Merge branch 'card-list': the thread pane as a list of cards

Replaces the five-column grid with a single column of three-line cards. Item 53
recorded that the columns, not the cues drawn inside them, were what made the
list read as a table of records; item 20 had already shipped finished, tested
and green and been rejected on sight for exactly that reason.

A card is sender and date, subject with the flag, attachment and reply-count
marks, and tags, at one uniform height. Replies indent under a continuous spine
and show only the tags their thread does not carry. The account colour runs down
the card's left edge, replacing the chip that used to eat a third of every
subject line, with matching swatches in the account dropdown. Sorting newest or
oldest first is new and remembered.

Closes items 20, 51, 53 and 60.

The four defects that mattered were all found by rendering cards to an image and
looking at them, with the suite green through every one: a date clipped on unread
cards because bold is wider than the font the layout measured, an accent bar
painted in a colour identical to the background, an expander pill in a palette
role a theme had made equal to Base, and three separate faults from trusting
notmuch's reply depth to mean structure when it only means how notmuch happened
to thread the mail.

1 files changed, 261 insertions, 0 deletions

diff --git a/src/carddelegate.cpp b/src/carddelegate.cpp
new file mode 100644
index 0000000..f13205e
--- /dev/null
+++ b/src/carddelegate.cpp
@@ -0,0 +1,261 @@
+/*
+ * qtmaildir - a Qt6 mail client for notmuch-indexed Maildirs
+ * Copyright (C) 2026 Danilo M. <danix@danix.xyz>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#include "carddelegate.h"
+
+#include "cardlayout.h"
+#include "threadlistmodel.h"
+
+#include <QApplication>
+#include <QDateTime>
+#include <QGuiApplication>
+#include <QPainter>
+#include <QRegularExpression>
+#include <QStyle>
+
+namespace {
+
+CardLayout::Input inputFor(const QModelIndex &index)
+{
+    CardLayout::Input in;
+    in.isMessage = index.data(ThreadListModel::IsMessageRole).toBool();
+    in.depth = index.data(ThreadListModel::MessageDepthRole).toInt();
+    in.replyCount = index.data(ThreadListModel::ReplyCountRole).toInt();
+    return in;
+}
+
+}  // namespace
+
+QRect CardDelegate::expanderRectFor(const QStyleOptionViewItem &option,
+                                    const QModelIndex &index)
+{
+    return CardLayout::compute(inputFor(index), option.rect, option.font)
+        .expanderRect;
+}
+
+QColor CardDelegate::accentLineColour(const QColor &accountColour)
+{
+    if (!accountColour.isValid())
+        return ThreadListModel::threadLineColour();
+
+    // 0.35 toward Base was the first attempt and produced an INVISIBLE bar on
+    // a dark theme: rendered against a Base of (0.169, 0.169, 0.169) it landed
+    // at (0.18, 0.22, 0.26), which is the background. The weight is a fraction
+    // OF THE ACCOUNT COLOUR, so a low one keeps the background, not the hue.
+    //
+    // The bar is the account's colour, undiluted. Blending it toward Base at
+    // all was the mistake: a chip's colour is chosen to carry text on top and
+    // is therefore already muted, and three pixels of a muted colour on a dark
+    // background is nothing at all. There is no text on this bar, so nothing
+    // needs the contrast a chip's fill was picked for.
+    //
+    // What DOES step back is the spine, below: a line running the height of a
+    // whole expansion has to be followable without competing with the senders
+    // beside it, which is a different problem from a 3px edge marker.
+    return accountColour;
+}
+
+QSize CardDelegate::sizeHint(const QStyleOptionViewItem &option,
+                             const QModelIndex &index) const
+{
+    Q_UNUSED(index);
+    // One height for every row, thread and reply alike. Asserted directly in
+    // test_cardlayout rather than left to two cards happening to agree.
+    return QSize(option.rect.width(), CardLayout::heightFor(option.font));
+}
+
+void CardDelegate::paint(QPainter *painter, const QStyleOptionViewItem &option,
+                         const QModelIndex &index) const
+{
+    // Background, selection and any model fill first, through the style, so a
+    // selected or doomed card looks right before anything is drawn on top.
+    QStyleOptionViewItem chrome = option;
+    initStyleOption(&chrome, index);
