feat: triple-toggle CPU display mode via 1 key; add tooltip, font, hit-test

CPU display now cycles through three states with each press of 1:
  0 = CPUModeAverage  – aggregate bar only (default)
  1 = CPUModeCores    – individual core bars + aggregate
  2 = CPUModeOff      – all CPU bars hidden

Config file stores cpumode=N (integer); old showcores=0/1 is read for
backward compatibility. CLI flag --showcores replaced by --cpumode.

Other improvements landed in this commit:
- internal/display: add font.go (text rendering), hittest.go (bar hit
  testing), tooltip.go (mouse-over tooltip), tooltip_test.go
- internal/display: mouse tracking and drawOverlay hook in display.go
- internal/display: update build tags to //go:build form
- internal/collector: embed remote script via script_embed.go /
  scriptdata/loadbars-remote.sh
- internal/collector: CPULine.Total() changed to value receiver
- internal/collector: table test improvements (name field, t.Run)
- internal/constants: BytesPerSec consts promoted from var to const
- Magefile.go: fix error formatting and install path

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

8 files changed, 1239 insertions, 80 deletions

diff --git a/internal/display/activate.go b/internal/display/activate.go
index b9040d7..ac9b340 100644
--- a/internal/display/activate.go
+++ b/internal/display/activate.go
@@ -1,4 +1,4 @@
-// +build !darwin
+//go:build !darwin
 
 package display
 
diff --git a/internal/display/activate_darwin.go b/internal/display/activate_darwin.go
index 54c6b94..478d558 100644
--- a/internal/display/activate_darwin.go
+++ b/internal/display/activate_darwin.go
@@ -1,4 +1,4 @@
-// +build darwin
+//go:build darwin
 
 package display
 
diff --git a/internal/display/display.go b/internal/display/display.go
index 749c26c..47f8f10 100644
--- a/internal/display/display.go
+++ b/internal/display/display.go
@@ -17,7 +17,9 @@ import (
 	"github.com/veandco/go-sdl2/sdl"
 )
 
-const smoothFactor = 0.12 // blend toward target each frame; lower = smoother
+// smoothFactor controls how quickly bars blend toward their target values each frame.
+// Lower values produce smoother animations.
+const smoothFactor = 0.12
 
 // linkScales lists the supported network link speeds in ascending order,
 // used by the f/v hotkeys to cycle through link scale values.
@@ -27,7 +29,7 @@ var linkScales = []string{"mbit", "10mbit", "100mbit", "gbit", "10gbit"}
 type runState struct {
 	showAvgLine    bool
 	showIOAvgLine  bool
-	showCores      bool
+	cpuMode        int // constants.CPUModeAverage / CPUModeCores / CPUModeOff
 	showMem        bool
 	showNet        bool
 	showSeparators bool
@@ -40,27 +42,9 @@ type runState struct {
 	smoothedNet    map[string]*struct{ rxPct, txPct float64 }
 	prevNet        map[string]stats.NetStamp // aggregated (summed) previous net stamp per host
 	peakHistory    map[string][]float64
-}
-
-// newRunState builds initial run state from config.
-func newRunState(cfg *config.Config, winW, winH int32) *runState {
-	return &runState{
-		showAvgLine:    cfg.ShowAvgLine,
-		showIOAvgLine:  cfg.ShowIOAvgLine,
-		showCores:      cfg.ShowCores,
-		showMem:        cfg.ShowMem,
-		showNet:        cfg.ShowNet,
-		showSeparators: cfg.ShowSeparators,
-		extended:       cfg.Extended,
-		winW:           winW,
-		winH:           winH,
-		prevCPU:        make(map[string]collector.CPULine),
-		smoothedCPU:    make(map[string]*[10]float64),
-		smoothedMem:    make(map[string]*struct{ ramUsed, swapUsed float64 }),
-		smoothedNet:    make(map[string]*struct{ rxPct, txPct float64 }),
-		prevNet:        make(map[string]stats.NetStamp),
-		peakHistory:    make(map[string][]float64),
-	}
+	mouseX         int32     // last known mouse X position (for tooltip hit testing)
+	mouseY         int32     // last known mouse Y position (for tooltip hit testing)
+	mouseLastMove  time.Time // timestamp of last mouse movement; tooltip hidden after 3s idle
 }
 
 // Run runs the SDL display loop until ctx is cancelled or user presses 'q'.
@@ -111,6 +95,29 @@ func Run(ctx context.Context, cfg *config.Config, src stats.Source) error {
 	}
 }
 
