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Diffstat (limited to 'third_party/freetype/include/freetype/ftlcdfil.h')
| -rw-r--r-- | third_party/freetype/include/freetype/ftlcdfil.h | 286 |
1 files changed, 0 insertions, 286 deletions
diff --git a/third_party/freetype/include/freetype/ftlcdfil.h b/third_party/freetype/include/freetype/ftlcdfil.h deleted file mode 100644 index 928bb0f3ea..0000000000 --- a/third_party/freetype/include/freetype/ftlcdfil.h +++ /dev/null @@ -1,286 +0,0 @@ -/***************************************************************************/ -/* */ -/* ftlcdfil.h */ -/* */ -/* FreeType API for color filtering of subpixel bitmap glyphs */ -/* (specification). */ -/* */ -/* Copyright 2006-2017 by */ -/* David Turner, Robert Wilhelm, and Werner Lemberg. */ -/* */ -/* This file is part of the FreeType project, and may only be used, */ -/* modified, and distributed under the terms of the FreeType project */ -/* license, LICENSE.TXT. By continuing to use, modify, or distribute */ -/* this file you indicate that you have read the license and */ -/* understand and accept it fully. */ -/* */ -/***************************************************************************/ - - -#ifndef FTLCDFIL_H_ -#define FTLCDFIL_H_ - -#include <ft2build.h> -#include FT_FREETYPE_H - -#ifdef FREETYPE_H -#error "freetype.h of FreeType 1 has been loaded!" -#error "Please fix the directory search order for header files" -#error "so that freetype.h of FreeType 2 is found first." -#endif - - -FT_BEGIN_HEADER - - /*************************************************************************** - * - * @section: - * lcd_filtering - * - * @title: - * LCD Filtering - * - * @abstract: - * Reduce color fringes of subpixel-rendered bitmaps. - * - * @description: - * Subpixel rendering exploits the color-striped structure of LCD - * pixels, increasing the available resolution in the direction of the - * stripe (usually horizontal RGB) by a factor of~3. Since these - * subpixels are color pixels, using them unfiltered creates severe - * color fringes. Use the @FT_Library_SetLcdFilter API to specify a - * low-pass filter, which is then applied to subpixel-rendered bitmaps - * generated through @FT_Render_Glyph. The filter sacrifices some of - * the higher resolution to reduce color fringes, making the glyph image - * slightly blurrier. Positional improvements will remain. - * - * Note that no filter is active by default, and that this function is - * *not* implemented in default builds of the library. You need to - * #define FT_CONFIG_OPTION_SUBPIXEL_RENDERING in your `ftoption.h' file - * in order to activate it and explicitly call @FT_Library_SetLcdFilter - * to enable it. - * - * A filter should have two properties: - * - * 1) It should be normalized, meaning the sum of the 5~components - * should be 256 (0x100). It is possible to go above or under this - * target sum, however: going under means tossing out contrast, going - * over means invoking clamping and thereby non-linearities that - * increase contrast somewhat at the expense of greater distortion - * and color-fringing. Contrast is better enhanced through stem - * darkening. - * - * 2) It should be color-balanced, meaning a filter `{~a, b, c, b, a~}' - * where a~+ b~=~c. It distributes the computed coverage for one - * subpixel to all subpixels equally, sacrificing some won resolution - * but drastically reducing color-fringing. Positioning improvements - * remain! Note that color-fringing can only really be minimized - * when using a color-balanced filter and alpha-blending the glyph - * onto a surface in linear space; see @FT_Render_Glyph. - * - * Regarding the form, a filter can be a `boxy' filter or a `beveled' - * filter. Boxy filters are sharper but are less forgiving of non-ideal - * gamma curves of a screen (viewing angles!), beveled filters are - * fuzzier but more tolerant. - * - * Examples: - * - * - [0x10 0x40 0x70 0x40 0x10] is beveled and neither balanced nor - * normalized. - * - * - [0x1A 0x33 0x4D 0x33 0x1A] is beveled and balanced but not - * normalized. - * - * - [0x19 0x33 0x66 0x4c 0x19] is beveled and normalized but not - * balanced. - * - * - [0x00 0x4c 0x66 0x4c 0x00] is boxily beveled and normalized but not - * balanced. - * - * - [0x00 0x55 0x56 0x55 0x00] is boxy, normalized, and almost - * balanced. - * - * - [0x08 0x4D 0x56 0x4D 0x08] is beveled, normalized and, almost - * balanced. - * - * The filter affects glyph bitmaps rendered through @FT_Render_Glyph, - * @FT_Load_Glyph, and @FT_Load_Char. It does _not_ affect the output - * of @FT_Outline_Render and @FT_Outline_Get_Bitmap. - * - * If this feature is activated, the dimensions of LCD glyph bitmaps are - * either wider or taller than the dimensions of the corresponding - * outline with regard to the pixel grid. For example, for - * @FT_RENDER_MODE_LCD, the filter adds 3~subpixels to the left, and - * 3~subpixels to the right. The bitmap offset values are adjusted - * accordingly, so clients shouldn't need to modify their layout and - * glyph positioning code when enabling the filter. - * - * It is important to understand that linear alpha blending and gamma - * correction is critical for correctly rendering glyphs onto surfaces - * without artifacts and even more critical when subpixel rendering is - * involved. - * - * Each of the 3~alpha