代码语言：javascript复制
switch (blendMode) {
case kCGBlendModeNormal: {
strMsg = @"kCGBlendModeNormal: 正常；也是默认的模式。前景图会覆盖背景图";
break;
}
case kCGBlendModeMultiply: {
strMsg = @"kCGBlendModeMultiply: 正片叠底；混合了前景和背景的颜色，最终颜色比原先的都暗";
break;
}
case kCGBlendModeScreen: {
strMsg = @"kCGBlendModeScreen: 滤色；把前景和背景图的颜色先反过来，然后混合";
break;
}
case kCGBlendModeOverlay: {
strMsg = @"kCGBlendModeOverlay: 覆盖；能保留灰度信息，结合kCGBlendModeSaturation能保留透明度信息，在imageWithBlendMode方法中两次执行drawInRect方法实现我们基本需求";
break;
}
case kCGBlendModeDarken: {
strMsg = @"kCGBlendModeDarken: 变暗"; //将线条色变为黑色，背景色设置为目的色
break;
}
case kCGBlendModeLighten: {
strMsg = @"kCGBlendModeLighten: 变亮";
break;
}
case kCGBlendModeColorDodge: {
strMsg = @"kCGBlendModeColorDodge: 颜色变淡";
break;
}
case kCGBlendModeColorBurn: {
strMsg = @"kCGBlendModeColorBurn: 颜色加深"; //线条颜色（原本）加深，背景色设置为目的色
break;
}
case kCGBlendModeSoftLight: {
strMsg = @"kCGBlendModeSoftLight: 柔光";
break;
}
case kCGBlendModeHardLight: {
strMsg = @"kCGBlendModeHardLight: 强光"; //全为目的色
break;
}
case kCGBlendModeDifference: {
strMsg = @"kCGBlendModeDifference: 插值";
break;
}
case kCGBlendModeExclusion: {
strMsg = @"kCGBlendModeExclusion: 排除";
break;
}
case kCGBlendModeHue: {
strMsg = @"kCGBlendModeHue: 色调";
break;
}
case kCGBlendModeSaturation: {
strMsg = @"kCGBlendModeSaturation: 饱和度";
break;
}
case kCGBlendModeColor: {
strMsg = @"kCGBlendModeColor: 颜色"; //感觉将图片线条色设置为白色，背景色设置为目的色，之后再再图片上加一个有透明度的目的色
break;
}
case kCGBlendModeLuminosity: {
strMsg = @"kCGBlendModeLuminosity: 亮度";
break;
}
//Apple额外定义的枚举
//R: premultiplied result, 表示混合结果
//S: Source, 表示源颜色(Sa对应透明度值: 0.0-1.0)
//D: destination colors with alpha, 表示带透明度的目标颜色(Da对应透明度值: 0.0-1.0)
case kCGBlendModeClear: {
strMsg = @"kCGBlendModeClear: R = 0"; //1.清空（如果图标背景色为白色则为全白）
break;
}
case kCGBlendModeCopy: {
strMsg = @"kCGBlendModeCopy: R = S"; //2全色覆盖整个图片
break;
}
case kCGBlendModeSourceIn: {
strMsg = @"kCGBlendModeSourceIn: R = S*Da"; //3.线条变色
break;
}
case kCGBlendModeSourceOut: {
strMsg = @"kCGBlendModeSourceOut: R = S*(1 - Da)"; //4.背景变为目的色,线条自动变为白色（比如图标线条原为蓝色，会自动变为白色）
break;
}
case kCGBlendModeSourceAtop: {
strMsg = @"kCGBlendModeSourceAtop: R = S*Da D*(1 - Sa)"; //5.线条变色，目前感觉和SourceIn效果一致
break;
}
case kCGBlendModeDestinationOver: {
strMsg = @"kCGBlendModeDestinationOver: R = S*(1 - Da) D"; //6.背景色变为目的色，线条色不变
break;
}
case kCGBlendModeDestinationIn: {
strMsg = @"kCGBlendModeDestinationIn: R = D*Sa；能保留透明度信息"; //7.只看到线条色（本色），无其他颜色
break;
}
case kCGBlendModeDestinationOut: {
strMsg = @"kCGBlendModeDestinationOut: R = D*(1 - Sa)"; //8.空白什么都没哟
break;
}
case kCGBlendModeDestinationAtop: {
strMsg = @"kCGBlendModeDestinationAtop: R = S*(1 - Da) D*Sa"; //9.会把整个矩形的背景填充目的色（如图9系列）原色保留
break;
}
case kCGBlendModeXOR: {
strMsg = @"kCGBlendModeXOR: R = S*(1 - Da) D*(1 - Sa)"; //10.线条变白，背景色变为目的色
break;
}
case kCGBlendModePlusDarker: {
strMsg = @"kCGBlendModePlusDarker: R = MAX(0, (1 - D) (1 - S))"; //11.线条变为黑色， 背景色变为目的色
break;
}
case kCGBlendModePlusLighter: {
strMsg = @"kCGBlendModePlusLighter: R = MIN(1, S D)（最后一种混合模式）"; //12.线条变为白色（混合色：如color为红色，就是偏粉色的白，有一定透明度的感觉）
break;
}
default: {
break;
} 
