forked from minhngoc25a/freetype2
[base] API for Harmony LCD rendering.
This introduces `FT_Library_SetLcdGeometry' for setting up arbitrary LCD subpixel geometry including non-striped patterns. * src/base/ftlcdfil.c (FT_Library_SetLcdGeometry): New function. * include/freetype/ftlcdfil.h: Document it. * include/freetype/freetype.h: Minor. * include/freetype/ftchapters.h: Minor.
This commit is contained in:
Alexei Podtelezhnikov
parent
44580515d8
commit
8f1ed54877
18
ChangeLog
18
ChangeLog
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@ -1,3 +1,15 @@
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2018-06-07 Alexei Podtelezhnikov <apodtele@gmail.com>
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[base] API for Harmony LCD rendering.
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This introduces `FT_Library_SetLcdGeometry' for setting up arbitrary
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LCD subpixel geometry including non-striped patterns.
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* src/base/ftlcdfil.c (FT_Library_SetLcdGeometry): New function.
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* include/freetype/ftlcdfil.h: Document it.
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* include/freetype/freetype.h: Minor.
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* include/freetype/ftchapters.h: Minor.
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2018-06-06 Werner Lemberg <wl@gnu.org>
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ftcolor.h: Redesign API.
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@ -5,7 +17,7 @@
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While going to implement it I noticed that I need access to most of
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the `CPAL' elements; I thus plan to add a `cpal' field to
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`TT_FaceRec', which makes most of the previously suggested API
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functions obsolete because the fields will be directly accessable.
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functions obsolete because the fields will be directly accessible.
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2018-06-06 Parth Wazurkar <parthwazurkar@gmail.com>
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@ -657,7 +669,7 @@
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The CPack definitions have been cleaned up, the `make dist' has been
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removed. Source packages generated with CPack don't contain Autotools
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files and aren't used by the maintainters anyway.
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files and aren't used by the maintainers anyway.
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On Windows, src/base/ftver.rc is compiled to decorate the library with
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version and copyright information.
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@ -1872,7 +1884,7 @@
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https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=3514.
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* src/raster/ftrend1.c (ft_raster1_render): Exlicitly signed height.
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* src/raster/ftrend1.c (ft_raster1_render): Explicitly signed height.
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* src/smooth/ftsmooth.c (ft_smooth_render_generic): Ditto.
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* src/base/ftobjs.c (ft_glyphslot_preset_bitmap): Explicitly unsigned
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subtraction.
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@ -3500,7 +3500,7 @@ FT_BEGIN_HEADER
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* with subpixel-rendered glyphs to prevent color-fringing! A
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* subpixel-rendered glyph must first be filtered with a filter that
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* gives equal weight to the three color primaries and does not
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* exceed a sum of 0x100, see section @lcd_filtering. Then the
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* exceed a sum of 0x100, see section @lcd_rendering. Then the
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* only difference to gray linear blending is that subpixel-rendered
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* linear blending is done 3~times per pixel: red foreground subpixel
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* to red background subpixel and so on for green and blue.
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@ -120,7 +120,7 @@
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* gzip
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* lzw
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* bzip2
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* lcd_filtering
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* lcd_rendering
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*
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*/
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@ -36,28 +36,29 @@ FT_BEGIN_HEADER
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/***************************************************************************
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*
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* @section:
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* lcd_filtering
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* lcd_rendering
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*
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* @title:
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* LCD Filtering
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* Subpixel Rendering
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*
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* @abstract:
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* Remove color fringes of subpixel-rendered bitmaps.
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* API to control subpixel rendering.
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*
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* @description:
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* FreeType provides two alternative subpixel rendering technologies.
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* Should you #define FT_CONFIG_OPTION_SUBPIXEL_RENDERING in your
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* `ftoption.h', which enables patented ClearType-style rendering,
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* the LCD-optimized glyph bitmaps should be filtered to reduce color
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* fringes inherent to this technology. The default FreeType LCD
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* rendering uses different technology, and API described below,
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* although available, does nothing.
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* `ftoption.h', this enables patented ClearType-style rendering.
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* Otherwise, Harmony LCD rendering is enabled. These technologies are
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* controlled differently and API described below, although always
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* available, performs its function when appropriate method is enabled
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* and does nothing otherwise.