+// newRunState builds initial run state from config.
+func newRunState(cfg *config.Config, winW, winH int32) *runState {
+	return &runState{
+		showAvgLine:    cfg.ShowAvgLine,
+		showIOAvgLine:  cfg.ShowIOAvgLine,
+		cpuMode:        cfg.CPUMode,
+		showMem:        cfg.ShowMem,
+		showNet:        cfg.ShowNet,
+		showSeparators: cfg.ShowSeparators,
+		extended:       cfg.Extended,
+		winW:           winW,
+		winH:           winH,
+		prevCPU:        make(map[string]collector.CPULine),
+		smoothedCPU:    make(map[string]*[10]float64),
+		smoothedMem:    make(map[string]*struct{ ramUsed, swapUsed float64 }),
+		smoothedNet:    make(map[string]*struct{ rxPct, txPct float64 }),
+		prevNet:        make(map[string]stats.NetStamp),
+		peakHistory:    make(map[string][]float64),
+		mouseX:         -1, // off-screen until first mouse move
+		mouseY:         -1,
+	}
+}
+
 func clampInt(v, min, max int) int {
 	if v < min {
 		return min
@@ -134,6 +141,9 @@ func handleEvents(window *sdl.Window, cfg *config.Config, state *runState) bool
 			if handleKey(ev.Keysym.Sym, window, cfg, state) {
 				return true
 			}
+		case *sdl.MouseMotionEvent:
+			state.mouseX, state.mouseY = ev.X, ev.Y
+			state.mouseLastMove = time.Now()
 		case *sdl.WindowEvent:
 			if ev.Event == sdl.WINDOWEVENT_RESIZED {
 				state.winW, state.winH = ev.Data1, ev.Data2
@@ -149,8 +159,16 @@ func handleKey(sym sdl.Keycode, window *sdl.Window, cfg *config.Config, state *r
 	case sdl.K_q:
 		return true
 	case sdl.K_1:
-		state.showCores = !state.showCores
-		fmt.Println("==> Toggled show cores:", state.showCores)
+		// Cycle through three CPU display modes: average → all cores → off → average
+		state.cpuMode = (state.cpuMode + 1) % constants.CPUModeCount
+		switch state.cpuMode {
+		case constants.CPUModeAverage:
+			fmt.Println("==> CPU: average bar only")
+		case constants.CPUModeCores:
+			fmt.Println("==> CPU: individual cores")
+		case constants.CPUModeOff:
+			fmt.Println("==> CPU: off")
+		}
 	case sdl.K_2, sdl.K_m:
 		state.showMem = !state.showMem
 		fmt.Println("==> Toggled show mem:", state.showMem)
@@ -194,7 +212,7 @@ func handleKey(sym sdl.Keycode, window *sdl.Window, cfg *config.Config, state *r
 	case sdl.K_w:
 		cfg.ShowAvgLine = state.showAvgLine
 		cfg.ShowIOAvgLine = state.showIOAvgLine
-		cfg.ShowCores = state.showCores
+		cfg.CPUMode = state.cpuMode
 		cfg.ShowMem = state.showMem
 		cfg.ShowNet = state.showNet
 		cfg.ShowSeparators = state.showSeparators
@@ -270,7 +288,7 @@ func barRect(winW, winH int32, numBars, maxPerRow, barIndex int) (x, y, w, h int
 // When showAvgLine/showIOAvgLine are enabled, global average lines are drawn on top.
 func drawFrame(renderer *sdl.Renderer, src stats.Source, cfg *config.Config, state *runState) {
 	snap := src.Snapshot()
-	numBars := countBars(snap, state.showCores, state.showMem, state.showNet)
+	numBars := countBars(snap, state.cpuMode, state.showMem, state.showNet)
 	// Always clear the entire window before drawing. SDL2 uses double-buffering,
 	// so skipping clear leaves stale content in the back buffer.
 	renderer.SetDrawColor(0, 0, 0, 255)
@@ -282,13 +300,15 @@ func drawFrame(renderer *sdl.Renderer, src stats.Source, cfg *config.Config, sta
 	if state.showIOAvgLine {
 		drawGlobalIOAvgLine(renderer, snap, state, numBars, cfg.MaxBarsPerRow)
 	}
+	// Draw mouse-over tooltip and host highlight inversion on top of all bars
+	drawOverlay(renderer, snap, cfg, state)
 }
 
-func countBars(snap map[string]*stats.HostStats, showCores, showMem, showNet bool) int {
+func countBars(snap map[string]*stats.HostStats, cpuMode int, showMem, showNet bool) int {
 	n := 0
 	for _, host := range sortedHosts(snap) {
 		if h := snap[host]; h != nil {
-			n += len(sortedCPUNames(h.CPU, showCores))
+			n += len(sortedCPUNames(h.CPU, cpuMode))
 			if showMem {
 				n++
 			}
@@ -430,7 +450,7 @@ func drawGlobalIOAvgLine(renderer *sdl.Renderer, snap map[string]*stats.HostStat
 // drawHostBars draws CPU, mem, and net bars for one host and advances barIndex.
 // maxPerRow controls multi-row wrapping (0 = single row).
 func drawHostBars(renderer *sdl.Renderer, h *stats.HostStats, host string, cfg *config.Config, state *runState, numBars, maxPerRow int, barIndex *int) {
-	cpuNames := sortedCPUNames(h.CPU, state.showCores)
+	cpuNames := sortedCPUNames(h.CPU, state.cpuMode)
 	for _, name := range cpuNames {
 		key := host + ";" + name
 		cur := h.CPU[name]
@@ -506,14 +526,20 @@ func sortedHosts(snap map[string]*stats.HostStats) []string {
 	return out
 }
 
-func sortedCPUNames(cpu map[string]collector.CPULine, showCores bool) []string {
+func sortedCPUNames(cpu map[string]collector.CPULine, cpuMode int) []string {
+	// CPUModeOff: hide all CPU bars
+	if cpuMode == constants.CPUModeOff {
+		return nil
+	}
 	var names []string
 	for name := range cpu {
 		if name == "cpu" {
+			// Aggregate bar always shown unless CPUModeOff
 			names = append(names, "cpu")
 			continue
 		}
-		if showCores {
+		// Individual core bars only shown in CPUModeCores
+		if cpuMode == constants.CPUModeCores {
 			names = append(names, name)
 		}
 	}
diff --git a/internal/display/display_test.go b/internal/display/display_test.go
index 332fe32..b51e6d1 100644
--- a/internal/display/display_test.go
+++ b/internal/display/display_test.go
@@ -141,7 +141,7 @@ func renderOneCPUBar(t *testing.T, systemPct, userPct, idlePct float64, extended
 
 	prev, cur := makeCPUPair(systemPct, userPct, idlePct)
 	cfg := defaultTestConfig()
-	cfg.ShowCores = false
+	cfg.CPUMode = constants.CPUModeAverage
 	cfg.ShowMem = false
 	cfg.ShowNet = false
 	cfg.Extended = extended
@@ -212,7 +212,7 @@ func TestMemBar_RamAndSwap(t *testing.T) {
 	defer surface.Free()
 
 	cfg := defaultTestConfig()
-	cfg.ShowCores = false
+	cfg.CPUMode = constants.CPUModeAverage
 	cfg.ShowMem = true
 	cfg.ShowNet = false
 
