rescale font size when fallbacks to fallback fonts

and make FreeSerif font the default font instead of DroidSansFallback

This patch should fix #272.

frontend/ui/font.lua

@@ -3,12 +3,12 @@ require "dbg" -- for DEBUG()
 Font = {
 	fontmap = {
 		-- default font for menu contents
-		cfont = "droid/DroidSansFallback.ttf",
+		cfont = "freefont/FreeSerif.ttf",
 		-- default font for title
 		--tfont = "NimbusSanL-BoldItal.cff",
-		tfont = "droid/DroidSansFallback.ttf",
+		tfont = "freefont/FreeSerif.ttf",
 		-- default font for footer
-		ffont = "droid/DroidSansFallback.ttf",
+		ffont = "freefont/FreeSerif.ttf",
 
 		-- default font for reading position info
 		rifont = "droid/DroidSans.ttf",
@@ -32,9 +32,9 @@ Font = {
 		infofont = "droid/DroidSans.ttf",
 	},
 	fallbacks = {
-		[1] = "freefont/FreeSans.ttf",
-		[2] = "droid/DroidSans.ttf",
-		[3] = "droid/DroidSansFallback.ttf",
+		[1] = "droid/DroidSansFallback.ttf",
+		[2] = "freefont/FreeSans.ttf",
+		[3] = "droid/DroidSans.ttf",
 	},
 
 	fontdir = os.getenv("FONTDIR") or "./fonts",
@@ -50,7 +50,7 @@ function Font:getFace(font, size)
 		font = self.cfont
 	end
 
-	local size = math.floor(scaleByDPI(size))
+	local size = scaleByDPI(size)
 
 	local face = self.faces[font..size]
 	-- build face if not found

frontend/ui/rendertext.lua

@@ -68,10 +68,11 @@ function getGlyph(face, charcode, bgcolor, fgcolor)
 	local rendered_glyph = face.ftface:renderGlyph(charcode, bgcolor, fgcolor)
 	if face.ftface:checkGlyph(charcode) == 0 then
 		for index, font in pairs(Font.fallbacks) do
-			DEBUG("fallback to font", font)
-			local fb_face = Font:getFace(font, face.size)
+			-- rescale face size by DPI since it will be scaled in getFace again
+			local fb_face = Font:getFace(font, rescaleByDPI(face.size))
 			if fb_face.ftface:checkGlyph(charcode) ~= 0 then
 				rendered_glyph = fb_face.ftface:renderGlyph(charcode, bgcolor, fgcolor)
+				DEBUG("fallback to font", font)
 				break
 			end
 		end

frontend/ui/screen.lua

@@ -134,11 +134,20 @@ function Screen:scaleByDPI(px)
 	return math.floor(px * self:getDPI()/167)
 end
 
+function Screen:rescaleByDPI(px)
+	return math.ceil(px * 167/self:getDPI())
+end
+
 -- make a shortcut to Screen:scaleByDPI
 function scaleByDPI(px)
 	return Screen:scaleByDPI(px)
 end
 
+-- make a shortcut to Screen:rescaleByDPI
+function rescaleByDPI(px)
+	return Screen:rescaleByDPI(px)
+end
+
 function Screen:getPitch()
 	return self.fb:getPitch()
 end