Pad/internal/editor/font_scale_test.go

package editor

import (
	"fmt"
	"math"
	"math/rand"
	"testing"

	"pad/internal/io/pool/types"
	"pad/internal/ui"
)

// These tests prove the tap/scroll bookkeeping follows the RENDERED line
// pitch under a non-default user font-size setting. On Android,
// Metric.PxPerSp = fontScale * PxPerDp, and the shaper draws baselines at
// Sp(fontSize*LineHeightScale) physical px, so the rendered line pitch in
// density-dp is EditorLineHeight()*fontScale. Every consumer must use
// EffectiveLineHeight (window start, sub-line remainder, tap mapping, scroll
// clamp); at fontScale != 1 the raw EditorLineHeight would misplace taps by
// up to (fontScale-1) viewportfuls of lines.

func TestEffectiveLineHeight_FollowsFontScale(t *testing.T) {
	TheState = NewState()
	defer func() { TheState.fontScale = 0 }()

	cases := []struct {
		fs   float32
		want float64
	}{
		{0, float64(EditorLineHeight())}, // unknown -> 1.0
		{1, float64(EditorLineHeight())}, // default
		{1.3, float64(EditorLineHeight()) * 1.3},
		{0.8, float64(EditorLineHeight()) * 0.8},
	}
	for _, c := range cases {
		TheState.fontScale = c.fs
		got := float64(EffectiveLineHeight())
		if math.Abs(got-c.want) > 1e-5 { // float32 ui.Dp rounding
			t.Errorf("fontScale=%v: EffectiveLineHeight=%v want %v", c.fs, got, c.want)
		}
	}
}

// Generalizes TestTapPosition_ScrollInvariant_Property to fontScale=1.3:
// the windowed layout is fabricated the way the shaper produces it with the
// scaled line pitch (baseline of display line j = (j+1)*lh, lh already
// font-scaled), and the tapped line must equal the drawn line under the
// finger for random scroll offsets and finger positions.
func TestTapPosition_FontScale_Property(t *testing.T) {
	const (
		lines        = 400
		bytesPerLine = 5
		regionTop    = float64(62)
		viewportH    = float64(760)
		fs           = float32(1.3)
	)

	var file string
	for i := 0; i < lines; i++ {
		file += fmt.Sprintf("L%03d\n", i)
	}
	cb := NewChunkedBuffer("/fs.txt", DefaultChunkSize, nil, "")
	cb.SetContent([]byte(file))

	offsets := []int32{0}
	for i := 0; i < len(file); i++ {
		if file[i] == '\n' {
			offsets = append(offsets, int32(i+1))
		}
	}
	cb.LineIndex = types.NewLineIndex(offsets, 0, int64(len(file)))

	lh := float64(EffectiveLineHeightAt(fs))
	if math.Abs(lh-float64(EditorLineHeight())*float64(fs)) > 1e-5 { // float32 ui.Dp rounding
		t.Fatalf("effective line height %v != %v*%v", lh, float64(EditorLineHeight()), fs)
	}

	rng := rand.New(rand.NewSource(7))
	maxS := float64(lines) * lh

	for tc := 0; tc < 2000; tc++ {
		var s float64
		switch tc % 4 {
		case 0:
			s = rng.Float64() * maxS
		case 1:
			s = float64(int(rng.Float64() * maxS))
		case 2:
			s = float64(rng.Intn(lines)) * lh
		case 3:
			s = float64(rng.Intn(lines))*lh + rng.Float64()*(lh-1)
		}
		sOff := ui.Dp(s)

		// What layoutFrame/visibleByteRangePrecise does with the effective
		// line height: window starts at content line k = floor(s/lh).
		start, _, _ := cb.VisibleByteRange(sOff, 0, ui.Dp(viewportH), EffectiveLineHeightAt(fs), false, ui.GlyphLayout{}, nil)
		if start%bytesPerLine != 0 {
			t.Fatalf("test setup: window start %d not on a line boundary", start)
		}
		k := start / bytesPerLine

		// Fabricate the windowed GlyphLayout exactly as the shaper would
		// with the scaled line pitch: display line j = content line k+j.
		nWin := int(math.Min(viewportH/lh+2, float64(lines-k)))
		var gl ui.GlyphLayout
		gl.LineHeight = EffectiveLineHeightAt(fs)
		for j := 0; j < nWin; j++ {
			gl.ByteOffsets = append(gl.ByteOffsets, j*bytesPerLine)
			gl.X = append(gl.X, 10)
			gl.Y = append(gl.Y, ui.Dp(float64(j+1)*lh))
			gl.Advance = append(gl.Advance, 10)
		}

		TheState = NewState()
		TheState.fontScale = fs
		TheState.Editor.ChunkedBuffer = cb
		TheState.Editor.GlyphLayout = gl
		TheState.Editor.IMEWindowStartByte = start
		TheState.ScrollOffset = sOff
		TheState.EditorRegion = ui.Region{X: 10, Y: ui.Dp(regionTop), W: 390, H: ui.Dp(viewportH)}

		a := rng.Float64() * viewportH // tap y relative to region top
		HandleTapAt(15, ui.Dp(regionTop+a))

		// Independent ground truth: content_y = a + s -> content line.
		wantLine := int(math.Floor((a + s) / lh))
		if wantLine >= lines {
			wantLine = lines - 1
		}
		if k+nWin-1 < wantLine {
			wantLine = k + nWin - 1
		}
		got := TheState.Editor.CursorPosition
		wantLo, wantHi := wantLine*bytesPerLine, wantLine*bytesPerLine+bytesPerLine
		if got < wantLo || got >= wantHi {
			t.Fatalf("fs=%v s=%.2f (k=%d) tap a=%.2f: cursor=%d, want line %d [bytes %d,%d)",
				fs, s, k, a, got, wantLine, wantLo, wantHi)
		}
	}
}