Fix cursor Y positioning logic in editor

internal/editor/state.go

@@ -457,47 +457,72 @@ func SetCursorFromPoint(x, y float64) {
 		return
 	}
 
-	// 1. Find the best line based on y
-	bestLineY := layout.Y[0]
-	minYDist := 1e9
-	for _, yVal := range layout.Y {
-		yDist := float64(yVal) - y
-		if yDist < 0 {
-			yDist = -yDist
+	lineHeight := float64(EditorLineHeight())
+
+	// 1. Identify the intended line index based on y
+	// layout.Y values are relative to the text region origin.
+	// We need to account for scroll offset.
+	visualLine := int((y + float64(TheState.ScrollOffset)) / lineHeight)
+
+	// Group glyphs by their Y-baseline
+	type lineGroup struct {
+		y       float64
+		indices []int
 	}
-		if yDist < minYDist {
-			minYDist = yDist
-			bestLineY = yVal
+	groups := []lineGroup{}
+	seenY := make(map[float64]int) // maps Y to group index
+
+	for i, yVal := range layout.Y {
+		yFloat := float64(yVal)
+		idx, ok := seenY[yFloat]
+		if !ok {
+			idx = len(groups)
+			groups = append(groups, lineGroup{y: yFloat, indices: []int{}})
+			seenY[yFloat] = idx
 		}
+		groups[idx].indices = append(groups[idx].indices, i)
+	}
+	// Sort groups by Y
+	sort.Slice(groups, func(i, j int) bool { return groups[i].y < groups[j].y })
+
+	// If visualLine is out of bounds, clamp
+	if visualLine < 0 {
+		visualLine = 0
+	}
+	if visualLine >= len(groups) {
+		visualLine = len(groups) - 1
 	}
 
-	// 2. Identify glyphs on this line and find the rightmost extent
+	targetGroup := groups[visualLine]
+
+	// 3. Identify rightmost extent on this line
 	rightmostX := 0.0
 	rightmostIdx := -1
-	for i, yVal := range layout.Y {
-		if yVal == bestLineY {
+	for _, i := range targetGroup.indices {
 		xEnd := float64(layout.X[i] + layout.Advance[i])
 		if xEnd > rightmostX {
 			rightmostX = xEnd
 			rightmostIdx = i
 		}
 	}
-	}
 
-	// 3. Check if tap is to the right of the last character on this line
+	// 4. Check if tap is to the right of the last character
 	if rightmostIdx != -1 && x > rightmostX {
-		// Position after the last character on this line
+		// Position at the end of the line content, before any trailing newline.
 		start := layout.ByteOffsets[rightmostIdx]
-		_, size := utf8.DecodeRuneInString(TheState.Editor.Buffer[start:])
+		r, size := utf8.DecodeRuneInString(TheState.Editor.Buffer[start:])
+		if r == '\n' {
+			TheState.Editor.CursorPosition = start
+		} else {
 			TheState.Editor.CursorPosition = start + size
+		}
 		return
 	}
 
-	// 4. Otherwise, find the closest glyph on this line.
+	// 5. Otherwise, find the closest glyph on this line.
 	bestIdx := -1
 	minDist := float64(1e9)
-	for i, yVal := range layout.Y {
-		if yVal == bestLineY {
+	for _, i := range targetGroup.indices {
 		if bestIdx == -1 {
 			bestIdx = i
 		}
@@ -512,7 +537,6 @@ func SetCursorFromPoint(x, y float64) {
 			bestIdx = i
 		}
 	}
-	}
 	if bestIdx != -1 {
 		TheState.Editor.CursorPosition = layout.ByteOffsets[bestIdx]
 	}