forked from minhngoc25a/freetype2
complete revision
This commit is contained in:
Werner Lemberg
parent
cd8cb7f5c4
commit
9a2a55a48f
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@ -39,7 +39,7 @@
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<p>This is the first section of the FreeType 2 tutorial. It will
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teach you to do the following:</p>
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<ul>
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<li>initialize the library</li>
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<li>open a font file by creating a new face object</li>
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@ -48,7 +48,7 @@
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<li>render a very simple string of text</li>
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<li>render a rotated string of text easily</li>
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</ul>
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<hr>
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<h3>
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@ -343,13 +343,13 @@
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cousins), it <em>automatically</em> creates a new size object for the
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returned face. This size object is directly accessible as
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<tt>face->size</tt>.</p>
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<p><em>NOTA BENE: A single face object can deal with one or more size
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objects at a time; however, this is something that few programmers
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really need to do. We have thus have decided to simplify the API for
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the most common use (i.e. one size per face), while keeping this feature
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available through additional functions.</em></p>
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<p><em>A single face object can deal with one or more size objects at a
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time; however, this is something that few programmers really need to do.
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We have thus have decided to simplify the API for the most common use
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(i.e. one size per face), while keeping this feature available through
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additional functions.</em></p>
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<p>When a new face object is created, its size object defaults to the
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character size of 10 pixels (both horizontally and vertically) for
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scalable formats. For fixed-sizes formats, the size is more or less
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@ -374,7 +374,7 @@
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<ul>
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<li>
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The character width and heights are specified in 1/64th of points.
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The character width and heights are specified in 1/64th of points.
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A point is a <em>physical</em> distance, equaling 1/72th of an inch;
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it's not a pixel.
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</li>
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@ -396,7 +396,7 @@
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means 72 dpi, which is the default.
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</li>
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<li>
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The first argument is a handle to a face object, not a size object.
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The first argument is a handle to a face object, not a size object.
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That's normal, and must be seen as a convenience.
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</li>
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</ul>
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@ -414,7 +414,7 @@
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16 ); /* pixel_height */</pre>
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</font>
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<p>This example will set the character pixel sizes to 16x16 pixels.
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<p>This example will set the character pixel sizes to 16x16 pixels.
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As previously, a value of 0 for one of the dimensions means
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<em>same as the other</em>.</p>
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@ -452,7 +452,7 @@
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Unicode character codes if it finds one. Otherwise, it tries to find
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support for Latin-1, then ASCII.</p>
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<p>We will describe later how to look for specific charmaps in a face.
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<p>We will describe later how to look for specific charmaps in a face.
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For now, we will assume that the face contains at least a Unicode
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charmap that was selected during <tt>FT_New_Face()</tt>. To convert a
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Unicode character code to a font glyph index, we use
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@ -479,13 +479,13 @@
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<p>Once you have a glyph index, you can load the corresponding glyph
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image. The latter can be stored in various formats within the font
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file. For fixed-size formats like FNT or PCF, each image is a bitmap.
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file. For fixed-size formats like FNT or PCF, each image is a bitmap.
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Scalable formats like TrueType or Type 1 use vectorial shapes,
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named <em>outlines</em> to describe each glyph. Some formats may have
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even more exotic ways of representing glyph (e.g. MetaFont).
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even more exotic ways of representing glyph (e.g. MetaFont).
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Fortunately, FreeType 2 is flexible enough to support any kind of
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glyph format through a simple API.</p>
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<p>The glyph image is always stored in a special object called a
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<em>glyph slot</em>. As its name suggests, a glyph slot is a
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container that is able to hold one glyph image at a time, be it a
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@ -497,7 +497,7 @@
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<font color="blue">
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<pre>
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error = FT_Load_Glyph(
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error = FT_Load_Glyph(
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face, /* handle to face object */
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glyph_index, /* glyph index */
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load_flags ); /* load flags, see below */</pre>
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@ -506,10 +506,10 @@
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<p>The <tt>load_flags</tt> value is a set of bit flags used to
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indicate some special operations. The default value
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<tt>FT_LOAD_DEFAULT</tt> is 0.</p>
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<p>This function will try to load the corresponding glyph image from
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the face. Basically, this means that</p>
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<ul>
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<li>
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<p>If a bitmap is found for the corresponding glyph and pixel
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@ -524,7 +524,7 @@
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for certain formats like TrueType and Type 1.</p>
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</li>
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</ul>
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<p>The field <tt>glyph->format</tt> describes the format used to store
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the glyph image in the slot. If it is not
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<tt>ft_glyph_format_bitmap</tt>, it is possible to immedialy convert
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@ -536,7 +536,7 @@
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face->glyph, /* glyph slot */
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render_mode ); /* render mode */</pre>
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</font>
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<p>The parameter <tt>render_mode</tt> specifies how to render the
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glyph image. Set it <tt>ft_render_mode_normal</tt> to render a
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high-quality anti-aliased (256 gray levels) bitmap. You can
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@ -547,11 +547,11 @@
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through <tt>glyph->bitmap</tt> (a simple bitmap descriptor), and
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position it with <tt>glyph->bitmap_left</tt> and
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<tt>glyph->bitmap_top</tt>.</p>
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<p>Note that <tt>bitmap_left</tt> is the horizontal distance from the
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current pen position to the left-most border of the glyph bitmap,
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while <tt>bitmap_top</tt> is the vertical distance from the pen
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position (on the baseline) to the top-most border of the glyph bitmap.
