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diff --git a/docs/usermanual-hello-harfbuzz.xml b/docs/usermanual-hello-harfbuzz.xml new file mode 100644 index 0000000..34db017 --- /dev/null +++ b/docs/usermanual-hello-harfbuzz.xml @@ -0,0 +1,183 @@ +<chapter id="hello-harfbuzz"> + <title>Hello, Harfbuzz</title> + <para> + Here's the simplest Harfbuzz that can possibly work. We will improve + it later. + </para> + <orderedlist numeration="arabic"> + <listitem> + <para> + Create a buffer and put your text in it. + </para> + </listitem> + </orderedlist> + <programlisting language="C"> + #include <hb.h> + hb_buffer_t *buf; + buf = hb_buffer_create(); + hb_buffer_add_utf8(buf, text, strlen(text), 0, strlen(text)); +</programlisting> + <orderedlist numeration="arabic"> + <listitem override="2"> + <para> + Guess the script, language and direction of the buffer. + </para> + </listitem> + </orderedlist> + <programlisting language="C"> + hb_buffer_guess_segment_properties(buf); +</programlisting> + <orderedlist numeration="arabic"> + <listitem override="3"> + <para> + Create a face and a font, using FreeType for now. + </para> + </listitem> + </orderedlist> + <programlisting language="C"> + #include <hb-ft.h> + FT_New_Face(ft_library, font_path, index, &face) + hb_font_t *font = hb_ft_font_create(face); +</programlisting> + <orderedlist numeration="arabic"> + <listitem override="4"> + <para> + Shape! + </para> + </listitem> + </orderedlist> + <programlisting> + hb_shape(font, buf, NULL, 0); +</programlisting> + <orderedlist numeration="arabic"> + <listitem override="5"> + <para> + Get the glyph and position information. + </para> + </listitem> + </orderedlist> + <programlisting language="C"> + hb_glyph_info_t *glyph_info = hb_buffer_get_glyph_infos(buf, &glyph_count); + hb_glyph_position_t *glyph_pos = hb_buffer_get_glyph_positions(buf, &glyph_count); +</programlisting> + <orderedlist numeration="arabic"> + <listitem override="6"> + <para> + Iterate over each glyph. + </para> + </listitem> + </orderedlist> + <programlisting language="C"> + for (i = 0; i < glyph_count; ++i) { + glyphid = glyph_info[i].codepoint; + x_offset = glyph_pos[i].x_offset / 64.0; + y_offset = glyph_pos[i].y_offset / 64.0; + x_advance = glyph_pos[i].x_advance / 64.0; + y_advance = glyph_pos[i].y_advance / 64.0; + draw_glyph(glyphid, cursor_x + x_offset, cursor_y + y_offset); + cursor_x += x_advance; + cursor_y += y_advance; + } +</programlisting> + <orderedlist numeration="arabic"> + <listitem override="7"> + <para> + Tidy up. + </para> + </listitem> + </orderedlist> + <programlisting language="C"> + hb_buffer_destroy(buf); + hb_font_destroy(hb_ft_font); +</programlisting> + <section id="what-harfbuzz-doesnt-do"> + <title>What Harfbuzz doesn't do</title> + <para> + The code above will take a UTF8 string, shape it, and give you the + information required to lay it out correctly on a single + horizontal (or vertical) line using the font provided. That is the + extent of Harfbuzz's responsibility. + </para> + <para> + If you are implementing a text layout engine you may have other + responsibilities, that Harfbuzz will not help you with: + </para> + <itemizedlist> + <listitem> + <para> + Harfbuzz won't help you with bidirectionality. If you want to + lay out text with mixed Hebrew and English, you will need to + ensure that the buffer provided to Harfbuzz has those + characters in the correct layout order. This will be different + from the logical order in which the Unicode text is stored. In + other words, the user will hit the keys in the following + sequence: + </para> + <programlisting> +A B C [space] ג ב א [space] D E F + </programlisting> + <para> + but will expect to see in the output: + </para> + <programlisting> +ABC אבג DEF + </programlisting> + <para> + This reordering is called <emphasis>bidi processing</emphasis> + ("bidi" is short for bidirectional), and there's an + algorithm as an annex to the Unicode Standard which tells you how + to reorder a string from logical order into presentation order. + Before sending your string to Harfbuzz, you may need to apply the + bidi algorithm to it. Libraries such as ICU and fribidi can do + this for you. + </para> + </listitem> + <listitem> + <para> + Harfbuzz won't help you with text that contains different font + properties. For instance, if you have the string "a + <emphasis>huge</emphasis> breakfast", and you expect + "huge" to be italic, you will need to send three + strings to Harfbuzz: <literal>a</literal>, in your Roman font; + <literal>huge</literal> using your italic font; and + <literal>breakfast</literal> using your Roman font again. + Similarly if you change font, font size, script, language or + direction within your string, you will need to shape each run + independently and then output them independently. Harfbuzz + expects to shape a run of characters sharing the same + properties. + </para> + </listitem> + <listitem> + <para> + Harfbuzz won't help you with line breaking, hyphenation or + justification. As mentioned above, it lays out the string + along a <emphasis>single line</emphasis> of, notionally, + infinite length. If you want to find out where the potential + word, sentence and line break points are in your text, you + could use the ICU library's break iterator functions. + </para> + <para> + Harfbuzz can tell you how wide a shaped piece of text is, which is + useful input to a justification algorithm, but it knows nothing + about paragraphs, lines or line lengths. Nor will it adjust the + space between words to fit them proportionally into a line. If you + want to layout text in paragraphs, you will probably want to send + each word of your text to Harfbuzz to determine its shaped width + after glyph substitutions, then work out how many words will fit + on a line, and then finally output each word of the line separated + by a space of the correct size to fully justify the paragraph. + </para> + </listitem> + </itemizedlist> + <para> + As a layout engine implementor, Harfbuzz will help you with the + interface between your text and your font, and that's something + that you'll need - what you then do with the glyphs that your font + returns is up to you. The example we saw above enough to get us + started using Harfbuzz. Now we are going to use the remainder of + Harfbuzz's API to refine that example and improve our text shaping + capabilities. + </para> + </section> +</chapter>
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