Rendering Arabic text with Pango & Cairo VS Pango & FreeType

[Nicolas Lacombe <n lacombe gmail com>]

Hi, 

I want to use Pango high level functionnality to render arabic tex in a FreeType environnement.

Using Pango with Cairo, it works perfectly, the text is correctly rendered with ligatures typographic ligature.

However, in a freetype environnement, ligature disapear! I can still see the text, but only the original form of each glyph, thus without any contextual interpretation. 

Am I doing anything wrong?


PANGO & CAIRO RENDERING (WORKING AS INTENDED)

cairo_surface_t *surface;
cairo_t *cr;


PangoLayout *layout;


surface = cairo_image_surface_create(CAIRO_FORMAT_A8, 512, 512);
cr = cairo_create(surface);
cairo_set_source_rgba(cr, 1., 1., 1., 0.0);
cairo_paint(cr);

layout = pango_cairo_create_layout(cr);
PangoFontDescription *desc;
desc = pango_font_description_from_string("Arial, 20");
pango_layout_set_font_description  (layout, desc);
pango_font_description_free(desc);

pango_layout_set_text(layout, txt, -1);
cairo_set_line_width(cr, 0.5);
cairo_set_source_rgba(cr, 0.0, 0.0, 0.0, 1.0);

pango_cairo_update_layout(cr, layout);
pango_cairo_show_layout(cr, layout);



PANGO & FREETYPE RENDERING (no contextual analysis of the arabic text)


PangoContext *context;

PangoFontMap* PFM = pango_ft2_font_map_new();
pango_ft2_font_map_set_resolution(PANGO_FT2_FONT_MAP(PFM), width, height);
context = pango_font_map_create_context(PANGO_FONT_MAP(PFM));


FT_Bitmap* bm;
bm = g_slice_new(FT_Bitmap);
bm->rows = height;
bm->width = width;
bm->pitch = width;
bm->num_grays = 256;
bm->pixel_mode = FT_PIXEL_MODE_GRAY;

bm->buffer = (unsigned char*)g_malloc (bm->pitch * bm->rows);
memset(bm->buffer, 0x00, bm->pitch * bm->rows);

layout = pango_layout_new(context);    
static PangoFontDescription *desc;

desc = pango_font_description_from_string("Arial, 20");
pango_layout_set_font_description(layout, desc);
pango_font_description_free(desc);

pango_layout_set_auto_dir (layout, 1);
pango_layout_set_text(layout, txt, -1);

pango_layout_context_changed(layout);
pango_ft2_render_layout(bm, layout, 0, 0);