add check/hack to avoid drawing outside of the clip for hairlines

git-svn-id: http://skia.googlecode.com/svn/trunk@134 2bbb7eff-a529-9590-31e7-b0007b416f81

3 files changed, 185 insertions, 1 deletions

diff --git a/samplecode/SampleHairline.cpp b/samplecode/SampleHairline.cpp
new file mode 100644
index 0000000000..9763d0f1dd
--- /dev/null
+++ b/samplecode/SampleHairline.cpp
@@ -0,0 +1,157 @@
+#include "SampleCode.h"
+#include "SkView.h"
+#include "SkCanvas.h"
+#include "Sk64.h"
+#include "SkCornerPathEffect.h"
+#include "SkGradientShader.h"
+#include "SkGraphics.h"
+#include "SkImageDecoder.h"
+#include "SkKernel33MaskFilter.h"
+#include "SkPath.h"
+#include "SkRandom.h"
+#include "SkRegion.h"
+#include "SkShader.h"
+#include "SkUtils.h"
+#include "SkColorPriv.h"
+#include "SkColorFilter.h"
+#include "SkTime.h"
+#include "SkTypeface.h"
+#include "SkXfermode.h"
+
+#include "SkStream.h"
+#include "SkXMLParser.h"
+#include "SkColorPriv.h"
+#include "SkImageDecoder.h"
+
+static SkRandom gRand;
+
+static void test_chromium_9005() {
+    SkBitmap bm;
+    bm.setConfig(SkBitmap::kARGB_8888_Config, 800, 600);
+    bm.allocPixels();
+
+    SkCanvas canvas(bm);
+
+    SkPoint pt0 = { SkFloatToScalar(799.33374f), SkFloatToScalar(1.2360189f) };
+    SkPoint pt1 = { SkFloatToScalar(808.49969f), SkFloatToScalar(-7.4338055f) };
+    
+    SkPaint paint;
+    paint.setAntiAlias(true);
+    canvas.drawLine(pt0.fX, pt0.fY, pt1.fX, pt1.fY, paint);
+}
+
+static void generate_pts(SkPoint pts[], int count, int w, int h) {
+    for (int i = 0; i < count; i++) {
+        pts[i].set(gRand.nextUScalar1() * 3 * w - SkIntToScalar(w),
+                   gRand.nextUScalar1() * 3 * h - SkIntToScalar(h));
+    }
+}
+
+static bool check_zeros(const SkPMColor pixels[], int count, int skip) {
+    for (int i = 0; i < count; i++) {
+        if (*pixels) {
+            return false;
+        }
+        pixels += skip;
+    }
+    return true;
+}
+
+static bool check_bitmap_margin(const SkBitmap& bm, int margin) {
+    size_t rb = bm.rowBytes();
+    for (int i = 0; i < margin; i++) {
+        if (!check_zeros(bm.getAddr32(0, i), bm.width(), 1)) {
+            return false;
+        }
+        int bottom = bm.height() - i - 1;
+        if (!check_zeros(bm.getAddr32(0, bottom), bm.width(), 1)) {
+            return false;
+        }
+        // left column
+        if (!check_zeros(bm.getAddr32(i, 0), bm.height(), rb >> 2)) {
+            return false;
+        }
+        int right = bm.width() - margin + i;
+        if (!check_zeros(bm.getAddr32(right, 0), bm.height(), rb >> 2)) {
+            return false;
+        }
+    }
+    return true;
+}
+
+#define WIDTH   80
+#define HEIGHT  60
+#define MARGIN  4
+
+class HairlineView : public SkView {
+public:
+	HairlineView() {}
+    
+protected:
+    // overrides from SkEventSink
+    virtual bool onQuery(SkEvent* evt) {
+        if (SampleCode::TitleQ(*evt)) {
+            SampleCode::TitleR(evt, "Hairines");
+            return true;
+        }
+        return this->INHERITED::onQuery(evt);
+    }
+    
+    void show_bitmaps(SkCanvas* canvas, const SkBitmap& b0, const SkBitmap& b1,
+                      const SkIRect& inset) {
+        canvas->drawBitmap(b0, 0, 0, NULL);
+        canvas->drawBitmap(b1, SkIntToScalar(b0.width()), 0, NULL);
+    }
+
+    void drawBG(SkCanvas* canvas) {
+//        canvas->drawColor(0xFFDDDDDD);
+        canvas->drawColor(SK_ColorWHITE);
+   //     canvas->drawColor(SK_ColorBLACK);
+    }
+
+    virtual void onDraw(SkCanvas* canvas) {
+        this->drawBG(canvas);
+        
+        if (true) {
+            test_chromium_9005();
+        }
+        
+        SkBitmap bm, bm2;
+        bm.setConfig(SkBitmap::kARGB_8888_Config,
+                     WIDTH + MARGIN*2,
+                     HEIGHT + MARGIN*2);
+        bm.allocPixels();
+        // this will erase our margin, which we want to always stay 0
+        bm.eraseColor(0);
+
+        bm2.setConfig(SkBitmap::kARGB_8888_Config, WIDTH, HEIGHT,
+                      bm.rowBytes());
+        bm2.setPixels(bm.getAddr32(MARGIN, MARGIN));
+        
+        SkCanvas c2(bm2);
+        SkPaint paint;
+        paint.setAntiAlias(true);
+        for (int i = 0; i < 10000; i++) {
+            SkPoint pts[2];
+            generate_pts(pts, 2, WIDTH, HEIGHT);
+            bm2.eraseColor(0);
+            c2.drawLine(pts[0].fX, pts[0].fY, pts[1].fX, pts[1].fY, paint);
+            if (!check_bitmap_margin(bm, MARGIN)) {
+                SkDebugf("---- hairline failure (%g %g) (%g %g)\n",
+                         pts[0].fX, pts[0].fY, pts[1].fX, pts[1].fY);
+                break;
+            }
+        }
+        
+        this->inval(NULL);
+    }
+
+private:
+    typedef SkView INHERITED;
+};
+
+//////////////////////////////////////////////////////////////////////////////
+
+static SkView* MyFactory() { return new HairlineView; }
+static SkViewRegister reg(MyFactory);
+
diff --git a/src/core/SkScan_Antihair.cpp b/src/core/SkScan_Antihair.cpp
index 3344698f86..b54057344d 100644
--- a/src/core/SkScan_Antihair.cpp
+++ b/src/core/SkScan_Antihair.cpp
@@ -21,6 +21,21 @@
 #include "SkRegion.h"
 #include "SkFDot6.h"
 
