Use Analytic AA in SkAAClip

src/core/SkScan_AAAPath.cpp

Index: src/core/SkScan_AAAPath.cpp
diff --git a/src/core/SkScan_AAAPath.cpp b/src/core/SkScan_AAAPath.cpp
index 147c24c3feafd5013e85a547354e2e463a023a29..1a3b1ed222ab0cd56592d5086e4e93dbf5275a6f 100644
--- a/src/core/SkScan_AAAPath.cpp
+++ b/src/core/SkScan_AAAPath.cpp
@@ -273,6 +273,19 @@ public:
 
     int getWidth() override;
 
+    // This should only be called when forceRLE = true which implies that SkAAClip
+    // is calling us.
+    // SkAAClip requires that we blit in scan-line order so we have to flush
+    // for each row in order. Without this, we may have the first row unflushed,
+    // then blit the 2nd and the 3rd row with full alpha (so we won't flush the first row);
+    // finally when we blit the fourth row, we trigger the first row to flush, and this
+    // would cause SkAAClip to crash.
+    inline void flush_if_y_changed(SkFixed y, SkFixed nextY) {
+        if ((y >> 16) != (nextY >> 16)) {

[caryclark, 2016/10/20 16:58:14]

maybe overly wordy, but a macro like SkFixedFloorToInt(y) instead of y >> 16
will help the reader know where the >> 16 comes from, here and below

[liyuqian, 2016/10/20 17:19:50]

Thanks, done.

+            this->flush();
+        }
+    }
+
 private:
     SkBlitter* fRealBlitter;
 
@@ -721,10 +734,6 @@ static inline void blit_trapezoid_row(AdditiveBlitter* blitter, int y,
     SkFixed joinLeft = SkFixedCeilToFixed(ll);
     SkFixed joinRite = SkFixedFloorToFixed(ur);
     if (joinLeft <= joinRite) { // There's a rect from joinLeft to joinRite that we can blit
-        if (joinLeft < joinRite) {
-            blit_full_alpha(blitter, y, joinLeft >> 16, (joinRite - joinLeft) >> 16, fullAlpha,
-                            maskRow, isUsingMask);
-        }
         if (ul < joinLeft) {
             int len = SkFixedCeilToInt(joinLeft - ul);
             if (len == 1) {
@@ -741,6 +750,12 @@ static inline void blit_trapezoid_row(AdditiveBlitter* blitter, int y,
                                        fullAlpha, maskRow, isUsingMask);
             }
         }
+        // SkAAClip requires that we blit from left to right.
+        // Hence we must blit [ul, joinLeft] before blitting [joinLeft, joinRite]
+        if (joinLeft < joinRite) {
+            blit_full_alpha(blitter, y, joinLeft >> 16, (joinRite - joinLeft) >> 16, fullAlpha,
+                            maskRow, isUsingMask);
+        }
         if (lr > joinRite) {
             int len = SkFixedCeilToInt(lr - joinRite);
             if (len == 1) {
@@ -880,7 +895,7 @@ static inline bool isSmoothEnough(SkAnalyticEdge* leftE, SkAnalyticEdge* riteE,
 
 static inline void aaa_walk_convex_edges(SkAnalyticEdge* prevHead, AdditiveBlitter* blitter,
                            int start_y, int stop_y, SkFixed leftBound, SkFixed riteBound,
-                           bool isUsingMask) {
+                           bool isUsingMask, bool forceRLE) {
     validate_sort((SkAnalyticEdge*)prevHead->fNext);
 
     SkAnalyticEdge* leftE = (SkAnalyticEdge*) prevHead->fNext;
@@ -961,24 +976,27 @@ static inline void aaa_walk_convex_edges(SkAnalyticEdge* prevHead, AdditiveBlitt
             }
 
