modules/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 {
SkScalar littleRound(SkScalar a) {
    // This rounding is done to match Flutter tests. Must be removed..
  return SkScalarRoundToScalar(a * 100.0)/100.0;
}
}

// 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());

    for (auto cluster = fEndLine.endCluster(); cluster < endOfClusters; ++cluster) {
        // TODO: Trying to deal with flutter rounding problem. Must be removed...
        auto width = fWords.width() + fClusters.width() + cluster->width();
        auto roundedWidth = littleRound(width);
        if (cluster->isHardBreak()) {
        } else if (roundedWidth > maxWidth) {
            if (cluster->isWhitespaces()) {
                // It's the end of the word
                fClusters.extend(cluster);
                fMinIntrinsicWidth = std::max(fMinIntrinsicWidth, getClustersTrimmedWidth());
                fWords.extend(fClusters);
                break;
            }

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

        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->isWhitespaces();
         --cluster) {
        fEndLine.trim(cluster);
    }
    fEndLine.trim();
}

SkScalar TextWrapper::getClustersTrimmedWidth() {
    // Move the end of the line to the left
    SkScalar width = fClusters.width();
    auto cluster = fClusters.endCluster();
    for (; cluster > fClusters.startCluster() && cluster->isWhitespaces(); --cluster) {
        width -= cluster->width();
    }
    if (cluster >= fClusters.startCluster()) {
        if (cluster->isWhitespaces()) {
            width -= cluster->width();
        } else {
            width -= (cluster->width() - cluster->trimmedWidth(cluster->endPos()));
        }
    }
    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->isWhitespaces()) {
            width += cluster->width();
            ++cluster;
        }
        return std::make_tuple(fEndLine.breakCluster() + 1, 0, width);
    }

    auto width = fEndLine.widthWithGhostSpaces();
    auto cluster = fEndLine.breakCluster();
    if (fEndLine.endCluster() != fEndLine.startCluster() ||
        fEndLine.endPos() != fEndLine.startPos()) {
        ++cluster;
        while (cluster < endOfClusters && cluster->isWhitespaces()) {
            width += cluster->width();
            ++cluster;
        }
    } else {
        // Nothing fits the line - no need to check for spaces
    }

    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& ellipsisStr = parent->paragraphStyle().getEllipsis();
    auto align = parent->paragraphStyle().effective_align();
    auto unlimitedLines = maxLines == std::numeric_limits<size_t>::max();
    auto endlessLine = !SkScalarIsFinite(maxWidth);
    auto hasEllipsis = !ellipsisStr.isEmpty();

    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) {
            if (cluster->run() == lastRun) {
                continue;
            }
            lastRun = cluster->run();
            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 text(fEndLine.startCluster()->textRange().start, fEndLine.endCluster()->textRange().end);
        TextRange textWithSpaces(fEndLine.startCluster()->textRange().start, startLine->textRange().start);
        if (startLine == end) {
            textWithSpaces.end = parent->text().size();
        }
        ClusterRange clusters(fEndLine.startCluster() - start, fEndLine.endCluster() - start + 1);
        ClusterRange clustersWithGhosts(fEndLine.startCluster() - start, startLine - start);
        addLine(text, textWithSpaces, clusters, clustersWithGhosts, widthWithSpaces,
                fEndLine.startPos(),
                fEndLine.endPos(),
                SkVector::Make(0, fHeight),
                SkVector::Make(fEndLine.width(), fEndLine.metrics().height()),
                fEndLine.metrics(),
                needEllipsis && !fHardLineBreak);

        softLineMaxIntrinsicWidth += widthWithSpaces;

        fMaxIntrinsicWidth = std::max(fMaxIntrinsicWidth, softLineMaxIntrinsicWidth);
        if (fHardLineBreak) {
            softLineMaxIntrinsicWidth = 0;
        }
        // Start a new line
        fHeight += fEndLine.metrics().height();
        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()) {
                fMaxIntrinsicWidth = std::max(fMaxIntrinsicWidth, softLineMaxIntrinsicWidth);
                softLineMaxIntrinsicWidth = 0;
                fMinIntrinsicWidth = std::max(fMinIntrinsicWidth, lastWordLength);
                lastWordLength = 0;
            } else if (cluster->isWhitespaces()) {
                SkASSERT(cluster->isWhitespaces());
                softLineMaxIntrinsicWidth += cluster->width();
                fMinIntrinsicWidth = std::max(fMinIntrinsicWidth, lastWordLength);
                lastWordLength = 0;
            } else {
                softLineMaxIntrinsicWidth += cluster->width();
                lastWordLength += cluster->width();
            }
            ++cluster;
        }
        fMinIntrinsicWidth = std::max(fMinIntrinsicWidth, lastWordLength);
        fMaxIntrinsicWidth = std::max(fMaxIntrinsicWidth, softLineMaxIntrinsicWidth);
        // In case we could not place a single cluster on the line
        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());
        }
        TextRange empty(fEndLine.breakCluster()->textRange().start, fEndLine.breakCluster()->textRange().start);
        TextRange hardBreak(fEndLine.breakCluster()->textRange().end, fEndLine.breakCluster()->textRange().end);
        ClusterRange clusters(fEndLine.breakCluster() - start, fEndLine.endCluster() - start);
        addLine(empty, hardBreak, 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