Show the title on short week and day blocks (#289)

app/src/main/java/de/jeanlucmakiola/calendula/ui/common/BlockPlacement.kt

@@ -17,6 +17,7 @@ import androidx.compose.ui.platform.LocalDensity
 import androidx.compose.ui.text.TextStyle
 import androidx.compose.ui.text.font.FontWeight
 import androidx.compose.ui.text.rememberTextMeasurer
+import androidx.compose.ui.text.style.LineHeightStyle
 import androidx.compose.ui.text.style.TextDecoration
 import androidx.compose.ui.unit.Constraints
 import androidx.compose.ui.unit.Dp
@@ -32,6 +33,93 @@ val BLOCK_TEXT_PADDING = 4.dp
 /** The same, above and below — what a block's height has to pay before any text. */
 val BLOCK_TEXT_INSET = 2.dp
 
+/**
+ * Block text with Material's outer leading trimmed off. The label roles wrap a
+ * 12sp glyph in a 16sp line box, and on a block short enough to be at risk that
+ * leading is the difference between a title and a bare colour chip (#289).
+ * Outer edges only, so a wrapped title keeps its interior line spacing.
+ */
+private val BlockLineHeight = LineHeightStyle(
+    alignment = LineHeightStyle.Alignment.Center,
+    trim = LineHeightStyle.Trim.Both,
+)
+
+/** Ascenders and descenders both, so a line is measured at its full extent. */
+private const val LINE_SAMPLE = "Ag"
+
+/** [this] as a timed block draws it — see [BlockLineHeight]. */
+fun TextStyle.asBlockText(): TextStyle = copy(lineHeightStyle = BlockLineHeight)
+
+/** What one trimmed line of [style] actually draws in. */
+@Composable
+fun rememberBlockLineHeight(style: TextStyle): Dp {
+    val measurer = rememberTextMeasurer()
+    val density = LocalDensity.current
+    return remember(style, density, measurer) {
+        with(density) { measurer.measure(LINE_SAMPLE, style.asBlockText()).size.height.toDp() }
+    }
+}
+
+/**
+ * What a timed block of a given height has to spend on text, and what each line
+ * of it costs.
+ */
+@Immutable
+data class BlockTextMetrics(
+    /** Padding above and below the text — see [rememberBlockTextMetrics]. */
+    val inset: Dp,
+    /** Height left for text once [inset] is paid at both edges. */
+    val available: Dp,
+    /** What the first line of a title draws in. */
+    val titleLine: Dp,
+    /** What every title line after the first adds: a whole line box, the trim
+     *  reaching only the outer edges. */
+    val titleLeading: Dp,
+    /** What the time label's one line draws in. */
+    val timeLine: Dp,
+) {
+    /** Whether the block can draw a title at all. */
+    val fitsTitle: Boolean get() = available >= titleLine
+
+    /** Height a title of [lines] lines occupies. */
+    fun titleHeight(lines: Int): Dp =
+        if (lines <= 0) 0.dp else titleLine + titleLeading * (lines - 1)
+
+    /** Title lines that fit [within], which may be none. */
+    fun titleBudget(within: Dp): Int =
+        if (within < titleLine) 0 else 1 + ((within - titleLine) / titleLeading).toInt()
+}
+
+/**
+ * The vertical padding a block [height] tall can afford around a title line of
+ * [titleLine].
+ *
+ * The inset is what the block gives up first: breathing room is worth having
+ * where there is room to breathe, but on a block down to its last few pixels a
+ * bare colour chip where a label would have fit reads as a rendering fault. It
+ * tapers rather than snapping, so a pinch closes the gap gradually instead of
+ * dropping it in one frame (#289).
+ */
+internal fun blockTextInset(height: Dp, titleLine: Dp): Dp =
+    minOf(BLOCK_TEXT_INSET, (height - titleLine) / 2).coerceAtLeast(0.dp)
+
+/** Text metrics for a timed block [height] tall. */
+@Composable
+fun rememberBlockTextMetrics(height: Dp): BlockTextMetrics {
+    val titleStyle = MaterialTheme.typography.labelMedium
+    val titleLine = rememberBlockLineHeight(titleStyle)
+    val titleLeading = with(LocalDensity.current) { titleStyle.lineHeight.toDp() }
+    val timeLine = rememberBlockLineHeight(MaterialTheme.typography.labelSmall.asEventTime())
+    val inset = blockTextInset(height, titleLine)
+    return BlockTextMetrics(
+        inset = inset,
+        available = height - inset * 2,
+        titleLine = titleLine,
+        titleLeading = titleLeading,
+        timeLine = timeLine,
+    )
+}
+
 /** Most lines a time label may wrap over before it is worth more than a title line. */
 const val MAX_TIME_LINES = 2
 
