利用drawInRect直接在屏幕上绘制图片

1 UIImage *iv = [UIImage imageNamed:@"bc.png"];
2 [iv drawInRect:CGRectMake(0, 0, 100, 100)
3      blendMode:kCGBlendModeColorDodge
4          alpha:1.0]; // blendMode 设定图片与背景融合方式