gfx/skia/skia/src/gpu/GrPathRenderer.h
author Wes Kocher <wkocher@mozilla.com>
Wed, 10 May 2017 10:01:18 -0700
changeset 407965 ce2218406119c36a551e3faea4e192186ee46cc5
parent 407937 af6f19870b2a00759ac1d83dedc3db57213abfee
child 408167 0ded74baeaf23d7985401fe9bbabdb3d9385ac22
permissions -rw-r--r--
Backed out 9 changesets (bug 1340627) for graphical glitches a=backout Backed out changeset 0b1371055c7f (bug 1340627) Backed out changeset f152be1fadb7 (bug 1340627) Backed out changeset c691e2ab6a0c (bug 1340627) Backed out changeset 3cb4bceb8d79 (bug 1340627) Backed out changeset 026aadd76d06 (bug 1340627) Backed out changeset fdbd5d281287 (bug 1340627) Backed out changeset 75fb0d9858a9 (bug 1340627) Backed out changeset 0d4ec7d38a00 (bug 1340627) Backed out changeset af6f19870b2a (bug 1340627) MozReview-Commit-ID: 9dHr7xMZezY

/*
 * Copyright 2011 Google Inc.
 *
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */

#ifndef GrPathRenderer_DEFINED
#define GrPathRenderer_DEFINED

#include "GrCaps.h"
#include "GrDrawContext.h"
#include "GrPaint.h"
#include "GrResourceProvider.h"
#include "GrShape.h"

#include "SkDrawProcs.h"
#include "SkTArray.h"

class SkPath;
class GrFixedClip;
struct GrPoint;

/**
 *  Base class for drawing paths into a GrDrawTarget.
 *
 *  Derived classes can use stages GrPaint::kTotalStages through GrPipelineBuilder::kNumStages-1.
 *  The stages before GrPaint::kTotalStages are reserved for setting up the draw (i.e., textures and
 *  filter masks).
 */
class SK_API GrPathRenderer : public SkRefCnt {
public:
    GrPathRenderer();

    /**
     * A caller may wish to use a path renderer to draw a path into the stencil buffer. However,
     * the path renderer itself may require use of the stencil buffer. Also a path renderer may
     * use a GrProcessor coverage stage that sets coverage to zero to eliminate pixels that are
     * covered by bounding geometry but outside the path. These exterior pixels would still be
     * rendered into the stencil.
     *
     * A GrPathRenderer can provide three levels of support for stenciling paths:
     * 1) kNoRestriction: This is the most general. The caller sets up the GrPipelineBuilder on the target
     *                    and calls drawPath(). The path is rendered exactly as the draw state
     *                    indicates including support for simultaneous color and stenciling with
     *                    arbitrary stenciling rules. Pixels partially covered by AA paths are
     *                    affected by the stencil settings.
     * 2) kStencilOnly: The path renderer cannot apply arbitrary stencil rules nor shade and stencil
     *                  simultaneously. The path renderer does support the stencilPath() function
     *                  which performs no color writes and writes a non-zero stencil value to pixels
     *                  covered by the path.
     * 3) kNoSupport: This path renderer cannot be used to stencil the path.
     */
    enum StencilSupport {
        kNoSupport_StencilSupport,
        kStencilOnly_StencilSupport,
        kNoRestriction_StencilSupport,
    };

    /**
     * This function is to get the stencil support for a particular path. The path's fill must
     * not be an inverse type. The path will always be filled and not stroked.
     *
     * @param shape   the shape that will be drawn. Must be simple fill styled and non-inverse
     *                filled.
     */
    StencilSupport getStencilSupport(const GrShape& shape) const {
        SkDEBUGCODE(SkPath path;)
        SkDEBUGCODE(shape.asPath(&path);)
        SkASSERT(shape.style().isSimpleFill());
        SkASSERT(!path.isInverseFillType());
        return this->onGetStencilSupport(shape);
    }