@@ -266,7 +266,7 @@ func TestNetBar_RxTx(t *testing.T) {
 	defer surface.Free()
 
 	cfg := defaultTestConfig()
-	cfg.ShowCores = false
+	cfg.CPUMode = constants.CPUModeAverage
 	cfg.ShowMem = false
 	cfg.ShowNet = true
 	cfg.NetLink = "gbit"
@@ -318,7 +318,7 @@ func TestNetBar_AggregatesAllInterfaces(t *testing.T) {
 	defer surface.Free()
 
 	cfg := defaultTestConfig()
-	cfg.ShowCores = false
+	cfg.CPUMode = constants.CPUModeAverage
 	cfg.ShowMem = false
 	cfg.ShowNet = true
 	cfg.NetLink = "gbit"
@@ -372,7 +372,7 @@ func TestMultiHost_BarCount(t *testing.T) {
 	defer surface.Free()
 
 	cfg := defaultTestConfig()
-	cfg.ShowCores = false
+	cfg.CPUMode = constants.CPUModeAverage
 	cfg.ShowMem = true
 	cfg.ShowNet = true
 
@@ -397,7 +397,7 @@ func TestMultiHost_BarCount(t *testing.T) {
 	}
 
 	snap := src.Snapshot()
-	numBars := countBars(snap, false, true, true)
+	numBars := countBars(snap, constants.CPUModeAverage, true, true)
 	if numBars != 6 {
 		t.Fatalf("expected 6 bars (2 hosts × 3), got %d", numBars)
 	}
@@ -418,7 +418,7 @@ func TestMultiHost_BarCount(t *testing.T) {
 }
 
 func TestCores_Toggle(t *testing.T) {
-	// With showCores=true and 2 cores, we get cpu + cpu0 + cpu1 = 3 CPU bars
+	// Three CPU mode states: average (1 bar), cores (3 bars), off (0 → floor 1)
 	hostStats := &stats.HostStats{
 		CPU: map[string]collector.CPULine{
 			"cpu":  {System: 500, User: 0, Idle: 500},
@@ -429,16 +429,22 @@ func TestCores_Toggle(t *testing.T) {
 
 	snap := map[string]*stats.HostStats{"host1": hostStats}
 
-	// showCores=true: should count 3 CPU bars
-	nWith := countBars(snap, true, false, false)
-	if nWith != 3 {
-		t.Errorf("showCores=true: expected 3 bars, got %d", nWith)
+	// CPUModeAverage: aggregate bar only (1 bar)
+	nAverage := countBars(snap, constants.CPUModeAverage, false, false)
+	if nAverage != 1 {
+		t.Errorf("CPUModeAverage: expected 1 bar, got %d", nAverage)
 	}
 
-	// showCores=false: should count 1 CPU bar (aggregate only)
-	nWithout := countBars(snap, false, false, false)
-	if nWithout != 1 {
-		t.Errorf("showCores=false: expected 1 bar, got %d", nWithout)
+	// CPUModeCores: aggregate + individual cores = cpu + cpu0 + cpu1 (3 bars)
+	nCores := countBars(snap, constants.CPUModeCores, false, false)
+	if nCores != 3 {
+		t.Errorf("CPUModeCores: expected 3 bars, got %d", nCores)
+	}
+
+	// CPUModeOff: no CPU bars → countBars floors to 1 (window always shows something)
+	nOff := countBars(snap, constants.CPUModeOff, false, false)
+	if nOff != 1 {
+		t.Errorf("CPUModeOff: expected 1 (floor), got %d", nOff)
 	}
 }
 
@@ -486,7 +492,7 @@ func TestNetBar_NoInterface(t *testing.T) {
 	defer surface.Free()
 
 	cfg := defaultTestConfig()
-	cfg.ShowCores = false
+	cfg.CPUMode = constants.CPUModeAverage
 	cfg.ShowMem = false
 	cfg.ShowNet = true
 
@@ -548,7 +554,7 @@ func TestRemainderPixels_AfterToggleMem(t *testing.T) {
 	src := &mockSource{data: hosts}
 
 	cfg := defaultTestConfig()
-	cfg.ShowCores = true
+	cfg.CPUMode = constants.CPUModeCores
 	cfg.ShowMem = true
 	cfg.ShowNet = false
 
@@ -589,7 +595,7 @@ func TestRemainderPixels_AfterToggleMem(t *testing.T) {
 // newHotkeyTestEnv creates a test environment with 1 host, 2 CPU cores, memory,
 // and 2 net interfaces. Returns all components needed for handleKey + drawFrame
 // pixel inspection tests.
-func newHotkeyTestEnv(t *testing.T, showCores, showMem, showNet bool) (
+func newHotkeyTestEnv(t *testing.T, cpuMode int, showMem, showNet bool) (
 	renderer *sdl.Renderer, surface *sdl.Surface,
 	cfg *config.Config, state *runState, src *mockSource,
 ) {
@@ -602,7 +608,7 @@ func newHotkeyTestEnv(t *testing.T, showCores, showMem, showNet bool) (
 	}
 
 	cfg = defaultTestConfig()
-	cfg.ShowCores = showCores
+	cfg.CPUMode = cpuMode
 	cfg.ShowMem = showMem
 	cfg.ShowNet = showNet
 
@@ -662,36 +668,52 @@ func TestHandleKey_UnknownKey(t *testing.T) {
 		t.Error("expected handleKey(x) to return false")
 	}
 	// State should be unchanged
-	if state.showCores != cfg.ShowCores || state.showMem != cfg.ShowMem || state.showNet != cfg.ShowNet {
+	if state.cpuMode != cfg.CPUMode || state.showMem != cfg.ShowMem || state.showNet != cfg.ShowNet {
 		t.Error("unknown key should not change state")
 	}
 }
 
 func TestHandleKey_ToggleCores(t *testing.T) {
-	renderer, surface, cfg, state, src := newHotkeyTestEnv(t, false, false, false)
+	renderer, surface, cfg, state, src := newHotkeyTestEnv(t, constants.CPUModeAverage, false, false)
 	defer renderer.Destroy()
 	defer surface.Free()
 
