skia2/include/gpu/GrClip.h

/*
 * Copyright 2010 Google Inc.
 *
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */

#ifndef GrClip_DEFINED
#define GrClip_DEFINED

#include "GrFragmentProcessor.h"
#include "GrTypesPriv.h"

class GrDrawContext;

/**
 * Produced by GrClip. It provides a set of modifications to the drawing state that are used to
 * create the final GrPipeline for a GrBatch.
 */
class GrAppliedClip : public SkNoncopyable {
public:
    GrAppliedClip(const SkRect& drawBounds)
        : fHasStencilClip(false)
        , fClippedDrawBounds(drawBounds) {
    }

    const GrScissorState& scissorState() const { return fScissorState; }
    GrFragmentProcessor* clipCoverageFragmentProcessor() const { return fClipCoverageFP.get(); }
    bool hasStencilClip() const { return fHasStencilClip; }

    /**
     * Intersects the applied clip with the provided rect. Returns false if the draw became empty.
     */
    bool addScissor(const SkIRect& irect) {
        return fScissorState.intersect(irect) && fClippedDrawBounds.intersect(SkRect::Make(irect));
    }

    void addCoverageFP(sk_sp<GrFragmentProcessor> fp) {
        SkASSERT(!fClipCoverageFP);
        fClipCoverageFP = fp;
    }

    void addStencilClip() {
        SkASSERT(!fHasStencilClip);
        fHasStencilClip = true;
    }

    /**
     * Returns the device bounds of the draw after clip has been applied. TODO: Ideally this would
     * consider the combined effect of all clipping techniques in play (scissor, stencil, fp, etc.).
     */
    const SkRect& clippedDrawBounds() const { return fClippedDrawBounds; }

private:
    GrScissorState             fScissorState;
    sk_sp<GrFragmentProcessor> fClipCoverageFP;
    bool                       fHasStencilClip;
    SkRect                     fClippedDrawBounds;
    typedef SkNoncopyable INHERITED;
};

/**
 * GrClip is an abstract base class for applying a clip. It constructs a clip mask if necessary, and
 * fills out a GrAppliedClip instructing the caller on how to set up the draw state.
 */
class GrClip {
public:
    virtual bool quickContains(const SkRect&) const = 0;
    virtual bool quickContains(const SkRRect& rrect) const {
        return this->quickContains(rrect.getBounds());
    }
    virtual void getConservativeBounds(int width, int height, SkIRect* devResult,
                                       bool* isIntersectionOfRects = nullptr) const = 0;
    virtual bool apply(GrContext*, GrDrawContext*, bool useHWAA, bool hasUserStencilSettings,
                       GrAppliedClip* out) const = 0;

    virtual ~GrClip() {}

    /**
     * This is the maximum distance that a draw may extend beyond a clip's boundary and still count
     * count as "on the other side". We leave some slack because floating point rounding error is
     * likely to blame. The rationale for 1e-3 is that in the coverage case (and barring unexpected
     * rounding), as long as coverage stays within 0.5 * 1/256 of its intended value it shouldn't
     * have any effect on the final pixel values.
     */
    constexpr static SkScalar kBoundsTolerance = 1e-3f;

    /**
     * Returns true if the given query bounds count as entirely inside the clip.
     *
     * @param innerClipBounds   device-space rect contained by the clip (SkRect or SkIRect).
     * @param queryBounds       device-space bounds of the query region.
     */
    template<typename TRect> constexpr static bool IsInsideClip(const TRect& innerClipBounds,
                                                                const SkRect& queryBounds) {
        return innerClipBounds.fRight - innerClipBounds.fLeft > kBoundsTolerance &&
               innerClipBounds.fBottom - innerClipBounds.fTop > kBoundsTolerance &&
               innerClipBounds.fLeft < queryBounds.fLeft + kBoundsTolerance &&
               innerClipBounds.fTop < queryBounds.fTop + kBoundsTolerance &&
               innerClipBounds.fRight > queryBounds.fRight - kBoundsTolerance &&
               innerClipBounds.fBottom > queryBounds.fBottom - kBoundsTolerance;
    }

