如何重新创建UITabBarItem图像过滤器？ [英] How to recreate the UITabBarItem image filter?

问题描述

我正在写一个自定义UITabBar替换，我想知道如何重新创建内置实现与UITabBarItem图像过滤器 - 选定的选项卡上的蓝色和未选择的灰色渐变。我想这是一个问题，使用源图像alpha值作为掩码，并覆盖它与预先制作的蓝色（或任何颜色）闪亮的图像和另一个灰色的，但我想知道什么是最好的方法从代码的观点。

I'm writing a custom UITabBar replacement, and I would like to know how to recreate the filter that the built-in implementation does with the UITabBarItem image - that blue shining on selected tabs and gray gradient on unselected ones. I guess it's a matter of using the source image alpha value as a mask and overlay it with a pre-made blue (or whatever color) shining image and another one grayed out, but I would like to know what is the best approach from a code point of view.

最好，

推荐答案

蓝色过滤器有点

Edit2：清理灰色过滤器

Fixed up the blue filter a little
Cleaned up the grey filter

我需要的代码来做这些效果，所以我写了几个函数

I required code to do these effects, so I wrote a couple functions for them:

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;
}

要使蓝色滤镜效果生效，您需要将此图片您的项目为selection_gradient.png：

此外，您可能想要播放与定义得到的效果完全如何你喜欢，我没有花很多时间来完善他们，虽然他们对我看起来不错。

To make the blue filter effect work you'll need to include this image in your project as "selection_gradient.png":
Also, you may want to play with the defines to get the effect exactly how you like, I didn't take much time to perfect them, though they look good enough to me.

当然，我不知道苹果应用的确切的过滤器，但我客人他们，他们看起来对我很好。我不知道这些功能是否与iPhone 4兼容，因为我只是在iPad应用程序中使用它们，但它不会很难根据您的喜好编辑它们。

Of course I don't know the exact filters that Apple applied, but I "guestimated" them and they look alright to me. I'm not sure if these functions are iPhone 4 compatible because I'm only using them in an iPad app, but it wouldn't be hard to edit them to your liking.

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