Minor fixes.

This commit is contained in:
Werner Lemberg 2000-11-08 20:21:38 +00:00
parent a6c747d2b5
commit f42e6595e6
1 changed files with 76 additions and 77 deletions

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@ -104,19 +104,19 @@
<ul><p>
<li>
<a href="#other-color">How can I set the color of text rendered
by FreeType ?</a>
by FreeType?</a>
</li>
<li>
<a href="#other-depth">Can I use FreeType to draw text on a pixmap
with arbitrary depth ?</a>
with arbitrary depth?</a>
</li>
<li>
<a href="#other-size">I set the pixel size to 8x8, but the resulting
glyphs are larger than that. Why ?</a>
<a href="#other-size">I set the pixel size to 8x8, but the
resulting glyphs are larger than that. Why?</a>
</li>
<li>
<a href="#other-bbox">How can I compute the bounding box of a text
string without loading its glyphs ?</a>
string without loading its glyphs?</a>
</li>
<li>
<a href="#other-antialias">Which anti-aliasing algorithm is
@ -567,112 +567,111 @@
<a name="other-depth">
<h3>
IV.1 Can I use FreeType to draw text on a pixmap with arbitratry depth ?
IV.1 Can I use FreeType to draw text on a pixmap with arbitratry depth?
</h3>
<p>No directly, as FreeType is a font library, not a general purpose
graphics library or text rendering service. However, note that the
<p>Not directly, as FreeType is a font library, not a general purpose
graphics library or text rendering service. However, note that the
anti-aliased renderer allows you to convert a vectorial glyph outline
into a list of "spans" (i.e. horizontal pixel segments with same coverage)
that can be rendered through user-provided callbacks.</p>
into a list of "spans" (i.e. horizontal pixel segments with same
coverage) that can be rendered through user-provided callbacks.</p>
<p>By providing the appropriate span callback, you can render anti-aliased
text to any kind of surface. You can also use any color or fill
pattern/image if you want to. This process is called
<em>direct rendering</em>. For more information, please read the
documentation contained in the following files:</p>
<p>By providing the appropriate span callback, you can render
anti-aliased text to any kind of surface. You can also use any color or
fill pattern/image if you want to. This process is called <em>direct
rendering</em>. For more information, please read the documentation
contained in the following files:</p>
<ul>
<li><p>
<b><tt>&lt;freetype/ftimage.h&gt;</tt></b> contains the definition
of the <tt>FT_Raster_Params</tt> type used with direct rendering.
</p></li>
<li><p>
<b><tt>&lt;freetype/ftoutln.h&gt;</tt></b> contains the definition
of the <tt>FT_Outline_Render</tt> function that can be used to
convert vectorial outlines to span lists.
</p></li>
</ul>
<ul>
<li>
<p><tt>&lt;freetype/ftimage.h&gt;</tt> contains the definition of
the <tt>FT_Raster_Params</tt> type used with direct rendering.</p>
</li>
<li>
<p><tt>&lt;freetype/ftoutln.h&gt;</tt> contains the definition of
the <tt>FT_Outline_Render()</tt> function that can be used to
convert vectorial outlines to span lists.</p>
</li>
</ul>
<p>Here's some code that uses them:</p>
<font color="blue"><pre>
<p>Here's some code that uses them:</p>
<font color="blue"><pre>
FT_Raster_Params params;
FT_Outline outline;
... load vectorial glyph in "outline" ...
params.flags = ft_raster_flag_aa | ft_raster_flag_direct;
params.gray_spans = (FT_Raster_Span_Func)your_own_span_function_here;
params.user = your_own_data_pointer;
error = FT_Outline_Render( library, &amp;outline, &amp;params );</pre>
</font>
FT_Raster_Params params;
FT_Outline outline;
.. load vectorial glyph in "outline"
params.flags = ft_raster_flag_aa | ft_raster_flag_direct;
params.gray_spans = (FT_Raster_Span_Func)your_own_span_function_here;
params.user = your_own_data_pointer;
error = FT_Outline_Render( library, &amp;outline, &amp;params );
</pre></font>
<p>Note that direct rendering is <em>not</em> available with monochrome
output, as the current renderer uses a two-pass algorithm to generate
glyphs with correct drop-out control.</p>
<p>Note that direct rendering is <em>not</em> available with monochrome
output, as the current renderer uses a two-pass algorithm to generate
glyphs with correct drop-out control.</p>
<hr>
<a name="other-color">
<h3>
IV.2 How can I set the color of text rendered by FreeType ?