    /**
     * Returns true if the given query bounds count as entirely outside the clip.
     *
     * @param outerClipBounds   device-space rect that contains the clip (SkRect or SkIRect).
     * @param queryBounds       device-space bounds of the query region.
     */
    template<typename TRect> constexpr static bool IsOutsideClip(const TRect& outerClipBounds,
                                                                 const SkRect& queryBounds) {
        return outerClipBounds.fRight - outerClipBounds.fLeft <= kBoundsTolerance ||
               outerClipBounds.fBottom - outerClipBounds.fTop <= kBoundsTolerance ||
               outerClipBounds.fLeft >= queryBounds.fRight - kBoundsTolerance ||
               outerClipBounds.fTop >= queryBounds.fBottom - kBoundsTolerance ||
               outerClipBounds.fRight <= queryBounds.fLeft + kBoundsTolerance ||
               outerClipBounds.fBottom <= queryBounds.fTop + kBoundsTolerance;
    }

    /**
     * Returns the minimal integer rect that counts as containing a given set of bounds.
     */
    static SkIRect GetPixelIBounds(const SkRect& bounds) {
        return SkIRect::MakeLTRB(SkScalarFloorToInt(bounds.fLeft + kBoundsTolerance),
                                 SkScalarFloorToInt(bounds.fTop + kBoundsTolerance),
                                 SkScalarCeilToInt(bounds.fRight - kBoundsTolerance),
                                 SkScalarCeilToInt(bounds.fBottom - kBoundsTolerance));
    }

    /**
     * Returns the minimal pixel-aligned rect that counts as containing a given set of bounds.
     */
    static SkRect GetPixelBounds(const SkRect& bounds) {
        return SkRect::MakeLTRB(SkScalarFloorToScalar(bounds.fLeft + kBoundsTolerance),
                                SkScalarFloorToScalar(bounds.fTop + kBoundsTolerance),
                                SkScalarCeilToScalar(bounds.fRight - kBoundsTolerance),
                                SkScalarCeilToScalar(bounds.fBottom - kBoundsTolerance));
    }

    /**
     * Returns true if the given rect counts as aligned with pixel boundaries.
     */
    static bool IsPixelAligned(const SkRect& rect) {
        return SkScalarAbs(SkScalarRoundToScalar(rect.fLeft) - rect.fLeft) <= kBoundsTolerance &&
               SkScalarAbs(SkScalarRoundToScalar(rect.fTop) - rect.fTop) <= kBoundsTolerance &&
               SkScalarAbs(SkScalarRoundToScalar(rect.fRight) - rect.fRight) <= kBoundsTolerance &&
               SkScalarAbs(SkScalarRoundToScalar(rect.fBottom) - rect.fBottom) <= kBoundsTolerance;
    }
};

/**
 * Specialized implementation for no clip.
 */
class GrNoClip final : public GrClip {
private:
    bool quickContains(const SkRect&) const final { return true; }
    void getConservativeBounds(int width, int height, SkIRect* devResult,
                               bool* isIntersectionOfRects) const final;
    bool apply(GrContext*, GrDrawContext*, bool, bool, GrAppliedClip*) const final { return true; }
};

/**
 * GrFixedClip is a clip that can be represented by fixed-function hardware. It never modifies the
 * stencil buffer itself, but can be configured to use whatever clip is already there.
 */
class GrFixedClip final : public GrClip {
public:
    GrFixedClip() : fHasStencilClip(false) {}
    GrFixedClip(const SkIRect& scissorRect)
        : fScissorState(scissorRect)
        , fHasStencilClip(false) {}

    void reset() {
        fScissorState.setDisabled();
        fHasStencilClip = false;
    }

    void reset(const SkIRect& scissorRect) {
        fScissorState.set(scissorRect);
        fHasStencilClip = false;
    }

    void enableStencilClip() { fHasStencilClip = true; }
    void disableStencilClip() { fHasStencilClip = false; }

    bool quickContains(const SkRect&) const final;
    void getConservativeBounds(int width, int height, SkIRect* devResult,
                               bool* isIntersectionOfRects) const final;

private:
    bool apply(GrContext*, GrDrawContext*, bool useHWAA, bool hasUserStencilSettings,
               GrAppliedClip* out) const final;

    GrScissorState   fScissorState;
    bool             fHasStencilClip;
};

#endif