+    chrome.text.clear();
+    const QWidget *widget = option.widget;
+    QStyle *style = widget ? widget->style() : QApplication::style();
+    style->drawControl(QStyle::CE_ItemViewItem, &chrome, painter, widget);
+
+    const CardLayout card =
+        CardLayout::compute(inputFor(index), option.rect, option.font);
+
+    painter->save();
+
+    // The account's colour, for both the accent bar and the spines.
+    //
+    // A reply must resolve its THREAD's colour, not its own: AccountColourRole
+    // is empty on a message row, and a spine that fell back to the neutral
+    // line under an accented root would break the one continuous edge this
+    // design is built on. index.parent() is the thread for a depth-1 reply and
+    // the containing subtree for a deeper one, so walk to the root.
+    QModelIndex root = index;
+    while (root.parent().isValid())
+        root = root.parent();
+    const QColor accountColour =
+        root.data(ThreadListModel::AccountColourRole).value<QColor>();
+    const QColor lineColour = accentLineColour(accountColour);
+
+    // The accent bar, thread cards only. Drawn after the chrome so the
+    // selection highlight cannot cover it: which account a card belongs to
+    // must stay readable on the row the user is looking at.
+    if (!card.accentRect.isEmpty())
+        painter->fillRect(card.accentRect, lineColour);
+
+    // Spines, under everything else, in the account's hue so an expanded thread
+    // is bounded by one colour from its root to its last reply. Muted against
+    // the pane's own background, unlike the accent bar: this line runs the full
+    // height of every reply and at full strength it shouts.
+    if (!card.spines.isEmpty()) {
+        const QColor base =
+            QGuiApplication::palette().color(QPalette::Base);
+        constexpr qreal kSpineWeight = 0.55;
+        const qreal inverse = 1.0 - kSpineWeight;
+        const QColor spineColour = QColor::fromRgbF(
+            lineColour.redF() * kSpineWeight + base.redF() * inverse,
+            lineColour.greenF() * kSpineWeight + base.greenF() * inverse,
+            lineColour.blueF() * kSpineWeight + base.blueF() * inverse);
+        for (const QRect &spine : card.spines)
+            painter->fillRect(spine, spineColour);
+    }
+
+    // Selection outranks the model's foreground, and the order matters: a read
+    // card carries a dimmed colour blended against the UNSELECTED background,
+    // so over the highlight it lands grey-on-highlight and close to unreadable.
+    const QVariant foreground = index.data(Qt::ForegroundRole);
+    if (option.state & QStyle::State_Selected)
+        painter->setPen(option.palette.highlightedText().color());
+    else if (foreground.isValid())
+        painter->setPen(foreground.value<QBrush>().color());
+    else
+        painter->setPen(option.palette.text().color());
+
+    // The model's font carries bold for unread and strike-out for deleted;
+    // initStyleOption resolved it into chrome.font.
+    painter->setFont(chrome.font);
+    const QFontMetrics metrics(chrome.font);
+
+    // Line 1: sender, then the date flush right.
+    painter->drawText(card.senderRect, Qt::AlignVCenter | Qt::AlignLeft,
+                      metrics.elidedText(
+                          index.data(ThreadListModel::SendersRole).toString(),
+                          Qt::ElideRight, card.senderRect.width()));
+    const QDateTime date =
+        index.data(ThreadListModel::DateRole).toDateTime();
+    painter->drawText(card.dateRect, Qt::AlignVCenter | Qt::AlignRight,
+                      CardLayout::formatDate(date));
+
+    // Line 2: the flag mark, the subject, the attachment mark.
+    QString subject = index.data(ThreadListModel::SubjectRole).toString();
+    if (index.data(ThreadListModel::IsMessageRole).toBool()) {
+        // Every reply repeating "Re: <the thread's subject>" is the visual
+        // signature of a table of records, which is what item 53 is about.
+        static const QRegularExpression re(
+            QStringLiteral("^\\s*(?:[Rr][Ee]\\s*:\\s*)+"));
+        subject.remove(re);
+    }
+    QString line2;
+    if (index.data(ThreadListModel::IsFlaggedRole).toBool())
+        line2 += ThreadListModel::flagGlyph() + QLatin1Char(' ');
+    line2 += subject;
+    if (index.data(ThreadListModel::HasAttachmentRole).toBool())
+        line2 += QLatin1Char(' ') + ThreadListModel::attachmentGlyph();
