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authorLiang Qi <liang.qi@qt.io>2019-02-08 09:28:00 +0100
committerEdward Welbourne <edward.welbourne@qt.io>2019-02-08 12:31:02 +0100
commitfbfacd33be482fa3cf0aa5cffaf7006d538a2f92 (patch)
tree92da72786b3740e37004623612c4fc1c9640d30f /src/3rdparty/freetype/include/freetype/ftlcdfil.h
parentc1f4286a5cbc1794fe7be5bdbbd6a0bf29ef84d4 (diff)
parent74e04d6ace7aa949db97ae2e46c38a4dc0d4d36a (diff)
Merge remote-tracking branch 'origin/5.12' into 5.13
Conflicts: src/android/templates/AndroidManifest.xml src/network/ssl/qsslsocket_mac.cpp src/widgets/styles/qstylesheetstyle.cpp tests/auto/corelib/kernel/qtimer/BLACKLIST tests/auto/testlib/selftests/blacklisted/tst_blacklisted.cpp tests/auto/testlib/selftests/expected_blacklisted.lightxml tests/auto/testlib/selftests/expected_blacklisted.tap tests/auto/testlib/selftests/expected_blacklisted.teamcity tests/auto/testlib/selftests/expected_blacklisted.txt tests/auto/testlib/selftests/expected_blacklisted.xml tests/auto/testlib/selftests/expected_blacklisted.xunitxml tests/auto/testlib/selftests/expected_float.tap tests/auto/testlib/selftests/expected_float.teamcity tests/auto/testlib/selftests/expected_float.txt tests/auto/testlib/selftests/expected_float.xunitxml Done-With: Christian Ehrlicher <ch.ehrlicher@gmx.de> Done-With: Edward Welbourne <edward.welbourne@qt.io> Done-With: Timur Pocheptsov <timur.pocheptsov@qt.io> Change-Id: If93cc432a56ae3ac1b6533d0028e4dc497415a52
Diffstat (limited to 'src/3rdparty/freetype/include/freetype/ftlcdfil.h')
-rw-r--r--src/3rdparty/freetype/include/freetype/ftlcdfil.h216
1 files changed, 137 insertions, 79 deletions
diff --git a/src/3rdparty/freetype/include/freetype/ftlcdfil.h b/src/3rdparty/freetype/include/freetype/ftlcdfil.h
index 4cd999a4b3..2a27196cbb 100644
--- a/src/3rdparty/freetype/include/freetype/ftlcdfil.h
+++ b/src/3rdparty/freetype/include/freetype/ftlcdfil.h
@@ -5,7 +5,7 @@
/* FreeType API for color filtering of subpixel bitmap glyphs */
/* (specification). */
/* */
-/* Copyright 2006-2015 by */
+/* Copyright 2006-2018 by */
/* David Turner, Robert Wilhelm, and Werner Lemberg. */
/* */
/* This file is part of the FreeType project, and may only be used, */
@@ -17,11 +17,12 @@
/***************************************************************************/
-#ifndef __FT_LCD_FILTER_H__
-#define __FT_LCD_FILTER_H__
+#ifndef FTLCDFIL_H_
+#define FTLCDFIL_H_
#include <ft2build.h>
#include FT_FREETYPE_H
+#include FT_PARAMETER_TAGS_H
#ifdef FREETYPE_H
#error "freetype.h of FreeType 1 has been loaded!"
@@ -41,56 +42,92 @@ FT_BEGIN_HEADER
* LCD Filtering
*
* @abstract:
- * Reduce color fringes of LCD-optimized bitmaps.
+ * Reduce color fringes of subpixel-rendered bitmaps.
*
* @description:
- * The @FT_Library_SetLcdFilter API can be used to specify a low-pass
- * filter, which is then applied to LCD-optimized bitmaps generated
- * through @FT_Render_Glyph. This is useful to reduce color fringes
- * that would occur with unfiltered rendering.
- *
- * 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.
- *
- * FreeType generates alpha coverage maps, which are linear by nature.
- * For instance, the value 0x80 in bitmap representation means that
- * (within numerical precision) 0x80/0xFF fraction of that pixel is
- * covered by the glyph's outline. The blending function for placing
- * text over a background is
- *
- * {
- * dst = alpha * src + (1 - alpha) * dst ,
- * }
- *
- * which is known as OVER. However, when calculating the output of the
- * OVER operator, the source colors should first be transformed to a
- * linear color space, then alpha blended in that space, and transformed
- * back to the output color space.