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*
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* ClearType-style LCD rendering exploits the color-striped structure of
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* LCD pixels, increasing the available resolution in the direction of
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* the stripe (usually horizontal RGB) by a factor of~3. Using the
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* subpixels coverages unfiltered can create severe color fringes
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* especially when rendering thin features. Indeed, to produce
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* black-on-white text, the color components must be dimmed equally.
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* black-on-white text, the nearby color subpixels must be dimmed equally.
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*
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* A good 5-tap FIR filter should be applied to subpixel coverages
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* regardless of pixel boundaries and should have these properties:
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@ -72,31 +73,54 @@ FT_BEGIN_HEADER
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* 3) It should be normalized, meaning 2a~+ 2b~+ c~=~1.0 to maintain
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* overall brightness.
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*
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* Use the @FT_Library_SetLcdFilter API to specify a low-pass filter,
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* which is then applied to subpixel-rendered bitmaps generated through
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* @FT_Render_Glyph. The filter affects glyph bitmaps rendered through
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* @FT_Render_Glyph, @FT_Load_Glyph, and @FT_Load_Char. It does _not_
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* affect the output of @FT_Outline_Render and @FT_Outline_Get_Bitmap.
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* The distribution of density values by the color-balanced filter assumes
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* alpha blending is done in linear space; only then color artifacts
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* cancel out. Boxy 3-tap filter {0, 1/3, 1/3, 1/3, 0} is sharper but is
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* less forgiving of non-ideal gamma curves of a screen (viewing angles!),
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* beveled filters are fuzzier but more tolerant.
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*
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* If this feature is activated, the dimensions of LCD glyph bitmaps are
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* either wider or taller than the dimensions of the corresponding
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* outline with regard to the pixel grid. For example, for
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* @FT_RENDER_MODE_LCD, the filter adds 2~subpixels to the left, and
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* Use the @FT_Library_SetLcdFilter or @FT_Library_SetLcdFilterWeights
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* API to specify a low-pass filter, which is then applied to
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* subpixel-rendered bitmaps generated through @FT_Render_Glyph.
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*
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* Harmony LCD rendering is suitable to panels with any regular subpixel
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* structure, not just monitors with 3 color striped subpixels, as long as
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* the color subpixels have fixed positions relative to the pixel center.
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* In this case, each color channel is then rendered separately after
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* shifting the outline opposite to the subpixel shift so that the
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* coverage maps are aligned. This method is immune to color fringes
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* because the shifts do not change integral coverage.
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*
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* The subpixel geometry must be specified by xy-coordinates for each
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* subpixel. By convention they may come in the RGB order:
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*
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* {{-1/3, 0}, {0, 0}, {1/3, 0}} for hRGB striped panel (default),
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* {{1/3, 0}, {0, 0}, {-1/3, 0}} for hBGR striped panel,
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* {{0, 1/3}, {0, 0}, {0, -1/3}} for vRGB striped panel,
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* {{-1/6, 1/4}, {-1/6, -1/4}, {1/3, 0}} for a certain PenTile panel.
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*
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* Use the @FT_Library_SetLcdGeometry API to specify subpixel positions.
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* If one follows the RGB order convention, the same order applies
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* to the resulting @FT_PIXEL_MODE_LCD and @FT_PIXEL_MODE_LCD_V bitmaps.
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* Note, however, that the coordinate frame for the latter must be rotated
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* clockwise. Harmony with default LCD geometry is equivalent to
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* ClearType with light filter.
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*
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* As a result of ClearType filtering or Harmony rendering, the dimensions
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* of LCD bitmaps can be either wider or taller than the dimensions of
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* the corresponding outline with regard to the pixel grid. For example,
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* for @FT_RENDER_MODE_LCD, the filter adds 2~subpixels to the left, and
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* 2~subpixels to the right. The bitmap offset values are adjusted
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* accordingly, so clients shouldn't need to modify their layout and
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* glyph positioning code when enabling the filter.
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*
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* Only filtering along with gamma-corrected alpha blending can completely
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* remove color fringes. Boxy 3-tap filter {0, 1/3, 1/3, 1/3, 0} is
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* sharper but is less forgiving of non-ideal gamma curves of a screen
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* (viewing angles!), beveled filters are fuzzier but more tolerant.
