Subpixel glyph rendering support.
This patch adds support for rendering subpixel glyphs (using
Freetype). In order to control this rendering see
SkPaint::setLCDRenderText in SkPaint.h.
To setup the LCD mode, see SkFontHost::SetSubpixelOrientation and
SkFontHost::SetSubpixelOrder in SkFontHost.h.
This patch also adds more fine grained control over hinting (again,
only for Freetype currently). One can now control the hinting with
SkPaint::setHinting.
git-svn-id: http://skia.googlecode.com/svn/trunk@275 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/src/ports/SkFontHost_FreeType.cpp b/src/ports/SkFontHost_FreeType.cpp
index b30aba5..5367439 100644
--- a/src/ports/SkFontHost_FreeType.cpp
+++ b/src/ports/SkFontHost_FreeType.cpp
@@ -15,6 +15,7 @@
** limitations under the License.
*/
+#include "SkColorPriv.h"
#include "SkScalerContext.h"
#include "SkBitmap.h"
#include "SkCanvas.h"
@@ -32,6 +33,11 @@
#include FT_OUTLINE_H
#include FT_SIZES_H
#include FT_TRUETYPE_TABLES_H
+
+#if defined(SK_BUILD_SUBPIXEL)
+#include FT_LCD_FILTER_H
+#endif
+
#ifdef FT_ADVANCES_H
#include FT_ADVANCES_H
#endif
@@ -43,6 +49,7 @@
#include <freetype/ftsizes.h>
#include <freetype/tttables.h>
#include <freetype/ftadvanc.h>
+#include <freetype/ftlcdfil.h>
#endif
//#define ENABLE_GLYPH_SPEW // for tracing calls
@@ -69,6 +76,21 @@
/////////////////////////////////////////////////////////////////////////
+static bool
+InitFreetype() {
+ FT_Error err = FT_Init_FreeType(&gFTLibrary);
+ if (err)
+ return false;
+
+#if defined(SK_BUILD_SUBPIXEL)
+ // Setup LCD filtering. This reduces colour fringes for LCD rendered
+ // glyphs.
+ err = FT_Library_SetLcdFilter(gFTLibrary, FT_LCD_FILTER_DEFAULT);
+#endif
+
+ return true;
+}
+
class SkScalerContext_FreeType : public SkScalerContext {
public:
SkScalerContext_FreeType(const SkDescriptor* desc);
@@ -247,9 +269,8 @@
FT_Error err;
if (gFTCount == 0) {
- err = FT_Init_FreeType(&gFTLibrary);
-// SkDEBUGF(("FT_Init_FreeType returned %d\n", err));
- SkASSERT(err == 0);
+ const bool success = InitFreetype();
+ SkASSERT(success);
}
++gFTCount;
@@ -275,7 +296,7 @@
SkScalarToFloat(fRec.fPreScaleX), SkScalarToFloat(fRec.fPreSkewX),
SkScalarToFloat(fRec.fPost2x2[0][0]), SkScalarToFloat(fRec.fPost2x2[0][1]),
SkScalarToFloat(fRec.fPost2x2[1][0]), SkScalarToFloat(fRec.fPost2x2[1][1]),
- fRec.fHints, fRec.fMaskFormat, keyString.c_str());
+ fRec.getHinting(), fRec.fMaskFormat, keyString.c_str());
#endif
// now compute our scale factors
@@ -305,42 +326,27 @@
// compute the flags we send to Load_Glyph
{
- uint32_t flags = FT_LOAD_DEFAULT;
- uint32_t render_flags = FT_LOAD_TARGET_NORMAL;
+ FT_Int32 hintingFlags = FT_LOAD_DEFAULT;
- // we force autohinting at the moment
-
- switch (fRec.fHints) {
- case kNo_Hints:
- flags |= FT_LOAD_NO_HINTING;
+ switch (fRec.getHinting()) {
+ case SkPaint::kNo_Hinting:
+ hintingFlags = FT_LOAD_NO_HINTING;
break;
- case kSubpixel_Hints:
- flags |= FT_LOAD_FORCE_AUTOHINT;
- render_flags = FT_LOAD_TARGET_LIGHT;
+ case SkPaint::kSlight_Hinting:
+ hintingFlags = FT_LOAD_TARGET_LIGHT; // This implies FORCE_AUTOHINT
break;
- case kNormal_Hints:
-#ifdef ANDROID
- // The following line disables the font's hinting tables. For
- // Chromium we want font hinting on so that we can generate
- // baselines that look at little like Firefox. It's expected that
- // Mike Reed will rework this code sometime soon so we don't wish
- // to make more extensive changes.
- flags |= FT_LOAD_FORCE_AUTOHINT;
- /* Switch to light hinting (vertical only) to address some chars
- that behaved poorly with NORMAL. In the future we could consider
- making this choice exposed at runtime to the caller.
