色彩合成: 设alpha,red,green,blue都是0~255之间的数 color32 = alpha << 24 | red << 16 | green << 8 | blue;
色彩提取: alpha = color32 >> 24; red = color32 >> 16 & 0xFF; green = color32 >> 8 & 0xFF; blue = color32 & 0xFF;