Use OVER operator for drawing text (#2908)

For opaque text, SOURCE is not any different from OVER. However, when
drawing color glyphs (which consist of RGBA pixels instead of strokes)
SOURCE's handling of alpha is not what we want.

I stumbled across this because cairo 1.15.8 seems to clear the surface
before drawing color emoji if the operator is SOURCE, deleting every-
thing drawn before. Arguably, the area outside the glyph bounds should
not be touched, but even if this is a cairo bug the problem of alpha
within the glyph remains.

diff --git a/libi3/font.c b/libi3/font.c
index 81091ea74a31da11d392864c1158ed387b0da1cd..aef8427b5396c3d8d9082308e64a30ea94dcec6e 100644 (file)
--- a/libi3/font.c
+++ b/libi3/font.c
@@ -105,7 +105,7 @@ static void draw_text_pango(const char *text, size_t text_len,
         pango_layout_set_text(layout, text, text_len);
 
     /* Do the drawing */
-    cairo_set_operator(cr, CAIRO_OPERATOR_SOURCE);
+    cairo_set_operator(cr, CAIRO_OPERATOR_OVER);
     cairo_set_source_rgb(cr, pango_font_red, pango_font_green, pango_font_blue);
     pango_cairo_update_layout(cr, layout);
     pango_layout_get_pixel_size(layout, NULL, &height);