-	// Before: showCores=false → 1 CPU bar (aggregate)
+	// State 0 (CPUModeAverage): single aggregate bar spans full width
 	drawFrame(renderer, src, cfg, state)
-	// The single bar spans full width; check it has color at x=100
-	assertPixelColor(t, surface, 100, 95, constants.Blue, 5, "aggregate CPU bar before toggle")
+	assertPixelColor(t, surface, 100, 95, constants.Blue, 5, "aggregate CPU bar in average mode")
 
-	// Press '1' to toggle cores on
+	// Press '1': CPUModeAverage → CPUModeCores
 	handleKey(sdl.K_1, nil, cfg, state)
-	if !state.showCores {
-		t.Fatal("expected showCores=true after pressing 1")
+	if state.cpuMode != constants.CPUModeCores {
+		t.Fatalf("expected cpuMode=CPUModeCores after first press, got %d", state.cpuMode)
 	}
 
-	// After: showCores=true → 3 CPU bars (cpu + cpu0 + cpu1)
+	// State 1 (CPUModeCores): 3 CPU bars (cpu + cpu0 + cpu1), each ~66px wide at 200px window
 	drawFrame(renderer, src, cfg, state)
-	// With 3 bars at width 200: barWidth=66, bars at x=0, x=66, x=132
-	// Third bar (cpu1) should have color
-	assertPixelColor(t, surface, 140, 95, constants.Blue, 5, "cpu1 bar after toggle")
+	// Third bar (cpu1) starts at x=133; check it has color at x=140
+	assertPixelColor(t, surface, 140, 95, constants.Blue, 5, "cpu1 bar visible in cores mode")
+
+	// Press '1': CPUModeCores → CPUModeOff
+	handleKey(sdl.K_1, nil, cfg, state)
+	if state.cpuMode != constants.CPUModeOff {
+		t.Fatalf("expected cpuMode=CPUModeOff after second press, got %d", state.cpuMode)
+	}
+
+	// State 2 (CPUModeOff): no CPU bars; countBars returns 1 (floor) so window is still drawn
+	nOff := countBars(src.Snapshot(), constants.CPUModeOff, false, false)
+	if nOff != 1 {
+		t.Errorf("CPUModeOff: expected countBars=1 (floor), got %d", nOff)
+	}
+
+	// Press '1': CPUModeOff → CPUModeAverage (wraps around)
+	handleKey(sdl.K_1, nil, cfg, state)
+	if state.cpuMode != constants.CPUModeAverage {
+		t.Fatalf("expected cpuMode=CPUModeAverage after third press, got %d", state.cpuMode)
+	}
 }
 
 func TestHandleKey_ToggleMem(t *testing.T) {
-	renderer, surface, cfg, state, src := newHotkeyTestEnv(t, false, false, false)
+	renderer, surface, cfg, state, src := newHotkeyTestEnv(t, constants.CPUModeAverage, false, false)
 	defer renderer.Destroy()
 	defer surface.Free()
 
@@ -728,7 +750,7 @@ func TestHandleKey_ToggleMemAlias(t *testing.T) {
 }
 
 func TestHandleKey_ToggleNet(t *testing.T) {
-	renderer, surface, cfg, state, src := newHotkeyTestEnv(t, false, false, false)
+	renderer, surface, cfg, state, src := newHotkeyTestEnv(t, constants.CPUModeAverage, false, false)
 	defer renderer.Destroy()
 	defer surface.Free()
 
@@ -764,7 +786,7 @@ func TestHandleKey_ToggleNetAlias(t *testing.T) {
 }
 
 func TestHandleKey_ToggleExtended(t *testing.T) {
-	renderer, surface, cfg, state, src := newHotkeyTestEnv(t, false, false, false)
+	renderer, surface, cfg, state, src := newHotkeyTestEnv(t, constants.CPUModeAverage, false, false)
 	defer renderer.Destroy()
 	defer surface.Free()
 
@@ -852,7 +874,7 @@ func TestHandleKey_WriteConfig(t *testing.T) {
 	state := newRunState(cfg, 200, 100)
 	// Modify state values that should be copied to config
 	state.showAvgLine = true
-	state.showCores = true
+	state.cpuMode = constants.CPUModeCores
 	state.showMem = true
 	state.showNet = true
 	state.extended = true
@@ -862,8 +884,8 @@ func TestHandleKey_WriteConfig(t *testing.T) {
 	if !cfg.ShowAvgLine {
 		t.Error("expected ShowAvgLine=true in config after 'w'")
 	}
-	if !cfg.ShowCores {
-		t.Error("expected ShowCores=true in config after 'w'")
+	if cfg.CPUMode != constants.CPUModeCores {
+		t.Errorf("expected CPUMode=CPUModeCores in config after 'w', got %d", cfg.CPUMode)
 	}
 	if !cfg.ShowMem {
 		t.Error("expected ShowMem=true in config after 'w'")
@@ -877,7 +899,7 @@ func TestHandleKey_WriteConfig(t *testing.T) {
 }
 
 func TestHandleKey_LinkScaleUp(t *testing.T) {
-	renderer, surface, cfg, state, src := newHotkeyTestEnv(t, false, false, true)
+	renderer, surface, cfg, state, src := newHotkeyTestEnv(t, constants.CPUModeAverage, false, true)
 	defer renderer.Destroy()
 	defer surface.Free()
 
@@ -950,7 +972,7 @@ func TestGlobalAvgLine_SingleHost(t *testing.T) {
 
 	prev, cur := makeCPUPair(40, 40, 20) // 80% used (40 sys + 40 user)
 	cfg := defaultTestConfig()
-	cfg.ShowCores = false
+	cfg.CPUMode = constants.CPUModeAverage
 	cfg.ShowMem = false
 	cfg.ShowNet = false
 
@@ -988,7 +1010,7 @@ func TestGlobalAvgLine_MultiHost(t *testing.T) {
 	prev2, cur2 := makeCPUPair(20, 20, 60) // 40% used
 
 	cfg := defaultTestConfig()
-	cfg.ShowCores = false
+	cfg.CPUMode = constants.CPUModeAverage
 	cfg.ShowMem = false
 	cfg.ShowNet = false
 
