Add raster.separable_filter function.

Originally committed to SVN as r1483.

OverLua/docs/overlua.txt

@@ -161,6 +161,22 @@ For RGB24 surfaces, all channels are inverted.
 For A8 and A1 surfaces the alpha is inverted.
 
 
+raster.separable_filter(surface, filter, divisor)
+
+Apply a custom separable filter over the image.
+
+The filter must be a table of integers. After the convoluted value of each
+pixel is calculated, it is divided by divisor before it's stored back to the
+image.
+
+Note that this function can only work on integers, floating point values in
+the filter or divisor will be rounded first. To get higher precision, scale
+up the filter and divisor. (Treat it as fixed-point math.)
+
+The filter is one-dimensional, but is applied first horizontally and then
+vertically ovre the image to get the final image.
+
+
 More filtering functions are planned, though no specifics yet.
 
 Wishes/suggestions are welcome, and so are patches to add more functions.

OverLua/docs/test3.lua

@@ -1,6 +1,7 @@
 function render_frame(f, t)
 	local surf = f.create_cairo_surface()
-	raster.gaussian_blur(surf, t)--1+(1-math.cos(t*10))*2)
-	raster.invert(surf)
+	--raster.gaussian_blur(surf, t)--1+(1-math.cos(t*10))*2)
+	--raster.invert(surf)
+	raster.separable_filter(surf, {-1, 3, -1}, 1) 
 	f.overlay_cairo_surface(surf, 0, 0)
 end

OverLua/raster_ops.cpp

@@ -408,10 +408,44 @@ static int invert_image(lua_State *L)
 }
 
 
+static int separable_filter(lua_State *L)
+{
+	cairo_surface_t *surf = CheckSurface(L, 1);
+	if (!lua_istable(L, 2)) {
+		luaL_error(L, "Expected table as second argument to raster.separable_filter, got %s", luaL_typename(L, 2));
+		return 0;
+	}
+	int divisor = luaL_checkint(L, 3);
+
+	int width = (int)lua_objlen(L, 2);
+	if (width < 1) {
+		luaL_error(L, "Cannot apply empty filter");
+		return 0;
+	}
+	int *kernel = new int[width];
+	int i = 0;
+	lua_pushnil(L);
+	while (lua_next(L, 2)) {
+		if (lua_isnumber(L, -1)) {
+			kernel[i] = (int)lua_tointeger(L, -1);
+		}
+		i++;
+		lua_pop(L, 1);
+	}
+
+	ApplySeparableFilter(L, surf, kernel, width, divisor);
+
+	delete[] kernel;
+
+	return 0;
+}
+
+
 // Registration
 
 static luaL_Reg rasterlib[] = {
 	{"gaussian_blur", gaussian_blur}, {"box_blur", box_blur},
+	{"separable_filter", separable_filter},
 	{"invert", invert_image},
 	{NULL, NULL}
 };