    /** Args to canDrawPath()
     *
     * fShaderCaps       The shader caps
     * fPipelineBuilder  The pipelineBuilder
     * fViewMatrix       The viewMatrix
     * fShape            The shape to draw
     * fAntiAlias        True if anti-aliasing is required.
     */
    struct CanDrawPathArgs {
        const GrShaderCaps*         fShaderCaps;
        const SkMatrix*             fViewMatrix;
        const GrShape*              fShape;
        bool                        fAntiAlias;

        // These next two are only used by GrStencilAndCoverPathRenderer
        bool                        fHasUserStencilSettings;
        bool                        fIsStencilBufferMSAA;

#ifdef SK_DEBUG
        void validate() const {
            SkASSERT(fShaderCaps);
            SkASSERT(fViewMatrix);
            SkASSERT(fShape);
        }
#endif
    };

    /**
     * Returns true if this path renderer is able to render the path. Returning false allows the
     * caller to fallback to another path renderer This function is called when searching for a path
     * renderer capable of rendering a path.
     *
     * @return  true if the path can be drawn by this object, false otherwise.
     */
    bool canDrawPath(const CanDrawPathArgs& args) const {
        SkDEBUGCODE(args.validate();)
        return this->onCanDrawPath(args);
    }

    /**
     * Args to drawPath()
     *
     * fTarget                The target that the path will be rendered to
     * fResourceProvider      The resource provider for creating gpu resources to render the path
     * fPipelineBuilder       The pipelineBuilder
     * fClip                  The clip
     * fColor                 Color to render with
     * fViewMatrix            The viewMatrix
     * fShape                 The shape to draw
     * fAntiAlias             true if anti-aliasing is required.
     * fGammaCorrect          true if gamma-correct rendering is to be used.
     */
    struct DrawPathArgs {
        GrResourceProvider*         fResourceProvider;
        const GrPaint*              fPaint;
        const GrUserStencilSettings*fUserStencilSettings;

        GrDrawContext*              fDrawContext;
        const GrClip*               fClip;
        const SkMatrix*             fViewMatrix;
        const GrShape*              fShape;
        bool                        fAntiAlias;
        bool                        fGammaCorrect;
#ifdef SK_DEBUG
        void validate() const {
            SkASSERT(fResourceProvider);
            SkASSERT(fPaint);
            SkASSERT(fUserStencilSettings);
            SkASSERT(fDrawContext);
            SkASSERT(fClip);
            SkASSERT(fViewMatrix);
            SkASSERT(fShape);
        }
#endif
    };

    /**
     * Draws the path into the draw target. If getStencilSupport() would return kNoRestriction then
     * the subclass must respect the stencil settings of the GrPipelineBuilder.
     */
    bool drawPath(const DrawPathArgs& args) {
        SkDEBUGCODE(args.validate();)
#ifdef SK_DEBUG
        CanDrawPathArgs canArgs;
        canArgs.fShaderCaps = args.fResourceProvider->caps()->shaderCaps();
        canArgs.fViewMatrix = args.fViewMatrix;
        canArgs.fShape = args.fShape;
        canArgs.fAntiAlias = args.fAntiAlias;

        canArgs.fHasUserStencilSettings = !args.fUserStencilSettings->isUnused();
        canArgs.fIsStencilBufferMSAA = args.fDrawContext->isStencilBufferMultisampled();
        SkASSERT(this->canDrawPath(canArgs));
        if (!args.fUserStencilSettings->isUnused()) {
            SkPath path;
            args.fShape->asPath(&path);
            SkASSERT(args.fShape->style().isSimpleFill());
            SkASSERT(kNoRestriction_StencilSupport == this->getStencilSupport(*args.fShape));
        }
#endif
        return this->onDrawPath(args);
    }

