skparagraph/src/TextWrapper.cpp

// Copyright 2019 Google LLC.
#include "modules/skparagraph/src/ParagraphImpl.h"
#include "modules/skparagraph/src/TextWrapper.h"

namespace skia {
namespace textlayout {

namespace {
struct LineBreakerWithLittleRounding {
    LineBreakerWithLittleRounding(SkScalar maxWidth)
        : fLower(maxWidth - 0.25f)
        , fMaxWidth(maxWidth)
        , fUpper(maxWidth + 0.25f) {}

    bool breakLine(SkScalar width) const {
        if (width < fLower) {
            return false;
        } else if (width > fUpper) {
            return true;
        }

        auto val = std::fabs(width);
        SkScalar roundedWidth;
        if (val < 10000) {
            roundedWidth = SkScalarRoundToScalar(width * 100) * (1.0f/100);
        } else if (val < 100000) {
            roundedWidth = SkScalarRoundToScalar(width *  10) * (1.0f/10);
        } else {
            roundedWidth = SkScalarFloorToScalar(width);
        }
        return roundedWidth > fMaxWidth;
    }

    const SkScalar fLower, fMaxWidth, fUpper;
};
}  // namespace

// Since we allow cluster clipping when they don't fit
// we have to work with stretches - parts of clusters
void TextWrapper::lookAhead(SkScalar maxWidth, Cluster* endOfClusters) {

    reset();
    fEndLine.metrics().clean();
    fWords.startFrom(fEndLine.startCluster(), fEndLine.startPos());
    fClusters.startFrom(fEndLine.startCluster(), fEndLine.startPos());
    fClip.startFrom(fEndLine.startCluster(), fEndLine.startPos());

    LineBreakerWithLittleRounding breaker(maxWidth);
    Cluster* nextNonBreakingSpace = nullptr;
    for (auto cluster = fEndLine.endCluster(); cluster < endOfClusters; ++cluster) {
        if (cluster->isHardBreak()) {
        } else if (
                // TODO: Trying to deal with flutter rounding problem. Must be removed...
                SkScalar width = fWords.width() + fClusters.width() + cluster->width();
                breaker.breakLine(width)) {
            if (cluster->isWhitespaceBreak()) {
                // It's the end of the word
                fClusters.extend(cluster);
                fMinIntrinsicWidth = std::max(fMinIntrinsicWidth, getClustersTrimmedWidth());
                fWords.extend(fClusters);
                continue;
            } else if (cluster->run().isPlaceholder()) {
                if (!fClusters.empty()) {
                    // Placeholder ends the previous word
                    fMinIntrinsicWidth = std::max(fMinIntrinsicWidth, getClustersTrimmedWidth());
                    fWords.extend(fClusters);
                }

                if (cluster->width() > maxWidth && fWords.empty()) {
                    // Placeholder is the only text and it's longer than the line;
                    // it does not count in fMinIntrinsicWidth
                    fClusters.extend(cluster);
                    fTooLongCluster = true;
                    fTooLongWord = true;
                } else {
                    // Placeholder does not fit the line; it will be considered again on the next line
                }
                break;
            }

            // Walk further to see if there is a too long word, cluster or glyph
            SkScalar nextWordLength = fClusters.width();
            SkScalar nextShortWordLength = nextWordLength;
            for (auto further = cluster; further != endOfClusters; ++further) {
                if (further->isSoftBreak() || further->isHardBreak() || further->isWhitespaceBreak()) {
                    break;
                }
                if (further->run().isPlaceholder()) {
                  // Placeholder ends the word
                  break;
                }

                if (nextWordLength > 0 && nextWordLength <= maxWidth && further->isIntraWordBreak()) {
                    // The cluster is spaces but not the end of the word in a normal sense
                    nextNonBreakingSpace = further;
                    nextShortWordLength = nextWordLength;
                }

