src/gpu/GrShape.h

/*
 * Copyright 2016 Google Inc.
 *
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */

#ifndef GrShape_DEFINED
#define GrShape_DEFINED

#include "GrStyle.h"
#include "SkPath.h"
#include "SkRRect.h"
#include "SkTemplates.h"
#include "SkTLazy.h"

/**
 * Represents a geometric shape (rrect or path) and the GrStyle that it should be rendered with.
 * It is possible to apply the style to the GrShape to produce a new GrShape where the geometry
 * reflects the styling information (e.g. is stroked). It is also possible to apply just the
 * path effect from the style. In this case the resulting shape will include any remaining
 * stroking information that is to be applied after the path effect.
 *
 * Shapes can produce keys that represent only the geometry information, not the style. Note that
 * when styling information is applied to produce a new shape then the style has been converted
 * to geometric information and is included in the new shape's key. When the same style is applied
 * to two shapes that reflect the same underlying geometry the computed keys of the stylized shapes
 * will be the same.
 *
 * Currently this can only be constructed from a rrect, though it can become a path by applying
 * style to the geometry. The idea is to expand this to cover most or all of the geometries that
 * have SkCanvas::draw APIs.
 */
class GrShape {
public:
    GrShape() : fType(Type::kEmpty) {}

    explicit GrShape(const SkPath& path)
            : fType(Type::kPath)
            , fPath(&path) {
        this->attemptToReduceFromPath();
    }

    explicit GrShape(const SkRRect& rrect)
        : fType(Type::kRRect)
        , fRRect(rrect) {
        this->attemptToReduceFromRRect();
    }

    explicit GrShape(const SkRect& rect)
        : fType(Type::kRRect)
        , fRRect(SkRRect::MakeRect(rect)) {
        this->attemptToReduceFromRRect();
    }

    GrShape(const SkPath& path, const GrStyle& style)
        : fType(Type::kPath)
        , fPath(&path)
        , fStyle(style) {
        this->attemptToReduceFromPath();
    }

    GrShape(const SkRRect& rrect, const GrStyle& style)
        : fType(Type::kRRect)
        , fRRect(rrect)
        , fStyle(style) {
        this->attemptToReduceFromRRect();
    }

    GrShape(const SkRect& rect, const GrStyle& style)
        : fType(Type::kRRect)
        , fRRect(SkRRect::MakeRect(rect))
        , fStyle(style) {
        this->attemptToReduceFromRRect();
    }

    GrShape(const SkPath& path, const SkPaint& paint)
        : fType(Type::kPath)
        , fPath(&path)
        , fStyle(paint) {
        this->attemptToReduceFromPath();
    }

    GrShape(const SkRRect& rrect, const SkPaint& paint)
        : fType(Type::kRRect)
        , fRRect(rrect)
        , fStyle(paint) {
        this->attemptToReduceFromRRect();
    }

    GrShape(const SkRect& rect, const SkPaint& paint)
        : fType(Type::kRRect)
        , fRRect(SkRRect::MakeRect(rect))
        , fStyle(paint) {
        this->attemptToReduceFromRRect();
    }

    GrShape(const GrShape&);
    GrShape& operator=(const GrShape& that);

    ~GrShape() {
        if (Type::kPath == fType) {
            fPath.reset();
        }
    }

    const GrStyle& style() const { return fStyle; }

    /**
     * Returns a GrShape where the shape's geometry fully reflects the original shape's GrStyle.
     * The GrStyle of the returned shape will either be fill or hairline.
     */
    GrShape applyFullStyle() { return GrShape(*this, false); }

    /**
     * Similar to above but applies only the path effect. Path effects take the original geometry
     * and fill/stroking information and compute a new geometry and residual fill/stroking
     * information to be applied. The path effect's output geometry and stroking will be captured
     * in the returned GrShape.
     */
    GrShape applyPathEffect() { return GrShape(*this, true); }

    bool asRRect(SkRRect* rrect) const {
        if (Type::kRRect != fType) {
            return false;
        }
        if (rrect) {
            *rrect = fRRect;
        }
        return true;
    }

    void asPath(SkPath* out) const {
        switch (fType) {
            case Type::kRRect:
                out->reset();
                out->addRRect(fRRect);
                break;
            case Type::kPath:
                *out = *fPath.get();
                break;
            case Type::kEmpty:
                out->reset();
                break;
        }
    }

    /**
     * Gets the size of the key for the shape represented by this GrShape (ignoring its styling).
     * A negative value is returned if the shape has no key (shouldn't be cached).
     */
    int unstyledKeySize() const;

    /**
     * Writes unstyledKeySize() bytes into the provided pointer. Assumes that there is enough
     * space allocated for the key and that unstyledKeySize() does not return a negative value
     * for this shape.
     */
    void writeUnstyledKey(uint32_t* key) const;

private:
    enum class Type {
        kEmpty,
        kRRect,
        kPath,
    };

    /**
     * Computes the key length for a GrStyle. The return will be negative if it cannot be turned
     * into a key.
     */
    static int StyleKeySize(const GrStyle& , bool stopAfterPE);

    /**
     * Writes a unique key for the style into the provided buffer. This function assumes the buffer
     * has room for at least StyleKeySize() values. It assumes that StyleKeySize() returns a
     * positive value for the style and stopAfterPE param. This is written so that the key for just
     * dash application followed by the key for the remaining SkStrokeRec is the same as the
     * key for applying dashing and SkStrokeRec all at once.
     */
    static void StyleKey(uint32_t*, const GrStyle&, bool stopAfterPE);

    /** Constructor used by Apply* functions */
    GrShape(const GrShape& parentShape, bool stopAfterPE);

    /**
     * Determines the key we should inherit from the input shape's geometry and style when
     * we are applying the style to create a new shape.
     */
    void setInheritedKey(const GrShape& parentShape, bool stopAfterPE);

    void attemptToReduceFromPath() {
        SkASSERT(Type::kPath == fType);
        fType = AttemptToReduceFromPathImpl(*fPath.get(), &fRRect, fStyle.pathEffect(),
                                            fStyle.strokeRec());
        if (Type::kPath != fType) {
            fPath.reset();
            fInheritedKey.reset(0);
        }
    }

    void attemptToReduceFromRRect() {
        SkASSERT(Type::kRRect == fType);
        SkASSERT(!fInheritedKey.count());
        if (fRRect.isEmpty()) {
            fType = Type::kEmpty;
        }
    }

    static Type AttemptToReduceFromPathImpl(const SkPath& path, SkRRect* rrect,
                                            const SkPathEffect* pe, const SkStrokeRec& strokeRec) {
        if (path.isEmpty()) {
            return Type::kEmpty;
        }
        if (path.isRRect(rrect)) {
            SkASSERT(!rrect->isEmpty());
            return Type::kRRect;
        }
        SkRect rect;
        if (path.isOval(&rect)) {
            rrect->setOval(rect);
            return Type::kRRect;
        }
        bool closed;
        if (path.isRect(&rect, &closed, nullptr)) {
            if (closed || (!pe && strokeRec.isFillStyle())) {
                rrect->setRect(rect);
                return Type::kRRect;
            }
        }
        return Type::kPath;
    }

    Type                        fType;
    SkRRect                     fRRect;
    SkTLazy<SkPath>             fPath;
    GrStyle                     fStyle;
    SkAutoSTArray<8, uint32_t>  fInheritedKey;
};
#endif