SkAnalyticEdge.h

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/*
 * Copyright 2006 The Android Open Source Project
 *
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */
 
#ifndef SkAnalyticEdge_DEFINED
#define SkAnalyticEdge_DEFINED
 
#include "include/private/base/SkAssert.h"
#include "include/private/base/SkDebug.h"
#include "include/private/base/SkFixed.h"
#include "include/private/base/SkSafe32.h"
#include "src/core/SkEdge.h"
 
#include <cstdint>
 
struct SkPoint;
 
struct SkAnalyticEdge {
    // Similar to SkEdge, the conic edges will be converted to quadratic edges
    enum Type {
        kLine_Type,
        kQuad_Type,
        kCubic_Type
    };
 
    SkAnalyticEdge* fNext;
    SkAnalyticEdge* fPrev;
 
    SkFixed fX;
    SkFixed fDX;
    SkFixed fUpperX;        // The x value when y = fUpperY
    SkFixed fY;             // The current y
    SkFixed fUpperY;        // The upper bound of y (our edge is from y = fUpperY to y = fLowerY)
    SkFixed fLowerY;        // The lower bound of y (our edge is from y = fUpperY to y = fLowerY)
    SkFixed fDY;            // abs(1/fDX); may be SK_MaxS32 when fDX is close to 0.
                            // fDY is only used for blitting trapezoids.
 
    Type    fEdgeType;      // Remembers the *initial* edge type
 
    int8_t  fCurveCount;    // only used by kQuad(+) and kCubic(-)
    uint8_t fCurveShift;    // appled to all Dx/DDx/DDDx except for fCubicDShift exception
    uint8_t fCubicDShift;   // applied to fCDx and fCDy only in cubic
    int8_t  fWinding;       // 1 or -1
 
    static const int kDefaultAccuracy = 2; // default accuracy for snapping
 
    static inline SkFixed SnapY(SkFixed y) {
        const int accuracy = kDefaultAccuracy;
        // This approach is safer than left shift, round, then right shift
        return ((unsigned)y + (SK_Fixed1 >> (accuracy + 1))) >> (16 - accuracy) << (16 - accuracy);
    }
 
    // Update fX, fY of this edge so fY = y
    inline void goY(SkFixed y) {
        if (y == fY + SK_Fixed1) {
            fX = fX + fDX;
            fY = y;
        } else if (y != fY) {
            // Drop lower digits as our alpha only has 8 bits
            // (fDX and y - fUpperY may be greater than SK_Fixed1)
            fX = fUpperX + SkFixedMul(fDX, y - fUpperY);
            fY = y;
        }
    }
 
    inline void goY(SkFixed y, int yShift) {
        SkASSERT(yShift >= 0 && yShift <= kDefaultAccuracy);
        SkASSERT(fDX == 0 || y - fY == SK_Fixed1 >> yShift);
        fY = y;
        fX += fDX >> yShift;
    }
 
    bool setLine(const SkPoint& p0, const SkPoint& p1);
    bool updateLine(SkFixed ax, SkFixed ay, SkFixed bx, SkFixed by, SkFixed slope);
 
    // return true if we're NOT done with this edge
    bool update(SkFixed last_y, bool sortY = true);
 
#ifdef SK_DEBUG
    void dump() const {
        SkDebugf("edge: upperY:%d lowerY:%d y:%g x:%g dx:%g w:%d\n",
                 fUpperY, fLowerY, SkFixedToFloat(fY), SkFixedToFloat(fX),
                 SkFixedToFloat(fDX), fWinding);
    }
 
    void validate() const {
         SkASSERT(fPrev && fNext);
         SkASSERT(fPrev->fNext == this);
         SkASSERT(fNext->fPrev == this);
 
         SkASSERT(fUpperY < fLowerY);
         SkASSERT(SkAbs32(fWinding) == 1);
    }
#endif
};
 
struct SkAnalyticQuadraticEdge : public SkAnalyticEdge {
    SkQuadraticEdge fQEdge;
 
    // snap y to integer points in the middle of the curve to accelerate AAA path filling
    SkFixed fSnappedX, fSnappedY;
 
    bool setQuadratic(const SkPoint pts[3]);
    bool updateQuadratic();
    inline void keepContinuous() {
        // We use fX as the starting x to ensure the continuouty.
        // Without it, we may break the sorted edge list.
        SkASSERT(SkAbs32(fX - SkFixedMul(fY - fSnappedY, fDX) - fSnappedX) < SK_Fixed1);
        SkASSERT(SkAbs32(fY - fSnappedY) < SK_Fixed1); // This may differ due to smooth jump
        fSnappedX = fX;
        fSnappedY = fY;
    }
};
 
struct SkAnalyticCubicEdge : public SkAnalyticEdge {
    SkCubicEdge fCEdge;
 
    SkFixed fSnappedY; // to make sure that y is increasing with smooth jump and snapping
 
    bool setCubic(const SkPoint pts[4], bool sortY = true);
    bool updateCubic(bool sortY = true);
    inline void keepContinuous() {
        SkASSERT(SkAbs32(fX - SkFixedMul(fDX, fY - SnapY(fCEdge.fCy)) - fCEdge.fCx) < SK_Fixed1);
        fCEdge.fCx = fX;
        fSnappedY = fY;
    }
};
 
#endif