                if (maxWidth == 0) {
                    // This is a tricky flutter case: layout(width:0) places 1 cluster on each line
                    nextWordLength = std::max(nextWordLength, further->width());
                } else {
                    nextWordLength += further->width();
                }
            }
            if (nextWordLength > maxWidth) {
                if (nextNonBreakingSpace != nullptr) {
                    // We only get here if the non-breaking space improves our situation
                    // (allows us to break the text to fit the word)
                    if (SkScalar shortLength = fWords.width() + nextShortWordLength;
                        !breaker.breakLine(shortLength)) {
                        // We can add the short word to the existing line
                        fClusters = TextStretch(fClusters.startCluster(), nextNonBreakingSpace, fClusters.metrics().getForceStrut());
                        fMinIntrinsicWidth = std::max(fMinIntrinsicWidth, nextShortWordLength);
                        fWords.extend(fClusters);
                    } else {
                        // We can place the short word on the next line
                        fClusters.clean();
                    }
                    // Either way we are not in "word is too long" situation anymore
                    break;
                }
                // If the word is too long we can break it right now and hope it's enough
                fMinIntrinsicWidth = std::max(fMinIntrinsicWidth, nextWordLength);
                if (fClusters.endPos() - fClusters.startPos() > 1 ||
                    fWords.empty()) {
                    fTooLongWord = true;
                } else {
                    // Even if the word is too long there is a very little space on this line.
                    // let's deal with it on the next line.
                }
            }

            if (cluster->width() > maxWidth) {
                fClusters.extend(cluster);
                fTooLongCluster = true;
                fTooLongWord = true;
            }
            break;
        }

        if (cluster->run().isPlaceholder()) {
            if (!fClusters.empty()) {
                // Placeholder ends the previous word (placeholders are ignored in trimming)
                fMinIntrinsicWidth = std::max(fMinIntrinsicWidth, getClustersTrimmedWidth());
                fWords.extend(fClusters);
            }

            // Placeholder is separate word and its width now is counted in minIntrinsicWidth
            fMinIntrinsicWidth = std::max(fMinIntrinsicWidth, cluster->width());
            fWords.extend(cluster);
        } else {
            fClusters.extend(cluster);

            // Keep adding clusters/words
            if (fClusters.endOfWord()) {
                fMinIntrinsicWidth = std::max(fMinIntrinsicWidth, getClustersTrimmedWidth());
                fWords.extend(fClusters);
            }
        }

        if ((fHardLineBreak = cluster->isHardBreak())) {
            // Stop at the hard line break
            break;
        }
    }
}

void TextWrapper::moveForward(bool hasEllipsis) {

    // We normally break lines by words.
    // The only way we may go to clusters is if the word is too long or
    // it's the first word and it has an ellipsis attached to it.
    // If nothing fits we show the clipping.
    if (!fWords.empty()) {
        fEndLine.extend(fWords);
        if (!fTooLongWord || hasEllipsis) {
            return;
        }
    }
    if (!fClusters.empty()) {
        fEndLine.extend(fClusters);
        if (!fTooLongCluster) {
            return;
        }
    }

    if (!fClip.empty()) {
        // Flutter: forget the clipped cluster but keep the metrics
        fEndLine.metrics().add(fClip.metrics());
    }
}

// Special case for start/end cluster since they can be clipped
void TextWrapper::trimEndSpaces(TextAlign align) {
    // Remember the breaking position
    fEndLine.saveBreak();
    // Skip all space cluster at the end
    for (auto cluster = fEndLine.endCluster();
         cluster >= fEndLine.startCluster() && cluster->isWhitespaceBreak();
         --cluster) {
        fEndLine.trim(cluster);
    }
    fEndLine.trim();
}

