added freetype text rendering (still buggy)

this allows to render glyphs and also brings a simple
engine for rendering UTF-8 strings onto the framebuffer.
blitting to uneven offset is implemented here, too, but
needs more work and is still buggy.

In the end, this will allow for a simple GUI.

rendertext.lua

@@ -0,0 +1,54 @@
+glyphcache_max_memsize = 256*1024 -- 256kB glyphcache
+glyphcache_current_memsize = 0
+glyphcache = {}
+glyphcache_max_age = 4096
+function glyphcacheclaim(size)
+	if(size > glyphcache_max_memsize) then
+		error("too much memory claimed")
+		return false
+	end
+	while glyphcache_current_memsize + size > glyphcache_max_memsize do
+		for k, _ in pairs(glyphcache) do
+			if glyphcache[k].age > 0 then
+				glyphcache[k].age = glyphcache[k].age - 1
+			else
+				glyphcache_current_memsize = glyphcache_current_memsize - glyphcache[k].size
+				glyphcache[k] = nil
+			end
+		end
+	end
+	glyphcache_current_memsize = glyphcache_current_memsize + size
+	return true
+end
+function getglyph(face, facehash, charcode)
+	local hash = glyphcachehash(facehash, charcode)
+	if glyphcache[hash] == nil then
+		print("render glyph")
+		local glyph = face:renderGlyph(charcode)
+		local size = glyph.bb:getWidth() * glyph.bb:getHeight() / 2 + 32
+		print("cache claim")
+		glyphcacheclaim(size);
+		glyphcache[hash] = {
+			age = glyphcache_max_age,
+			size = size,
+			g = glyph
+		}
+	end
+	return glyphcache[hash].g
+end
+function glyphcachehash(face, charcode)
+	return face..'_'..charcode;
+end
+function clearglyphcache()
+	glyphcache = {}
+end
+
+function renderUtf8Text(x, y, face, facehash, text)
+	local pen_x = 0
+	for uchar in string.gfind(text, "([%z\1-\127\194-\244][\128-\191]*)") do
+		local glyph = getglyph(face, facehash, util.utf8charcode(uchar))
+		fb:blitFrom(glyph.bb, x + pen_x + glyph.l, y - glyph.t, 0, 0, glyph.bb:getWidth(), glyph.bb:getHeight())
+		pen_x = pen_x + glyph.ax
+	end
+end
+