koreader/frontend/ui/rendertext.lua

require "cache"

--[[
TODO: all these functions should probably be methods on Face objects
]]--

function getGlyph(face, charcode)
	local hash = "glyph|"..face.hash.."|"..charcode
	local glyph = Cache:check(hash)
	if glyph then
		-- cache hit
		return glyph[1]
	end
	local rendered_glyph = face.ftface:renderGlyph(charcode)
	if not rendered_glyph then
		DEBUG("error rendering glyph (charcode=", charcode, ") for face", face)
		return
	end
	glyph = CacheItem:new{rendered_glyph}
	glyph.size = glyph[1].bb:getWidth() * glyph[1].bb:getHeight() / 2 + 32
	Cache:insert(hash, glyph)
	return glyph[1]
end

function getSubTextByWidth(text, face, width, kerning)
	local pen_x = 0
	local prevcharcode = 0
	local char_list = {}
	for uchar in string.gfind(text, "([%z\1-\127\194-\244][\128-\191]*)") do
		if pen_x < width then
			local charcode = util.utf8charcode(uchar)
			local glyph = getGlyph(face, charcode)
			if kerning and prevcharcode then
				local kern = face.ftface:getKerning(prevcharcode, charcode)
				pen_x = pen_x + kern
			end
			pen_x = pen_x + glyph.ax
			if pen_x <= width then
				prevcharcode = charcode
				table.insert(char_list, uchar)
			else
				break
			end
		end
	end
	return table.concat(char_list)
end

function sizeUtf8Text(x, width, face, text, kerning)
	if text == nil then
		DEBUG("sizeUtf8Text called without text");
		return
	end
	-- may still need more adaptive pen placement when kerning,
	-- see: http://freetype.org/freetype2/docs/glyphs/glyphs-4.html
	local pen_x = 0
	local pen_y_top = 0
	local pen_y_bottom = 0
	local prevcharcode = 0
	for uchar in string.gfind(text, "([%z\1-\127\194-\244][\128-\191]*)") do
		if pen_x < (width - x) then
			local charcode = util.utf8charcode(uchar)
			local glyph = getGlyph(face, charcode)
			if kerning and prevcharcode then
				local kern = face.ftface:getKerning(prevcharcode, charcode)
				pen_x = pen_x + kern
				--DEBUG("prev:"..string.char(prevcharcode).." curr:"..string.char(charcode).." kern:"..kern)
			else
				--DEBUG("curr:"..string.char(charcode))
			end
			pen_x = pen_x + glyph.ax
			pen_y_top = math.max(pen_y_top, glyph.t)
			pen_y_bottom = math.max(pen_y_bottom, glyph.bb:getHeight() - glyph.t)
			--DEBUG("ax:"..glyph.ax.." t:"..glyph.t.." r:"..glyph.r.." h:"..glyph.bb:getHeight().." w:"..glyph.bb:getWidth().." yt:"..pen_y_top.." yb:"..pen_y_bottom)
			prevcharcode = charcode
		end
	end
	return { x = pen_x, y_top = pen_y_top, y_bottom = pen_y_bottom}
end

function renderUtf8Text(buffer, x, y, face, text, kerning)
	if text == nil then
		DEBUG("renderUtf8Text called without text");
		return 0
	end
	-- may still need more adaptive pen placement when kerning,
	-- see: http://freetype.org/freetype2/docs/glyphs/glyphs-4.html
	local pen_x = 0
	local prevcharcode = 0
	for uchar in string.gfind(text, "([%z\1-\127\194-\244][\128-\191]*)") do
		if pen_x < buffer:getWidth() then
			local charcode = util.utf8charcode(uchar)
			local glyph = getGlyph(face, charcode)
			if kerning and prevcharcode then
				local kern = face.ftface:getKerning(prevcharcode, charcode)
				pen_x = pen_x + kern
				--DEBUG("prev:"..string.char(prevcharcode).." curr:"..string.char(charcode).." pen_x:"..pen_x.." kern:"..kern)
				buffer:addblitFrom(glyph.bb, x + pen_x + glyph.l, y - glyph.t, 0, 0, glyph.bb:getWidth(), glyph.bb:getHeight())
			else
				--DEBUG(" curr:"..string.char(charcode))
				buffer:blitFrom(glyph.bb, x + pen_x + glyph.l, y - glyph.t, 0, 0, glyph.bb:getWidth(), glyph.bb:getHeight())
			end
			pen_x = pen_x + glyph.ax
			prevcharcode = charcode
		end
	end
	return pen_x
end