Code:
	m_tex = clan::Texture2D(get_canvas(), 100,100);
        m_fb = FrameBuffer(get_canvas());
	m_fb.attach_color( 0, m_tex );
	clan::Canvas canvas(get_canvas(), m_fb);
 	//canvas.fill_rect(Sizef(50.0f, 50.0f),Colorf::white);
	m_font.draw_text(canvas,0,20, "test_string", Colorf::red);
	m_img_text = clan::Image(m_tex, Rect(0,0,100,100));
Just as code show, if i don't add fill_rect ,m_img_text draw nothing, Unless clear canvas or fill groundback.