Add device space "nudge" to gpu draws

This CL nudges all the GPU draws and clips slightly to match raster's round behavior for BW draws. We assume the effect will be negligible and do it for AA draws too.

BUG=423834

Committed: https://skia.googlesource.com/skia/+/2d55d07501c56310f97d2092d789a2bc9fa01b78

Review URL: https://codereview.chromium.org/877473005

4 files changed, 88 insertions, 83 deletions

diff --git a/samplecode/SampleClipDrawMatch.cpp b/samplecode/SampleClipDrawMatch.cpp
index 8e2fb46dc9..f897b7185e 100644
--- a/samplecode/SampleClipDrawMatch.cpp
+++ b/samplecode/SampleClipDrawMatch.cpp
@@ -16,6 +16,7 @@
 // fractionally (via an animator) to expose snapping bugs. The key bindings are:
 //      1-9: the different geometries
 //      t:   toggle which is drawn first the clip or the normal geometry
+//      f:   flip-flops which corner the bottom AA clip rect occupies in the complex clip cases
 
 // The possible geometric combinations to test
 enum Geometry {
@@ -35,6 +36,10 @@ static const float kMin = 100.5f;
 static const float kMid = 200.0f;
 static const float kMax = 299.5f;
 
+// The translation applied to the base AA rect  in the combination cases
+// (i.e., kRectAndRect through kRectAndConcave)
+static const float kXlate = 100.0f;
+
 SkRect create_rect(const SkPoint& offset) {
     SkRect r = SkRect::MakeLTRB(kMin, kMin, kMax, kMax);
     r.offset(offset);
@@ -79,62 +84,6 @@ SkPath create_concave_path(const SkPoint& offset) {
     return concavePath;
 }
 
-static void draw_clipped_geom(SkCanvas* canvas, const SkPoint& offset, int geom, bool useAA) {
-
-    int count = canvas->save();
-
-    switch (geom) {
-    case kRect_Geometry:
-        canvas->clipRect(create_rect(offset), SkRegion::kReplace_Op, useAA);
-        break;
-    case kRRect_Geometry:
-        canvas->clipRRect(create_rrect(offset), SkRegion::kReplace_Op, useAA);
-        break;
-    case kCircle_Geometry:
-        canvas->clipRRect(create_circle(offset), SkRegion::kReplace_Op, useAA);
-        break;
-    case kConvexPath_Geometry:
-        canvas->clipPath(create_convex_path(offset), SkRegion::kReplace_Op, useAA);
-        break;
-    case kConcavePath_Geometry:
-        canvas->clipPath(create_concave_path(offset), SkRegion::kReplace_Op, useAA);
-        break;
-    case kRectAndRect_Geometry: {
-        SkRect r = create_rect(offset);
-        r.offset(-100.0f, -100.0f);
-        canvas->clipRect(r, SkRegion::kReplace_Op, true); // AA here forces shader clips
-        canvas->clipRect(create_rect(offset), SkRegion::kIntersect_Op, useAA);
-        } break;
-    case kRectAndRRect_Geometry: {
-        SkRect r = create_rect(offset);
-        r.offset(-100.0f, -100.0f);
-        canvas->clipRect(r, SkRegion::kReplace_Op, true); // AA here forces shader clips
-        canvas->clipRRect(create_rrect(offset), SkRegion::kIntersect_Op, useAA);
-        } break;
-    case kRectAndConvex_Geometry: {
-        SkRect r = create_rect(offset);
-        r.offset(-100.0f, -100.0f);
-        canvas->clipRect(r, SkRegion::kReplace_Op, true); // AA here forces shader clips
-        canvas->clipPath(create_convex_path(offset), SkRegion::kIntersect_Op, useAA);
-        } break;
-    case kRectAndConcave_Geometry: {
-        SkRect r = create_rect(offset);
-        r.offset(-100.0f, -100.0f);
-        canvas->clipRect(r, SkRegion::kReplace_Op, true); // AA here forces shader clips
-        canvas->clipPath(create_concave_path(offset), SkRegion::kIntersect_Op, useAA);
-        } break;
-    } 
-
-    SkISize size = canvas->getDeviceSize();
-    SkRect bigR = SkRect::MakeWH(SkIntToScalar(size.width()), SkIntToScalar(size.height()));
-
-    SkPaint p;
-    p.setColor(SK_ColorRED);
-
-    canvas->drawRect(bigR, p);
-    canvas->restoreToCount(count);
-}
-
 static void draw_normal_geom(SkCanvas* canvas, const SkPoint& offset, int geom, bool useAA) {
     SkPaint p;
     p.setAntiAlias(useAA);
@@ -165,7 +114,7 @@ static void draw_normal_geom(SkCanvas* canvas, const SkPoint& offset, int geom,
 