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position (on the baseline) to the top-most border of the glyph bitmap.
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<em>It is positive to indicate an upwards distance</em>.</p>
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<p>The second part of the tutorial will describe the contents of a
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@ -572,23 +572,23 @@
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<p>There are two ways to select a different charmap with
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FreeType 2. The easiest is if the encoding you need already has
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a corresponding enumeration defined in
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<tt><freetype/freetype.h></tt>, as <tt>ft_encoding_big5</tt>.
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<tt><freetype/freetype.h></tt>, as <tt>ft_encoding_big5</tt>.
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In this case, you can simply call <tt>FT_Select_CharMap()</tt> as
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in</p>
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<font color="blue"><pre>
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error = FT_Select_CharMap(
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face, /* target face object */
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ft_encoding_big5 ); /* encoding */</pre>
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</font>
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<p>Another way is to manually parse the list of charmaps for the face,
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this is accessible through the fields <tt>num_charmaps</tt> and
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<tt>charmaps</tt> (notice the final 's') of the face object. As you
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could expect, the first is the number of charmaps in the face, while
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the second is <em>a table of pointers to the charmaps</em> embedded in
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the face.</p>
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<p>Each charmap has a few visible fields used to describe it more
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precisely. Mainly, one will look at <tt>charmap->platform_id</tt> and
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<tt>charmap->encoding_id</tt> which define a pair of values that can
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@ -605,7 +605,7 @@
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list. Bear in mind that some encodings correspond to several values
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pairs (yes, it's a real mess, but blame Apple and Microsoft on such
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stupidity). Here some code to do it:</p>
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<font color="blue">
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<pre>
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FT_CharMap found = 0;
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@ -642,9 +642,9 @@
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<p>It is possible to specify an affine transformation to be applied to
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glyph images when they are loaded. Of course, this will only work for
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scalable (vectorial) font formats.</p>
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<p>To do that, simply call <tt>FT_Set_Transform()</tt>, as in</p>
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<font color="blue">
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<pre>
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error = FT_Set_Transform(
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@ -652,22 +652,22 @@
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&matrix, /* pointer to 2x2 matrix */
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&delta ); /* pointer to 2d vector */</pre>
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</font>
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<p>This function will set the current transformation for a given face
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object. Its second parameter is a pointer to a <tt>FT_Matrix</tt>
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structure that describes a 2x2 affine matrix. The third parameter is
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a pointer to a <tt>FT_Vector</tt> structure that describes a simple 2d
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vector that is used to translate the glyph image <em>after</em> the
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2x2 transformation.</p>
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<p>Note that the matrix pointer can be set to NULL, in which case the
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identity transformation will be used. Coefficients of the matrix are
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otherwise in 16.16 fixed float units.</p>
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<p>The vector pointer can also be set to NULL in which case a delta
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vector of (0,0) will be used. The vector coordinates are expressed in
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1/64th of a pixel (also known as 26.6 fixed floats).</p>
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<p><em>The transformation is applied to every glyph that is loaded
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through <tt>FT_Load_Glyph()</tt> and is <b>completely independent of
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any hinting process.</b> This means that you won't get the same
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@ -682,7 +682,7 @@
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compute a new character pixel size, then the other one to call
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<tt>FT_Set_Transform()</tt>. This is explained in details in a later
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section of this tutorial.</p>
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<p>Note also that loading a glyph bitmap with a non-identity
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transformation will produce an error.</p>
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@ -695,7 +695,7 @@
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<p>We will now present you with a very simple example used to render a
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string of 8-bit Latin-1 text, assuming a face that contains a Unicode
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charmap</p>
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<p>The idea is to create a loop that will, on each iteration, load one
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glyph image, convert it to an anti-aliased bitmap, draw it on the target
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surface, then increment the current pen position.</p>
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@ -706,7 +706,7 @@
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<p>The following code performs our simple text rendering with the
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functions previously described.</p>
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<font color="blue">
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<pre>
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FT_GlyphSlot slot = face->glyph; /* a small shortcut */
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@ -716,37 +716,37 @@
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.. initialize library ..
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.. create face object ..
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.. set character size ..
