Fix cursor positioning for end-of-line clicks

internal/editor/state.go

@@ -456,21 +456,66 @@ func SetCursorFromPoint(x, y float64) {
 		return
 	}
 
-	// Simple heuristic: find the closest glyph by distance to (x, y)
-	bestIdx := 0
-	minDist := float64(1e9)
-	lineHeight := float64(EditorLineHeight())
+	// 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
+		}
+		if yDist < minYDist {
+			minYDist = yDist
+			bestLineY = yVal
+		}
+	}
 
-	for i := 0; i < len(layout.X); i++ {
-		dx := float64(layout.X[i]) - x
-		// layout.Y[i] is the baseline. Taps are generally near the middle of the line.
-		// Adjust to compare against the approximate vertical center of the line.
-		dy := float64(layout.Y[i] - ui.Dp(lineHeight/2)) - y
-		dist := dx*dx + dy*dy
+	// 2. Identify glyphs on this line and find the rightmost extent
+	rightmostX := 0.0
+	rightmostIdx := -1
+	for i, yVal := range layout.Y {
+		if yVal == bestLineY {
+			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
+	if rightmostIdx != -1 && x > rightmostX {
+		// If rightmostIdx is the last glyph of the entire document
+		if rightmostIdx == len(layout.X)-1 {
+			TheState.Editor.CursorPosition = len(TheState.Editor.Buffer)
+		} else {
+			// Position after the last character on this line
+			TheState.Editor.CursorPosition = layout.ByteOffsets[rightmostIdx+1]
+		}
+		return
+	}
+
+	// 4. Otherwise, find the closest glyph on this line.
+	bestIdx := -1
+	minDist := float64(1e9)
+	for i, yVal := range layout.Y {
+		if yVal == bestLineY {
+			if bestIdx == -1 {
+				bestIdx = i
+			}
+			// Calculate distance to the glyph center
+			glyphCenterX := float64(layout.X[i] + layout.Advance[i]/2)
+			dist := glyphCenterX - x
+			if dist < 0 {
+				dist = -dist
+			}
 			if dist < minDist {
 				minDist = dist
 				bestIdx = i
 			}
 		}
+	}
+	if bestIdx != -1 {
 		TheState.Editor.CursorPosition = layout.ByteOffsets[bestIdx]
 	}
+}