Better parameter checking for frame.overlay_cairo_surface and adding a more useful sample script.

Originally committed to SVN as r1482.

OverLua/docs/sample1.lua

@@ -0,0 +1,134 @@
+--[[
+
+Sample script for OverLua
+ - demonstrate basic reading in an ASS subtitle file and rendering its lines on the video
+ 
+Given into the public domain.
+(You can do anything you want with this file, with no restrictions whatsoever.
+ You don't get any warranties of any kind either, though.)
+ 
+Originally authored by Niels Martin Hansen.
+
+]]
+
+-- overlua_datastring is the string given to data= argument in Avisynth filter invocation
+timing_input_file = overlua_datastring
+-- You may want to get these from somewhere else
+-- Or just stick to hardcoding all styling information
+font_name = "Arial"
+font_size = 24
+
+-- A little check that an input file was actually given
+assert(timing_input_file, "Missing input file")
+
+
+-- An easier way to convert a string to a number and be guaranteed to get something useful
+function parsenum(str)
+	return tonumber(str) or 0
+end
+-- Convert an ASS timestamp into a number of seconds
+function parse_ass_time(ass)
+	local h, m, s, cs = ass:match("(%d+):(%d+):(%d+)%.(%d+)")
+	return parsenum(cs)/100 + parsenum(s) + parsenum(m)*60 + parsenum(h)*3600
+end
+
+-- Not used here, but do some basic \k timing parsing
+function parse_k_timing(text)
+	local syls = {}
+	local i = 1
+	for timing, syltext in text:gmatch("{\\k(%d+)}([^{]*)") do
+		local syl = {dur = parsenum(timing)/100, text = syltext, i = i}
+		table.insert(syls, syl)
+		i = i + 1
+	end
+	return syls
+end
+
+-- Really stupid ASS parser
+function read_input_file(name)
+	for line in io.lines(name) do
+		-- You can catch Style lines in the same way if you want
+		local start_time, end_time, style, fx, text = line:match("Dialogue: 0,(.-),(.-),(.-),.-,0000,0000,0000,(.-),(.*)")
+		if text then
+			local ls = {}
+			ls.start_time = parse_ass_time(start_time)
+			ls.end_time = parse_ass_time(end_time)
+			ls.style = style
+			ls.fx = fx
+			ls.rawtext = text
+			ls.kara = parse_k_timing(text)
+			-- Clear out override blocks
+			ls.cleantext = text:gsub("{.-}", "")
+			table.insert(lines, ls)
+		end
+	end
+end
+
+-- Initialisation function, intended to be run on the first frame
+-- I think it's better to delay initialisation until first frame is requested
+-- rather than doing it immediately at load time.
+-- I believe much encoding software might be more graceful about that.
+function init()
+	if inited then return end
+	inited = true
+	
+	lines = {}
+	read_input_file(timing_input_file)
+end
+
+
+-- Actual work function, this is what's called by OverLua for each frame
+-- f is a video frame object, what we'll be drawing to
+-- t is the timestamp of the frame, given in seconds (floating point)
+function render_frame(f, t)
+	-- Just call init() every time, init itself makes sure it doesn't init more than once
+	init()
+	
+	-- Find lines to be drawn
+	-- NOTE: This structure is very simplistic.
+	-- Advanced karaoke effects will probably need to build an object/effect list
+	-- as initialisation and then instead go over the list of objects/effects per frame,
+	-- instead of going over lines.
+	-- (Ie. preprocessing in the style of ASS karaoke generation.)
+	for i, line in pairs(lines) do
+		if line.start_time <= t and line.end_time > t then
+			-- Initial position of line
+			local x = 0
+			local y = f.height - 25
+			
+			-- Initialise drawing surface and context
+			local surf = cairo.image_surface_create(f.width, f.height, "argb32")
+			local c = surf.create_context()
+			
+			-- Select our font
+			c.select_font_face(font_name)
+			c.set_font_size(font_size)
+			
+			-- Get sizing information for font and line text
+			if not line.te then line.te = c.text_extents(line.cleantext); line.fe = c.font_extents() end
+			-- Calculate centered position
+			x = (f.width - line.te.width) / 2 - line.te.x_bearing
+			
+			-- Produce text path
+			c.move_to(x, y)
+			c.text_path(line.cleantext)
+			
+			-- Draw a black border
+			-- It will be centered on the text outline
+			c.set_line_width(4)
+			c.set_line_join("round") -- default is "miter"
+			c.set_source_rgba(0, 0, 0, 1)
+			-- "preserve" to keep the text path in the context
+			c.stroke_preserve()
+			-- Apply a little box blur to the border, effectively \be1
+			raster.box_blur(surf, 3)
+			
+			-- Draw a white fill - this will draw over the inner part of the border
+			c.set_source_rgba(1, 1, 1, 1)
+			c.fill()
+
+			-- Overlay on video
+			f.overlay_cairo_surface(surf, 0, 0)
+		end
+	end
+end

OverLua/video_frame.h

@@ -298,7 +298,7 @@ badtable:
 	{
 		// Get inputs
 		MyType **ud = (MyType**)lua_touserdata(L, lua_upvalueindex(1));
-		LuaCairoSurface *surfwrap = LuaCairoSurface::CheckPointer(*(void**)lua_touserdata(L, 1));
+		LuaCairoSurface *surfwrap = LuaCairoSurface::GetObjPointer(L, 1);
 		if (!surfwrap) {
 			lua_pushliteral(L, "Argument to frame.overlay_cairo_surface is not a Cairo surface");
 			lua_error(L);