 class ClipDrawMatchView : public SampleView {
 public:
-    ClipDrawMatchView() : fTrans(2, 5), fGeom(kRect_Geometry), fClipFirst(true) {
+    ClipDrawMatchView() : fTrans(2, 5), fGeom(kRect_Geometry), fClipFirst(true), fSign(1) {
         SkScalar values[2];
 
         fTrans.setRepeatCount(999);
@@ -199,6 +148,7 @@ protected:
                 case '7': fGeom = kRectAndRRect_Geometry; this->inval(NULL); return true;
                 case '8': fGeom = kRectAndConvex_Geometry; this->inval(NULL); return true;
                 case '9': fGeom = kRectAndConcave_Geometry; this->inval(NULL); return true;
+                case 'f': fSign = -fSign; this->inval(NULL); return true;
                 case 't': fClipFirst = !fClipFirst; this->inval(NULL); return true;
                 default: break;
             }
@@ -206,18 +156,74 @@ protected:
         return this->INHERITED::onQuery(evt);
     }
 
+    void drawClippedGeom(SkCanvas* canvas, const SkPoint& offset, bool useAA) {
+
+        int count = canvas->save();
+
+        switch (fGeom) {
+        case kRect_Geometry:
+            canvas->clipRect(create_rect(offset), SkRegion::kReplace_Op, useAA);
+            break;
+        case kRRect_Geometry:
+            canvas->clipRRect(create_rrect(offset), SkRegion::kReplace_Op, useAA);
+            break;
+        case kCircle_Geometry:
+            canvas->clipRRect(create_circle(offset), SkRegion::kReplace_Op, useAA);
+            break;
+        case kConvexPath_Geometry:
+            canvas->clipPath(create_convex_path(offset), SkRegion::kReplace_Op, useAA);
+            break;
+        case kConcavePath_Geometry:
+            canvas->clipPath(create_concave_path(offset), SkRegion::kReplace_Op, useAA);
+            break;
+        case kRectAndRect_Geometry: {
+            SkRect r = create_rect(offset);
+            r.offset(fSign * kXlate, fSign * kXlate);
+            canvas->clipRect(r, SkRegion::kReplace_Op, true); // AA here forces shader clips
+            canvas->clipRect(create_rect(offset), SkRegion::kIntersect_Op, useAA);
+            } break;
+        case kRectAndRRect_Geometry: {
+            SkRect r = create_rect(offset);
+            r.offset(fSign * kXlate, fSign * kXlate);
+            canvas->clipRect(r, SkRegion::kReplace_Op, true); // AA here forces shader clips
+            canvas->clipRRect(create_rrect(offset), SkRegion::kIntersect_Op, useAA);
+            } break;
+        case kRectAndConvex_Geometry: {
+            SkRect r = create_rect(offset);
+            r.offset(fSign * kXlate, fSign * kXlate);
+            canvas->clipRect(r, SkRegion::kReplace_Op, true); // AA here forces shader clips
+            canvas->clipPath(create_convex_path(offset), SkRegion::kIntersect_Op, useAA);
+            } break;
+        case kRectAndConcave_Geometry: {
+            SkRect r = create_rect(offset);
+            r.offset(fSign * kXlate, fSign * kXlate);
+            canvas->clipRect(r, SkRegion::kReplace_Op, true); // AA here forces shader clips
+            canvas->clipPath(create_concave_path(offset), SkRegion::kIntersect_Op, useAA);
+            } break;
+        } 
+
+        SkISize size = canvas->getDeviceSize();
+        SkRect bigR = SkRect::MakeWH(SkIntToScalar(size.width()), SkIntToScalar(size.height()));
+
+        SkPaint p;
+        p.setColor(SK_ColorRED);
+
+        canvas->drawRect(bigR, p);
+        canvas->restoreToCount(count);
+    }
+
     // Draw a big red rect through some clip geometry and also draw that same
     // geometry in black. The order in which they are drawn can be swapped.
     // This tests whether the clip and normally drawn geometry match up.
     void drawGeometry(SkCanvas* canvas, const SkPoint& offset, bool useAA) {
         if (fClipFirst) {
-            draw_clipped_geom(canvas, offset, fGeom, useAA);
+            this->drawClippedGeom(canvas, offset, useAA);
         }
 
