Fix greenish text rendering on Linux.

https://codereview.appspot.com/6484048/


git-svn-id: http://skia.googlecode.com/svn/trunk@5280 2bbb7eff-a529-9590-31e7-b0007b416f81

4 files changed, 55 insertions, 17 deletions

diff --git a/src/core/SkMaskGamma.cpp b/src/core/SkMaskGamma.cpp
index 47903fbdbb..449a78de93 100644
--- a/src/core/SkMaskGamma.cpp
+++ b/src/core/SkMaskGamma.cpp
@@ -53,9 +53,12 @@ void SkTMaskGamma_build_correcting_lut(uint8_t table[256], U8CPU srcI, SkScalar
                                 const SkColorSpaceLuminance& dstConvert) {
     const float src = (float)srcI / 255.0f;
     const float linSrc = srcConvert.toLuma(src);
-    //Guess at the dst.
-    const float linDst = 1.0f - linSrc;
-    const float dst = dstConvert.fromLuma(linDst);
+    //Guess at the dst. The perceptual inverse provides smaller visual
+    //discontinuities when slight changes to desaturated colors cause a channel
+    //to map to a different correcting lut with neighboring srcI.
+    //See https://code.google.com/p/chromium/issues/detail?id=141425#c59 .
+    const float dst = 1.0f - src;
+    const float linDst = dstConvert.toLuma(dst);
 
     //Contrast value tapers off to 0 as the src luminance becomes white
     const float adjustedContrast = SkScalarToFloat(contrast) * linDst;
diff --git a/src/core/SkPaint.cpp b/src/core/SkPaint.cpp
index 9c810be214..6ea03b4c8e 100644
--- a/src/core/SkPaint.cpp
+++ b/src/core/SkPaint.cpp
@@ -1706,8 +1706,11 @@ void SkScalerContext::PostMakeRec(const SkPaint& paint, SkScalerContext::Rec* re
             SkColor color = rec->getLuminanceColor();
             SkAutoMutexAcquire ama(gMaskGammaCacheMutex);
             U8CPU lum = cachedPaintLuminance(rec->getPaintGamma())->computeLuminance(color);
-            // HACK: Prevents green from being pre-blended as white.
-            lum -= ((255 - lum) * lum) / 255;
+            //If we are asked to look like LCD, look like LCD.
+            if (!(rec->fFlags & SkScalerContext::kGenA8FromLCD_Flag)) {
+                // HACK: Prevents green from being pre-blended as white.
+                lum -= ((255 - lum) * lum) / 255;
+            }
 
             // reduce to our finite number of bits
             SkMaskGamma* maskGamma = cachedMaskGamma(rec->getContrast(),
diff --git a/src/core/SkScalerContext.h b/src/core/SkScalerContext.h
index 085e31d959..2443aafe6e 100644
--- a/src/core/SkScalerContext.h
+++ b/src/core/SkScalerContext.h
@@ -108,8 +108,9 @@ struct SkScalerContextRec {
 //The following typedef hides from the rest of the implementation the number of
 //most significant bits to consider when creating mask gamma tables. Two bits
 //per channel was chosen as a balance between fidelity (more bits) and cache
-//sizes (fewer bits).
-typedef SkTMaskGamma<2, 2, 2> SkMaskGamma;
+//sizes (fewer bits). Three bits per channel was chosen when #303942; (used by
+//the Chrome UI) turned out too green.
+typedef SkTMaskGamma<3, 3, 3> SkMaskGamma;
 
 class SkScalerContext {
 public:
diff --git a/src/ports/SkFontHost_FreeType.cpp b/src/ports/SkFontHost_FreeType.cpp
index 45ae7ecffc..3d6b574616 100644
--- a/src/ports/SkFontHost_FreeType.cpp
+++ b/src/ports/SkFontHost_FreeType.cpp
@@ -24,6 +24,9 @@
 #include "SkTemplates.h"
 #include "SkThread.h"
 
+#if defined(SK_CAN_USE_DLOPEN)
+#include <dlfcn.h>
+#endif
 #include <ft2build.h>
 #include FT_FREETYPE_H
 #include FT_OUTLINE_H
@@ -83,23 +86,51 @@ static bool         gLCDSupportValid;  // true iff |gLCDSupport| has been set.
 static bool         gLCDSupport;  // true iff LCD is supported by the runtime.
 static int          gLCDExtra;  // number of extra pixels for filtering.
 