values (subpixels) is independently used to blend - * one color channel. That is, red alpha blends the red channel of the - * text color with the red channel of the background pixel. The - * distribution of density values by the color-balanced filter assumes - * alpha blending is done in linear space; only then color artifacts - * cancel out. - */ - - - /**************************************************************************** - * - * @enum: - * FT_LcdFilter - * - * @description: - * A list of values to identify various types of LCD filters. - * - * @values: - * FT_LCD_FILTER_NONE :: - * Do not perform filtering. When used with subpixel rendering, this - * results in sometimes severe color fringes. - * - * FT_LCD_FILTER_DEFAULT :: - * The default filter reduces color fringes considerably, at the cost - * of a slight blurriness in the output. - * - * It is a beveled, normalized, and color-balanced five-tap filter - * that is more forgiving to screens with non-ideal gamma curves and - * viewing angles. Note that while color-fringing is reduced, it can - * only be minimized by using linear alpha blending and gamma - * correction to render glyphs onto surfaces. The default filter - * weights are [0x08 0x4D 0x56 0x4D 0x08]. - * - * FT_LCD_FILTER_LIGHT :: - * The light filter is a variant that is sharper at the cost of - * slightly more color fringes than the default one. - * - * It is a boxy, normalized, and color-balanced three-tap filter that - * is less forgiving to screens with non-ideal gamma curves and - * viewing angles. This filter works best when the rendering system - * uses linear alpha blending and gamma correction to render glyphs - * onto surfaces. The light filter weights are - * [0x00 0x55 0x56 0x55 0x00]. - * - * FT_LCD_FILTER_LEGACY :: - * This filter corresponds to the original libXft color filter. It - * provides high contrast output but can exhibit really bad color - * fringes if glyphs are not extremely well hinted to the pixel grid. - * In other words, it only works well if the TrueType bytecode - * interpreter is enabled *and* high-quality hinted fonts are used. - * - * This filter is only provided for comparison purposes, and might be - * disabled or stay unsupported in the future. - * - * FT_LCD_FILTER_LEGACY1 :: - * For historical reasons, the FontConfig library returns a different - * enumeration value for legacy LCD filtering. To make code work that - * (incorrectly) forwards FontConfig's enumeration value to - * @FT_Library_SetLcdFilter without proper mapping, it is thus easiest - * to have another enumeration value, which is completely equal to - * `FT_LCD_FILTER_LEGACY'. - * - * @since: - * 2.3.0 (`FT_LCD_FILTER_LEGACY1' since 2.6.2) - */ - typedef enum FT_LcdFilter_ - { - FT_LCD_FILTER_NONE = 0, - FT_LCD_FILTER_DEFAULT = 1, - FT_LCD_FILTER_LIGHT = 2, - FT_LCD_FILTER_LEGACY1 = 3, - FT_LCD_FILTER_LEGACY = 16, - - FT_LCD_FILTER_MAX /* do not remove */ - - } FT_LcdFilter; - - - /************************************************************************** - * - * @func: - * FT_Library_SetLcdFilter - * - * @description: - * This function is used to apply color filtering to LCD decimated - * bitmaps, like the ones used when calling @FT_Render_Glyph with - * @FT_RENDER_MODE_LCD or @FT_RENDER_MODE_LCD_V. - * - * @input: - * library :: - * A handle to the target library instance. - * - * filter :: - * The filter type. - * - * You can use @FT_LCD_FILTER_NONE here to disable this feature, or - * @FT_LCD_FILTER_DEFAULT to use a default filter that should work - * well on most LCD screens. - * - * @return: - * FreeType error code. 0~means success. - * - * @note: - * This feature is always disabled by default. Clients must make an - * explicit call to this function with a `filter' value other than - * @FT_LCD_FILTER_NONE in order to enable it. - * - * Due to *PATENTS* covering subpixel rendering, this function doesn't - * do anything except returning `FT_Err_Unimplemented_Feature' if the - * configuration macro FT_CONFIG_OPTION_SUBPIXEL_RENDERING is not - * defined in your build of the library, which should correspond to all - * default builds of FreeType. - * - * @since: - * 2.3.0 - */ - FT_EXPORT( FT_Error ) - FT_Library_SetLcdFilter( FT_Library library, - FT_LcdFilter filter ); - - - /************************************************************************** - * - * @func: - * FT_Library_SetLcdFilterWeights - * - * @description: - * This function can be used to enable LCD filter with custom weights, - * instead of using presets in @FT_Library_SetLcdFilter. - * - * @input: - * library :: - * A handle to the target library instance. - * - * weights :: - * A pointer to an array; the function copies the first five bytes and - * uses them to specify the filter weights. - * - * @return: - * FreeType error code. 0~means success. - * - * @note: - * Due to *PATENTS* covering subpixel rendering, this function doesn't - * do anything except returning `FT_Err_Unimplemented_Feature' if the - * configuration macro FT_CONFIG_OPTION_SUBPIXEL_RENDERING is not - * defined in your build of the library, which should correspond to all - * default builds of FreeType. - * - * @since: - * 2.4.0 - */ - FT_EXPORT( FT_Error ) - FT_Library_SetLcdFilterWeights( FT_Library library, - unsigned char *weights ); - - /* */ - - -FT_END_HEADER - -#endif /* FTLCDFIL_H_ */ - - -/* END */ |