         draw_normal_geom(canvas, offset, fGeom, useAA);
 
         if (!fClipFirst) {
-            draw_clipped_geom(canvas, offset, fGeom, useAA);
+            this->drawClippedGeom(canvas, offset, useAA);
         }
     }
 
@@ -239,6 +245,7 @@ private:
     SkInterpolator  fTrans;
     Geometry        fGeom;
     bool            fClipFirst;
+    int             fSign;
 
     typedef SampleView INHERITED;
 };
diff --git a/src/core/SkClipStack.cpp b/src/core/SkClipStack.cpp
index 515596a969..863dc9a387 100644
--- a/src/core/SkClipStack.cpp
+++ b/src/core/SkClipStack.cpp
@@ -418,19 +418,6 @@ void SkClipStack::Element::updateBoundAndGenID(const Element* prior) {
             break;
     }
 
-    if (!fDoAA) {
-        // Here we mimic a non-anti-aliased scanline system. If there is
-        // no anti-aliasing we can integerize the bounding box to exclude
-        // fractional parts that won't be rendered.
-        // Note: the left edge is handled slightly differently below. We
-        // are a bit more generous in the rounding since we don't want to
-        // risk missing the left pixels when fLeft is very close to .5
-        fFiniteBound.set(SkScalarFloorToScalar(fFiniteBound.fLeft+0.45f),
-                         SkScalarRoundToScalar(fFiniteBound.fTop),
-                         SkScalarRoundToScalar(fFiniteBound.fRight),
-                         SkScalarRoundToScalar(fFiniteBound.fBottom));
-    }
-
     // Now determine the previous Element's bound information taking into
     // account that there may be no previous clip
     SkRect prevFinite;
diff --git a/src/gpu/effects/GrConvexPolyEffect.cpp b/src/gpu/effects/GrConvexPolyEffect.cpp
index 7035094fa6..615c341ef2 100644
--- a/src/gpu/effects/GrConvexPolyEffect.cpp
+++ b/src/gpu/effects/GrConvexPolyEffect.cpp
@@ -137,10 +137,14 @@ void GLAARectEffect::emitCode(GrGLFPBuilder* builder,
         fsBuilder->codeAppendf("\t\tfloat alpha = (1.0 + max(xSub, -1.0)) * (1.0 + max(ySub, -1.0));\n");
     } else {
         fsBuilder->codeAppendf("\t\tfloat alpha = 1.0;\n");
-        fsBuilder->codeAppendf("\t\talpha *= (%s.x - %s.x) > -0.5 ? 1.0 : 0.0;\n", fragmentPos, rectName);
-        fsBuilder->codeAppendf("\t\talpha *= (%s.z - %s.x) > -0.5 ? 1.0 : 0.0;\n", rectName, fragmentPos);
-        fsBuilder->codeAppendf("\t\talpha *= (%s.y - %s.y) > -0.5 ? 1.0 : 0.0;\n", fragmentPos, rectName);
-        fsBuilder->codeAppendf("\t\talpha *= (%s.w - %s.y) > -0.5 ? 1.0 : 0.0;\n", rectName, fragmentPos);
+        fsBuilder->codeAppendf("\t\talpha *= (%s.x - %s.x) > -0.5 ? 1.0 : 0.0;\n",
+                               fragmentPos, rectName);
+        fsBuilder->codeAppendf("\t\talpha *= (%s.z - %s.x) > -0.5 ? 1.0 : 0.0;\n",
+                               rectName, fragmentPos);
+        fsBuilder->codeAppendf("\t\talpha *= (%s.y - %s.y) > -0.5 ? 1.0 : 0.0;\n",
+                               fragmentPos, rectName);
+        fsBuilder->codeAppendf("\t\talpha *= (%s.w - %s.y) > -0.5 ? 1.0 : 0.0;\n",
+                               rectName, fragmentPos);
     }
 