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pen_x = 300;
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pen_y = 200;
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for ( n = 0; n < num_chars; n++ )
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{
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FT_UInt glyph_index;
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/* retrieve glyph index from character code */
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glyph_index = FT_Get_Char_Index( face, text[n] );
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/* load glyph image into the slot (erase previous one) */
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error = FT_Load_Glyph( face, glyph_index, FT_LOAD_DEFAULT );
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if ( error ) continue; /* ignore errors */
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/* convert to an anti-aliased bitmap */
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error = FT_Render_Glyph( face->glyph, ft_render_mode_normal );
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if ( error ) continue;
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/* now, draw to our target surface */
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my_draw_bitmap( &slot->bitmap,
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pen_x + slot->bitmap_left,
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pen_y - slot->bitmap_top );
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/* increment pen position */
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pen_x += slot->advance.x >> 6;
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pen_y += slot->advance.y >> 6; /* not useful for now */
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}</pre>
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</font>
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</font>
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<p>This code needs a few explanations:</p>
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<ul>
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@ -778,13 +778,13 @@
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to <tt>pen_y</tt> instead of adding it.
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</li>
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</ul>
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<h4>b. refined code</h4>
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<p>The following code is a refined version of the example above. It
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uses features and functions of FreeType 2 that have not yet been
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introduced, and which will be explained below.</p>
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<font color="blue">
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<pre>
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FT_GlyphSlot slot = face->glyph; /* a small shortcut */
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@ -795,29 +795,29 @@
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.. initialize library ..
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.. create face object ..
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.. set character size ..
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pen_x = 300;
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pen_y = 200;
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for ( n = 0; n < num_chars; n++ )
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{
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/* load glyph image into the slot (erase previous one) */
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error = FT_Load_Char( face, text[n], FT_LOAD_RENDER );
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if ( error ) continue; /* ignore errors */
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/* now, draw to our target surface */
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my_draw_bitmap( &slot->bitmap,
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pen_x + slot->bitmap_left,
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pen_y - slot->bitmap_top );
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/* increment pen position */
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pen_x += slot->advance.x >> 6;
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}</pre>
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</font>
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</font>
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<p>We have reduced the size of our code, but it does exactly the same
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thing.</p>
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<ul>
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<li>
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<p>We use the function <tt>FT_Load_Char()</tt> instead of
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@ -828,20 +828,20 @@
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<li>
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<p>We do not use <tt>FT_LOAD_DEFAULT</tt> for the loading mode but
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the bit flag <tt>FT_LOAD_RENDER</tt>. It indicates that the glyph
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image must be immediately converted to an anti-aliased bitmap.
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image must be immediately converted to an anti-aliased bitmap.
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This is of course a shortcut that avoids calling
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<tt>FT_Render_Glyph()</tt> explicitly but is strictly
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equivalent.</p>
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<p>Note that you can also specify that you want a monochrome
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bitmap instead by using the additional <tt>FT_LOAD_MONOCHROME</tt>
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load flag.</p>
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</li>
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</ul>
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</ul>
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<h4>c. more advanced rendering</h4>
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<p>We now render transformed text (for example through a rotation).
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<p>We now render transformed text (for example through a rotation).
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To do that we use <tt>FT_Set_Transform()</tt>:</p>
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<font color="blue">
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matrix.xy = (FT_Fixed)(-sin( angle ) * 0x10000L );
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matrix.yx = (FT_Fixed)( sin( angle ) * 0x10000L );
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matrix.yy = (FT_Fixed)( cos( angle ) * 0x10000L );
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/* the pen position in 26.6 cartesian space coordinates */
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pen.x = 300 * 64;
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pen.y = ( my_target_height - 200 ) * 64;
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for ( n = 0; n < num_chars; n++ )
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{
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/* set transformation */
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FT_Set_Transform( face, &matrix, &pen );
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/* load glyph image into the slot (erase previous one) */
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error = FT_Load_Char( face, text[n], FT_LOAD_RENDER );
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if ( error ) continue; /* ignore errors */
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/* now, draw to our target surface (convert position) */
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my_draw_bitmap( &slot->bitmap,
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slot->bitmap_left,
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my_target_height - slot->bitmap_top );
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/* increment pen position */
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pen.x += slot->advance.x;
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pen.y += slot->advance.y;
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}</pre>
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</font>
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</font>
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<p>Notes:</p>
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@ -916,7 +916,7 @@
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is <em>not</em> rounded this time.
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</li>
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</ul>
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<p>It is important to note that, while this example is a bit more
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complex than the previous one, it is strictly equivalent for the case
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where the transformation is the identity. Hence it can be used as a
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@ -934,11 +934,11 @@
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<p>In this first section, you have learned the basics of
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FreeType 2, as well as sufficient knowledge how to render rotated
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text.</p>
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<p>The next part will dive into more details of the API in order to let
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you access glyph metrics and images directly, as well as how to deal
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with scaling, hinting, kerning, etc.</p>
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<p>The third part will discuss issues like modules, caching, and a few
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other advanced topics like how to use multiple size objects with a
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single face.</p>
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|
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