adding to git.i0t.app

internal/compositor/compositor_test.go

@@ -0,0 +1,35 @@
+package compositor
+
+import "testing"
+
+func TestGridRectsCoverExactly(t *testing.T) {
+	cases := []struct {
+		w, h, cols, rows int
+	}{
+		{1920, 1080, 2, 2},
+		{1920, 1080, 3, 3},
+		{1920, 1080, 1, 1},
+		{1366, 768, 3, 2}, // odd dimensions to exercise remainder handling
+	}
+	for _, tc := range cases {
+		rects := GridRects(tc.w, tc.h, tc.cols, tc.rows)
+		if len(rects) != tc.cols*tc.rows {
+			t.Fatalf("%dx%d grid %dx%d: got %d rects", tc.w, tc.h, tc.cols, tc.rows, len(rects))
+		}
+		// Sum of areas must equal the whole output with no gaps or overlap on
+		// the axis boundaries: verify the last column reaches the right edge
+		// and the last row reaches the bottom edge.
+		last := rects[len(rects)-1]
+		if last.X+last.W != tc.w {
+			t.Errorf("%dx%d grid %dx%d: last cell right edge %d != %d", tc.w, tc.h, tc.cols, tc.rows, last.X+last.W, tc.w)
+		}
+		if last.Y+last.H != tc.h {
+			t.Errorf("%dx%d grid %dx%d: last cell bottom edge %d != %d", tc.w, tc.h, tc.cols, tc.rows, last.Y+last.H, tc.h)
+		}
+		for i, r := range rects {
+			if r.W <= 0 || r.H <= 0 {
+				t.Errorf("cell %d has non-positive size %+v", i, r)
+			}
+		}
+	}
+}