SkScalar TextWrapper::getClustersTrimmedWidth() {
    // Move the end of the line to the left
    SkScalar width = 0;
    bool trailingSpaces = true;
    for (auto cluster = fClusters.endCluster(); cluster >= fClusters.startCluster(); --cluster) {
        if (cluster->run().isPlaceholder()) {
            continue;
        }
        if (trailingSpaces) {
            if (!cluster->isWhitespaceBreak()) {
                width += cluster->trimmedWidth(cluster->endPos());
                trailingSpaces = false;
            }
            continue;
        }
        width += cluster->width();
    }
    return width;
}

// Trim the beginning spaces in case of soft line break
std::tuple<Cluster*, size_t, SkScalar> TextWrapper::trimStartSpaces(Cluster* endOfClusters) {

    if (fHardLineBreak) {
        // End of line is always end of cluster, but need to skip \n
        auto width = fEndLine.width();
        auto cluster = fEndLine.endCluster() + 1;
        while (cluster < fEndLine.breakCluster() && cluster->isWhitespaceBreak())  {
            width += cluster->width();
            ++cluster;
        }
        return std::make_tuple(fEndLine.breakCluster() + 1, 0, width);
    }

    // breakCluster points to the end of the line;
    // It's a soft line break so we need to move lineStart forward skipping all the spaces
    auto width = fEndLine.widthWithGhostSpaces();
    auto cluster = fEndLine.breakCluster() + 1;
    while (cluster < endOfClusters && cluster->isWhitespaceBreak()) {
        width += cluster->width();
        ++cluster;
    }

    if (fEndLine.breakCluster()->isWhitespaceBreak() && fEndLine.breakCluster() < endOfClusters) {
        // In case of a soft line break by the whitespace
        // fBreak should point to the beginning of the next line
        // (it only matters when there are trailing spaces)
        fEndLine.shiftBreak();
    }

    return std::make_tuple(cluster, 0, width);
}

// TODO: refactor the code for line ending (with/without ellipsis)
void TextWrapper::breakTextIntoLines(ParagraphImpl* parent,
                                     SkScalar maxWidth,
                                     const AddLineToParagraph& addLine) {
    fHeight = 0;
    fMinIntrinsicWidth = std::numeric_limits<SkScalar>::min();
    fMaxIntrinsicWidth = std::numeric_limits<SkScalar>::min();

    auto span = parent->clusters();
    if (span.size() == 0) {
        return;
    }
    auto maxLines = parent->paragraphStyle().getMaxLines();
    auto align = parent->paragraphStyle().effective_align();
    auto unlimitedLines = maxLines == std::numeric_limits<size_t>::max();
    auto endlessLine = !SkScalarIsFinite(maxWidth);
    auto hasEllipsis = parent->paragraphStyle().ellipsized();

    auto disableFirstAscent = parent->paragraphStyle().getTextHeightBehavior() & TextHeightBehavior::kDisableFirstAscent;
    auto disableLastDescent = parent->paragraphStyle().getTextHeightBehavior() & TextHeightBehavior::kDisableLastDescent;
    bool firstLine = true; // We only interested in fist line if we have to disable the first ascent

    SkScalar softLineMaxIntrinsicWidth = 0;
    fEndLine = TextStretch(span.begin(), span.begin(), parent->strutForceHeight());
    auto end = span.end() - 1;
    auto start = span.begin();
    InternalLineMetrics maxRunMetrics;
    bool needEllipsis = false;
    while (fEndLine.endCluster() != end) {

        lookAhead(maxWidth, end);

        auto lastLine = (hasEllipsis && unlimitedLines) || fLineNumber >= maxLines;
        needEllipsis = hasEllipsis && !endlessLine && lastLine;

        moveForward(needEllipsis);
        needEllipsis &= fEndLine.endCluster() < end - 1; // Only if we have some text to ellipsize

        // Do not trim end spaces on the naturally last line of the left aligned text
        trimEndSpaces(align);