+/*  Our attempt to compute the worst case "bounds" for the horizontal and
+    vertical cases has some numerical bug in it, and we sometimes undervalue
+    our extends. The bug is that when this happens, we will set the clip to
+    NULL (for speed), and thus draw outside of the clip by a pixel, which might
+    only look bad, but it might also access memory outside of the valid range
+    allcoated for the device bitmap.
+ 
+    This define enables our fix to outset our "bounds" by 1, thus avoiding the
+    chance of the bug, but at the cost of sometimes taking the rectblitter
+    case (i.e. not setting the clip to NULL) when we might not actually need
+    to. If we can improve/fix the actual calculations, then we can remove this
+    step.
+ */
+#define OUTSET_BEFORE_CLIP_TEST     true
+
 #define HLINE_STACK_BUFFER      100
 
 static inline int SmallDot6Scale(int value, int dot6) {
@@ -290,6 +305,10 @@ static void do_anti_hairline(SkFDot6 x0, SkFDot6 y0, SkFDot6 x1, SkFDot6 y1,
                 bottom = SkFixedCeil(fstart + SK_FixedHalf);
                 top = SkFixedFloor(fstart + (istop - istart - 1) * slope - SK_FixedHalf);
             }
+            if (OUTSET_BEFORE_CLIP_TEST) {
+                top -= 1;
+                bottom += 1;
+            }
             if (top >= clip->fBottom || bottom <= clip->fTop)
                 return;
             if (clip->fTop <= top && clip->fBottom >= bottom)
@@ -363,6 +382,10 @@ static void do_anti_hairline(SkFDot6 x0, SkFDot6 y0, SkFDot6 x1, SkFDot6 y1,
                 right = SkFixedCeil(fstart + SK_FixedHalf);
                 left = SkFixedFloor(fstart + (istop - istart - 1) * slope - SK_FixedHalf);
             }
+            if (OUTSET_BEFORE_CLIP_TEST) {
+                left -= 1;
+                right += 1;
+            }
             if (left >= clip->fRight || right <= clip->fLeft)
                 return;
             if (clip->fLeft <= left && clip->fRight >= right)
diff --git a/xcode/sampleapp/SampleApp.xcodeproj/project.pbxproj b/xcode/sampleapp/SampleApp.xcodeproj/project.pbxproj
index e172db7628..dcfaa36dc3 100644
--- a/xcode/sampleapp/SampleApp.xcodeproj/project.pbxproj
+++ b/xcode/sampleapp/SampleApp.xcodeproj/project.pbxproj
@@ -65,6 +65,7 @@
 		007A7CC00F01658C00A2D6EE /* SampleVertices.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 007A7CB10F01658C00A2D6EE /* SampleVertices.cpp */; };
 		007A7CC10F01658C00A2D6EE /* SampleXfermodes.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 007A7CB20F01658C00A2D6EE /* SampleXfermodes.cpp */; };
 		007C785E0F3B4C230004B142 /* SamplePathClip.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 007C785D0F3B4C230004B142 /* SamplePathClip.cpp */; };
+		008C4D980F77DAEE0056981C /* SampleHairline.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 008C4D970F77DAEE0056981C /* SampleHairline.cpp */; };
 		009CC9190F65918A002185BE /* SampleFontScalerTest.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 009CC9180F65918A002185BE /* SampleFontScalerTest.cpp */; };
