-java is used as an "app runtime", we may
+    // want to treat it like B2G and use linear zoom only for the web
+    // browser process, not other apps.
+    return true;
+#endif
+
+#ifdef MOZ_B2G
+    // On B2G, we need linear zoom for the browser, but otherwise prefer
+    // the improved glyph spacing that results from respecting the device
+    // pixel resolution for glyph layout (see bug 816614).
+    return XRE_GetProcessType() == GeckoProcessType_Content &&
+           ContentChild::GetSingleton()->IsForBrowser();
+#endif
+
+    NS_NOTREACHED("oops, what platform is this?");
+    return gfxPlatform::RequiresLinearZoom();
 }
 
 int

gfx/thebes/gfxAndroidPlatform.h

@@ -65,6 +65,7 @@ public:
                                           gfxUserFontSet* aUserFontSet);
 
     virtual bool FontHintingEnabled() MOZ_OVERRIDE;
+    virtual bool RequiresLinearZoom() MOZ_OVERRIDE;
 
     FT_Library GetFTLibrary();
 

gfx/thebes/gfxFT2FontList.cpp

@@ -128,7 +128,7 @@ FT2FontEntry::CreateScaledFont(const gfxFontStyle *aStyle)
 
     cairo_font_options_t *fontOptions = cairo_font_options_create();
 
-    if (!gfxPlatform::GetPlatform()->FontHintingEnabled()) {
+    if (gfxPlatform::GetPlatform()->RequiresLinearZoom()) {
         cairo_font_options_set_hint_metrics(fontOptions, CAIRO_HINT_METRICS_OFF);
     }
 

gfx/thebes/gfxPlatform.h

@@ -329,6 +329,22 @@ public:
      */
     virtual bool FontHintingEnabled() { return true; }
 
+    /**
+     * True when zooming should not require reflow, so glyph metrics and
+     * positioning should not be adjusted for device pixels.
+     * If this is TRUE, then FontHintingEnabled() should be FALSE,
+     * but the converse is not necessarily required; in particular,
+     * B2G always has FontHintingEnabled FALSE, but RequiresLinearZoom
+     * is only true for the browser process, not Gaia or other apps.
+     *
+     * Like FontHintingEnabled (above), this setting shouldn't
+     * change per gecko process, while the process is live.  If so the
+     * results are not defined.
+     *
+     * NB: this bit is only honored by the FT2 backend, currently.
+     */
+    virtual bool RequiresLinearZoom() { return false; }
+
     bool UsesSubpixelAATextRendering() {
 #ifdef MOZ_GFX_OPTIMIZE_MOBILE
 	return false;