        // For soft line breaks add to the line all the spaces next to it
        Cluster* startLine;
        size_t pos;
        SkScalar widthWithSpaces;
        std::tie(startLine, pos, widthWithSpaces) = trimStartSpaces(end);

        if (needEllipsis && !fHardLineBreak) {
            // This is what we need to do to preserve a space before the ellipsis
            fEndLine.restoreBreak();
            widthWithSpaces = fEndLine.widthWithGhostSpaces();
        }

        // If the line is empty with the hard line break, let's take the paragraph font (flutter???)
        if (fHardLineBreak && fEndLine.width() == 0) {
            fEndLine.setMetrics(parent->getEmptyMetrics());
        }

        // Deal with placeholder clusters == runs[@size==1]
        Run* lastRun = nullptr;
        for (auto cluster = fEndLine.startCluster(); cluster <= fEndLine.endCluster(); ++cluster) {
            auto r = cluster->runOrNull();
            if (r == lastRun) {
                continue;
            }
            lastRun = r;
            if (lastRun->placeholderStyle() != nullptr) {
                SkASSERT(lastRun->size() == 1);
                // Update the placeholder metrics so we can get the placeholder positions later
                // and the line metrics (to make sure the placeholder fits)
                lastRun->updateMetrics(&fEndLine.metrics());
            }
        }

        // Before we update the line metrics with struts,
        // let's save it for GetRectsForRange(RectHeightStyle::kMax)
        maxRunMetrics = fEndLine.metrics();
        maxRunMetrics.fForceStrut = false;

        if (parent->strutEnabled()) {
            // Make sure font metrics are not less than the strut
            parent->strutMetrics().updateLineMetrics(fEndLine.metrics());
        }

        // TODO: keep start/end/break info for text and runs but in a better way that below
        TextRange textExcludingSpaces(fEndLine.startCluster()->textRange().start, fEndLine.endCluster()->textRange().end);
        TextRange text(fEndLine.startCluster()->textRange().start, fEndLine.breakCluster()->textRange().start);
        TextRange textIncludingNewlines(fEndLine.startCluster()->textRange().start, startLine->textRange().start);
        if (startLine == end) {
            textIncludingNewlines.end = parent->text().size();
            text.end = parent->text().size();
        }
        ClusterRange clusters(fEndLine.startCluster() - start, fEndLine.endCluster() - start + 1);
        ClusterRange clustersWithGhosts(fEndLine.startCluster() - start, startLine - start);

        if (disableFirstAscent && firstLine) {
            fEndLine.metrics().fAscent = fEndLine.metrics().fRawAscent;
        }
        if (disableLastDescent && (lastLine || (startLine == end && !fHardLineBreak ))) {
            fEndLine.metrics().fDescent = fEndLine.metrics().fRawDescent;
        }

        SkScalar lineHeight = fEndLine.metrics().height();
        firstLine = false;

        if (fEndLine.empty()) {
            // Correct text and clusters (make it empty for an empty line)
            textExcludingSpaces.end = textExcludingSpaces.start;
            clusters.end = clusters.start;
        }

        // In case of a force wrapping we don't have a break cluster and have to use the end cluster
        text.end = std::max(text.end, textExcludingSpaces.end);

        addLine(textExcludingSpaces,
                text,
                textIncludingNewlines, clusters, clustersWithGhosts, widthWithSpaces,
                fEndLine.startPos(),
                fEndLine.endPos(),
                SkVector::Make(0, fHeight),
                SkVector::Make(fEndLine.width(), lineHeight),
                fEndLine.metrics(),
                needEllipsis && !fHardLineBreak);

        softLineMaxIntrinsicWidth += widthWithSpaces;

        fMaxIntrinsicWidth = std::max(fMaxIntrinsicWidth, softLineMaxIntrinsicWidth);
        if (fHardLineBreak) {
            softLineMaxIntrinsicWidth = 0;
        }
        // Start a new line
        fHeight += lineHeight;
        if (!fHardLineBreak || startLine != end) {
            fEndLine.clean();
        }
        fEndLine.startFrom(startLine, pos);
        parent->fMaxWidthWithTrailingSpaces = std::max(parent->fMaxWidthWithTrailingSpaces, widthWithSpaces);

        if (hasEllipsis && unlimitedLines) {
            // There is one case when we need an ellipsis on a separate line
            // after a line break when width is infinite
            if (!fHardLineBreak) {
                break;
            }
        } else if (lastLine) {
            // There is nothing more to draw
            fHardLineBreak = false;
            break;
        }