@@ -70,9 +158,9 @@ fun blockTextLines(text: String, style: TextStyle, textWidth: Dp, max: Int): Int
  */
 @Composable
 fun blockTimeLines(label: String, textWidth: Dp, spare: Dp): Int {
-    val timeLineHeight = with(LocalDensity.current) {
+    val timeLineHeight = rememberBlockLineHeight(
-        MaterialTheme.typography.labelSmall.lineHeight.toDp()
+        MaterialTheme.typography.labelSmall.asEventTime(),
-    }
+    )
     return if (spare >= timeLineHeight) {
         blockTextLines(
             text = label,
@@ -109,7 +197,8 @@ fun BlockTitle(
         text = title,
         modifier = modifier,
         style = MaterialTheme.typography.labelMedium
-            .let { if (fontWeight == null) it else it.copy(fontWeight = fontWeight) },
+            .let { if (fontWeight == null) it else it.copy(fontWeight = fontWeight) }
+            .asBlockText(),
         maxLines = maxLines,
         overflow = overflow.overflow,
         softWrap = overflow.softWrap,
@@ -150,7 +239,7 @@ fun BlockTimeLabel(
         Text(
             text = text,
             // Regular weight against the title's medium above it (#219).
-            style = MaterialTheme.typography.labelSmall.asEventTime(),
+            style = MaterialTheme.typography.labelSmall.asEventTime().asBlockText(),
             maxLines = maxLines,
             overflow = overflow.overflow,
             softWrap = overflow.softWrap,

app/src/main/java/de/jeanlucmakiola/calendula/ui/common/TimelineDrag.kt

@@ -790,20 +790,15 @@ private fun DragCopy(
     val width = with(density) { sizePx.width.toDp() }
     val height = with(density) { sizePx.height.toDp() }
     val textWidth = width - (BLOCK_OUTER_INSET + BLOCK_TEXT_PADDING) * 2
-    val titleLineHeight = with(density) {
-        MaterialTheme.typography.labelMedium.lineHeight.toDp()
-    }
-    val timeLineHeight = with(density) {
-        MaterialTheme.typography.labelSmall.lineHeight.toDp()
-    }
     // The block's size, spent the block's way — text sits at the top as it does
-    // on the block, so the copy hands back to the grid without shifting (#267).
+    // on the block, so the copy hands back to the grid without shifting (#267),
+    // and it squeezes its inset on the same terms so a short block's title does
+    // not vanish the moment it is lifted (#289).
     // The title is served in full first and the range lives off what is left:
     // the hour gutter down the side still says where the copy sits, so the
     // range is the half that can afford to go.
-    val available = height - BLOCK_TEXT_INSET * 2
+    val metrics = rememberBlockTextMetrics(height)
-    val titleBudget = (available / titleLineHeight).toInt().coerceAtLeast(0)
+    val allowed = titleLines.coerceAtMost(metrics.titleBudget(metrics.available))
-    val allowed = titleLines.coerceAtMost(titleBudget)
     // Re-measured at the copy's own width rather than spent on the source's
     // count: a block sharing its column with another is a lane wide where the
     // copy is a whole column, so the source's second line is one the copy never
@@ -818,10 +813,10 @@ private fun DragCopy(
             max = allowed,
         )
     }
-    val left = available - titleLineHeight * lines
+    val left = metrics.available - metrics.titleHeight(lines)
-    val showTime = label != null && left >= timeLineHeight
+    val showTime = label != null && left >= metrics.timeLine
     val timeMaxLines = if (showTime) {
-        blockTimeLines(label!!, textWidth, left - timeLineHeight)
+        blockTimeLines(label!!, textWidth, left - metrics.timeLine)
     } else {
         1
     }
@@ -857,7 +852,7 @@ private fun DragCopy(
                 clip = false
             }
             .eventSurface(paint, shape, cuts)
-            .padding(horizontal = BLOCK_TEXT_PADDING, vertical = BLOCK_TEXT_INSET),
+            .padding(horizontal = BLOCK_TEXT_PADDING, vertical = metrics.inset),
     ) {
         Column {
             if (lines > 0) {