+    painter->drawText(card.subjectRect, Qt::AlignVCenter | Qt::AlignLeft,
+                      metrics.elidedText(line2, Qt::ElideRight,
+                                         card.subjectRect.width()));
+
+    // The reply count, which is also the expander, drawn as a PILL.
+    //
+    // A bare "3" on the card's own background read as an unexplained number
+    // beside the subject and gave no hint that it could be clicked. The chip
+    // shape says "this is a control", matching the tag chips on line 3, and the
+    // word says what the number counts.
+    if (!card.expanderRect.isEmpty()) {
+        const int count = index.data(ThreadListModel::ReplyCountRole).toInt();
+        const QString label = CardLayout::expanderLabel(
+            count, option.state & QStyle::State_Open);
+
+        painter->save();
+        painter->setFont(CardLayout::smallFont(chrome.font));
+
+        // Blended from Text toward Base rather than taken from a palette ROLE.
+        // QPalette::Button is the role this obviously wants and it is
+        // #2b2b2b against a Base of #2b2b2b on the user's theme: byte
+        // identical, so the pill was invisible. A theme is free to make any two
+        // roles equal, and several do; a blend cannot collide with the surface
+        // it sits on because it is defined relative to it.
+        //
+        // Toward Text, so it darkens on a light theme and lightens on a dark
+        // one, the same trick replyBackground() and threadLineColour() use.
+        const QColor base = option.palette.color(QPalette::Base);
+        const QColor text = option.palette.color(QPalette::Text);
+        constexpr qreal kFillWeight = 0.18;
+        const QColor fill = QColor::fromRgbF(
+            text.redF() * kFillWeight + base.redF() * (1.0 - kFillWeight),
+            text.greenF() * kFillWeight + base.greenF() * (1.0 - kFillWeight),
+            text.blueF() * kFillWeight + base.blueF() * (1.0 - kFillWeight));
+        painter->setRenderHint(QPainter::Antialiasing, true);
+        painter->setPen(Qt::NoPen);
+        painter->setBrush(fill);
+        // Fully rounded ends, the same shape TagChip paints: the radius is half
+        // the height, so the pill cannot look like a rectangle with soft corners.
+        const qreal radius = card.expanderRect.height() / 2.0;
+        painter->drawRoundedRect(card.expanderRect, radius, radius);
+
+        // The pen is restored from the card's own text colour rather than
+        // ButtonText, which belongs to the role that just proved unreliable.
+        painter->setPen(option.state & QStyle::State_Selected
+                            ? option.palette.highlightedText().color()
+                            : text);
+        painter->drawText(card.expanderRect, Qt::AlignCenter, label);
+        painter->restore();
+    }
+
+    painter->restore();
+
+    // Line 3: the chips. A thread card draws its own tags; a reply draws only
+    // the tags its thread does not already carry, so the thread's chips are
+    // not repeated down the whole expansion.
+    const bool isMessage =
+        index.data(ThreadListModel::IsMessageRole).toBool();
+    const QStringList tags =
+        index.data(isMessage ? ThreadListModel::MessageOwnTagsRole
+                             : ThreadListModel::PillTagsRole)
+            .toStringList();
+    const QVariantList colours =
+        index.data(isMessage ? ThreadListModel::MessageOwnColoursRole
+                             : ThreadListModel::PillColoursRole)
+            .toList();
+
+    const QFont chipFont = CardLayout::smallFont(chrome.font);
+    const QFontMetrics chipMetrics(chipFont);
+    painter->save();
+    painter->setFont(chipFont);
+    int x = card.tagRect.left();
+    for (int i = 0; i < tags.size(); ++i) {
+        const QSize size = TagChip::sizeFor(chipMetrics, tags.at(i));
+        if (x + size.width() > card.tagRect.right())
+            break;  // Out of room; a clipped chip reads as a rendering fault.
+        const QColor colour = i < colours.size()
+                                  ? colours.at(i).value<QColor>()
+                                  : QColor(0x55, 0x55, 0x5f);
+        TagChip::paint(painter, QRect(QPoint(x, card.tagRect.top()), size),
+                       tags.at(i), colour);
+        x += size.width() + TagChip::kSpacing;
+    }
+    painter->restore();
+}