DXR is a code search and navigation tool aimed at making sense of large projects. It supports full-text and regex searches as well as structural queries.

Header

Mercurial (d8847129d134)

VCS Links

Line Code
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283

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

template <typename T> T pin_unsorted(T value, T limit0, T limit1) {
    if (limit1 < limit0) {
        SkTSwap(limit0, limit1);
    }
    // now the limits are sorted
    SkASSERT(limit0 <= limit1);

    if (value < limit0) {
        value = limit0;
    } else if (value > limit1) {
        value = limit1;
    }
    return value;
}

// return X coordinate of intersection with horizontal line at Y
static SkScalar sect_with_horizontal(const SkPoint src[2], SkScalar Y) {
    SkScalar dy = src[1].fY - src[0].fY;
    if (SkScalarNearlyZero(dy)) {
        return SkScalarAve(src[0].fX, src[1].fX);
    } else {
        // need the extra precision so we don't compute a value that exceeds
        // our original limits
        double X0 = src[0].fX;
        double Y0 = src[0].fY;
        double X1 = src[1].fX;
        double Y1 = src[1].fY;
        double result = X0 + ((double)Y - Y0) * (X1 - X0) / (Y1 - Y0);

        // The computed X value might still exceed [X0..X1] due to quantum flux
        // when the doubles were added and subtracted, so we have to pin the
        // answer :(
        return (float)pin_unsorted(result, X0, X1);
    }
}

// return Y coordinate of intersection with vertical line at X
static SkScalar sect_with_vertical(const SkPoint src[2], SkScalar X) {
    SkScalar dx = src[1].fX - src[0].fX;
    if (SkScalarNearlyZero(dx)) {
        return SkScalarAve(src[0].fY, src[1].fY);
    } else {
        // need the extra precision so we don't compute a value that exceeds
        // our original limits
        double X0 = src[0].fX;
        double Y0 = src[0].fY;
        double X1 = src[1].fX;
        double Y1 = src[1].fY;
        double result = Y0 + ((double)X - X0) * (Y1 - Y0) / (X1 - X0);
        return (float)result;
    }
}

///////////////////////////////////////////////////////////////////////////////

static inline bool nestedLT(SkScalar a, SkScalar b, SkScalar dim) {
    return a <= b && (a < b || dim > 0);
}

// returns true if outer contains inner, even if inner is empty.
// note: outer.contains(inner) always returns false if inner is empty.
static inline bool containsNoEmptyCheck(const SkRect& outer,
                                        const SkRect& inner) {
    return  outer.fLeft <= inner.fLeft && outer.fTop <= inner.fTop &&
            outer.fRight >= inner.fRight && outer.fBottom >= inner.fBottom;
}

bool SkLineClipper::IntersectLine(const SkPoint src[2], const SkRect& clip,
                                  SkPoint dst[2]) {
    SkRect bounds;

    bounds.set(src, 2);
    if (containsNoEmptyCheck(clip, bounds)) {
        if (src != dst) {
            memcpy(dst, src, 2 * sizeof(SkPoint));
        }
        return true;
    }
    // check for no overlap, and only permit coincident edges if the line
    // and the edge are colinear
    if (nestedLT(bounds.fRight, clip.fLeft, bounds.width()) ||
        nestedLT(clip.fRight, bounds.fLeft, bounds.width()) ||
        nestedLT(bounds.fBottom, clip.fTop, bounds.height()) ||
        nestedLT(clip.fBottom, bounds.fTop, bounds.height())) {
        return false;
    }

    int index0, index1;

    if (src[0].fY < src[1].fY) {
        index0 = 0;
        index1 = 1;
    } else {
        index0 = 1;
        index1 = 0;
    }

    SkPoint tmp[2];
    memcpy(tmp, src, sizeof(tmp));

    // now compute Y intersections
    if (tmp[index0].fY < clip.fTop) {
        tmp[index0].set(sect_with_horizontal(src, clip.fTop), clip.fTop);
    }
    if (tmp[index1].fY > clip.fBottom) {
        tmp[index1].set(sect_with_horizontal(src, clip.fBottom), clip.fBottom);
    }

    if (tmp[0].fX < tmp[1].fX) {
        index0 = 0;
        index1 = 1;
    } else {
        index0 = 1;
        index1 = 0;
    }

    // check for quick-reject in X again, now that we may have been chopped
    if ((tmp[index1].fX <= clip.fLeft || tmp[index0].fX >= clip.fRight) &&
        tmp[index0].fX < tmp[index1].fX) {
        // only reject if we have a non-zero width
        return false;
    }

    if (tmp[index0].fX < clip.fLeft) {
        tmp[index0].set(clip.fLeft, sect_with_vertical(src, clip.fLeft));
    }
    if (tmp[index1].fX > clip.fRight) {
        tmp[index1].set(clip.fRight, sect_with_vertical(src, clip.fRight));
    }
#ifdef SK_DEBUG
    bounds.set(tmp, 2);
    SkASSERT(containsNoEmptyCheck(clip, bounds));
#endif
    memcpy(dst, tmp, sizeof(tmp));
    return true;
}

