Add Dashing gpu effect for simple dashed lines

src/gpu/effects/GrDashingEffect.h

Index: src/gpu/effects/GrDashingEffect.h
diff --git a/src/gpu/effects/GrDashingEffect.h b/src/gpu/effects/GrDashingEffect.h
new file mode 100644
index 0000000000000000000000000000000000000000..129c78491d64aeb4d21c662014eb0d79738dce29
--- /dev/null
+++ b/src/gpu/effects/GrDashingEffect.h
@@ -0,0 +1,75 @@
+
+/*
+ * Copyright 2014 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef GrDashingEffect_DEFINED
+#define GrDashingEffect_DEFINED
+
+#include "GrCoordTransform.h"
+#include "GrDrawTargetCaps.h"
+#include "GrEffect.h"
+#include "GrTypesPriv.h"
+#include "SkPathEffect.h"
+
+class GrGLDashingEffect;
+class SkPath;
+
+/**
+ * An effect that renders a dashed line. It is intended to be used as a coverage effect.
+ * The effect is meant for dashed lines that only have a single on/off interval pair.
+ * Bounding geometry is rendered and the effect computes coverage based on the fragment's
+ * position relative to the dashed line.
+ */
+
+class GrDashingEffect : public GrEffect {

[bsalomon, 2014/05/13 09:10:33]

AFAICT none of the public members or the function are relevant to the caller of
Create() but rather facilitate extracting out params for the GrGLEffect subclass
or are virtuals used by the GrEffect shader building system. It's a virtue that
the creator gets back a generic effect rather than having any knowledge that
it's a GrDrashingEffect. Maybe this should be shuffled around so that the
GrEffect subclass itself is private to the cpp file (a la
GrConvexPolyEffect.h/cpp).

[egdaniel, 2014/05/13 14:00:11]

Slightly confused here. I thought I understood your various arguments in the
first half of what you wrote, but then when you said like GrConvexPolyEffect you
lost me. To me GrCPE and GrDE are set up almost identically. Unless are you
referring the AARectEffect class that is inside GrCPE?

On 2014/05/13 09:10:33, bsalomon wrote:

[bsalomon, 2014/05/13 14:14:36]

You're right. I picked a bad example. See GrRRectEffect. GrConvexPolyEffect
should probably follow this pattern as well.

+public:
+    typedef SkPathEffect::DashInfo DashInfo;
+
+    /**
+     * The effect calculates the coverage for the case of a horizontal line in device space.
+     * The matrix that is passed in should be able to convert a line in source space to a
+     * horizontal line in device space. Additionally, the coord transform matrix should translate
+     * the the start of line to origin, and the shift it along the positive x-axis by the phase
+     * and half the off interval.
+     */
+    static GrEffectRef* Create(GrEffectEdgeType edgeType, const DashInfo& info,
+                               const SkMatrix& matrix, SkScalar strokeWidth);
+
+    virtual ~GrDashingEffect();
+
+    static const char* Name() { return "DashingEffect"; }
+
+    GrEffectEdgeType getEdgeType() const { return fEdgeType; }
+
+    const SkRect& getRect() const { return fRect; }
+
+    const SkScalar& getIntervalLength() const { return fIntervalLength; }
+
+    typedef GrGLDashingEffect GLEffect;
+
+    virtual void getConstantColorComponents(GrColor* color, uint32_t* validFlags) const SK_OVERRIDE;
+
+    virtual const GrBackendEffectFactory& getFactory() const SK_OVERRIDE;
+
+private:
+    GrDashingEffect(GrEffectEdgeType edgeType, const DashInfo& info, const SkMatrix& matrix,
+                    SkScalar strokeWidth);
+
+    virtual bool onIsEqual(const GrEffect& other) const SK_OVERRIDE;
+
+    GrEffectEdgeType    fEdgeType;
+    GrCoordTransform    fCoordTransform;
+    SkRect              fRect;
+    SkScalar            fIntervalLength;
+
+    GR_DECLARE_EFFECT_TEST;
+
+    typedef GrEffect INHERITED;
+};
+
+
+#endif