如何重新创建UITabBarItem图像过滤器？

Question

我正在编写一个自定义的UITabBar替换,我想知道如何重新创建内置实现使用UITabBarItem图像的过滤器 - 蓝色照射在选定的选项卡上,灰色渐变在未选择的选项卡上.我想这是使用源图像alpha值作为遮罩并用预先制作的蓝色(或任何颜色)闪亮图像覆盖它而另一个遮盖了灰色的问题,但我想知道什么是最好的方法来自代码观点.

最好,

Answer 1

编辑:修正了蓝色滤镜一点点
Edit2:清理了灰色滤镜

我需要代码来做这些效果,所以我为它们写了几个函数:

UIImage *grayTabBarItemFilter(UIImage *image) {
    int width = image.size.width, height = image.size.height;
    UIImage *result = image;
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
    if (colorSpace == NULL) {
        return result;
    }
    CGContextRef context = CGBitmapContextCreate(NULL, width, height, 8, width * 4, colorSpace, kCGImageAlphaPremultipliedLast);
    if (context == NULL) {
        CGColorSpaceRelease(colorSpace);
        return result;
    }
    CGFloat colors[8] = {80/255.0,80/255.0,80/255.0,1, 175/255.0,175/255.0,175/255.0,1};
    CGGradientRef gradient = CGGradientCreateWithColorComponents(colorSpace, colors, NULL, 2);
    CGContextDrawLinearGradient(context, gradient, CGPointMake(0,-(32-height)/2.0), CGPointMake(0,height+(32-height)/2.0), 0);
    CGGradientRelease(gradient);
    CGContextSetBlendMode(context, kCGBlendModeDestinationIn);
    CGContextDrawImage(context, CGRectMake(0,0,width,height), image.CGImage);
    CGImageRef newImage = CGBitmapContextCreateImage(context);
    if (newImage != NULL) {
        result = [UIImage imageWithCGImage:newImage];
        CGImageRelease(newImage);
    }
    CGContextRelease(context);
    CGColorSpaceRelease(colorSpace);
    return result;
}

struct RGBA {
    unsigned char red;
    unsigned char green;
    unsigned char blue;
    unsigned char alpha;
};

#define BLUE_ALPHA_THRESHOLD 128
#define BLUE_BRIGHTNESS_ADJUST 30

UIImage *blueTabBarItemFilter(UIImage *image) {
    int width = image.size.width,
        height = image.size.height;
    UIImage *result = image;
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
    if (colorSpace == NULL) {
        return result;
    }
    CGContextRef context = CGBitmapContextCreate(NULL, width, height, 8, width * 4, colorSpace, kCGImageAlphaPremultipliedLast);
    if (context == NULL) {
        CGColorSpaceRelease(colorSpace);
        return result;
    }
    UIImage *gradient = [UIImage imageNamed:@"selection_gradient.png"];
    CGContextDrawImage(context, CGRectMake(-(gradient.size.width - width) / 2.0, -(gradient.size.height - height) / 2.0, gradient.size.width, gradient.size.height), gradient.CGImage);
    CGContextSetBlendMode(context, kCGBlendModeDestinationIn);
    CGContextDrawImage(context, CGRectMake(0,0,width,height), image.CGImage);
    struct RGBA *pixels = CGBitmapContextGetData(context);
    if (pixels != NULL) {
        for (int y = 0; y < height; y++) {
            for (int x = 0; x < width; x++) {
                int offset = x+y*width;
                if (pixels[offset].alpha >= BLUE_ALPHA_THRESHOLD && 
                    ((x == 0 || x == width-1 || y == 0 || y == height-1) ||
                     (pixels[x+(y-1)*width].alpha < BLUE_ALPHA_THRESHOLD) ||
                     (pixels[x+1+y*width].alpha < BLUE_ALPHA_THRESHOLD) ||
                     (pixels[x+(y+1)*width].alpha < BLUE_ALPHA_THRESHOLD) ||
                     (pixels[x-1+y*width].alpha < BLUE_ALPHA_THRESHOLD))) {
                    pixels[offset].red = MIN(pixels[offset].red + BLUE_BRIGHTNESS_ADJUST,255);
                    pixels[offset].green = MIN(pixels[offset].green + BLUE_BRIGHTNESS_ADJUST,255);
                    pixels[offset].blue = MIN(pixels[offset].blue + BLUE_BRIGHTNESS_ADJUST,255);
                }
            }
        }
        CGImageRef image = CGBitmapContextCreateImage(context);
        if (image != NULL) {
            result = [UIImage imageWithCGImage:image];
            CGImageRelease(image);
        }
    }
    CGContextRelease(context);
    CGColorSpaceRelease(colorSpace);
    return result;
}

要使蓝色滤镜效果起作用,您需要将此图像作为"selection_gradient.png"包含在项目中:selection_gradient.png http://oi55.tinypic.com/bgwv0j.jpg
此外,您可能想要使用定义为了获得你想要的效果,我没有花太多时间来完善它们,尽管它们对我来说看起来很好.

当然我不知道Apple应用的确切过滤器,但我"估计"了它们,它们看起来对我来说没问题.我不确定这些功能是否与iPhone 4兼容,因为我只在iPad应用程序中使用它们,但根据自己的喜好编辑它们并不困难.