#ifdef SK_DEBUG
// return value between the two limits, where the limits are either ascending
// or descending.
static bool is_between_unsorted(SkScalar value,
                                SkScalar limit0, SkScalar limit1) {
    if (limit0 < limit1) {
        return limit0 <= value && value <= limit1;
    } else {
        return limit1 <= value && value <= limit0;
    }
}
#endif

#ifdef SK_DEBUG
// This is an example of why we need to pin the result computed in
// sect_with_horizontal. If we didn't explicitly pin, is_between_unsorted would
// fail.
//
static void sect_with_horizontal_test_for_pin_results() {
    const SkPoint pts[] = {
        { -540000,    -720000 },
        { -9.10000017e-05f, 9.99999996e-13f }
    };
    float x = sect_with_horizontal(pts, 0);
    SkASSERT(is_between_unsorted(x, pts[0].fX, pts[1].fX));
}
#endif

int SkLineClipper::ClipLine(const SkPoint pts[], const SkRect& clip,
                            SkPoint lines[]) {
#ifdef SK_DEBUG
    {
        static bool gOnce;
        if (!gOnce) {
            sect_with_horizontal_test_for_pin_results();
            gOnce = true;
        }
    }
#endif

    int index0, index1;

    if (pts[0].fY < pts[1].fY) {
        index0 = 0;
        index1 = 1;
    } else {
        index0 = 1;
        index1 = 0;
    }

    // Check if we're completely clipped out in Y (above or below

    if (pts[index1].fY <= clip.fTop) {  // we're above the clip
        return 0;
    }
    if (pts[index0].fY >= clip.fBottom) {  // we're below the clip
        return 0;
    }

    // Chop in Y to produce a single segment, stored in tmp[0..1]

    SkPoint tmp[2];
    memcpy(tmp, pts, sizeof(tmp));

    // now compute intersections
    if (pts[index0].fY < clip.fTop) {
        tmp[index0].set(sect_with_horizontal(pts, clip.fTop), clip.fTop);
        SkASSERT(is_between_unsorted(tmp[index0].fX, pts[0].fX, pts[1].fX));
    }
    if (tmp[index1].fY > clip.fBottom) {
        tmp[index1].set(sect_with_horizontal(pts, clip.fBottom), clip.fBottom);
        SkASSERT(is_between_unsorted(tmp[index1].fX, pts[0].fX, pts[1].fX));
    }

    // Chop it into 1..3 segments that are wholly within the clip in X.

    // temp storage for up to 3 segments
    SkPoint resultStorage[kMaxPoints];
    SkPoint* result;    // points to our results, either tmp or resultStorage
    int lineCount = 1;
    bool reverse;

    if (pts[0].fX < pts[1].fX) {
        index0 = 0;
        index1 = 1;
        reverse = false;
    } else {
        index0 = 1;
        index1 = 0;
        reverse = true;
    }

    if (tmp[index1].fX <= clip.fLeft) {  // wholly to the left
        tmp[0].fX = tmp[1].fX = clip.fLeft;
        result = tmp;
        reverse = false;
    } else if (tmp[index0].fX >= clip.fRight) {    // wholly to the right
        tmp[0].fX = tmp[1].fX = clip.fRight;
        result = tmp;
        reverse = false;
    } else {
        result = resultStorage;
        SkPoint* r = result;

        if (tmp[index0].fX < clip.fLeft) {
            r->set(clip.fLeft, tmp[index0].fY);
            r += 1;
            r->set(clip.fLeft, sect_with_vertical(tmp, clip.fLeft));
            SkASSERT(is_between_unsorted(r->fY, tmp[0].fY, tmp[1].fY));
        } else {
            *r = tmp[index0];
        }
        r += 1;

        if (tmp[index1].fX > clip.fRight) {
            r->set(clip.fRight, sect_with_vertical(tmp, clip.fRight));
            SkASSERT(is_between_unsorted(r->fY, tmp[0].fY, tmp[1].fY));
            r += 1;
            r->set(clip.fRight, tmp[index1].fY);
        } else {
            *r = tmp[index1];
        }

        lineCount = SkToInt(r - result);
    }

    // Now copy the results into the caller's lines[] parameter
    if (reverse) {
        // copy the pts in reverse order to maintain winding order
        for (int i = 0; i <= lineCount; i++) {
            lines[lineCount - i] = result[i];
        }
    } else {
        memcpy(lines, result, (lineCount + 1) * sizeof(SkPoint));
    }
    return lineCount;
}