From c8de54d1c2f195e3669a4cd7355288701045a36d Mon Sep 17 00:00:00 2001
From: davotoula <david.kaspar@gmail.com>
Date: Tue, 9 Jun 2026 19:41:55 +0200
Subject: [PATCH] fix(math): align inline equations to the text baseline

---
 .../amethyst/ui/components/LatexEquation.kt   | 33 +++++++++++++++++--
 1 file changed, 30 insertions(+), 3 deletions(-)

diff --git a/amethyst/src/main/java/com/vitorpamplona/amethyst/ui/components/LatexEquation.kt b/amethyst/src/main/java/com/vitorpamplona/amethyst/ui/components/LatexEquation.kt
index 2042fb82a1..ea0f43dffc 100644
--- a/amethyst/src/main/java/com/vitorpamplona/amethyst/ui/components/LatexEquation.kt
+++ b/amethyst/src/main/java/com/vitorpamplona/amethyst/ui/components/LatexEquation.kt
@@ -36,6 +36,7 @@ import androidx.compose.ui.graphics.drawscope.drawIntoCanvas
 import androidx.compose.ui.graphics.nativeCanvas
 import androidx.compose.ui.graphics.toArgb
 import androidx.compose.ui.platform.LocalDensity
+import androidx.compose.ui.text.rememberTextMeasurer
 import androidx.compose.ui.unit.TextUnit
 import androidx.compose.ui.unit.TextUnitType
 import androidx.compose.ui.unit.sp
@@ -91,12 +92,33 @@ fun LatexEquation(
         return
     }
 
+    // Baseline alignment. The parent FlowRow centers each word vertically, so a
+    // tight equation bitmap floats above the line — most of a formula's mass sits
+    // above the baseline, so centering its box lifts the baseline above the text.
+    // We pad the box so that, once centered, the equation's baseline coincides
+    // with a surrounding text word's baseline. With text ascent/descent A/Dsc and
+    // icon total height H and depth-below-baseline Dp, the padded box satisfies
+    // `baseline-from-center = (A - Dsc) / 2` — the same value a Text box has — when
+    //   pad = (A - Dsc) - H + 2*Dp   (on top if positive, on bottom if negative).
+    val resolvedStyle = LocalTextStyle.current.let { if (fontSize.isUsable()) it else it.copy(fontSize = 16.sp) }
+    val measurer = rememberTextMeasurer()
+    val (drawTopPx, boxHeightPx) =
+        remember(drawable, resolvedStyle) {
+            val text = measurer.measure("Mg", resolvedStyle)
+            val ascent = text.firstBaseline
+            val descent = text.size.height - ascent
+            val iconHeight = drawable.intrinsicHeight.toFloat()
+            val iconDepth = drawable.icon().iconDepth.toFloat()
+            val pad = (ascent - descent) - iconHeight + 2f * iconDepth
+            maxOf(pad, 0f) to (iconHeight + maxOf(pad, 0f) + maxOf(-pad, 0f))
+        }
+
     val widthDp = with(density) { drawable.intrinsicWidth.toDp() }
-    val heightDp = with(density) { drawable.intrinsicHeight.toDp() }
+    val boxHeightDp = with(density) { boxHeightPx.toDp() }
 
     // Wide display equations can overflow the column; allow them to scroll
     // horizontally instead of being clipped.
-    val equationSize = Modifier.size(widthDp, heightDp)
+    val equationSize = Modifier.size(widthDp, boxHeightDp)
     val equationModifier = if (displayMode) Modifier.horizontalScroll(rememberScrollState()).then(equationSize) else equationSize
 
     // Row keeps leading/trailing punctuation (the `(` and `)` in `($x$)`) hugging
@@ -107,8 +129,13 @@ fun LatexEquation(
         }
         Canvas(modifier = equationModifier) {
             drawIntoCanvas { canvas ->
+                val native = canvas.nativeCanvas
+                val checkpoint = native.save()
+                // Position the icon's baseline on the text baseline within the padded box.
+                native.translate(0f, drawTopPx)
                 drawable.setBounds(0, 0, drawable.intrinsicWidth, drawable.intrinsicHeight)
-                drawable.draw(canvas.nativeCanvas)
+                drawable.draw(native)
+                native.restoreToCount(checkpoint)
             }
         }
         if (trailing.isNotEmpty()) {