Fix cursor movement bug in scrolled editor and add regression test

internal/editor/state.go

@@ -514,8 +514,11 @@ func SetCursorFromPoint(x, y float64) {
 
 	// 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)
+	// We need to account for scroll offset: y is passed as relative to the text region top + scroll offset.
+	// So y is the position in the *content*.
+	visualLine := int(y / lineHeight)
+	
+	log.Printf("SetCursorFromPoint: y=%f, scroll=%f, visualLine=%d, lineHeight=%f", y, float64(TheState.ScrollOffset), visualLine, lineHeight)
 
 	// Group glyphs by their Y-baseline
 	type lineGroup struct {
@@ -523,27 +526,56 @@ func SetCursorFromPoint(x, y float64) {
 		indices []int
 	}
 	groups := []lineGroup{}
-	seenY := make(map[float64]int) // maps Y to group index
-
+	
+	// Find all unique baseline Ys
+	// The tap Y is based on line height (top of line).
+	// We need to associate Y-baseline with visual line index.
+	
+	// Create map from visual line (0, 1, 2...) to baseline Y.
+	// Since line height is fixed:
+	// Line 0 baseline is at some Y0.
+	// Line 1 baseline is at Y0 + lineHeight.
+	
+	// Let's find Y0 first.
+	minY := 1e9
+	for _, yVal := range layout.Y {
+		if float64(yVal) < minY {
+			minY = float64(yVal)
+		}
+	}
+	
+	// Now group by baseline
+	groups = []lineGroup{} // Reset groups
 	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
+		lineIdx := int((yFloat - minY) / lineHeight + 0.5) // round to nearest line
+		if lineIdx < 0 { lineIdx = 0 }
+		
+		// Ensure enough groups
+		for len(groups) <= lineIdx {
+			groups = append(groups, lineGroup{
+				y: minY + float64(len(groups))*lineHeight,
+				indices: []int{},
+			})
 		}
-		groups[idx].indices = append(groups[idx].indices, i)
+		groups[lineIdx].indices = append(groups[lineIdx].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
+	if visualLine >= len(groups) || len(groups[visualLine].indices) == 0 {
+		// Clamp to last valid group that has indices
+		for i := len(groups) - 1; i >= 0; i-- {
+			if len(groups[i].indices) > 0 {
+				visualLine = i
+				break
+			}
+		}
+	}
+	if len(groups[visualLine].indices) == 0 {
+		return
 	}
 
 	targetGroup := groups[visualLine]
@@ -558,6 +590,7 @@ func SetCursorFromPoint(x, y float64) {
 			rightmostIdx = i
 		}
 	}
+	log.Printf("TargetGroup: Y=%f, Indices=%v, rightmostIdx=%d, x=%f, rightmostX=%f", targetGroup.y, targetGroup.indices, rightmostIdx, x, rightmostX)
 
 	// 4. Check if tap is to the right of the last character
 	if rightmostIdx != -1 && x > rightmostX {
@@ -585,12 +618,15 @@ func SetCursorFromPoint(x, y float64) {
 		if dist < 0 {
 			dist = -dist
 		}
+		log.Printf("Checking glyph %d: x=%f, centerX=%f, dist=%f", i, x, glyphCenterX, dist)
 		if dist < minDist {
 			minDist = dist
 			bestIdx = i
 		}
 	}
+	log.Printf("BestIdx=%d, ByteOffset=%d", bestIdx, layout.ByteOffsets[bestIdx])
 	if bestIdx != -1 {
 		TheState.Editor.CursorPosition = layout.ByteOffsets[bestIdx]
+		log.Printf("After SetCursor: CursorPosition=%d", TheState.Editor.CursorPosition)
 	}
 }

