Posters: re-place after a resize, measure cell size without padding, log failed posters

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

internal/ui/app.go

@@ -66,6 +66,7 @@ type App struct {
 	covers     bool // poster thumbnails enabled
 	coverStyle coverStyle
 	gfx        *kittyGraphics // real-image posters, nil when not used
+	lastWindow [3]int         // columns, rows and cell shape at the last draw
 	cellAspect float64        // height of a terminal cell divided by its width
 	coverCache *coverCache
 }
@@ -181,6 +182,7 @@ func New(cfg *config.Config) *App {
 		s.HideCursor()
 		a.screen = s
 		a.cellAspect = cellAspectOf(s)
+		a.noteWindow(s)
 		return false
 	})
 	a.app.SetRoot(&toastRoot{Flex: layout, app: a}, true).EnableMouse(false)
@@ -190,6 +192,22 @@ func New(cfg *config.Config) *App {
 	return a
 }
 
+// noteWindow notices when the terminal's size or cell size changed. The
+// placements of real-image posters are then made again: the picture would
+// otherwise rely on the terminal rescaling an existing placement correctly.
+func (a *App) noteWindow(s tcell.Screen) {
+	w, h := s.Size()
+	win := [3]int{w, h, int(a.cellAspect * 1000)}
+	if win == a.lastWindow {
+		return
+	}
+	first := a.lastWindow == [3]int{}
+	a.lastWindow = win
+	if !first && a.gfx != nil {
+		a.gfx.invalidate()
+	}
+}
+
 // writeTerminal sends raw bytes (graphics commands) to the terminal through the
 // screen's own connection. UI goroutine only, so it stays in step with drawing.
 func (a *App) writeTerminal(b []byte) error {
@@ -208,13 +226,29 @@ func (a *App) writeTerminal(b []byte) error {
 // pixels; 2 when the terminal does not report pixel sizes.
 func cellAspectOf(s tcell.Screen) float64 {
 	if tty, ok := s.Tty(); ok {
-		if ws, err := tty.WindowSize(); err == nil && ws.Width > 0 && ws.Height > 0 && ws.PixelWidth > 0 && ws.PixelHeight > 0 {
-			return (float64(ws.PixelHeight) / float64(ws.Height)) / (float64(ws.PixelWidth) / float64(ws.Width))
+		if ws, err := tty.WindowSize(); err == nil {
+			return cellAspectFromWindow(ws.Width, ws.Height, ws.PixelWidth, ws.PixelHeight)
 		}
 	}
 	return 2
 }
 
+// cellAspectFromWindow derives the cell shape from the window size in cells
+// and pixels. The pixel size usually includes some padding around the cell
+// grid, which would skew a plain division (more with a small grid, and it
+// changes while the window is resized); cell sizes are whole pixels, so the
+// division is rounded down, which drops that padding.
+func cellAspectFromWindow(cols, rows, pixelW, pixelH int) float64 {
+	if cols <= 0 || rows <= 0 || pixelW <= 0 || pixelH <= 0 {
+		return 2
+	}
+	cw, ch := pixelW/cols, pixelH/rows
+	if cw <= 0 || ch <= 0 {
+		return 2
+	}
+	return float64(ch) / float64(cw)
+}
+
 // coverMaxHeight is how tall the stored poster copies are: real images keep
 // more detail than block characters need.
 func (a *App) coverMaxHeight() int {