+// FT_Library_SetLcdFilterWeights was introduced in FreeType 2.4.0.
+// The following platforms provide FreeType of at least 2.4.0.
+// Ubuntu >= 11.04 (previous deprecated April 2013)
+// Debian >= 6.0 (good)
+// OpenSuse >= 11.4 (previous deprecated January 2012 / Nov 2013 for Evergreen 11.2)
+// Fedora >= 14 (good)
+// Android >= Gingerbread (good)
+typedef FT_Error (*FT_Library_SetLcdFilterWeightsProc)(FT_Library, unsigned char*);
+
 /////////////////////////////////////////////////////////////////////////
 
-static bool
-InitFreetype() {
+static bool InitFreetype() {
     FT_Error err = FT_Init_FreeType(&gFTLibrary);
     if (err) {
         return false;
     }
 
-    // Setup LCD filtering. This reduces colour fringes for LCD rendered
-    // glyphs.
+    // Setup LCD filtering. This reduces color fringes for LCD smoothed glyphs.
 #ifdef FT_LCD_FILTER_H
-    err = FT_Library_SetLcdFilter(gFTLibrary, FT_LCD_FILTER_DEFAULT);
-//    err = FT_Library_SetLcdFilter(gFTLibrary, FT_LCD_FILTER_LIGHT);
-    gLCDSupport = err == 0;
-    if (gLCDSupport) {
-        gLCDExtra = 2; //DEFAULT and LIGHT add one pixel to each side.
+    //Use light as default, as FT_LCD_FILTER_DEFAULT adds up to 0x110.
+    err = FT_Library_SetLcdFilter(gFTLibrary, FT_LCD_FILTER_LIGHT);
+    if (0 == err) {
+        gLCDSupport = true;
+        gLCDExtra = 2; //Using a filter adds one full pixel to each side.
+
+        static unsigned char gaussianLikeWeights[] = { 0x17, 0x40, 0x52, 0x40, 0x17 };
+        //static unsigned char triangleLikeWeights[] = { 0x1C, 0x39, 0x56, 0x39, 0x1C };
+
+#if defined(SK_FONTHOST_FREETYPE_RUNTIME_VERSION) && \
+            SK_FONTHOST_FREETYPE_RUNTIME_VERSION > 0x020400
+        err = FT_Library_SetLcdFilterWeights(gFTLibrary, gaussianLikeWeights);
+#elif defined(SK_CAN_USE_DLOPEN) && SK_CAN_USE_DLOPEN == 1
+        //The FreeType library is already loaded, so symbols are available in process.
+        void* self = dlopen(NULL, RTLD_LAZY);
+        if (NULL != self) {
+            FT_Library_SetLcdFilterWeightsProc setLcdFilterWeights;
+            //The following cast is non-standard, but safe for POSIX.
+            *reinterpret_cast<void**>(&setLcdFilterWeights) = dlsym(self, "FT_Library_SetLcdFilterWeights");
+            dlclose(self);
+
+            if (NULL != setLcdFilterWeights) {
+                err = setLcdFilterWeights(gFTLibrary, gaussianLikeWeights);
+            }
+        }
+#endif
     }
 #else
     gLCDSupport = false;
@@ -610,7 +641,7 @@ void SkFontHost::FilterRec(SkScalerContext::Rec* rec) {
     if (rec->fTextSize > SkIntToScalar(1 << 14)) {
       rec->fTextSize = SkIntToScalar(1 << 14);
     }
-
+    
     if (!gLCDSupportValid) {
         InitFreetype();
         FT_Done_FreeType(gFTLibrary);