        ++fLineNumber;
    }

    // We finished formatting the text but we need to scan the rest for some numbers
    // TODO: make it a case of a normal flow
    if (fEndLine.endCluster() != nullptr) {
        auto lastWordLength = 0.0f;
        auto cluster = fEndLine.endCluster();
        while (cluster != end || cluster->endPos() < end->endPos()) {
            fExceededMaxLines = true;
            if (cluster->isHardBreak()) {
                // Hard line break ends the word and the line
                fMaxIntrinsicWidth = std::max(fMaxIntrinsicWidth, softLineMaxIntrinsicWidth);
                softLineMaxIntrinsicWidth = 0;
                fMinIntrinsicWidth = std::max(fMinIntrinsicWidth, lastWordLength);
                lastWordLength = 0;
            } else if (cluster->isWhitespaceBreak()) {
                // Whitespaces end the word
                softLineMaxIntrinsicWidth += cluster->width();
                fMinIntrinsicWidth = std::max(fMinIntrinsicWidth, lastWordLength);
                lastWordLength = 0;
            } else if (cluster->run().isPlaceholder()) {
                // Placeholder ends the previous word and creates a separate one
                fMinIntrinsicWidth = std::max(fMinIntrinsicWidth, lastWordLength);
                // Placeholder width now counts in fMinIntrinsicWidth
                softLineMaxIntrinsicWidth += cluster->width();
                fMinIntrinsicWidth = std::max(fMinIntrinsicWidth, cluster->width());
                lastWordLength = 0;
            } else {
                // Nothing out of ordinary - just add this cluster to the word and to the line
                softLineMaxIntrinsicWidth += cluster->width();
                lastWordLength += cluster->width();
            }
            ++cluster;
        }
        fMinIntrinsicWidth = std::max(fMinIntrinsicWidth, lastWordLength);
        fMaxIntrinsicWidth = std::max(fMaxIntrinsicWidth, softLineMaxIntrinsicWidth);

        if (parent->lines().empty()) {
            // In case we could not place even a single cluster on the line
            if (disableFirstAscent) {
                fEndLine.metrics().fAscent = fEndLine.metrics().fRawAscent;
            }
            if (disableLastDescent && !fHardLineBreak) {
                fEndLine.metrics().fDescent = fEndLine.metrics().fRawDescent;
            }
            fHeight = std::max(fHeight, fEndLine.metrics().height());
        }
    }

    if (fHardLineBreak) {
        // Last character is a line break
        if (parent->strutEnabled()) {
            // Make sure font metrics are not less than the strut
            parent->strutMetrics().updateLineMetrics(fEndLine.metrics());
        }

        if (disableLastDescent) {
            fEndLine.metrics().fDescent = fEndLine.metrics().fRawDescent;
        }

        ClusterRange clusters(fEndLine.breakCluster() - start, fEndLine.endCluster() - start);
        addLine(fEndLine.breakCluster()->textRange(),
                fEndLine.breakCluster()->textRange(),
                fEndLine.endCluster()->textRange(),
                clusters,
                clusters,
                0,
                0,
                0,
                SkVector::Make(0, fHeight),
                SkVector::Make(0, fEndLine.metrics().height()),
                fEndLine.metrics(),
                needEllipsis);
        fHeight += fEndLine.metrics().height();
        parent->lines().back().setMaxRunMetrics(maxRunMetrics);
    }
}

}  // namespace textlayout
}  // namespace skia