             if (fullRite >= fullLeft) {
-                // Blit all full-height rows from fullTop to fullBot
-                if (fullBot > fullTop) {
-                    blitter->getRealBlitter()->blitAntiRect(fullLeft - 1, fullTop,
-                                                            fullRite - fullLeft, fullBot - fullTop,
-                                                            f2a(partialLeft), f2a(partialRite));
-                }
-
                 if (partialTop > 0) { // blit first partial row
                     if (partialLeft > 0) {
                         blitter->blitAntiH(fullLeft - 1, fullTop - 1,
                                 f2a(SkFixedMul_lowprec(partialTop, partialLeft)));
                     }
+                    blitter->blitAntiH(fullLeft, fullTop - 1, fullRite - fullLeft,
+                                       f2a(partialTop));
                     if (partialRite > 0) {
                         blitter->blitAntiH(fullRite, fullTop - 1,
                                 f2a(SkFixedMul_lowprec(partialTop, partialRite)));
                     }
-                    blitter->blitAntiH(fullLeft, fullTop - 1, fullRite - fullLeft,
-                                       f2a(partialTop));
+                    if (forceRLE) {
+                        ((RunBasedAdditiveBlitter*)blitter)->flush_if_y_changed(y, y + partialTop);
+                    }
+                }
+
+                // Blit all full-height rows from fullTop to fullBot
+                if (fullBot > fullTop) {
+                    blitter->getRealBlitter()->blitAntiRect(fullLeft - 1, fullTop,
+                                                            fullRite - fullLeft, fullBot - fullTop,
+                                                            f2a(partialLeft), f2a(partialRite));
                 }
 
                 if (partialBot > 0) { // blit last partial row
@@ -986,25 +1004,28 @@ static inline void aaa_walk_convex_edges(SkAnalyticEdge* prevHead, AdditiveBlitt
                         blitter->blitAntiH(fullLeft - 1, fullBot,
                                            f2a(SkFixedMul_lowprec(partialBot, partialLeft)));
                     }
+                    blitter->blitAntiH(fullLeft, fullBot, fullRite - fullLeft, f2a(partialBot));
                     if (partialRite > 0) {
                         blitter->blitAntiH(fullRite, fullBot,
                                            f2a(SkFixedMul_lowprec(partialBot, partialRite)));
                     }
-                    blitter->blitAntiH(fullLeft, fullBot, fullRite - fullLeft, f2a(partialBot));
                 }
             } else { // left and rite are within the same pixel
                 if (partialTop > 0) {
                     blitter->getRealBlitter()->blitV(fullLeft - 1, fullTop - 1, 1,
                             f2a(SkFixedMul_lowprec(partialTop, rite - left)));
-                }
-                if (partialBot > 0) {
-                    blitter->getRealBlitter()->blitV(fullLeft - 1, fullBot, 1,
-                            f2a(SkFixedMul_lowprec(partialBot, rite - left)));
+                    if (forceRLE) {
+                        ((RunBasedAdditiveBlitter*)blitter)->flush_if_y_changed(y, y + partialTop);
+                    }
                 }
                 if (fullBot >= fullTop) {
                     blitter->getRealBlitter()->blitV(fullLeft - 1, fullTop, fullBot - fullTop,
                             f2a(rite - left));
                 }
+                if (partialBot > 0) {
+                    blitter->getRealBlitter()->blitV(fullLeft - 1, fullBot, 1,
+                            f2a(SkFixedMul_lowprec(partialBot, rite - left)));
+                }
             }
 
             y = local_bot_fixed;
@@ -1048,6 +1069,9 @@ static inline void aaa_walk_convex_edges(SkAnalyticEdge* prevHead, AdditiveBlitt
                     blit_trapezoid_row(blitter, y >> 16, left & kSnapMask, rite & kSnapMask,
                             nextLeft & kSnapMask, nextRite & kSnapMask, leftE->fDY, riteE->fDY,
                             getPartialAlpha(0xFF, dY), maskRow, isUsingMask);
+                    if (forceRLE) {
+                        ((RunBasedAdditiveBlitter*)blitter)->flush_if_y_changed(y, nextY);
+                    }
                     left = nextLeft; rite = nextRite; y = nextY;
                 }
 