- *
- * When linear light blending is used, the default FIR5 filtering
- * weights (as given by FT_LCD_FILTER_DEFAULT) are no longer optimal, as
- * they have been designed for black on white rendering while lacking
- * gamma correction. To preserve color neutrality, weights for a FIR5
- * filter should be chosen according to two free parameters `a' and `c',
- * and the FIR weights should be
- *
- * {
- * [a - c, a + c, 2 * a, a + c, a - c] .
- * }
- *
- * This formula generates equal weights for all the color primaries
- * across the filter kernel, which makes it colorless. One suggested
- * set of weights is
- *
- * {
- * [0x10, 0x50, 0x60, 0x50, 0x10] ,
- * }
- *
- * where `a' has value 0x30 and `b' value 0x20. The weights in filter
- * may have a sum larger than 0x100, which increases coloration slightly
- * but also improves contrast.
+ * Should you #define FT_CONFIG_OPTION_SUBPIXEL_RENDERING in your
+ * `ftoption.h', which enables patented ClearType-style rendering,
+ * the LCD-optimized glyph bitmaps should be filtered to reduce color
+ * fringes inherent to this technology. The default FreeType LCD
+ * rendering uses different technology, and API described below,
+ * although available, does nothing.
+ *
+ * ClearType-style LCD 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.
+ *
+ * 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.
*/
@@ -111,10 +148,23 @@ FT_BEGIN_HEADER
* 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 produces less blurriness at the
- * cost of slightly more color fringes than the default one. It might
- * be better, depending on taste, your monitor, or your personal vision.
+ * 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
@@ -126,14 +176,23 @@ FT_BEGIN_HEADER
* 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
+ * 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 */
@@ -176,22 +235,6 @@ FT_BEGIN_HEADER
* defined in your build of the library, which should correspond to all
* default builds of FreeType.
*
- * The filter affects glyph bitmaps rendered through @FT_Render_Glyph,
- * @FT_Outline_Get_Bitmap, @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 larger or taller than the dimensions of the corresponding
- * outline with regards to the pixel grid. For example, for
- * @FT_RENDER_MODE_LCD, the filter adds up to 3~pixels to the left, and
- * up to 3~pixels to the right.
- *
- * The bitmap offset values are adjusted correctly, so clients shouldn't
- * need to modify their layout and glyph positioning code when enabling
- * the filter.
- *
* @since:
* 2.3.0
*/
@@ -206,11 +249,8 @@ FT_BEGIN_HEADER
* FT_Library_SetLcdFilterWeights
*
* @description:
- * Use this function to override the filter weights selected by
- * @FT_Library_SetLcdFilter. By default, FreeType uses the quintuple
- * (0x00, 0x55, 0x56, 0x55, 0x00) for FT_LCD_FILTER_LIGHT, and (0x10,
- * 0x40, 0x70, 0x40, 0x10) for FT_LCD_FILTER_DEFAULT and
- * FT_LCD_FILTER_LEGACY.
+ * This function can be used to enable LCD filter with custom weights,
+ * instead of using presets in @FT_Library_SetLcdFilter.
*
* @input:
* library ::
@@ -230,8 +270,8 @@ FT_BEGIN_HEADER
* defined in your build of the library, which should correspond to all
* default builds of FreeType.
*
- * This function must be called after @FT_Library_SetLcdFilter to have
- * any effect.
+ * LCD filter weights can also be set per face using @FT_Face_Properties
+ * with @FT_PARAM_TAG_LCD_FILTER_WEIGHTS.
*
* @since:
* 2.4.0
@@ -240,12 +280,30 @@ FT_BEGIN_HEADER
FT_Library_SetLcdFilterWeights( FT_Library library,
unsigned char *weights );
+
+ /*
+ * @type:
+ * FT_LcdFiveTapFilter
+ *
+ * @description:
+ * A typedef for passing the five LCD filter weights to
+ * @FT_Face_Properties within an @FT_Parameter structure.
+ *
+ * @since:
+ * 2.8
+ *
+ */
+#define FT_LCD_FILTER_FIVE_TAPS 5
+
+ typedef FT_Byte FT_LcdFiveTapFilter[FT_LCD_FILTER_FIVE_TAPS];
+
+
/* */
FT_END_HEADER
-#endif /* __FT_LCD_FILTER_H__ */
+#endif /* FTLCDFIL_H_ */
/* END */