bitmap-font-maker: fontc - .font glyph grids -> atlas PNG + metrics JSON + text rendering

- .font format: glyph sections with #/. grids, proportional widths,
  literal unicode glyph names, spacing/space-width/line-height/baseline
- build (atlas white-on-transparent + JSON metrics), render (text -> PNG
  with \n, scale, color), info, preview (terminal half-blocks)
- example tiny5 font: A-Z, ÅÄÖ, 0-9, punctuation (47 glyphs, 3x5)
- go tests: parsing, errors, atlas metrics, text rendering

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01MmdG9GqfSWCzts7AkDwRDh

bitmap-font-maker/font/font_test.go

@@ -0,0 +1,144 @@
+package font
+
+import (
+	"bytes"
+	"encoding/json"
+	"image/color"
+	"strings"
+	"testing"
+)
+
+const tiny = `
+font: t
+spacing: 1
+space-width: 2
+
+glyph A:
+.#.
+#.#
+###
+
+glyph I:
+#
+#
+#
+`
+
+func parseOK(t *testing.T, src string) *Font {
+	t.Helper()
+	ft, err := Parse(strings.NewReader(src))
+	if err != nil {
+		t.Fatalf("parse: %v", err)
+	}
+	return ft
+}
+
+func TestParseBasics(t *testing.T) {
+	ft := parseOK(t, tiny)
+	if ft.Name != "t" || ft.Height != 3 || len(ft.Order) != 2 {
+		t.Errorf("name=%q height=%d glyphs=%d", ft.Name, ft.Height, len(ft.Order))
+	}
+	a := ft.Glyphs['A']
+	if a.W != 3 || a.H != 3 {
+		t.Errorf("A is %dx%d, want 3x3", a.W, a.H)
+	}
+	if !a.Rows[1][0] || a.Rows[0][0] {
+		t.Error("A pixel pattern wrong")
+	}
+	i := ft.Glyphs['I']
+	if i.W != 1 {
+		t.Errorf("I width = %d, want 1 (proportional)", i.W)
+	}
+	if ft.LineHeight != 4 || ft.Baseline != 3 {
+		t.Errorf("defaults: lineHeight=%d baseline=%d", ft.LineHeight, ft.Baseline)
+	}
+}
+
+func TestParseErrors(t *testing.T) {
+	cases := map[string]string{
+		"no glyphs":      "font: x\n",
+		"ragged glyph":   "glyph A:\n##\n#\n",
+		"height differs": "glyph A:\n#\n#\n\nglyph B:\n#\n",
+		"dup glyph":      "glyph A:\n#\n\nglyph A:\n#\n",
+		"bad name":       "glyph AB:\n#\n",
+		"unknown key":    "wat: 3\nglyph A:\n#\n",
+	}
+	for name, src := range cases {
+		if _, err := Parse(strings.NewReader(src)); err == nil {
+			t.Errorf("%s: expected error", name)
+		}
+	}
+}
+
+func TestGlyphNameColon(t *testing.T) {
+	ft := parseOK(t, "glyph ::\n#\n#\n")
+	if _, ok := ft.Glyphs[':']; !ok {
+		t.Error("glyph ':' not parsed")
+	}
+}
+
+func TestAtlasAndMetrics(t *testing.T) {
+	ft := parseOK(t, tiny)
+	img, m := ft.BuildAtlas("t.png")
+	if m.Glyphs["A"].Advance != 4 {
+		t.Errorf("A advance = %d, want 4 (w3 + spacing1)", m.Glyphs["A"].Advance)
+	}
+	g := m.Glyphs["A"]
+	// center-top pixel of A within its atlas cell: (x+1, y+0)
+	if img.NRGBAAt(g.X+1, g.Y).A == 0 {
+		t.Error("A apex pixel missing in atlas")
+	}
+	if img.NRGBAAt(g.X, g.Y).A != 0 {
+		t.Error("A corner should be empty")
+	}
+	var buf bytes.Buffer
+	if err := WriteMetrics(&buf, m); err != nil {
+		t.Fatal(err)
+	}
+	var back Metrics
+	if err := json.Unmarshal(buf.Bytes(), &back); err != nil {
+		t.Fatalf("metrics json invalid: %v", err)
+	}
+	if back.Glyphs["I"].W != 1 {
+		t.Errorf("metrics roundtrip: I.w = %d", back.Glyphs["I"].W)
+	}
+}
+
+func TestRenderText(t *testing.T) {
+	ft := parseOK(t, tiny)
+	white := color.NRGBA{255, 255, 255, 255}
+	img, warns := ft.RenderText("AI", 1, white)
+	if len(warns) != 0 {
+		t.Errorf("warnings: %v", warns)
+	}
+	// width: A(3) + spacing(1) + I(1) = 5
+	if b := img.Bounds(); b.Dx() != 5 || b.Dy() != 3 {
+		t.Errorf("size = %dx%d, want 5x3", b.Dx(), b.Dy())
+	}
+	// I column at x=4
+	if img.NRGBAAt(4, 0).A == 0 {
+		t.Error("I pixel missing")
+	}
+
+	_, warns = ft.RenderText("AXA", 1, white)
+	if len(warns) != 1 {
+		t.Errorf("missing-glyph warning expected, got %v", warns)
+	}
+
+	img, _ = ft.RenderText(`A\nA`, 1, white)
+	if b := img.Bounds(); b.Dy() != ft.LineHeight+ft.Height {
+		t.Errorf("two-line height = %d, want %d", b.Dy(), ft.LineHeight+ft.Height)
+	}
+
+	img2, _ := ft.RenderText("A", 3, white)
+	if b := img2.Bounds(); b.Dx() != 9 || b.Dy() != 9 {
+		t.Errorf("scaled size = %dx%d, want 9x9", b.Dx(), b.Dy())
+	}
+}
+
+func TestSpaceWidthDefaultFromZero(t *testing.T) {
+	ft := parseOK(t, "glyph 0:\n####\n####\n")
+	if ft.SpaceWidth != 4 {
+		t.Errorf("space-width = %d, want 4 (width of '0')", ft.SpaceWidth)
+	}
+}