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diff --git a/freetype/docs/reference/ft2-tt_driver.html b/freetype/docs/reference/ft2-tt_driver.html index 5d71829e4..9264d7cf6 100644 --- a/freetype/docs/reference/ft2-tt_driver.html +++ b/freetype/docs/reference/ft2-tt_driver.html @@ -3,7 +3,7 @@ <html> <head> <meta http-equiv="Content-Type" content="text/html; charset=utf-8"> -<title>FreeType-2.5.5 API Reference</title> +<title>FreeType-2.6 API Reference</title> <style type="text/css"> a:link { color: #0000EF; } a:visited { color: #51188E; } @@ -100,7 +100,7 @@ <body> <table class="index-toc-link"><tr><td class="left">[<a href="ft2-index.html">Index</a>]</td><td class="right">[<a href="ft2-toc.html">TOC</a>]</td></tr></table> -<h1>FreeType-2.5.5 API Reference</h1> +<h1>FreeType-2.6 API Reference</h1> <h1>The TrueType driver</h1> <h2>Synopsis</h2> @@ -116,7 +116,7 @@ <h3 id="interpreter-version">interpreter-version</h3> <p>Currently, two versions are available, representing the bytecode interpreter with and without subpixel hinting support, respectively. The default is subpixel support if TT_CONFIG_OPTION_SUBPIXEL_HINTING is defined, and no subpixel support otherwise (since it isn't available then).</p> -<p>If subpixel hinting is on, many TrueType bytecode instructions behave differently compared to B/W or grayscale rendering. The main idea is to render at a much increased horizontal resolution, then sampling down the created output to subpixel precision. However, many older fonts are not suited to this and must be specially taken care of by applying (hardcoded) font-specific tweaks.</p> +<p>If subpixel hinting is on, many TrueType bytecode instructions behave differently compared to B/W or grayscale rendering (except if ‘native ClearType’ is selected by the font). The main idea is to render at a much increased horizontal resolution, then sampling down the created output to subpixel precision. However, many older fonts are not suited to this and must be specially taken care of by applying (hardcoded) font-specific tweaks.</p> <p>Details on subpixel hinting and some of the necessary tweaks can be found in Greg Hitchcock's whitepaper at ‘<a href="http://www.microsoft.com/typography/cleartype/truetypecleartype.aspx">http://www.microsoft.com/typography/cleartype/truetypecleartype.aspx</a>’.</p> <p>The following example code demonstrates how to activate subpixel hinting (omitting the error handling).</p> <pre class="colored"> @@ -162,19 +162,48 @@ <h4>note</h4> <p>This property controls the behaviour of the bytecode interpreter and thus how outlines get hinted. It does <b>not</b> control how glyph get rasterized! In particular, it does not control subpixel color filtering.</p> <p>If FreeType has not been compiled with configuration option FT_CONFIG_OPTION_SUBPIXEL_HINTING, selecting version 38 causes an ‘FT_Err_Unimplemented_Feature’ error.</p> -<p>Depending on the graphics framework, Microsoft uses different bytecode engines. As a consequence, the version numbers returned by a call to the ‘GETINFO[1]’ bytecode instruction are more convoluted than desired.</p> +<p>Depending on the graphics framework, Microsoft uses different bytecode and rendering engines. As a consequence, the version numbers returned by a call to the ‘GETINFO’ bytecode instruction are more convoluted than desired.</p> +<p>Here are two tables that try to shed some light on the possible values for the MS rasterizer engine, together with the additional features introduced by it.</p> <pre class="colored"> - framework Windows version result of GETINFO[1] - ---------------------------------------------------- - GDI before XP 35 - GDI XP and later 37 - GDI+ old before Vista 37 - GDI+ old Vista, 7 38 - GDI+ after 7 40 - DWrite before 8 39 - DWrite 8 and later 40 + GETINFO framework version feature + ------------------------------------------------------------------- + 3 GDI (Win 3.1), v1.0 16-bit, first version + TrueImage + 33 GDI (Win NT 3.1), v1.5 32-bit + HP Laserjet + 34 GDI (Win 95) v1.6 font smoothing, + new SCANTYPE opcode + 35 GDI (Win 98/2000) v1.7 (UN)SCALED_COMPONENT_OFFSET + bits in composite glyphs + 36 MGDI (Win CE 2) v1.6+ classic ClearType + 37 GDI (XP and later), v1.8 ClearType + GDI+ old (before Vista) + 38 GDI+ old (Vista, Win 7), v1.9 subpixel ClearType, + WPF Y-direction ClearType, + additional error checking + 39 DWrite (before Win 8) v2.0 subpixel ClearType flags + in GETINFO opcode, + bug fixes + 40 GDI+ (after Win 7), v2.1 Y-direction ClearType flag + DWrite (Win 8) in GETINFO opcode, + Gray ClearType </pre> -<p>Since FreeType doesn't provide all capabilities of DWrite ClearType, using version 38 seems justified.</p> +<p>The ‘version’ field gives a rough orientation only, since some applications provided certain features much earlier (as an example, Microsoft Reader used subpixel and Y-direction ClearType already in Windows 2000). Similarly, updates to a given framework might include improved hinting support.</p> +<pre class="colored"> + version sampling rendering comment + x y x y + -------------------------------------------------------------- + v1.0 normal normal B/W B/W bi-level + v1.6 high high gray gray grayscale + v1.8 high normal color-filter B/W (GDI) ClearType + v1.9 high high color-filter gray Color ClearType + v2.1 high normal gray B/W Gray ClearType + v2.1 high high gray gray Gray ClearType +</pre> +<p>Color and Gray ClearType are the two available variants of ‘Y-direction ClearType’, meaning grayscale rasterization along the Y-direction; the name used in the TrueType specification for this feature is ‘symmetric smoothing’. ‘Classic ClearType’ is the original algorithm used before introducing a modified version in Win XP. Another name for v1.6's grayscale rendering is ‘font smoothing’, and ‘Color ClearType’ is sometimes also called ‘DWrite ClearType’. To differentiate between today's Color ClearType and the earlier ClearType variant with B/W rendering along the vertical axis, the latter is sometimes called ‘GDI ClearType’.</p> +<p>‘Normal’ and ‘high’ sampling describe the (virtual) resolution to access the rasterized outline after the hinting process. ‘Normal’ means 1 sample per grid line (i.e., B/W). In the current Microsoft implementation, ‘high’ means an extra virtual resolution of 16x16 (or 16x1) grid lines per pixel for bytecode instructions like ‘MIRP’. After hinting, these 16 grid lines are mapped to 6x5 (or 6x1) grid lines for color filtering if Color ClearType is activated.</p> +<p>Note that ‘Gray ClearType’ is essentially the same as v1.6's grayscale rendering. However, the GETINFO instruction handles it differently: v1.6 returns bit 12 (hinting for grayscale), while v2.1 returns bits 13 (hinting for ClearType), 18 (symmetrical smoothing), and 19 (Gray ClearType). Also, this mode respects bits 2 and 3 for the version 1 gasp table exclusively (like Color ClearType), while v1.6 only respects the values of version 0 (bits 0 and 1).</p> +<p>FreeType doesn't provide all capabilities of the most recent ClearType incarnation, thus we identify our subpixel support as version 38.</p> <hr> <table class="index-toc-link"><tr><td class="left">[<a href="ft2-index.html">Index</a>]</td><td class="middle">[<a href="#">Top</a>]</td><td class="right">[<a href="ft2-toc.html">TOC</a>]</td></tr></table></div> |