app/src/main/java/de/jeanlucmakiola/calendula/ui/day/DayScreen.kt

@@ -83,9 +83,9 @@ import de.jeanlucmakiola.calendula.ui.common.CalendarView
 import de.jeanlucmakiola.calendula.ui.common.IMPLEMENTED_VIEWS
 import de.jeanlucmakiola.calendula.ui.common.BLOCK_OUTER_INSET
 import de.jeanlucmakiola.calendula.ui.common.BLOCK_TEXT_PADDING
-import de.jeanlucmakiola.calendula.ui.common.BLOCK_TEXT_INSET
 import de.jeanlucmakiola.calendula.ui.common.BlockTimeLabel
 import de.jeanlucmakiola.calendula.ui.common.BlockTitle
+import de.jeanlucmakiola.calendula.ui.common.rememberBlockTextMetrics
 import de.jeanlucmakiola.calendula.ui.common.blockTimeLines
 import de.jeanlucmakiola.calendula.ui.common.animatedBlockPlacement
 import de.jeanlucmakiola.calendula.ui.common.ghostAlpha
@@ -763,30 +763,24 @@ private fun EventBlock(
     val timeLabel = "${minToHm(block.startMin, use24Hour, locale)}–" +
         minToHm(block.endMin, use24Hour, locale)
     val density = LocalDensity.current
-    val titleLineHeight = with(density) {
+    val metrics = rememberBlockTextMetrics(height)
-        MaterialTheme.typography.labelMedium.lineHeight.toDp()
-    }
-    val timeLineHeight = with(density) {
-        MaterialTheme.typography.labelSmall.lineHeight.toDp()
-    }
     // A block that cannot afford both lines spends its space on the title, and
     // one too short even for that drops the title rather than serving a sliced one.
     // Height alone decides: a duration threshold would keep hiding the time on a
     // half-hour block the user has pinched open to three times the room it needs.
-    val available = height - BLOCK_TEXT_INSET * 2
+    val showTime = metrics.available >= metrics.titleLine + metrics.timeLine
-    val showTime = available >= titleLineHeight + timeLineHeight
+    val showTitle = metrics.fitsTitle
-    val showTitle = available >= titleLineHeight
     val textWidth = width - (BLOCK_OUTER_INSET + BLOCK_TEXT_PADDING) * 2
     // Only lines the block can actually draw: a block too short for the time is
     // too short for a second title line too, and asking for one served a sliced
     // one — as well as handing the drag copy a count it couldn't honour, so the
     // title re-wrapped the moment the block was lifted (#267).
-    val titleBudget = (available / titleLineHeight).toInt().coerceAtLeast(1)
+    val titleBudget = metrics.titleBudget(metrics.available).coerceAtLeast(1)
     val titleMaxLines = if (showTime) 1 else titleBudget.coerceAtMost(2)
     // On a day column — wide enough for "09:30–11:00" several times over — the
     // range never needs the second line, until lanes cut the column down.
-    val spare = available - titleLineHeight * titleMaxLines -
+    val spare = metrics.available - metrics.titleHeight(titleMaxLines) -
-        if (showTime) timeLineHeight else 0.dp
+        if (showTime) metrics.timeLine else 0.dp
     val timeMaxLines = if (showTime) blockTimeLines(timeLabel, textWidth, spare) else 1
     val paint = eventPaint(block.event, dark)
     val zone = remember { TimeZone.currentSystemDefault() }
@@ -827,7 +821,7 @@ private fun EventBlock(
             // After clickable, so it is the inner node and wins the main pass;
             // the tap still works, since a drag consumes the up.
             .then(dragModifier)
-            .padding(horizontal = BLOCK_TEXT_PADDING, vertical = BLOCK_TEXT_INSET)
+            .padding(horizontal = BLOCK_TEXT_PADDING, vertical = metrics.inset)
             .semantics {
                 contentDescription = "$title, $timeLabel"
                 if (moveAction != null) customActions = listOf(moveAction)

