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