 		00A41E4B0EFC312F00C9CBEB /* SampleArc.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 00A41E4A0EFC312F00C9CBEB /* SampleArc.cpp */; };
 		0156F80407C56A3000C6122B /* Foundation.framework in Frameworks */ = {isa = PBXBuildFile; fileRef = 0156F80307C56A3000C6122B /* Foundation.framework */; };
@@ -180,6 +181,7 @@
 		007A7CB10F01658C00A2D6EE /* SampleVertices.cpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; name = SampleVertices.cpp; path = ../../samplecode/SampleVertices.cpp; sourceTree = SOURCE_ROOT; };
 		007A7CB20F01658C00A2D6EE /* SampleXfermodes.cpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; name = SampleXfermodes.cpp; path = ../../samplecode/SampleXfermodes.cpp; sourceTree = SOURCE_ROOT; };
 		007C785D0F3B4C230004B142 /* SamplePathClip.cpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; name = SamplePathClip.cpp; path = ../../samplecode/SamplePathClip.cpp; sourceTree = SOURCE_ROOT; };
+		008C4D970F77DAEE0056981C /* SampleHairline.cpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; name = SampleHairline.cpp; path = ../../samplecode/SampleHairline.cpp; sourceTree = SOURCE_ROOT; };
 		009CC9180F65918A002185BE /* SampleFontScalerTest.cpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; name = SampleFontScalerTest.cpp; path = ../../samplecode/SampleFontScalerTest.cpp; sourceTree = SOURCE_ROOT; };
 		00A41E4A0EFC312F00C9CBEB /* SampleArc.cpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; name = SampleArc.cpp; path = ../../samplecode/SampleArc.cpp; sourceTree = SOURCE_ROOT; };
 		00D6B5CB0F72DC4300C466B9 /* SampleFuzz.cpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; name = SampleFuzz.cpp; path = ../../samplecode/SampleFuzz.cpp; sourceTree = SOURCE_ROOT; };
@@ -232,6 +234,7 @@
 				007A7CB10F01658C00A2D6EE /* SampleVertices.cpp */,
 				007A7CB20F01658C00A2D6EE /* SampleXfermodes.cpp */,
 				0041CE1E0F00A12400695E8C /* SampleBitmapRect.cpp */,
+				008C4D970F77DAEE0056981C /* SampleHairline.cpp */,
 				0041CE1F0F00A12400695E8C /* SampleCamera.cpp */,
 				0041CE200F00A12400695E8C /* SampleCircle.cpp */,
 				0041CE210F00A12400695E8C /* SampleCode.h */,
@@ -497,7 +500,6 @@
 				0041CE400F00A12400695E8C /* SampleFontCache.cpp in Sources */,
 				0041CE420F00A12400695E8C /* SampleImage.cpp in Sources */,
 				0041CE430F00A12400695E8C /* SampleLayers.cpp in Sources */,
-				0041CE440F00A12400695E8C /* SampleLines.cpp in Sources */,
 				0041CE450F00A12400695E8C /* SampleMeasure.cpp in Sources */,
 				0041CE480F00A12400695E8C /* SampleOverflow.cpp in Sources */,
 				0041CE4A0F00A12400695E8C /* SamplePatch.cpp in Sources */,
@@ -519,6 +521,8 @@
 				009CC9190F65918A002185BE /* SampleFontScalerTest.cpp in Sources */,
 				007A7CB30F01658C00A2D6EE /* SamplePicture.cpp in Sources */,
 				2714E7960F7733EE00E95AE0 /* SkDrawable.cpp in Sources */,
+				0041CE440F00A12400695E8C /* SampleLines.cpp in Sources */,
+				008C4D980F77DAEE0056981C /* SampleHairline.cpp in Sources */,
 			);
 			runOnlyForDeploymentPostprocessing = 0;
 		};