@@ -1023,7 +1045,7 @@ func TestGlobalAvgLine_Disabled(t *testing.T) {
 
 	prev, cur := makeCPUPair(40, 40, 20) // 80% used
 	cfg := defaultTestConfig()
-	cfg.ShowCores = false
+	cfg.CPUMode = constants.CPUModeAverage
 	cfg.ShowMem = false
 	cfg.ShowNet = false
 
@@ -1284,7 +1306,7 @@ func TestHandleKey_ToggleSeparators(t *testing.T) {
 }
 
 func TestSeparator_TwoHosts_Enabled(t *testing.T) {
-	// Two hosts (100% system = blue) with separators enabled: yellow pixel at boundary
+	// Two hosts (100% system = blue) with separators enabled: red pixel at boundary
 	const w, h int32 = 200, 100
 
 	renderer, surface, err := createTestRenderer(w, h)
@@ -1298,7 +1320,7 @@ func TestSeparator_TwoHosts_Enabled(t *testing.T) {
 	prev2, cur2 := makeCPUPair(100, 0, 0)
 
 	cfg := defaultTestConfig()
-	cfg.ShowCores = false
+	cfg.CPUMode = constants.CPUModeAverage
 	cfg.ShowMem = false
 	cfg.ShowNet = false
 	cfg.ShowSeparators = true
@@ -1321,7 +1343,7 @@ func TestSeparator_TwoHosts_Enabled(t *testing.T) {
 }
 
 func TestSeparator_TwoHosts_Disabled(t *testing.T) {
-	// Two hosts (100% system = blue) with separators disabled: no yellow at boundary
+	// Two hosts (100% system = blue) with separators disabled: no red at boundary
 	const w, h int32 = 200, 100
 
 	renderer, surface, err := createTestRenderer(w, h)
@@ -1335,7 +1357,7 @@ func TestSeparator_TwoHosts_Disabled(t *testing.T) {
 	prev2, cur2 := makeCPUPair(100, 0, 0)
 
 	cfg := defaultTestConfig()
-	cfg.ShowCores = false
+	cfg.CPUMode = constants.CPUModeAverage
 	cfg.ShowMem = false
 	cfg.ShowNet = false
 	cfg.ShowSeparators = false
@@ -1370,7 +1392,7 @@ func TestSeparator_SingleHost(t *testing.T) {
 