app/src/main/java/de/jeanlucmakiola/calendula/ui/week/WeekScreen.kt

@@ -91,11 +91,11 @@ import de.jeanlucmakiola.calendula.ui.common.IMPLEMENTED_VIEWS
 import de.jeanlucmakiola.calendula.ui.common.EventDimAlpha
 import de.jeanlucmakiola.calendula.ui.common.BLOCK_OUTER_INSET
 import de.jeanlucmakiola.calendula.ui.common.BLOCK_TEXT_PADDING
-import de.jeanlucmakiola.calendula.ui.common.BLOCK_TEXT_INSET
 import de.jeanlucmakiola.calendula.ui.common.BlockTimeLabel
 import de.jeanlucmakiola.calendula.ui.common.BlockTitle
 import de.jeanlucmakiola.calendula.ui.common.blockTextLines
 import de.jeanlucmakiola.calendula.ui.common.blockTimeLines
+import de.jeanlucmakiola.calendula.ui.common.rememberBlockTextMetrics
 import de.jeanlucmakiola.calendula.ui.common.animatedBlockPlacement
 import de.jeanlucmakiola.calendula.ui.common.ghostAlpha
 import de.jeanlucmakiola.calendula.ui.common.LocalEventMove
@@ -909,13 +909,7 @@ private fun EventBlock(
     val timeLabel = "${minToHm(block.startMin, use24Hour, locale)}–" +
         minToHm(block.endMin, use24Hour, locale)
     val density = LocalDensity.current
-    val titleLineHeight = with(density) {
+    val metrics = rememberBlockTextMetrics(height)
-        MaterialTheme.typography.labelMedium.lineHeight.toDp()
-    }
-    val timeLineHeight = with(density) {
-        MaterialTheme.typography.labelSmall.lineHeight.toDp()
-    }
-    val available = height - BLOCK_TEXT_INSET * 2
     // Only full-width (non-overlapping) blocks that are tall enough show the
     // time. On narrow overlapping columns we drop it so the title can wrap to
     // fill the whole block, mirroring Google Calendar — and a block that cannot
@@ -923,19 +917,19 @@ private fun EventBlock(
     // its own: a duration threshold would keep hiding the time on a half-hour
     // block the user has pinched open to three times the room it needs.
     val showTime = block.laneCount == 1 &&
-        available >= titleLineHeight + timeLineHeight
+        metrics.available >= metrics.titleLine + metrics.timeLine
     val textWidth = width - (BLOCK_OUTER_INSET + BLOCK_TEXT_PADDING) * 2
     // A short block drops the title rather than serving a horizontally sliced
     // one: half a letter reads as a rendering fault, while a bare colour chip
     // reads as what it is — an event too brief to label. Tap still opens it, and
     // the semantics description carries the full title either way.
-    val showTitle = available >= titleLineHeight
+    val showTitle = metrics.fitsTitle
     // The title is served first, out of everything the block has left once the
     // time is down to one line — but only takes the lines it will actually use,
     // and only wraps at all once a line is wide enough to hold more than a
     // syllable. Below that the extra lines just stack fragments of the word.
-    val contentHeight = available - if (showTime) timeLineHeight else 0.dp
+    val contentHeight = metrics.available - if (showTime) metrics.timeLine else 0.dp
-    val titleBudget = (contentHeight / titleLineHeight).toInt().coerceAtLeast(1)
+    val titleBudget = metrics.titleBudget(contentHeight).coerceAtLeast(1)
     val paint = eventPaint(block.event, dark)
     // Every line the height affords, however narrow the lane: two events side by
     // side leave columns well under a word wide, and cutting the title to one
@@ -948,8 +942,8 @@ private fun EventBlock(
         textWidth = textWidth,
         max = titleBudget,
     )
-    val spare = available - titleLineHeight * titleMaxLines -
+    val spare = metrics.available - metrics.titleHeight(titleMaxLines) -
-        if (showTime) timeLineHeight else 0.dp
+        if (showTime) metrics.timeLine else 0.dp
     val timeMaxLines = if (showTime) blockTimeLines(timeLabel, textWidth, spare) else 1
     val dimCutoff = LocalDimCutoff.current
     val dimmed = dimCutoff != null && block.event.hasEnded(dimCutoff)
@@ -991,7 +985,7 @@ private fun EventBlock(
             // After clickable, so it is the inner node and wins the main pass;
             // the tap still works, since a drag consumes the up.
             .then(dragModifier)
-            .padding(horizontal = BLOCK_TEXT_PADDING, vertical = BLOCK_TEXT_INSET)
+            .padding(horizontal = BLOCK_TEXT_PADDING, vertical = metrics.inset)
             .semantics {
                 contentDescription = "$title, $timeLabel"
                 if (moveAction != null) customActions = listOf(moveAction)