- */
- render_flags = FT_LOAD_TARGET_LIGHT;
-#endif
+ case SkPaint::kNormal_Hinting:
+ hintingFlags |= FT_LOAD_TARGET_NORMAL;
+ break;
+ case SkPaint::kFull_Hinting:
+ if (SkMask::kHorizontalLCD_Format == fRec.fMaskFormat)
+ hintingFlags = FT_LOAD_TARGET_LCD;
+ else if (SkMask::kVerticalLCD_Format == fRec.fMaskFormat)
+ hintingFlags = FT_LOAD_TARGET_LCD_V;
break;
}
- if (SkMask::kBW_Format == fRec.fMaskFormat)
- render_flags = FT_LOAD_TARGET_MONO;
- else if (SkMask::kLCD_Format == fRec.fMaskFormat)
- render_flags = FT_LOAD_TARGET_LCD;
-
- fLoadGlyphFlags = flags | render_flags;
+ fLoadGlyphFlags = hintingFlags;
}
// now create the FT_Size
@@ -433,10 +439,12 @@
static FT_Pixel_Mode compute_pixel_mode(SkMask::Format format) {
switch (format) {
+ case SkMask::kHorizontalLCD_Format:
+ case SkMask::kVerticalLCD_Format:
+ SkASSERT(!"An LCD format should never be passed here");
+ return FT_PIXEL_MODE_GRAY;
case SkMask::kBW_Format:
return FT_PIXEL_MODE_MONO;
- case SkMask::kLCD_Format:
- return FT_PIXEL_MODE_LCD;
case SkMask::kA8_Format:
default:
return FT_PIXEL_MODE_GRAY;
@@ -503,7 +511,7 @@
FT_Outline_Get_CBox(&fFace->glyph->outline, &bbox);
- if (kSubpixel_Hints == fRec.fHints) {
+ if (fRec.fSubpixelPositioning) {
int dx = glyph->getSubXFixed() >> 10;
int dy = glyph->getSubYFixed() >> 10;
// negate dy since freetype-y-goes-up and skia-y-goes-down
@@ -536,7 +544,7 @@
goto ERROR;
}
- if (kNormal_Hints == fRec.fHints) {
+ if (!fRec.fSubpixelPositioning) {
glyph->fAdvanceX = SkFDot6ToFixed(fFace->glyph->advance.x);
glyph->fAdvanceY = -SkFDot6ToFixed(fFace->glyph->advance.y);
if (fRec.fFlags & kDevKernText_Flag) {
@@ -554,6 +562,16 @@
#endif
}
+#if defined(SK_BUILD_SUBPIXEL)
+namespace skia_freetype_support {
+// extern functions from SkFontHost_FreeType_Subpixel
+extern void CopyFreetypeBitmapToLCDMask(const SkGlyph& dest, const FT_Bitmap& source);
+extern void CopyFreetypeBitmapToVerticalLCDMask(const SkGlyph& dest, const FT_Bitmap& source);
+}
+
+using namespace skia_freetype_support;
+#endif
+
void SkScalerContext_FreeType::generateImage(const SkGlyph& glyph) {
SkAutoMutexAcquire ac(gFTMutex);
@@ -572,6 +590,9 @@
return;
}
+ const bool lcdRenderMode = fRec.fMaskFormat == SkMask::kHorizontalLCD_Format ||
+ fRec.fMaskFormat == SkMask::kVerticalLCD_Format;
+
switch ( fFace->glyph->format ) {
case FT_GLYPH_FORMAT_OUTLINE: {
FT_Outline* outline = &fFace->glyph->outline;
@@ -579,7 +600,7 @@
FT_Bitmap target;
int dx = 0, dy = 0;
- if (kSubpixel_Hints == fRec.fHints) {
+ if (fRec.fSubpixelPositioning) {
dx = glyph.getSubXFixed() >> 10;
dy = glyph.getSubYFixed() >> 10;
// negate dy since freetype-y-goes-up and skia-y-goes-down
@@ -597,6 +618,23 @@
FT_Outline_Translate(outline, dx - ((bbox.xMin + dx) & ~63),
dy - ((bbox.yMin + dy) & ~63));
+#if defined(SK_BUILD_SUBPIXEL)
+ if (lcdRenderMode) {
+ // FT_Outline_Get_Bitmap cannot render LCD glyphs. In this case
+ // we have to call FT_Render_Glyph and memcpy the image out.
+ const bool isVertical = fRec.fMaskFormat == SkMask::kVerticalLCD_Format;
+ FT_Render_Mode mode = isVertical ? FT_RENDER_MODE_LCD_V : FT_RENDER_MODE_LCD;
+ FT_Render_Glyph(fFace->glyph, mode);
+
+ if (isVertical)
+ CopyFreetypeBitmapToVerticalLCDMask(glyph, fFace->glyph->bitmap);
+ else
+ CopyFreetypeBitmapToLCDMask(glyph, fFace->glyph->bitmap);
+
+ break;
+ }
+#endif
+
target.width = glyph.fWidth;
target.rows = glyph.fHeight;
target.pitch = glyph.rowBytes();
@@ -652,6 +690,10 @@
dst += glyph.rowBytes();
}
}
+
+ if (lcdRenderMode)
+ glyph.expandA8ToLCD();
+
} break;
default:
@@ -858,7 +900,7 @@
*/
SkTypeface::Style find_name_and_style(SkStream* stream, SkString* name) {
FT_Library library;
- if (FT_Init_FreeType(&library)) {
+ if (!InitFreetype()) {
name->set(NULL);
return SkTypeface::kNormal;
}
@@ -905,4 +947,3 @@
FT_Done_FreeType(library);
return (SkTypeface::Style)style;
}
-