screenshot: initial support for scroll capture mode

fixes #2871 port 1.5
2026-08-07 14:08:29 -04:00 · 2026-07-17 13:31:23 -04:00
parent 3c688cfbd3
commit f8fe16738e
13 changed files with 1866 additions and 72 deletions
@@ -0,0 +1,169 @@
+package screenshot
+
+import (
+	"bytes"
+	"math/rand"
+	"slices"
+	"testing"
+)
+
+const (
+	testStride = 512
+	testFrameH = 240
+)
+
+func makePage(t *testing.T, rows int) []byte {
+	t.Helper()
+	rng := rand.New(rand.NewSource(42))
+	page := make([]byte, rows*testStride)
+	rng.Read(page)
+	return page
+}
+
+func frameAt(page []byte, top int) []byte {
+	return page[top*testStride : (top+testFrameH)*testStride]
+}
+
+func pushFrame(st *stitcher, frame []byte) int {
+	n, _ := st.pushFrame(frame, st.rowSamples(frame))
+	return n
+}
+
+func TestStitchSlidingWindows(t *testing.T) {
+	page := makePage(t, 1000)
+
+	for _, delta := range []int{20, 60, 110} {
+		st := newStitcher(testStride)
+		lastTop := 0
+		for top := 0; top+testFrameH <= 900; top += delta {
+			lastTop = top
+			pushFrame(st, frameAt(page, top))
+		}
+
+		wantRows := lastTop + testFrameH
+		if st.rows() != wantRows {
+			t.Fatalf("delta %d: got %d rows, want %d", delta, st.rows(), wantRows)
+		}
+		if !bytes.Equal(st.canvas, page[:wantRows*testStride]) {
+			t.Fatalf("delta %d: canvas does not match source rows", delta)
+		}
+	}
+}
+
+func TestStitchDropsNoOverlap(t *testing.T) {
+	page := makePage(t, 1000)
+	st := newStitcher(testStride)
+
+	pushFrame(st, frameAt(page, 0))
+	if appended := pushFrame(st, frameAt(page, testFrameH+50)); appended != 0 {
+		t.Fatalf("unmatched jump appended %d rows", appended)
+	}
+	if !bytes.Equal(st.canvas, page[:testFrameH*testStride]) {
+		t.Fatal("canvas changed on unmatched frame")
+	}
+}
+
+func TestStitchNoGrowthCases(t *testing.T) {
+	page := makePage(t, 1000)
+	blank := make([]byte, testFrameH*testStride)
+
+	cases := []struct {
+		name          string
+		first, second []byte
+	}{
+		{"identical frame", frameAt(page, 0), frameAt(page, 0)},
+		{"jitter below min append", frameAt(page, 0), frameAt(page, stitchMinAppend-5)},
+		{"blank on blank", blank, blank},
+	}
+	for _, tc := range cases {
+		st := newStitcher(testStride)
+		pushFrame(st, tc.first)
+		if appended := pushFrame(st, tc.second); appended != 0 {
+			t.Fatalf("%s: appended %d rows", tc.name, appended)
+		}
+		if st.rows() != testFrameH {
+			t.Fatalf("%s: got %d rows, want %d", tc.name, st.rows(), testFrameH)
+		}
+	}
+}
+
+func TestStitchRevisitNeverDuplicates(t *testing.T) {
+	page := makePage(t, 1000)
+	st := newStitcher(testStride)
+
+	pushFrame(st, frameAt(page, 0))
+	pushFrame(st, frameAt(page, 100))
+	pushFrame(st, frameAt(page, 200))
+
+	for _, top := range []int{150, 60, 0, 80, 190} {
+		if appended := pushFrame(st, frameAt(page, top)); appended != 0 {
+			t.Fatalf("revisited frame at %d appended %d rows", top, appended)
+		}
+	}
+	pushFrame(st, frameAt(page, 300))
+
+	wantRows := 300 + testFrameH
+	if st.rows() != wantRows {
+		t.Fatalf("got %d rows, want %d", st.rows(), wantRows)
+	}
+	if !bytes.Equal(st.canvas, page[:wantRows*testStride]) {
+		t.Fatal("canvas corrupted by revisited frames")
+	}
+}
+
+func TestStitchScrollUpPrepends(t *testing.T) {
+	page := makePage(t, 1000)
+	st := newStitcher(testStride)
+
+	pushFrame(st, frameAt(page, 500))
+	if appended := pushFrame(st, frameAt(page, 420)); appended != 80 {
+		t.Fatalf("upward frame appended %d rows, want 80", appended)
+	}
+	pushFrame(st, frameAt(page, 560))
+
+	if !bytes.Equal(st.canvas, page[420*testStride:(560+testFrameH)*testStride]) {
+		t.Fatal("canvas does not match page range after prepend + append")
+	}
+}
+
+func TestStitchNoisyChromeStillMatches(t *testing.T) {
+	page := makePage(t, 1000)
+	st := newStitcher(testStride)
+
+	addChrome := func(frame []byte, seed byte) []byte {
+		f := slices.Clone(frame)
+		for y := range testFrameH {
+			for x := range 32 {
+				f[y*testStride+x] = seed + byte(y)
+			}
+		}
+		for y := 100; y < 124; y++ {
+			for x := testStride / 2; x < testStride/2+40; x++ {
+				f[y*testStride+x] ^= 0x08
+			}
+		}
+		return f
+	}
+
+	pushFrame(st, addChrome(frameAt(page, 0), 1))
+	if appended := pushFrame(st, addChrome(frameAt(page, 90), 2)); appended != 90 {
+		t.Fatalf("appended %d rows, want 90", appended)
+	}
+}
+
+func TestStitchMaxRowsCap(t *testing.T) {
+	page := makePage(t, 1000)
+	st := newStitcher(testStride)
+	st.maxRows = testFrameH + 10
+
+	pushFrame(st, frameAt(page, 0))
+	if appended := pushFrame(st, frameAt(page, 100)); appended != 10 {
+		t.Fatalf("appended %d rows past cap, want 10", appended)
+	}
+	if !st.full {
+		t.Fatal("stitcher not marked full at cap")
+	}
+	if pushFrame(st, frameAt(page, 300)) != 0 {
+		t.Fatal("push after full appended rows")
+	}
+}