Render covers with quadrant blocks for twice the horizontal detail

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

internal/ui/cover_test.go

@@ -77,39 +77,80 @@ func TestDecodeCover(t *testing.T) {
 	}
 }
 
-func TestCoverViewDrawsHalfBlocks(t *testing.T) {
+func TestQuadCell(t *testing.T) {
+	red, blue, black := color.RGBA{255, 0, 0, 255}, color.RGBA{0, 0, 255, 255}, color.RGBA{0, 0, 0, 255}
+	for _, tc := range []struct {
+		name     string
+		px       [4]color.RGBA
+		wantCh   rune
+		wantFg   color.RGBA
+		wantBg   color.RGBA
+		sameBoth bool
+	}{
+		{"flat", [4]color.RGBA{red, red, red, red}, ' ', red, red, true},
+		{"top half", [4]color.RGBA{red, red, blue, blue}, '▀', red, blue, false},
+		{"bottom half", [4]color.RGBA{blue, blue, red, red}, '▀', blue, red, false}, // same picture, canonical form
+		{"left half", [4]color.RGBA{red, blue, red, blue}, '▌', red, blue, false},
+		{"one corner", [4]color.RGBA{red, blue, blue, blue}, '▘', red, blue, false},
+		{"diagonal", [4]color.RGBA{red, black, black, red}, '▞', black, red, false},
+	} {
+		ch, fg, bg := quadCell(tc.px)
+		if ch != tc.wantCh || fg != tc.wantFg || bg != tc.wantBg {
+			t.Errorf("%s: %q fg=%v bg=%v, want %q fg=%v bg=%v", tc.name, ch, fg, bg, tc.wantCh, tc.wantFg, tc.wantBg)
+		}
+	}
+	// Nearly flat noise stays a flat cell instead of a distracting pattern.
+	n := color.RGBA{100, 100, 100, 255}
+	m := color.RGBA{102, 100, 101, 255}
+	if ch, _, _ := quadCell([4]color.RGBA{n, m, n, n}); ch != ' ' {
+		t.Errorf("noise rendered as %q", ch)
+	}
+}
+
+func TestCoverCells(t *testing.T) {
+	// A 2:3 poster in a roomy box is limited by the height: 10 rows are 20
+	// width units tall, so 13 columns.
+	if c, r := coverCells(40, 60, 30, 10); c != 13 || r != 10 {
+		t.Errorf("tall limit: %dx%d", c, r)
+	}
+	// In a narrow box the width limits it.
+	if c, r := coverCells(40, 60, 10, 20); c != 10 || r != 7 {
+		t.Errorf("narrow limit: %dx%d", c, r)
+	}
+}
+
+func TestCoverViewDraws(t *testing.T) {
 	screen := tcell.NewSimulationScreen("")
 	if err := screen.Init(); err != nil {
 		t.Fatal(err)
 	}
 	defer screen.Fini()
-	screen.SetSize(20, 10)
+	screen.SetSize(30, 10)
 
 	c := newCoverView()
-	c.setImage(stripes(40, 60)) // 2:3 poster
-	c.SetRect(0, 0, 20, 10)     // 20 columns × 20 pixel rows: a 13×20 pixel poster
-	c.Draw(screen)
+	c.setImage(stripes(40, 60)) // red above blue
+	c.SetRect(0, 0, 30, 10)     // fits 13 columns × 10 rows
 
-	// Row 0 holds pixel rows 0 (top) and 1: both red. The middle cell row
-	// (index 4/5) crosses into blue; the last row is blue on both halves.
+	c.Draw(screen)
 	rgba := func(c tcell.Color) color.RGBA {
 		r, g, b := c.RGB()
 		return color.RGBA{uint8(r), uint8(g), uint8(b), 255}
 	}
-	check := func(row int, wantFg, wantBg color.RGBA) {
-		t.Helper()
-		ch, _, style, _ := screen.GetContent(0, row)
-		fg, bg, _ := style.Decompose()
-		if ch != '▀' || rgba(fg) != wantFg || rgba(bg) != wantBg {
-			t.Errorf("row %d: %q fg=%v bg=%v", row, ch, rgba(fg), rgba(bg))
-		}
+	cell := func(x, y int) (rune, color.RGBA, color.RGBA) {
+		ch, _, st, _ := screen.GetContent(x, y)
+		fg, bg, _ := st.Decompose()
+		return ch, rgba(fg), rgba(bg)
 	}
 	red, blue := color.RGBA{255, 0, 0, 255}, color.RGBA{0, 0, 255, 255}
-	check(0, red, red)
-	check(9, blue, blue)
-	// Beyond the poster's width nothing is drawn.
-	if ch, _, _, _ := screen.GetContent(19, 0); ch == '▀' {
-		t.Error("poster stretched beyond its aspect ratio")
+	if _, fg, bg := cell(0, 0); fg != red || bg != red {
+		t.Errorf("top row = fg %v bg %v, want red", fg, bg)
+	}
+	if _, fg, bg := cell(12, 9); fg != blue || bg != blue {
+		t.Errorf("bottom right = fg %v bg %v, want blue", fg, bg)
+	}
+	// Outside the poster's footprint nothing is drawn.
+	if ch, _, _, _ := screen.GetContent(13, 0); ch != ' ' {
+		t.Errorf("poster stretched beyond its aspect ratio: %q", ch)
 	}
 }