IV.2 How can I set the color of text rendered by FreeType?
</h3>
<p>Basically, you can't do that, because FreeType is simply a font
library. In general, you'll need to use your favorite graphics library
to draw the FreeType glyphs with the appropriate color.</p>
library. In general, you will need to use your favorite graphics
library to draw the FreeType glyphs with the appropriate color.</p>
<p>Note that for anti-aliased glyphs, you can "set the color" by using
<em>direct rendering</em> as described in <a href="#other-depth">this
answer</a></p>
answer</a>.</p>
<hr>
<a name="other-size">
<h3>
IV.3 I set the pixel size to 8x8, but the resulting glyphs are larger
(or smaller) than that. Why ??
(or smaller) than that. Why?
</h3>
<p>A lot of people have a hard time understanding this topic, because
they think of glyphs as fixed-width/height "cells", like those of
fonts used in terminals/consoles. This assumption is simply not valid
with most "modern" font formats, even bitmapped-based ones like
PCF or BDF.</p>
<p>A lot of people have difficulties to understand this topic, because
they think of glyphs as fixed-width resp. fixed-height "cells", like
those of fonts used in terminals/consoles. This assumption is simply
not valid with most "modern" font formats, even bitmapped-based ones
like <tt>PCF</tt> or <tt>BDF</tt>.</p>
<p>Be aware that the <em>character size</em> that is set either through
<tt>FT_Set_Char_Size</tt> or <tt>FT_Set_Pixel_Sizes</tt> isn't directly
related to the dimension of the glyph bitmaps generated.</p>
<tt>FT_Set_Char_Size()</tt> or <tt>FT_Set_Pixel_Sizes()</tt> isn't
directly related to the dimension of the glyph bitmaps generated.</p>
<p>Rather, the character size is indeed the size of
<em>an abstract square</em>, called the <em>EM</em>, used by typographers
to design fonts. Scaling two distinct fonts to the same character size, be
it expressed in points or pixels, will generally result in bitmaps with
<em>distinct dimensions</em> !</p>
<p>Rather, the character size is indeed the size of <em>an abstract
square</em>, called the <em>EM</em>, used by typographers to design
fonts. Scaling two distinct fonts to the same character size, be it
expressed in points or pixels, will generally result in bitmaps with
<em>distinct dimensions</em>!</p>
<p>Note that historically, the EM corresponded to the width of a capital
"M" in Latin typefaces. However, later improvements in typography led to
the designs that greatly detract from this rule. Today, it is not possible
to connect the EM size to a specific font "feature" in a reliable way.</p>
"M" in Latin typefaces. However, later improvements in typography led
to designs that greatly detract from this rule. Today, it is not
possible to connect the EM size to a specific font "feature" in a
reliable way.</p>
<hr>
<a name="other-bbox">
<h3>
IV.4 How can I compute the bounding box of a given string of text without
loading its glyphs before ?
IV.4 How can I compute the bounding box of a given string of text
without loading its glyphs before?
</h3>
<p>A lot of people want to be able to compute the size in pixels of a simple
string of text with minimal overhead. For example, that can be useful to
draw centered text within a button.</p>
<p>A lot of people want to be able to compute the size in pixels of a
simple string of text with minimal overhead. For example, that can be
useful to draw centered text within a button. (to be continued...)</p>
<hr>
<a name="other-antialias">
<h3>
IV.1 Which anti-aliasing algorithm is used by FreeType&nbsp;2?</h3>
IV.5 Which anti-aliasing algorithm is used by FreeType&nbsp;2?</h3>
<p>The algorithm has been specifically designed for FreeType. It is
based on ideas that were originally found in the implementation of the
@ -699,7 +698,7 @@
<hr>
<a name="other-opentype">
<h3>
IV.2 When will FreeType&nbsp;2 support OpenType?
IV.6 When will FreeType&nbsp;2 support OpenType?
</h3>
<p>Well, the engine already reads OpenType/CFF files perfectly. What it
@ -707,7 +706,7 @@
<p>FreeType&nbsp;1 comes with a set of extensions that are used to load
and manage OpenType Layout tables. It even has a demonstration program
named "<tt>ftstrtto</tt>" to show its capabilities.</p>
named <tt>ftstrtto</tt> to show its capabilities.</p>
<p>For FreeType&nbsp;2, we have decided that the layout operations
provided through these tables are better placed in a specific