Add font_extents()

samples/sample_font_extents.jl

@@ -0,0 +1,52 @@
+## header to provide surface and context
+using Cairo
+c = CairoRGBSurface(1024,256);
+cr = CairoContext(c);
+
+save(cr);
+set_source_rgb(cr,0.8,0.8,0.8);    # light gray
+rectangle(cr,0.0,0.0,1024.0,256.0); # background
+fill(cr);
+restore(cr);
+
+save(cr);
+## original example, following here
+select_font_face(cr, "Sans", Cairo.FONT_SLANT_NORMAL,
+                 Cairo.FONT_WEIGHT_NORMAL);
+set_font_size(cr, 100.0);
+extents = font_extents(cr);
+
+#typedef struct {
+#    double ascent;
+#    double descent;
+#    double height;
+#    double max_x_advance;
+#    double max_y_advance;
+#} cairo_font_extents_t;
+
+x = 25.0;
+y = 150.0;
+
+move_to(cr, x, y);
+show_text(cr, "Cairo! abcdefghijklmnopqrstuvwxyz");
+
+# draw helping lines 
+set_source_rgba(cr, 1, 0.2, 0.2, 0.6);
+set_line_width(cr, 6.0);
+arc(cr, x, y, 10.0, 0, 2*pi);
+fill(cr);
+move_to(cr, x,y);
+rel_line_to(cr, 0, -extents[1]);
+rel_line_to(cr, 1024, 0);
+#rel_line_to(cr, extents[1], -extents[2]);
+stroke(cr);
+move_to(cr, x,y);
+rel_line_to(cr, 0, extents[2]);
+rel_line_to(cr, 1024, 0);
+stroke(cr);
+## mark picture with current date
+restore(cr);
+move_to(cr,0.0,12.0);
+set_source_rgb(cr, 0,0,0);
+show_text(cr,Libc.strftime(time()));
+write_to_png(c,"sample_font_extents.png");

src/Cairo.jl

@@ -102,6 +102,7 @@ export
     set_text, set_latex,
     set_font_face, set_font_size, select_font_face,
     textwidth, textheight, text_extents,
+    font_extents,
     TeXLexer, tex2pango, show_text, text_path,
     set_font_matrix, get_font_matrix,
 
@@ -1215,6 +1216,16 @@ function show_layout(ctx::CairoContext)
           (Ptr{Nothing},Ptr{Nothing}), ctx.ptr, ctx.layout)
 end
 
+font_extents(ctx::CairoContext) =
+    font_extents!(ctx, Matrix{Float64}(undef, 5, 1))
+
+function font_extents!(ctx::CairoContext,extents)
+    ccall((:cairo_font_extents, libcairo),
+          Nothing, (Ptr{Nothing}, Ptr{Float64}),
+          ctx.ptr, extents)
+    extents
+end
+
 text_extents(ctx::CairoContext,value::AbstractString) =
     text_extents!(ctx,value, Matrix{Float64}(undef, 6, 1))