gpu/src/GrPathUtils.cpp

/*
    Copyright 2011 Google Inc.

    Licensed under the Apache License, Version 2.0 (the "License");
    you may not use this file except in compliance with the License.
    You may obtain a copy of the License at

         http://www.apache.org/licenses/LICENSE-2.0

    Unless required by applicable law or agreed to in writing, software
    distributed under the License is distributed on an "AS IS" BASIS,
    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    See the License for the specific language governing permissions and
    limitations under the License.
 */

#include "GrPathUtils.h"
#include "GrPoint.h"

static const int MAX_POINTS_PER_CURVE = 1 << 10;
const GrScalar GrPathUtils::gMinCurveTol (GrFloatToScalar(0.0001f));

uint32_t GrPathUtils::quadraticPointCount(const GrPoint points[],
                                          GrScalar tol) {
    if (tol < gMinCurveTol) {
        tol = gMinCurveTol;
    }
    GrAssert(tol > 0);

    GrScalar d = points[1].distanceToLineSegmentBetween(points[0], points[2]);
    if (d <= tol) {
        return 1;
    } else {
        // Each time we subdivide, d should be cut in 4. So we need to
        // subdivide x = log4(d/tol) times. x subdivisions creates 2^(x)
        // points.
        // 2^(log4(x)) = sqrt(x);
        int temp = SkScalarCeil(SkScalarSqrt(SkScalarDiv(d, tol)));
        int pow2 = GrNextPow2(temp);
        // Because of NaNs & INFs we can wind up with a degenerate temp
        // such that pow2 comes out negative. Also, our point generator
        // will always output at least one pt.
        if (pow2 < 1) {
            pow2 = 1;
        }
        return GrMin(pow2, MAX_POINTS_PER_CURVE);
    }
}

uint32_t GrPathUtils::generateQuadraticPoints(const GrPoint& p0,
                                              const GrPoint& p1,
                                              const GrPoint& p2,
                                              GrScalar tolSqd,
                                              GrPoint** points,
                                              uint32_t pointsLeft) {
    if (pointsLeft < 2 ||
        (p1.distanceToLineSegmentBetweenSqd(p0, p2)) < tolSqd) {
        (*points)[0] = p2;
        *points += 1;
        return 1;
    }

    GrPoint q[] = {
        { GrScalarAve(p0.fX, p1.fX), GrScalarAve(p0.fY, p1.fY) },
        { GrScalarAve(p1.fX, p2.fX), GrScalarAve(p1.fY, p2.fY) },
    };
    GrPoint r = { GrScalarAve(q[0].fX, q[1].fX), GrScalarAve(q[0].fY, q[1].fY) };

    pointsLeft >>= 1;
    uint32_t a = generateQuadraticPoints(p0, q[0], r, tolSqd, points, pointsLeft);
    uint32_t b = generateQuadraticPoints(r, q[1], p2, tolSqd, points, pointsLeft);
    return a + b;
}

uint32_t GrPathUtils::cubicPointCount(const GrPoint points[],
                                           GrScalar tol) {
    if (tol < gMinCurveTol) {
        tol = gMinCurveTol;
    }
    GrAssert(tol > 0);

    GrScalar d = GrMax(
        points[1].distanceToLineSegmentBetweenSqd(points[0], points[3]),
        points[2].distanceToLineSegmentBetweenSqd(points[0], points[3]));
    d = SkScalarSqrt(d);
    if (d <= tol) {
        return 1;
    } else {
        int temp = SkScalarCeil(SkScalarSqrt(SkScalarDiv(d, tol)));
        int pow2 = GrNextPow2(temp);
        // Because of NaNs & INFs we can wind up with a degenerate temp
        // such that pow2 comes out negative. Also, our point generator
        // will always output at least one pt.
        if (pow2 < 1) {
            pow2 = 1;
        }
        return GrMin(pow2, MAX_POINTS_PER_CURVE);
    }
}

uint32_t GrPathUtils::generateCubicPoints(const GrPoint& p0,
                                          const GrPoint& p1,
                                          const GrPoint& p2,
                                          const GrPoint& p3,
                                          GrScalar tolSqd,
                                          GrPoint** points,
                                          uint32_t pointsLeft) {
    if (pointsLeft < 2 ||
        (p1.distanceToLineSegmentBetweenSqd(p0, p3) < tolSqd &&
         p2.distanceToLineSegmentBetweenSqd(p0, p3) < tolSqd)) {
            (*points)[0] = p3;
            *points += 1;
            return 1;
        }
    GrPoint q[] = {
        { GrScalarAve(p0.fX, p1.fX), GrScalarAve(p0.fY, p1.fY) },
        { GrScalarAve(p1.fX, p2.fX), GrScalarAve(p1.fY, p2.fY) },
        { GrScalarAve(p2.fX, p3.fX), GrScalarAve(p2.fY, p3.fY) }
    };
    GrPoint r[] = {
        { GrScalarAve(q[0].fX, q[1].fX), GrScalarAve(q[0].fY, q[1].fY) },
        { GrScalarAve(q[1].fX, q[2].fX), GrScalarAve(q[1].fY, q[2].fY) }
    };
    GrPoint s = { GrScalarAve(r[0].fX, r[1].fX), GrScalarAve(r[0].fY, r[1].fY) };
    pointsLeft >>= 1;
    uint32_t a = generateCubicPoints(p0, q[0], r[0], s, tolSqd, points, pointsLeft);
    uint32_t b = generateCubicPoints(s, r[1], q[2], p3, tolSqd, points, pointsLeft);
    return a + b;
}

int GrPathUtils::worstCasePointCount(const GrPath& path, int* subpaths,
                                     GrScalar tol) {
    if (tol < gMinCurveTol) {
        tol = gMinCurveTol;
    }
    GrAssert(tol > 0);

    int pointCount = 0;
    *subpaths = 1;

    bool first = true;

    SkPath::Iter iter(path, false);
    GrPathCmd cmd;

    GrPoint pts[4];
    while ((cmd = (GrPathCmd)iter.next(pts)) != kEnd_PathCmd) {

        switch (cmd) {
            case kLine_PathCmd:
                pointCount += 1;
                break;
            case kQuadratic_PathCmd:
                pointCount += quadraticPointCount(pts, tol);
                break;
            case kCubic_PathCmd:
                pointCount += cubicPointCount(pts, tol);
                break;
            case kMove_PathCmd:
                pointCount += 1;
                if (!first) {
                    ++(*subpaths);
                }
                break;
            default:
                break;
        }
        first = false;
    }
    return pointCount;
}