我正在编写一个自定义UITabBar替代品,我想知道如何重新创建内置实现与UITabBarItem图像过滤器相同的效果-即所选标签上的蓝色闪光和未选中标签上的灰色渐变。我猜这涉及使用源图像alpha值作为掩码,并将其叠加在预制的蓝色(或任何颜色)发光图像和另一个灰色的图像上,但我希望从代码方面了解最佳方法。
此致,
最好的。
此致,
最好的。
编辑:稍微改进了蓝色滤镜
编辑2:清理了灰色滤镜
我需要实现这些效果的代码,所以我写了几个函数:
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;
}
为了让蓝色滤镜效果生效,您需要将名称为"selection_gradient.png"的图像包含在您的项目中:result = [UIImage imageWithCGImage:newImage];
更改为result = [UIImage imageWithCGImage:newImage scale:[UIScreen mainScreen].scale orientation:UIImageOrientationUp];
即可。 - poiuy_qwert试试这个,它更短:
+ (UIImage *)blendImageBlue:(UIImage *)senderImage {
UIImage *image = [UIImage imageNamed:@"selection_gradient"];
CGSize newSize = CGSizeMake(senderImage.size.width, senderImage.size.height);
UIGraphicsBeginImageContextWithOptions(newSize, NO, [UIScreen mainScreen].scale);
[senderImage drawInRect:CGRectMake(0,0,newSize.width,newSize.height)];
[image drawInRect:CGRectMake(0,0,newSize.width,newSize.height) blendMode:kCGBlendModeSourceAtop alpha:0.8];
UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return newImage;
}
编辑:使用 @poiuy_qwert 的 "selection_gradient.png"
UIImage *grayTabBarItemFilter(UIImage *image) {
UITabBar* bar = [[UITabBar alloc] init];
UITabBarItem* item = [[UITabBarItem alloc] initWithTitle:@"" image:image tag:0];
[bar setItems:@[item]];
[[[[UIApplication sharedApplication] windows] lastObject] addSubview:bar];
UIImage* returnImage;
for(UIView* view in bar.subviews) {
for(UIView* small in view.subviews) {
if([small respondsToSelector:@selector(image)]) {
returnImage = [(UIImageView*)small image];
}
}
}
[bar removeFromSuperview];
return returnImage ? returnImage : image;
}
UIImage *blueTabBarItemFilter(UIImage *image) {
UITabBar* bar = [[UITabBar alloc] init];
UITabBarItem* item = [[UITabBarItem alloc] initWithTitle:@"" image:image tag:0];
[bar setItems:@[item]];
[bar setSelectedItem:item];
[[[[UIApplication sharedApplication] windows] lastObject] addSubview:bar];
UIImage* returnImage;
for(UIView* view in bar.subviews) {
NSInteger count = 0;
for(UIView* small in view.subviews) {
if([small respondsToSelector:@selector(image)]) {
count++;
if(count > 1) {
returnImage = [(UIImageView*)small image];
}
}
}
}
[bar removeFromSuperview];
return returnImage ? returnImage : image;
}
我知道这只是一个不太稳定的解决方案,但如果你对完美的复制品感兴趣,这里就有了。