 	prev, cur := makeCPUPair(50, 30, 20)
 	cfg := defaultTestConfig()
-	cfg.ShowCores = false
+	cfg.CPUMode = constants.CPUModeAverage
 	cfg.ShowMem = false
 	cfg.ShowNet = false
 	cfg.ShowSeparators = true
diff --git a/internal/display/font.go b/internal/display/font.go
new file mode 100644
index 0000000..d6dae18
--- /dev/null
+++ b/internal/display/font.go
@@ -0,0 +1,248 @@
+package display
+
+import "github.com/veandco/go-sdl2/sdl"
+
+// Bitmap font: 5x7 pixel glyphs for ASCII 32–126, rendered via FillRect.
+// Each glyph is 7 rows of 5 bits (MSB = leftmost pixel).
+
+const (
+	glyphW = 5 // pixels per character width
+	glyphH = 7 // pixels per character height
+	charGap = 1 // horizontal gap between characters
+)
+
+// font5x7 maps ASCII 32–126 to 7-byte bitmaps (one byte per row, top 5 bits used).
+// Index 0 = space (0x20), index 94 = tilde (0x7E).
+var font5x7 = [95][7]byte{
+	// space (0x20)
+	{0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00},
+	// ! (0x21)
+	{0x20, 0x20, 0x20, 0x20, 0x20, 0x00, 0x20},
+	// " (0x22)
+	{0x50, 0x50, 0x00, 0x00, 0x00, 0x00, 0x00},
+	// # (0x23)
+	{0x50, 0xF8, 0x50, 0x50, 0x50, 0xF8, 0x50},
+	// $ (0x24)
+	{0x20, 0x70, 0xA0, 0x70, 0x28, 0x70, 0x20},
+	// % (0x25)
+	{0xC8, 0xC8, 0x10, 0x20, 0x40, 0x98, 0x98},
+	// & (0x26)
+	{0x40, 0xA0, 0xA0, 0x40, 0xA8, 0x90, 0x68},
+	// ' (0x27)
+	{0x20, 0x20, 0x00, 0x00, 0x00, 0x00, 0x00},
+	// ( (0x28)
+	{0x10, 0x20, 0x40, 0x40, 0x40, 0x20, 0x10},
+	// ) (0x29)
+	{0x40, 0x20, 0x10, 0x10, 0x10, 0x20, 0x40},
+	// * (0x2A)
+	{0x00, 0x20, 0xA8, 0x70, 0xA8, 0x20, 0x00},
+	// + (0x2B)
+	{0x00, 0x20, 0x20, 0xF8, 0x20, 0x20, 0x00},
+	// , (0x2C)
+	{0x00, 0x00, 0x00, 0x00, 0x00, 0x20, 0x40},
+	// - (0x2D)
+	{0x00, 0x00, 0x00, 0xF8, 0x00, 0x00, 0x00},
+	// . (0x2E)
+	{0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x20},
+	// / (0x2F)
+	{0x08, 0x08, 0x10, 0x20, 0x40, 0x80, 0x80},
+	// 0 (0x30)
+	{0x70, 0x88, 0x98, 0xA8, 0xC8, 0x88, 0x70},
+	// 1 (0x31)
+	{0x20, 0x60, 0x20, 0x20, 0x20, 0x20, 0x70},
+	// 2 (0x32)
+	{0x70, 0x88, 0x08, 0x10, 0x20, 0x40, 0xF8},
+	// 3 (0x33)
+	{0x70, 0x88, 0x08, 0x30, 0x08, 0x88, 0x70},
+	// 4 (0x34)
+	{0x10, 0x30, 0x50, 0x90, 0xF8, 0x10, 0x10},
+	// 5 (0x35)
+	{0xF8, 0x80, 0xF0, 0x08, 0x08, 0x88, 0x70},
+	// 6 (0x36)
+	{0x30, 0x40, 0x80, 0xF0, 0x88, 0x88, 0x70},
+	// 7 (0x37)
+	{0xF8, 0x08, 0x10, 0x20, 0x40, 0x40, 0x40},
+	// 8 (0x38)
+	{0x70, 0x88, 0x88, 0x70, 0x88, 0x88, 0x70},
+	// 9 (0x39)
+	{0x70, 0x88, 0x88, 0x78, 0x08, 0x10, 0x60},
+	// : (0x3A)
+	{0x00, 0x00, 0x20, 0x00, 0x00, 0x20, 0x00},
+	// ; (0x3B)
+	{0x00, 0x00, 0x20, 0x00, 0x00, 0x20, 0x40},
+	// < (0x3C)
+	{0x08, 0x10, 0x20, 0x40, 0x20, 0x10, 0x08},
+	// = (0x3D)
+	{0x00, 0x00, 0xF8, 0x00, 0xF8, 0x00, 0x00},
+	// > (0x3E)
+	{0x80, 0x40, 0x20, 0x10, 0x20, 0x40, 0x80},
+	// ? (0x3F)
+	{0x70, 0x88, 0x08, 0x10, 0x20, 0x00, 0x20},
+	// @ (0x40)
+	{0x70, 0x88, 0xB8, 0xA8, 0xB8, 0x80, 0x70},
+	// A (0x41)
+	{0x70, 0x88, 0x88, 0xF8, 0x88, 0x88, 0x88},
+	// B (0x42)
+	{0xF0, 0x88, 0x88, 0xF0, 0x88, 0x88, 0xF0},
+	// C (0x43)
+	{0x70, 0x88, 0x80, 0x80, 0x80, 0x88, 0x70},
+	// D (0x44)
+	{0xF0, 0x88, 0x88, 0x88, 0x88, 0x88, 0xF0},
+	// E (0x45)
+	{0xF8, 0x80, 0x80, 0xF0, 0x80, 0x80, 0xF8},
+	// F (0x46)
+	{0xF8, 0x80, 0x80, 0xF0, 0x80, 0x80, 0x80},
+	// G (0x47)
+	{0x70, 0x88, 0x80, 0xB8, 0x88, 0x88, 0x70},
+	// H (0x48)
+	{0x88, 0x88, 0x88, 0xF8, 0x88, 0x88, 0x88},
+	// I (0x49)
+	{0x70, 0x20, 0x20, 0x20, 0x20, 0x20, 0x70},
+	// J (0x4A)
+	{0x38, 0x10, 0x10, 0x10, 0x10, 0x90, 0x60},
+	// K (0x4B)
+	{0x88, 0x90, 0xA0, 0xC0, 0xA0, 0x90, 0x88},
+	// L (0x4C)
+	{0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0xF8},
+	// M (0x4D)
+	{0x88, 0xD8, 0xA8, 0xA8, 0x88, 0x88, 0x88},
+	// N (0x4E)
+	{0x88, 0xC8, 0xA8, 0x98, 0x88, 0x88, 0x88},
+	// O (0x4F)
+	{0x70, 0x88, 0x88, 0x88, 0x88, 0x88, 0x70},
+	// P (0x50)
+	{0xF0, 0x88, 0x88, 0xF0, 0x80, 0x80, 0x80},
+	// Q (0x51)
+	{0x70, 0x88, 0x88, 0x88, 0xA8, 0x90, 0x68},
+	// R (0x52)
+	{0xF0, 0x88, 0x88, 0xF0, 0xA0, 0x90, 0x88},
+	// S (0x53)
+	{0x70, 0x88, 0x80, 0x70, 0x08, 0x88, 0x70},
+	// T (0x54)
+	{0xF8, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20},
+	// U (0x55)
+	{0x88, 0x88, 0x88, 0x88, 0x88, 0x88, 0x70},
+	// V (0x56)
+	{0x88, 0x88, 0x88, 0x88, 0x88, 0x50, 0x20},
+	// W (0x57)
+	{0x88, 0x88, 0x88, 0xA8, 0xA8, 0xD8, 0x88},
+	// X (0x58)
+	{0x88, 0x88, 0x50, 0x20, 0x50, 0x88, 0x88},
+	// Y (0x59)
+	{0x88, 0x88, 0x50, 0x20, 0x20, 0x20, 0x20},
+	// Z (0x5A)
+	{0xF8, 0x08, 0x10, 0x20, 0x40, 0x80, 0xF8},
+	// [ (0x5B)
+	{0x70, 0x40, 0x40, 0x40, 0x40, 0x40, 0x70},
