Fix rendering according to test

test/test_rendering.gd

@@ -0,0 +1,35 @@
+# SPDX-FileCopyrightText: 2024 Leroy Hopson <godot-xterm@leroy.nix.nz>
+# SPDX-License-Identifier: MIT
+
+class_name RenderingTest extends GutTest
+
+var terminal: Terminal
+
+
+# Return the color in the center of the given cell.
+func pick_cell_color(cell := Vector2i(0, 0)) -> Color:
+	var cell_size = terminal.get_cell_size()
+	var pixelv = Vector2(cell) * cell_size + (cell_size / 2)
+	return get_viewport().get_texture().get_image().get_pixelv(cell_size / 2)
+
+
+func before_each():
+	terminal = Terminal.new()
+	terminal.add_theme_font_override("normal_font", preload("res://themes/fonts/regular.tres"))
+	terminal.set_anchors_and_offsets_preset(Control.PRESET_FULL_RECT)
+	call_deferred("add_child_autofree", terminal)
+	await wait_for_signal(terminal.ready, 5)
+
+
+class TestRendering:
+	extends RenderingTest
+
+	func test_update():
+		terminal.write("\u001b[38;2;255;0;0m")
+		terminal.write("█".repeat(terminal.get_cols() * terminal.get_rows()))
+		await get_tree().physics_frame
+		terminal.queue_redraw()
+		await wait_for_signal(terminal.draw, 3)
+		await wait_frames(10)
+		var cell_color = pick_cell_color(Vector2i(0, 0))
+		assert_eq(cell_color, Color.RED)