    /* Args to stencilPath().
     *
     * fResourceProvider      The resource provider for creating gpu resources to render the path
     * fDrawContext           The target of the draws
     * fViewMatrix            Matrix applied to the path.
     * fPath                  The path to draw.
     * fIsAA                  Is the path to be drawn AA (only set when MSAA is available)
     */
    struct StencilPathArgs {
        GrResourceProvider* fResourceProvider;
        GrDrawContext*      fDrawContext;
        const GrClip*       fClip;
        const SkMatrix*     fViewMatrix;
        bool                fIsAA;
        const GrShape*      fShape;

#ifdef SK_DEBUG
        void validate() const {
            SkASSERT(fResourceProvider);
            SkASSERT(fDrawContext);
            SkASSERT(fViewMatrix);
            SkASSERT(fShape);
            SkASSERT(fShape->style().isSimpleFill());
            SkPath path;
            fShape->asPath(&path);
            SkASSERT(!path.isInverseFillType());
        }
#endif
    };

    /**
     * Draws the path to the stencil buffer. Assume the writable stencil bits are already
     * initialized to zero. The pixels inside the path will have non-zero stencil values afterwards.
     */
    void stencilPath(const StencilPathArgs& args) {
        SkDEBUGCODE(args.validate();)
        SkASSERT(kNoSupport_StencilSupport != this->getStencilSupport(*args.fShape));
        this->onStencilPath(args);
    }

    // Helper for determining if we can treat a thin stroke as a hairline w/ coverage.
    // If we can, we draw lots faster (raster device does this same test).
    static bool IsStrokeHairlineOrEquivalent(const GrStyle& style, const SkMatrix& matrix,
                                             SkScalar* outCoverage) {
        if (style.pathEffect()) {
            return false;
        }
        const SkStrokeRec& stroke = style.strokeRec();
        if (stroke.isHairlineStyle()) {
            if (outCoverage) {
                *outCoverage = SK_Scalar1;
            }
            return true;
        }
        return stroke.getStyle() == SkStrokeRec::kStroke_Style &&
            SkDrawTreatAAStrokeAsHairline(stroke.getWidth(), matrix, outCoverage);
    }

protected:
    // Helper for getting the device bounds of a path. Inverse filled paths will have bounds set
    // by devSize. Non-inverse path bounds will not necessarily be clipped to devSize.
    static void GetPathDevBounds(const SkPath& path,
                                 int devW,
                                 int devH,
                                 const SkMatrix& matrix,
                                 SkRect* bounds);

private:
    /**
     * Subclass overrides if it has any limitations of stenciling support.
     */
    virtual StencilSupport onGetStencilSupport(const GrShape&) const {
        return kNoRestriction_StencilSupport;
    }

    /**
     * Subclass implementation of drawPath()
     */
    virtual bool onDrawPath(const DrawPathArgs& args) = 0;

    /**
     * Subclass implementation of canDrawPath()
     */
    virtual bool onCanDrawPath(const CanDrawPathArgs& args) const = 0;

    /**
     * Subclass implementation of stencilPath(). Subclass must override iff it ever returns
     * kStencilOnly in onGetStencilSupport().
     */
    virtual void onStencilPath(const StencilPathArgs& args) {
        static constexpr GrUserStencilSettings kIncrementStencil(
            GrUserStencilSettings::StaticInit<
                 0xffff,
                 GrUserStencilTest::kAlways,
                 0xffff,
                 GrUserStencilOp::kReplace,
                 GrUserStencilOp::kReplace,
                 0xffff>()
        );

        GrPaint paint;

        DrawPathArgs drawArgs;
        drawArgs.fResourceProvider = args.fResourceProvider;
        drawArgs.fPaint = &paint;
        drawArgs.fUserStencilSettings = &kIncrementStencil;
        drawArgs.fDrawContext = args.fDrawContext;
        drawArgs.fViewMatrix = args.fViewMatrix;
        drawArgs.fShape = args.fShape;
        drawArgs.fAntiAlias = false;  // In this case the MSAA handles the AA so we want to draw BW
        drawArgs.fGammaCorrect = false;
        this->drawPath(drawArgs);
    }

    typedef SkRefCnt INHERITED;
};

#endif