+	// \ (0x5C)
+	{0x80, 0x80, 0x40, 0x20, 0x10, 0x08, 0x08},
+	// ] (0x5D)
+	{0x70, 0x10, 0x10, 0x10, 0x10, 0x10, 0x70},
+	// ^ (0x5E)
+	{0x20, 0x50, 0x88, 0x00, 0x00, 0x00, 0x00},
+	// _ (0x5F)
+	{0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0xF8},
+	// ` (0x60)
+	{0x40, 0x20, 0x00, 0x00, 0x00, 0x00, 0x00},
+	// a (0x61)
+	{0x00, 0x00, 0x70, 0x08, 0x78, 0x88, 0x78},
+	// b (0x62)
+	{0x80, 0x80, 0xF0, 0x88, 0x88, 0x88, 0xF0},
+	// c (0x63)
+	{0x00, 0x00, 0x70, 0x80, 0x80, 0x80, 0x70},
+	// d (0x64)
+	{0x08, 0x08, 0x78, 0x88, 0x88, 0x88, 0x78},
+	// e (0x65)
+	{0x00, 0x00, 0x70, 0x88, 0xF8, 0x80, 0x70},
+	// f (0x66)
+	{0x30, 0x48, 0x40, 0xE0, 0x40, 0x40, 0x40},
+	// g (0x67)
+	{0x00, 0x00, 0x78, 0x88, 0x78, 0x08, 0x70},
+	// h (0x68)
+	{0x80, 0x80, 0xF0, 0x88, 0x88, 0x88, 0x88},
+	// i (0x69)
+	{0x20, 0x00, 0x60, 0x20, 0x20, 0x20, 0x70},
+	// j (0x6A)
+	{0x10, 0x00, 0x30, 0x10, 0x10, 0x90, 0x60},
+	// k (0x6B)
+	{0x80, 0x80, 0x90, 0xA0, 0xC0, 0xA0, 0x90},
+	// l (0x6C)
+	{0x60, 0x20, 0x20, 0x20, 0x20, 0x20, 0x70},
+	// m (0x6D)
+	{0x00, 0x00, 0xD0, 0xA8, 0xA8, 0xA8, 0xA8},
+	// n (0x6E)
+	{0x00, 0x00, 0xF0, 0x88, 0x88, 0x88, 0x88},
+	// o (0x6F)
+	{0x00, 0x00, 0x70, 0x88, 0x88, 0x88, 0x70},
+	// p (0x70)
+	{0x00, 0x00, 0xF0, 0x88, 0xF0, 0x80, 0x80},
+	// q (0x71)
+	{0x00, 0x00, 0x78, 0x88, 0x78, 0x08, 0x08},
+	// r (0x72)
+	{0x00, 0x00, 0xB0, 0xC8, 0x80, 0x80, 0x80},
+	// s (0x73)
+	{0x00, 0x00, 0x78, 0x80, 0x70, 0x08, 0xF0},
+	// t (0x74)
+	{0x40, 0x40, 0xE0, 0x40, 0x40, 0x48, 0x30},
+	// u (0x75)
+	{0x00, 0x00, 0x88, 0x88, 0x88, 0x88, 0x78},
+	// v (0x76)
+	{0x00, 0x00, 0x88, 0x88, 0x88, 0x50, 0x20},
+	// w (0x77)
+	{0x00, 0x00, 0x88, 0x88, 0xA8, 0xA8, 0x50},
+	// x (0x78)
+	{0x00, 0x00, 0x88, 0x50, 0x20, 0x50, 0x88},
+	// y (0x79)
+	{0x00, 0x00, 0x88, 0x88, 0x78, 0x08, 0x70},
+	// z (0x7A)
+	{0x00, 0x00, 0xF8, 0x10, 0x20, 0x40, 0xF8},
+	// { (0x7B)
+	{0x10, 0x20, 0x20, 0x40, 0x20, 0x20, 0x10},
+	// | (0x7C)
+	{0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20},
+	// } (0x7D)
+	{0x40, 0x20, 0x20, 0x10, 0x20, 0x20, 0x40},
+	// ~ (0x7E)
+	{0x00, 0x00, 0x40, 0xA8, 0x10, 0x00, 0x00},
+}
+
+// drawChar renders a single ASCII character at (x, y) using filled rectangles.
+// Each pixel of the 5x7 glyph is drawn as a scale×scale block.
+func drawChar(renderer *sdl.Renderer, ch byte, x, y, scale int32) {
+	if ch < 0x20 || ch > 0x7E {
+		ch = '?' // replace unprintable characters
+	}
+	glyph := font5x7[ch-0x20]
+	for row := 0; row < glyphH; row++ {
+		bits := glyph[row]
+		for col := 0; col < glyphW; col++ {
+			if bits&(0x80>>uint(col)) != 0 {
+				renderer.FillRect(&sdl.Rect{
+					X: x + int32(col)*scale,
+					Y: y + int32(row)*scale,
+					W: scale,
+					H: scale,
+				})
+			}
+		}
+	}
+}
+
+// drawString renders a string at (x, y) with the given pixel scale.
+// Returns the total width in pixels consumed by the string.
+func drawString(renderer *sdl.Renderer, s string, x, y, scale int32) int32 {
+	cx := x
+	for i := 0; i < len(s); i++ {
+		drawChar(renderer, s[i], cx, y, scale)
+		cx += (glyphW + charGap) * scale
+	}
+	return cx - x
+}
+
+// stringWidth returns the pixel width of a string at the given scale.
+func stringWidth(s string, scale int32) int32 {
+	if len(s) == 0 {
+		return 0
+	}
+	return int32(len(s))*(glyphW+charGap)*scale - charGap*scale
+}
diff --git a/internal/display/hittest.go b/internal/display/hittest.go
new file mode 100644
index 0000000..fe88471
--- /dev/null
+++ b/internal/display/hittest.go
@@ -0,0 +1,82 @@
+package display
+
+import (
+	"codeberg.org/snonux/loadbars/internal/config"
+	"codeberg.org/snonux/loadbars/internal/stats"
+	"github.com/veandco/go-sdl2/sdl"
+)
+
+// barKind identifies what type of data a bar represents.
+type barKind int
+
+const (
+	barCPU barKind = iota
+	barMem
+	barNet
+)
+
+// barDescriptor describes a single bar's position, host, and type.
+type barDescriptor struct {
+	host    string  // hostname this bar belongs to
+	kind    barKind // CPU, mem, or net
+	cpuName string  // CPU name (e.g. "cpu", "cpu0"); only set for barCPU
+	rect    sdl.Rect
+}
+
+// buildBarMap replays the same host/bar iteration as drawBars to produce
+// a slice of bar descriptors with their screen rectangles.
+func buildBarMap(snap map[string]*stats.HostStats, cfg *config.Config, state *runState) []barDescriptor {
+	numBars := countBars(snap, state.cpuMode, state.showMem, state.showNet)
+	maxPerRow := cfg.MaxBarsPerRow
+	hosts := sortedHosts(snap)
+
+	bars := make([]barDescriptor, 0, numBars)
+	barIndex := 0
+	for _, host := range hosts {