internal/test/e2e/scroll_cursor_test.go

@@ -0,0 +1,88 @@
+package e2e_test
+
+import (
+	"testing"
+	"time"
+
+	"pad/internal/editor"
+	"pad/internal/test/e2e"
+	"pad/internal/ui"
+)
+
+func TestEditorClickToMoveCursorWithScroll(t *testing.T) {
+	h := e2e.NewHarnessWithDefaults()
+	h.Run() // Start the harness!
+	defer h.Cleanup()
+
+	// Switch to editor page
+	editor.GoToEditor(nil)
+	h.SendConfig(780, 1688)
+	// Give it a moment to initialize
+	time.Sleep(200 * time.Millisecond)
+
+	// Wait for frame
+	_, err := h.WaitForFrameCount(1, 5*time.Second)
+	if err != nil {
+		t.Fatalf("timeout waiting for frame: %v", err)
+	}
+
+	// Setup:
+	// - 2 lines, each 10 chars + newline.
+	// - Line height = 14 * 1.2 = 16.8 (rounded?) Let's check EditorLineHeight()
+	// EditorLineHeight is 14 * 1.2 = 16.8.
+	lineHeight := 16.8
+	editor.TheState.Editor.Buffer = "Line 1\nLine 2\nLine 3"
+	
+	// Scroll to start of Line 2 (skip Line 1)
+	editor.TheState.ScrollOffset = ui.Dp(lineHeight)
+
+	// GlyphLayout:
+	// Line 1: y = 0
+	// Line 2: y = 16.8
+	// Line 3: y = 33.6
+	editor.TheState.Editor.GlyphLayout = ui.GlyphLayout{
+		ByteOffsets: []int{0, 7, 14}, // Start of each line
+		X:           []ui.Dp{10, 10, 10},
+		Y:           []ui.Dp{ui.Dp(0), ui.Dp(lineHeight), ui.Dp(lineHeight * 2)},
+		Advance:     []ui.Dp{10, 10, 10},
+	}
+
+	// Tap at y=10 (within the text area).
+	// Because of scroll=16.8, this should correspond to:
+	// visualLine = (y + scroll) / lineHeight = (10 + 16.8) / 16.8 = 26.8 / 16.8 = 1.59 -> 1
+	// Line 1 is index 0. Line 2 is index 1.
+	// So visualLine 1 should be Line 2.
+	
+	// The problem is that SetCursorFromPoint expects y in DP, but receives it as raw pixels
+	// if we're not careful. Let's pass the y value properly.
+	// The test harness sends raw pixel coordinates to handler.
+	// EditorLayout converts tap point:
+	// localY := float64(pt.Y - editorRegion.Y + TheState.ScrollOffset)
+	// So the handler receives Y as pt.Y, where pt.Y is relative to the screen.
+	// The test harness doesn't seem to account for region offset.
+	
+	// Let's debug by printing in the test.
+	t.Logf("ScrollOffset: %v", editor.TheState.ScrollOffset)
+	
+	h.SendInput([]ui.InputEvent{
+		{
+			Handler: func(data any) {
+				if pt, ok := data.(ui.Point); ok {
+					// Manually simulate the offset correction that EditorLayout does
+					// editorRegion.Y is margin(10) + statusBarH(52) = 62.
+					// Let's set pt.Y to 10 + 62 = 72.
+					localY := float64(pt.Y) - 62.0 + float64(editor.TheState.ScrollOffset)
+					editor.SetCursorFromPoint(float64(pt.X), localY)
+				}
+			},
+			Data: ui.Point{X: 10, Y: 72},
+		},
+	})
+
+	// Assert cursor moved to start of Line 2 (offset 7)
+	time.Sleep(100 * time.Millisecond) // Give logic goroutine a moment to process input
+	t.Logf("Cursor position: %d", editor.TheState.Editor.CursorPosition)
+	if editor.TheState.Editor.CursorPosition != 7 {
+		t.Errorf("expected cursor to move to 7 (Line 2), but got %d", editor.TheState.Editor.CursorPosition)
+	}
+}