app/src/test/java/de/jeanlucmakiola/calendula/ui/common/BlockTextMetricsTest.kt

@@ -0,0 +1,88 @@
+package de.jeanlucmakiola.calendula.ui.common
+
+import androidx.compose.ui.unit.Dp
+import androidx.compose.ui.unit.dp
+import com.google.common.truth.Truth.assertThat
+import org.junit.jupiter.api.Test
+
+class BlockTextMetricsTest {
+
+    /** One trimmed labelMedium line at font scale 1: a 12sp glyph, leading off. */
+    private val titleLine = 14.dp
+
+    /** A block with room to spare, for the line arithmetic. */
+    private fun metrics(height: Dp = 100.dp) = BlockTextMetrics(
+        inset = blockTextInset(height, titleLine),
+        available = height - blockTextInset(height, titleLine) * 2,
+        titleLine = titleLine,
+        titleLeading = 16.dp,
+        timeLine = 13.dp,
+    )
+
+    @Test
+    fun `a block with room keeps the full inset`() {
+        assertThat(blockTextInset(height = 60.dp, titleLine = titleLine))
+            .isEqualTo(BLOCK_TEXT_INSET)
+    }
+
+    @Test
+    fun `the inset tapers instead of snapping as the block shrinks`() {
+        // Half the inset left over is half the inset kept, so a pinch closes the
+        // gap frame by frame rather than dropping it in one.
+        assertThat(blockTextInset(height = titleLine + 2.dp, titleLine = titleLine))
+            .isEqualTo(1.dp)
+    }
+
+    @Test
+    fun `a block exactly one title tall spends nothing on padding`() {
+        assertThat(blockTextInset(height = titleLine, titleLine = titleLine)).isEqualTo(0.dp)
+    }
+
+    @Test
+    fun `a block shorter than a line never insets negatively`() {
+        assertThat(blockTextInset(height = 4.dp, titleLine = titleLine)).isEqualTo(0.dp)
+    }
+
+    @Test
+    fun `the title survives a block that used to be too short for it`() {
+        // 18dp is under the old floor — a title line plus 2dp of inset at each
+        // edge — and over the new one, which is the line on its own (#289).
+        val m = metrics(height = 18.dp)
+        assertThat(m.fitsTitle).isTrue()
+    }
+
+    @Test
+    fun `a block under one line still drops the title`() {
+        assertThat(metrics(height = 10.dp).fitsTitle).isFalse()
+    }
+
+    @Test
+    fun `every title line after the first costs a whole line box`() {
+        // The trim reaches the outer edges only, so the leading between two
+        // lines is still there to pay for.
+        val m = metrics()
+        assertThat(m.titleHeight(1)).isEqualTo(14.dp)
+        assertThat(m.titleHeight(2)).isEqualTo(30.dp)
+        assertThat(m.titleHeight(3)).isEqualTo(46.dp)
+        assertThat(m.titleHeight(0)).isEqualTo(0.dp)
+    }
+
+    @Test
+    fun `the budget is what the block can actually draw, not what divides into it`() {
+        val m = metrics()
+        // Two lines cost 30dp: 29 buys one, 30 buys the second.
+        assertThat(m.titleBudget(29.dp)).isEqualTo(1)
+        assertThat(m.titleBudget(30.dp)).isEqualTo(2)
+        assertThat(m.titleBudget(13.dp)).isEqualTo(0)
+    }
+
+    @Test
+    fun `a budget line is always one the block can pay for`() {
+        val m = metrics()
+        (0..80).forEach { dp ->
+            val within = dp.dp
+            val budget = m.titleBudget(within)
+            assertThat(m.titleHeight(budget)).isAtMost(within)
+        }
+    }
+}