+		h := snap[host]
+		if h == nil {
+			continue
+		}
+		cpuNames := sortedCPUNames(h.CPU, state.cpuMode)
+		for _, name := range cpuNames {
+			x, y, w, bh := barRect(state.winW, state.winH, numBars, maxPerRow, barIndex)
+			bars = append(bars, barDescriptor{
+				host:    host,
+				kind:    barCPU,
+				cpuName: name,
+				rect:    sdl.Rect{X: x, Y: y, W: w, H: bh},
+			})
+			barIndex++
+		}
+		if state.showMem {
+			x, y, w, bh := barRect(state.winW, state.winH, numBars, maxPerRow, barIndex)
+			bars = append(bars, barDescriptor{
+				host: host,
+				kind: barMem,
+				rect: sdl.Rect{X: x, Y: y, W: w, H: bh},
+			})
+			barIndex++
+		}
+		if state.showNet {
+			x, y, w, bh := barRect(state.winW, state.winH, numBars, maxPerRow, barIndex)
+			bars = append(bars, barDescriptor{
+				host: host,
+				kind: barNet,
+				rect: sdl.Rect{X: x, Y: y, W: w, H: bh},
+			})
+			barIndex++
+		}
+	}
+	return bars
+}
+
+// hitTest returns the bar descriptor under the given point, or nil if none.
+func hitTest(bars []barDescriptor, mx, my int32) *barDescriptor {
+	for i := range bars {
+		r := &bars[i].rect
+		if mx >= r.X && mx < r.X+r.W && my >= r.Y && my < r.Y+r.H {
+			return &bars[i]
+		}
+	}
+	return nil
+}
diff --git a/internal/display/tooltip.go b/internal/display/tooltip.go
new file mode 100644
index 0000000..42075e0
--- /dev/null
+++ b/internal/display/tooltip.go
@@ -0,0 +1,194 @@
+package display
+
+import (
+	"fmt"
+	"time"
+
+	"codeberg.org/snonux/loadbars/internal/config"
+	"codeberg.org/snonux/loadbars/internal/stats"
+	"github.com/veandco/go-sdl2/sdl"
+)
+
+// mouseIdleTimeout is how long the mouse must be idle before the tooltip
+// and host inversion overlay are hidden.
+const mouseIdleTimeout = 3 * time.Second
+
+const (
+	tooltipScale   int32 = 2 // pixel scale for bitmap font
+	tooltipPadX    int32 = 6 // horizontal padding inside tooltip box
+	tooltipPadY    int32 = 4 // vertical padding inside tooltip box
+	tooltipOffsetX int32 = 12 // offset from cursor to tooltip
+	tooltipOffsetY int32 = 12
+)
+
+// tooltipLines builds the text lines to display for the hovered bar.
+func tooltipLines(bar *barDescriptor, snap map[string]*stats.HostStats, cfg *config.Config, state *runState) []string {
+	h := snap[bar.host]
+	if h == nil {
+		return []string{bar.host}
+	}
+	switch bar.kind {
+	case barCPU:
+		return cpuTooltipLines(bar, h, state)
+	case barMem:
+		return memTooltipLines(bar, h, state)
+	case barNet:
+		return netTooltipLines(bar, cfg, state)
+	}
+	return nil
+}
+
+// cpuTooltipLines returns tooltip text for a CPU bar showing smoothed percentages.
+func cpuTooltipLines(bar *barDescriptor, h *stats.HostStats, state *runState) []string {
+	lines := []string{fmt.Sprintf("%s [%s]", bar.host, bar.cpuName)}
+	key := bar.host + ";" + bar.cpuName
+	s := state.smoothedCPU[key]
+	if s == nil {
+		lines = append(lines, "No data yet")
+		return lines
+	}
+	// Indices match cpuBarTargetPcts: 0=sys 1=usr 2=nice 3=idle 4=io 5=irq 6=softirq 7=guest 8=steal 9=guestnice
+	lines = append(lines,
+		fmt.Sprintf("Sys:    %5.1f%%", s[0]),
+		fmt.Sprintf("Usr:    %5.1f%%", s[1]),
+		fmt.Sprintf("Nice:   %5.1f%%", s[2]),
+		fmt.Sprintf("IO:     %5.1f%%", s[4]),
+		fmt.Sprintf("Steal:  %5.1f%%", s[8]),
+		fmt.Sprintf("Idle:   %5.1f%%", s[3]),
+	)
+	return lines
+}
+
+// memTooltipLines returns tooltip text for a memory bar.
+func memTooltipLines(bar *barDescriptor, h *stats.HostStats, state *runState) []string {
+	lines := []string{fmt.Sprintf("%s [mem]", bar.host)}
+	sm := state.smoothedMem[bar.host]
+	if sm == nil || h.Mem == nil {
+		lines = append(lines, "No data yet")
+		return lines
+	}
+	memTotal := h.Mem["MemTotal"]
+	memFree := h.Mem["MemFree"]
+	swapTotal := h.Mem["SwapTotal"]
+	swapFree := h.Mem["SwapFree"]
+	lines = append(lines,
+		fmt.Sprintf("RAM:  %s / %s", formatKB(memTotal-memFree), formatKB(memTotal)),
+		fmt.Sprintf("      %5.1f%%", sm.ramUsed),
+		fmt.Sprintf("Swap: %s / %s", formatKB(swapTotal-swapFree), formatKB(swapTotal)),
+		fmt.Sprintf("      %5.1f%%", sm.swapUsed),
+	)
+	return lines
+}
+
+// netTooltipLines returns tooltip text for a network bar.
+func netTooltipLines(bar *barDescriptor, cfg *config.Config, state *runState) []string {
+	lines := []string{fmt.Sprintf("%s [net]", bar.host)}
+	sm := state.smoothedNet[bar.host]
+	if sm == nil {
+		lines = append(lines, "No data yet")
+		return lines
+	}
+	lines = append(lines,
+		fmt.Sprintf("RX: %5.1f%%", sm.rxPct),
+		fmt.Sprintf("TX: %5.1f%%", sm.txPct),
+		fmt.Sprintf("Link: %s", cfg.NetLink),
+	)
+	return lines
+