add debugging wrapper blitter to ensure unclipped scan-conversion is safe

BUG=skia:

GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=4629

Change-Id: Ie6c35b28a6e8e87bf230e50f9940d3924d12969a
Reviewed-on: https://skia-review.googlesource.com/4629
Commit-Queue: Mike Reed <reed@google.com>
Reviewed-by: Yuqian Li <liyuqian@google.com>

4 files changed, 91 insertions, 0 deletions

diff --git a/src/core/SkBlitter.cpp b/src/core/SkBlitter.cpp
index 3643e66760..e5c935b60e 100644
--- a/src/core/SkBlitter.cpp
+++ b/src/core/SkBlitter.cpp
@@ -1021,3 +1021,49 @@ bool SkShaderBlitter::resetShaderContext(const SkShader::ContextRec& rec) {
     }
     return true;
 }
+
+///////////////////////////////////////////////////////////////////////////////////////////////////
+
+#ifdef SK_DEBUG
+
+void SkRectClipCheckBlitter::blitH(int x, int y, int width) {
+    SkASSERT(fClipRect.contains(SkIRect::MakeXYWH(x, y, width, 1)));
+    fBlitter->blitH(x, y, width);
+}
+
+void SkRectClipCheckBlitter::blitAntiH(int x, int y, const SkAlpha aa[], const int16_t runs[]) {
+    const int16_t* iter = runs;
+    for (; *iter; iter += *iter)
+        ;
+    int width = iter - runs;
+    SkASSERT(fClipRect.contains(SkIRect::MakeXYWH(x, y, width, 1)));
+    fBlitter->blitAntiH(x, y, aa, runs);
+}
+
+void SkRectClipCheckBlitter::blitV(int x, int y, int height, SkAlpha alpha) {
+    SkASSERT(fClipRect.contains(SkIRect::MakeXYWH(x, y, 1, height)));
+    fBlitter->blitV(x, y, height, alpha);
+}
+
+void SkRectClipCheckBlitter::blitRect(int x, int y, int width, int height) {
+    SkASSERT(fClipRect.contains(SkIRect::MakeXYWH(x, y, width, height)));
+    fBlitter->blitRect(x, y, width, height);
+}
+
+void SkRectClipCheckBlitter::blitAntiRect(int x, int y, int width, int height,
+                                     SkAlpha leftAlpha, SkAlpha rightAlpha) {
+    SkASSERT(fClipRect.contains(SkIRect::MakeXYWH(x, y, width + 2, height)));
+    fBlitter->blitAntiRect(x, y, width, height, leftAlpha, rightAlpha);
+}
+
+void SkRectClipCheckBlitter::blitMask(const SkMask& mask, const SkIRect& clip) {
+    SkASSERT(mask.fBounds.contains(clip));
+    SkASSERT(fClipRect.contains(clip));
+    fBlitter->blitMask(mask, clip);
+}
+
+const SkPixmap* SkRectClipCheckBlitter::justAnOpaqueColor(uint32_t* value) {
+    return fBlitter->justAnOpaqueColor(value);
+}
+
+#endif
diff --git a/src/core/SkBlitter.h b/src/core/SkBlitter.h
index 0e5fedd7eb..c9fed1ce22 100644
--- a/src/core/SkBlitter.h
+++ b/src/core/SkBlitter.h
@@ -240,6 +240,39 @@ private:
     const SkRegion* fRgn;
 };
 
+#ifdef SK_DEBUG
+class SkRectClipCheckBlitter : public SkBlitter {
+public:
+    void init(SkBlitter* blitter, const SkIRect& clipRect) {
+        SkASSERT(blitter);
+        SkASSERT(!clipRect.isEmpty());
+        fBlitter = blitter;
+        fClipRect = clipRect;
+    }
+
+    void blitH(int x, int y, int width) override;
+    void blitAntiH(int x, int y, const SkAlpha[], const int16_t runs[]) override;
+    void blitV(int x, int y, int height, SkAlpha alpha) override;
+    void blitRect(int x, int y, int width, int height) override;
+    void blitAntiRect(int x, int y, int width, int height,
+                              SkAlpha leftAlpha, SkAlpha rightAlpha) override;
+    void blitMask(const SkMask&, const SkIRect& clip) override;
+    const SkPixmap* justAnOpaqueColor(uint32_t* value) override;
+
+    int requestRowsPreserved() const override {
+        return fBlitter->requestRowsPreserved();
+    }
+
+    void* allocBlitMemory(size_t sz) override {
+        return fBlitter->allocBlitMemory(sz);
+    }
+
+private:
+    SkBlitter*  fBlitter;
+    SkIRect     fClipRect;
+};
+#endif
+
 /** Factory to set up the appropriate most-efficient wrapper blitter
     to apply a clip. Returns a pointer to a member, so lifetime must
     be managed carefully.
diff --git a/src/core/SkScanPriv.h b/src/core/SkScanPriv.h
index 798cae6d0f..4ff91bb455 100644
--- a/src/core/SkScanPriv.h
+++ b/src/core/SkScanPriv.h
@@ -23,6 +23,9 @@ public:
 private:
     SkRectClipBlitter   fRectBlitter;
     SkRgnClipBlitter    fRgnBlitter;
+#ifdef SK_DEBUG
+    SkRectClipCheckBlitter fRectClipCheckBlitter;
+#endif
     SkBlitter*          fBlitter;
     const SkIRect*      fClipRect;
 };
diff --git a/src/core/SkScan_Path.cpp b/src/core/SkScan_Path.cpp
index 884f785299..9ce18b0ee5 100644
--- a/src/core/SkScan_Path.cpp
+++ b/src/core/SkScan_Path.cpp
@@ -561,12 +561,21 @@ SkScanClipper::SkScanClipper(SkBlitter* blitter, const SkRegion* clip,
 
         if (clip->isRect()) {
             if (fClipRect->contains(ir)) {
+#ifdef SK_DEBUG
+                fRectClipCheckBlitter.init(blitter, *fClipRect);
+                blitter = &fRectClipCheckBlitter;
+#endif
                 fClipRect = nullptr;
             } else {
                 // only need a wrapper blitter if we're horizontally clipped
                 if (fClipRect->fLeft > ir.fLeft || fClipRect->fRight < ir.fRight) {
                     fRectBlitter.init(blitter, *fClipRect);
                     blitter = &fRectBlitter;
+                } else {
+#ifdef SK_DEBUG
+                    fRectClipCheckBlitter.init(blitter, *fClipRect);
+                    blitter = &fRectClipCheckBlitter;
+#endif
                 }
             }
         } else {