     if (GrProcessorEdgeTypeIsInverseFill(aare.getEdgeType())) {
@@ -154,8 +158,10 @@ void GLAARectEffect::setData(const GrGLProgramDataManager& pdman, const GrProces
     const AARectEffect& aare = processor.cast<AARectEffect>();
     const SkRect& rect = aare.getRect();
     if (rect != fPrevRect) {
-        pdman.set4f(fRectUniform, rect.fLeft + 0.5f, rect.fTop + 0.5f,
-                   rect.fRight - 0.5f, rect.fBottom - 0.5f);
+        // Add a device space "nudge" of 0.05f, 0.05f to match raster's rounding behavior for
+        // BW clipping/drawing
+        pdman.set4f(fRectUniform, rect.fLeft + 0.55f, rect.fTop + 0.55f,
+                                  rect.fRight - 0.45f, rect.fBottom - 0.45f);
         fPrevRect = rect;
     }
 }
@@ -221,7 +227,10 @@ void GrGLConvexPolyEffect::emitCode(GrGLFPBuilder* builder,
     fsBuilder->codeAppend("\t\tfloat edge;\n");
     const char* fragmentPos = fsBuilder->fragmentPosition();
     for (int i = 0; i < cpe.getEdgeCount(); ++i) {
-        fsBuilder->codeAppendf("\t\tedge = dot(%s[%d], vec3(%s.x, %s.y, 1));\n",
+        // Add a device space "nudge" of 0.05f, 0.05f to match raster's rounding behavior for
+        // BW clipping/drawing. Since we are "nudging" fragment positions we have to go in
+        // the opposite direction.
+        fsBuilder->codeAppendf("\t\tedge = dot(%s[%d], vec3(%s.x - 0.05, %s.y - 0.05, 1));\n",
                                edgeArrayName, i, fragmentPos, fragmentPos);
         if (GrProcessorEdgeTypeIsAA(cpe.getEdgeType())) {
             fsBuilder->codeAppend("\t\tedge = clamp(edge, 0.0, 1.0);\n");
diff --git a/src/gpu/gl/builders/GrGLVertexShaderBuilder.cpp b/src/gpu/gl/builders/GrGLVertexShaderBuilder.cpp
index f17e741169..f0b645ee42 100644
--- a/src/gpu/gl/builders/GrGLVertexShaderBuilder.cpp
+++ b/src/gpu/gl/builders/GrGLVertexShaderBuilder.cpp
@@ -47,13 +47,15 @@ void GrGLVertexBuilder::transformToNormalizedDeviceSpace(const GrShaderVar& posV
     // Transform from Skia's device coords to GL's normalized device coords. Note that
     // because we want to "nudge" the device space positions we are converting to 
     // non-homogeneous NDC.
+    // The "0.05" nudge serves to match the raster path's rounding for bw draws.
+    // For aa draws we just assume the impact will be minimal - so we always perform the nudge.
     if (kVec3f_GrSLType == posVar.getType()) {
-        this->codeAppendf("gl_Position = vec4(dot(%s.xz, %s.xy)/%s.z, dot(%s.yz, %s.zw)/%s.z, 0, 1);",
-                          posVar.c_str(), fRtAdjustName, posVar.c_str(),
-                          posVar.c_str(), fRtAdjustName, posVar.c_str());
+        this->codeAppendf("gl_Position = vec4((dot(%s.xz, %s.xy)/%s.z) + 0.05 * %s.x, (dot(%s.yz, %s.zw)/%s.z) + 0.05 * %s.z, 0, 1);",
+                          posVar.c_str(), fRtAdjustName, posVar.c_str(), fRtAdjustName,
+                          posVar.c_str(), fRtAdjustName, posVar.c_str(), fRtAdjustName);
     } else {
         SkASSERT(kVec2f_GrSLType == posVar.getType());
-        this->codeAppendf("gl_Position = vec4(%s.x * %s.x + %s.y, %s.y * %s.z + %s.w, 0, 1);",
+        this->codeAppendf("gl_Position = vec4((%s.x + 0.05) * %s.x + %s.y, (%s.y + 0.05) * %s.z + %s.w, 0, 1);",
                           posVar.c_str(), fRtAdjustName, fRtAdjustName,
                           posVar.c_str(), fRtAdjustName, fRtAdjustName);
     }