Fix degenerate and near-degenerate quadratic hairlines on the gpu

gm/hairlines.cpp

Index: gm/hairlines.cpp
diff --git a/gm/hairlines.cpp b/gm/hairlines.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..e73cc6ddf0747570855aa6d5b88c3353aa9f1b05
--- /dev/null
+++ b/gm/hairlines.cpp
@@ -0,0 +1,143 @@
+/*
+ * Copyright 2013 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "gm.h"
+#include "SkCanvas.h"
+#include "SkTArray.h"
+
+namespace skiagm {
+
+class HairlinesGM : public GM {
+protected:
+
+    virtual SkString onShortName() SK_OVERRIDE {
+        return SkString("hairlines");
+    }
+
+    virtual SkISize onISize() { return make_isize(800, 600); }
+
+    virtual void onOnceBeforeDraw() SK_OVERRIDE {
+        {
+            SkPath* lineAnglesPath = &fPaths.push_back();
+            enum {
+                kNumAngles = 15,
+                kRadius = 40,
+            };
+            for (int i = 0; i < kNumAngles; ++i) {
+                SkScalar angle = SK_ScalarPI * SkIntToScalar(i) / kNumAngles;
+                SkScalar x = kRadius * SkScalarCos(angle);
+                SkScalar y = kRadius * SkScalarSin(angle);
+                lineAnglesPath->moveTo(x, y);
+                lineAnglesPath->lineTo(-x, -y);
+            }
+        }
+
+        {
+            SkPath* kindaTightQuad = &fPaths.push_back();
+            kindaTightQuad->moveTo(0, -10 * SK_Scalar1);
+            kindaTightQuad->quadTo(SkIntToScalar(100), SkIntToScalar(100), -10 * SK_Scalar1, 0);
+        }
+
+        {
+            SkPath* tightQuad = &fPaths.push_back();
+            tightQuad->moveTo(0, -5 * SK_Scalar1);
+            tightQuad->quadTo(SkIntToScalar(100), SkIntToScalar(100), -5 * SK_Scalar1, 0);
+        }
+
+        {
+            SkPath* tighterQuad = &fPaths.push_back();
+            tighterQuad->moveTo(0, -2 * SK_Scalar1);
+            tighterQuad->quadTo(SkIntToScalar(100), SkIntToScalar(100), -2 * SK_Scalar1, 0);
+        }
+
+        {
+            SkPath* unevenTighterQuad = &fPaths.push_back();
+            unevenTighterQuad->moveTo(0, -1 * SK_Scalar1);
+            SkPoint p;
+            p.set(-2 * SK_Scalar1 + 3 * SkIntToScalar(102) / 4, SkIntToScalar(75));
+            unevenTighterQuad->quadTo(SkIntToScalar(100), SkIntToScalar(100), p.fX, p.fY);
+        }
+
+        {
+            SkPath* reallyTightQuad = &fPaths.push_back();
+            reallyTightQuad->moveTo(0, -1 * SK_Scalar1);
+            reallyTightQuad->quadTo(SkIntToScalar(100), SkIntToScalar(100), -1 * SK_Scalar1, 0);
+        }
+
+        {
+            SkPath* closedQuad = &fPaths.push_back();
+            closedQuad->moveTo(0, -0);
+            closedQuad->quadTo(SkIntToScalar(100), SkIntToScalar(100), 0, 0);
+        }
+
+        {
+            SkPath* unevenClosedQuad = &fPaths.push_back();
+            unevenClosedQuad->moveTo(0, -0);
+            unevenClosedQuad->quadTo(SkIntToScalar(100), SkIntToScalar(100),
+                                     SkIntToScalar(75), SkIntToScalar(75));
+        }
+    }
+
+    virtual void onDraw(SkCanvas* canvas) SK_OVERRIDE {
+        static const SkAlpha kAlphaValue[] = { 0xFF, 0x40 };
+
+        enum {
+            kMargin = 5,
+        };
+        int wrapX = canvas->getDeviceSize().fWidth - kMargin;
+
+        SkScalar maxH = 0;
+        canvas->translate(SkIntToScalar(kMargin), SkIntToScalar(kMargin));
+        canvas->save();
+
+        SkScalar x = SkIntToScalar(kMargin);
+        for (int p = 0; p < fPaths.count(); ++p) {
+            for (size_t a = 0; a < SK_ARRAY_COUNT(kAlphaValue); ++a) {
+                for (int aa = 0; aa < 2; ++aa) {
+                    const SkRect& bounds = fPaths[p].getBounds();
+
+                    if (x + bounds.width() > wrapX) {
+                        canvas->restore();
+                        canvas->translate(0, maxH + SkIntToScalar(kMargin));
+                        canvas->save();
+                        maxH = 0;
+                        x = SkIntToScalar(kMargin);
+                    }
+
+                    SkPaint paint;
+                    paint.setARGB(kAlphaValue[a], 0, 0, 0);
+                    paint.setAntiAlias(SkToBool(aa));
+                    paint.setStyle(SkPaint::kStroke_Style);
+                    paint.setStrokeWidth(0);
+
+                    canvas->save();
+                    canvas->translate(-bounds.fLeft, -bounds.fTop);
+                    canvas->drawPath(fPaths[p], paint);
+                    canvas->restore();
+
+                    maxH = SkMaxScalar(maxH, bounds.height());
+
+                    SkScalar dx = bounds.width() + SkIntToScalar(kMargin);
+                    x += dx;
+                    canvas->translate(dx, 0);
+                }
+            }
+        }
+        canvas->restore();
+    }
+
+private:
+    SkTArray<SkPath> fPaths;
+    typedef GM INHERITED;
+};
+
+//////////////////////////////////////////////////////////////////////////////
+
+static GM* MyFactory(void*) { return new HairlinesGM; }
+static GMRegistry reg(MyFactory);
+
+}