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*
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* Each of the 3~alpha values (subpixels) is independently used to blend
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* one color channel. That is, red alpha blends the red channel of the
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* text color with the red channel of the background pixel. The
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* distribution of density values by the color-balanced filter assumes
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* alpha blending is done in linear space; only then color artifacts
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* cancel out.
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* The ClearType and Harmony rendering is applicable to glyph bitmaps
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* rendered through @FT_Render_Glyph, @FT_Load_Glyph, and @FT_Load_Char.
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* @FT_RENDER_MODE_LCD or @FT_RENDER_MODE_LCD_V and these technologies do
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* not apply to @FT_Outline_Render and @FT_Outline_Get_Bitmap directly.
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* Each of the 3~alpha values (subpixels) must by independently used to
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* blend one color channel. That is, red alpha blends the red channel of
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* the text color with the red channel of the background pixel.
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*/
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@ -247,6 +271,53 @@ FT_BEGIN_HEADER
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typedef FT_Byte FT_LcdFiveTapFilter[FT_LCD_FILTER_FIVE_TAPS];
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/**************************************************************************
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*
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* @func:
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* FT_Library_SetLcdGeometry
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*
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* @description:
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* This function can be used to modify default positions of color
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* subpixels, which controls Harmony LCD rendering.
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*
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* @input:
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* library ::
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* A handle to the target library instance.
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*
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* sub ::
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* A pointer to an array of 3 vectors in 26.6 fractional pixel format;
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* the function modifies the default values, see the note below.
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*
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* @return:
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* FreeType error code. 0~means success.
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*
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* @note:
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* Subpixel geometry examples:
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*
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* - {{-21, 0}, {0, 0}, {21, 0}} is the default, corresponding 3 color
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* stripes shifted by a third of a pixel. This could be an RGB panel.
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*
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* - {{21, 0}, {0, 0}, {-21, 0}} looks the same as the default but
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* can specify a BGR panel instead, while keeping the bitmap in the same
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* RGB888 format.
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*
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* - {{0, 21}, {0, 0}, {0, -21}} is the vertical RGB, but the bitmap
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* stays RGB888 as a result.
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*
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* - {{-11, 16}, {-11, -16}, {22, 0}} is a certain PenTile arrangement.
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*
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* This function does nothing and returns `FT_Err_Unimplemented_Feature'
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* in the context of ClearType-style subpixel rendering when
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* FT_CONFIG_OPTION_SUBPIXEL_RENDERING is defined in your build of the
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* library.
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*
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* @since:
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* 2.10.0
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*/
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FT_EXPORT( FT_Error )
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FT_Library_SetLcdGeometry( FT_Library library,
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FT_Vector sub[3] );
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/* */
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@ -285,6 +285,8 @@
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#endif /* USE_LEGACY */
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/* documentation in ftlcdfil.h */
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FT_EXPORT_DEF( FT_Error )
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FT_Library_SetLcdFilterWeights( FT_Library library,
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unsigned char *weights )
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@ -302,6 +304,8 @@
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}
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/* documentation in ftlcdfil.h */
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FT_EXPORT_DEF( FT_Error )
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FT_Library_SetLcdFilter( FT_Library library,
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FT_LcdFilter filter )
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return FT_Err_Ok;
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}
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FT_EXPORT_DEF( FT_Error )
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FT_Library_SetLcdGeometry( FT_Library library,
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FT_Vector* sub )
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{
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FT_UNUSED( library );
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FT_UNUSED( sub );
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return FT_THROW( Unimplemented_Feature );
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}
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#else /* !FT_CONFIG_OPTION_SUBPIXEL_RENDERING */
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/* add padding to accommodate outline shifts */
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@ -399,6 +414,24 @@
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return FT_THROW( Unimplemented_Feature );
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}
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/* documentation in ftlcdfil.h */
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FT_EXPORT_DEF( FT_Error )
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FT_Library_SetLcdGeometry( FT_Library library,
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FT_Vector sub[3] )
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{
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if ( !library )
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return FT_THROW( Invalid_Library_Handle );
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if ( !sub )
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return FT_THROW( Invalid_Argument );
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ft_memcpy( library->lcd_geometry, sub, 3 * sizeof( FT_Vector ) );
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return FT_THROW( Unimplemented_Feature );
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}
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#endif /* !FT_CONFIG_OPTION_SUBPIXEL_RENDERING */
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