Implement canvas's globalCompositeOperation lighter properly....

skia/sgl/SkXfermode.cpp

 /*
  * Copyright (C) 2006 The Android Open Source Project
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
  *
  *      http://www.apache.org/licenses/LICENSE-2.0
  *
  * Unless required by applicable law or agreed to in writing, software
@@ skipping 25 matching lines @@
     SkASSERT(a <= 255);
     SkASSERT(b <= 255);
     SkASSERT(c <= 255);
     SkASSERT(d <= 255);
     unsigned prod = SkMulS16(a, b) + SkMulS16(c, d) + 128;
     unsigned result = (prod + (prod >> 8)) >> 8;
     SkASSERT(result <= 255);
     return result;
 }
 
+static unsigned saturated_add(unsigned a, unsigned b) {
+    SkASSERT(a <= 255);
+    SkASSERT(b <= 255);
+    unsigned sum = a + b;
+    if (sum > 255) {
+        sum = 255;
+    }
+    return sum;
+}
+
 ///////////////////////////////////////////////////////////////////////////////
 
 bool SkXfermode::asCoeff(Coeff* src, Coeff* dst) {
     return false;
 }
 
 SkPMColor SkXfermode::xferColor(SkPMColor src, SkPMColor dst) {
     // no-op. subclasses should override this
     return dst;
 }
@@ skipping 432 matching lines @@
 }
 
 static SkPMColor screen_modeproc(SkPMColor src, SkPMColor dst) {
     int a = screen_byte(SkGetPackedA32(src), SkGetPackedA32(dst));
     int r = screen_byte(SkGetPackedR32(src), SkGetPackedR32(dst));
     int g = screen_byte(SkGetPackedG32(src), SkGetPackedG32(dst));
     int b = screen_byte(SkGetPackedB32(src), SkGetPackedB32(dst));
     return SkPackARGB32(a, r, g, b);
 }
 
+static SkPMColor add_modeproc(SkPMColor src, SkPMColor dst) {
+    unsigned a = saturated_add(SkGetPackedA32(src), SkGetPackedA32(dst));
+    unsigned r = saturated_add(SkGetPackedR32(src), SkGetPackedR32(dst));
+    unsigned g = saturated_add(SkGetPackedG32(src), SkGetPackedG32(dst));
+    unsigned b = saturated_add(SkGetPackedB32(src), SkGetPackedB32(dst));
+    return SkPackARGB32(a, r, g, b);
+}
+
 ///////////////////////////////////////////////////////////////////////////////
 
 class SkClearXfermode : public SkProcCoeffXfermode {
 public:
     SkClearXfermode() : SkProcCoeffXfermode(clear_modeproc,
                                             kZero_Coeff, kZero_Coeff) {}
 
     virtual void xfer32(SK_RESTRICT SkPMColor dst[],
                         const SK_RESTRICT SkPMColor[], int count,
                         const SK_RESTRICT SkAlpha aa[]) {
@@ skipping 181 matching lines @@
 ///////////////////////////////////////////////////////////////////////////////
 
 #include "SkPorterDuff.h"
 
 struct ProcCoeff {
     SkXfermodeProc      fProc;
     SkXfermode::Coeff   fSC;
     SkXfermode::Coeff   fDC;
 };
 
+#define CANNOT_USE_COEFF    SkXfermode::Coeff(-1)
+
 static const ProcCoeff gProcCoeffs[] = {
     { clear_modeproc,   SkXfermode::kZero_Coeff,    SkXfermode::kZero_Coeff },
     { src_modeproc,     SkXfermode::kOne_Coeff,     SkXfermode::kZero_Coeff },
     { dst_modeproc,     SkXfermode::kZero_Coeff,    SkXfermode::kOne_Coeff },
     { srcover_modeproc, SkXfermode::kOne_Coeff,     SkXfermode::kISA_Coeff },
     { dstover_modeproc, SkXfermode::kIDA_Coeff,     SkXfermode::kOne_Coeff },
     { srcin_modeproc,   SkXfermode::kDA_Coeff,      SkXfermode::kZero_Coeff },
     { dstin_modeproc,   SkXfermode::kZero_Coeff,    SkXfermode::kSA_Coeff },
     { srcout_modeproc,  SkXfermode::kIDA_Coeff,     SkXfermode::kZero_Coeff },
     { dstout_modeproc,  SkXfermode::kZero_Coeff,    SkXfermode::kISA_Coeff },
     { srcatop_modeproc, SkXfermode::kDA_Coeff,      SkXfermode::kISA_Coeff },
     { dstatop_modeproc, SkXfermode::kIDA_Coeff,     SkXfermode::kSA_Coeff },
     { xor_modeproc,     SkXfermode::kIDA_Coeff,     SkXfermode::kISA_Coeff },
-    // these two can't be represented as coefficients
-    { darken_modeproc,  SkXfermode::Coeff(-1),      SkXfermode::Coeff(-1) },
-    { lighten_modeproc, SkXfermode::Coeff(-1),      SkXfermode::Coeff(-1) },
-    // these can use coefficients
+    { darken_modeproc,  CANNOT_USE_COEFF,           CANNOT_USE_COEFF },
+    { lighten_modeproc, CANNOT_USE_COEFF,           CANNOT_USE_COEFF },
     { mult_modeproc,    SkXfermode::kZero_Coeff,    SkXfermode::kSC_Coeff },
-    { screen_modeproc,  SkXfermode::kOne_Coeff,     SkXfermode::kISC_Coeff }
+    { screen_modeproc,  SkXfermode::kOne_Coeff,     SkXfermode::kISC_Coeff },
+    { add_modeproc,     CANNOT_USE_COEFF,           CANNOT_USE_COEFF }
 };
 
 SkXfermode* SkPorterDuff::CreateXfermode(SkPorterDuff::Mode mode) {
     SkASSERT(SK_ARRAY_COUNT(gProcCoeffs) == SkPorterDuff::kModeCount);
     SkASSERT((unsigned)mode < SkPorterDuff::kModeCount);
 
     switch (mode) {
         case kClear_Mode:
             return SkNEW(SkClearXfermode);
         case kSrc_Mode:
@@ skipping 241 matching lines @@
             proc16 = rec.fProc16_0;
         } else if (255 == a) {
             proc16 = rec.fProc16_255;
         } else {
             proc16 = rec.fProc16_General;
         }
     }
     return proc16;
 }