@@ -1060,6 +1084,9 @@ static inline void aaa_walk_convex_edges(SkAnalyticEdge* prevHead, AdditiveBlitt
                     blit_trapezoid_row(blitter, y >> 16, left & kSnapMask, rite & kSnapMask,
                             nextLeft & kSnapMask, nextRite & kSnapMask,
                             leftE->fDY, riteE->fDY, 0xFF, maskRow, isUsingMask);
+                    if (forceRLE) {
+                        ((RunBasedAdditiveBlitter*)blitter)->flush_if_y_changed(y, nextY);
+                    }
                     left = nextLeft; rite = nextRite; y = nextY;
                 }
             }
@@ -1072,11 +1099,15 @@ static inline void aaa_walk_convex_edges(SkAnalyticEdge* prevHead, AdditiveBlitt
             SkASSERT(dY <= SK_Fixed1);
             // Smooth jumping to integer y may make the last nextLeft/nextRite out of bound.
             // Take them back into the bound here.
-            SkFixed nextLeft = SkTMax(left + SkFixedMul_lowprec(dLeft, dY), leftBound);
-            SkFixed nextRite = SkTMin(rite + SkFixedMul_lowprec(dRite, dY), riteBound);
+            // Note that we substract kSnapHalf later so we have to add them to leftBound/riteBound
+            SkFixed nextLeft = SkTMax(left + SkFixedMul_lowprec(dLeft, dY), leftBound + kSnapHalf);
+            SkFixed nextRite = SkTMin(rite + SkFixedMul_lowprec(dRite, dY), riteBound + kSnapHalf);
             blit_trapezoid_row(blitter, y >> 16, left & kSnapMask, rite & kSnapMask,
                     nextLeft & kSnapMask, nextRite & kSnapMask, leftE->fDY, riteE->fDY,
                     getPartialAlpha(0xFF, dY), maskRow, isUsingMask);
+            if (forceRLE) {
+                ((RunBasedAdditiveBlitter*)blitter)->flush_if_y_changed(y, local_bot_fixed);
+            }
             left = nextLeft; rite = nextRite; y = local_bot_fixed;
             left -= kSnapHalf; rite -= kSnapHalf;
         }
@@ -1094,7 +1125,8 @@ END_WALK:
 }
 
 void SkScan::aaa_fill_path(const SkPath& path, const SkIRect* clipRect, AdditiveBlitter* blitter,
-                   int start_y, int stop_y, const SkRegion& clipRgn, bool isUsingMask) {
+                   int start_y, int stop_y, const SkRegion& clipRgn, bool isUsingMask,
+                   bool forceRLE) { // forceRLE implies that SkAAClip is calling us
     SkASSERT(blitter);
 
     if (path.isInverseFillType() || !path.isConvex()) {
@@ -1170,7 +1202,8 @@ void SkScan::aaa_fill_path(const SkPath& path, const SkIRect* clipRect, Additive
     if (!path.isInverseFillType() && path.isConvex()) {
         SkASSERT(count >= 2);   // convex walker does not handle missing right edges
         aaa_walk_convex_edges(&headEdge, blitter, start_y, stop_y,
-                              rect.fLeft << 16, rect.fRight << 16, isUsingMask);
+                              rect.fLeft << 16, rect.fRight << 16, isUsingMask,
+                              forceRLE);
     } else {
         SkFAIL("Concave AAA is not yet implemented!");
     }
@@ -1178,7 +1211,8 @@ void SkScan::aaa_fill_path(const SkPath& path, const SkIRect* clipRect, Additive
 
 ///////////////////////////////////////////////////////////////////////////////
 
-void SkScan::AAAFillPath(const SkPath& path, const SkRegion& origClip, SkBlitter* blitter) {
+void SkScan::AAAFillPath(const SkPath& path, const SkRegion& origClip, SkBlitter* blitter,
+                         bool forceRLE) {
     if (origClip.isEmpty()) {
         return;
     }
@@ -1244,12 +1278,14 @@ void SkScan::AAAFillPath(const SkPath& path, const SkRegion& origClip, SkBlitter
 
     SkASSERT(SkIntToScalar(ir.fTop) <= path.getBounds().fTop);
 
-    if (MaskAdditiveBlitter::canHandleRect(ir) && !isInverse) {
+    if (MaskAdditiveBlitter::canHandleRect(ir) && !isInverse && !forceRLE) {
         MaskAdditiveBlitter additiveBlitter(blitter, ir, *clipRgn, isInverse);
-        aaa_fill_path(path, clipRect, &additiveBlitter, ir.fTop, ir.fBottom, *clipRgn, true);
+        aaa_fill_path(path, clipRect, &additiveBlitter, ir.fTop, ir.fBottom, *clipRgn, true,
+                      forceRLE);
     } else {
         RunBasedAdditiveBlitter additiveBlitter(blitter, ir, *clipRgn, isInverse);
-        aaa_fill_path(path, clipRect, &additiveBlitter, ir.fTop, ir.fBottom, *clipRgn, false);
+        aaa_fill_path(path, clipRect, &additiveBlitter, ir.fTop, ir.fBottom, *clipRgn, false,
+                      forceRLE);
     }
 
     if (isInverse) {