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UIGraphicsBeginImageContext系列知识

發(fā)布時間：2025/7/14 编程问答 31 豆豆

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UIGraphicsBeginImageContext
創(chuàng)建一個基于位圖的上下文（context）,并將其設(shè)置為當(dāng)前上下文(context)。方法聲明如下：

參數(shù)size為新創(chuàng)建的位圖上下文的大小。它同時是由UIGraphicsGetImageFromCurrentImageContext函數(shù)返回的圖形大小。
該函數(shù)的功能同UIGraphicsBeginImageContextWithOptions的功能相同，相當(dāng)與UIGraphicsBeginImageContextWithOptions的opaque參數(shù)為NO,scale因子為1.0。

UIGraphicsBeginImageContextWithOptions
函數(shù)原型為：

size——同UIGraphicsBeginImageContext
opaque—透明開關(guān)，如果圖形完全不用透明，設(shè)置為YES以優(yōu)化位圖的存儲。
scale—–縮放因子

默認(rèn)創(chuàng)建一個透明的位圖上下文

UILabel根據(jù)text自動調(diào)整大小

C代碼 ?

label.text = @"**********";
CGRect frame = label.frame;
frame.size.height = 10000; // 設(shè)置一個很大的高度
label.frame = frame;
[label sizeToFit];
frame.size.height = label.frame.size.height;
label.frame = frame;

直接撥打有分機(jī)號的電話

C代碼 ?

[[UIApplication sharedApplication] openURL:[NSURL URLWithString:@"tel://01011112222,3333"]];

一些有關(guān)圖像處理的代碼片段

- (UIImage *)rescaleImage:(UIImage *)img ToSize:(CGSize)size; //圖片縮放裁剪

- (UIImage*)transformWidth:(CGFloat)width height:(CGFloat)height; //改變大小

+ (UIImage *)addImage:(UIImage *)image1 toImage:(UIImage *)image2; //合并圖片

+ (UIImage *)imageFromImage:(UIImage *)image inRect:(CGRect)rect; //裁剪部分圖片

+ (void)imageSavedToPhotosAlbum:(UIImage *)image

didFinishSavingWithError:(NSError *)error contextInfo:(void *)contextInfo; //保存圖片到媒體庫

零）重新設(shè)置圖片的尺寸

- (UIImage *)rescaleImage:(UIImage *)img ToSize:(CGSize)size {

　　CGRect rect = CGRectMake(0.0, 0.0, size.width, size.height);

　　UIGraphicsBeginImageContext(rect.size);

　　[img drawInRect:rect]; // scales image to rect

　　UIImage *resImage = UIGraphicsGetImageFromCurrentImageContext();

　　UIGraphicsEndImageContext();

　　return resImage;

}

－）根據(jù)給定得圖片，從其指定區(qū)域截取一張新得圖片

-(UIImage *)getImageFromImage{

　　//大圖bigImage

　　//定義myImageRect，截圖的區(qū)域

　　CGRect myImageRect = CGRectMake(10.0, 10.0, 57.0, 57.0);

　　UIImage* bigImage= [UIImage imageNamed:@"k00030.jpg"];

　　CGImageRef imageRef = bigImage.CGImage;

　　CGImageRef subImageRef = CGImageCreateWithImageInRect(imageRef, myImageRect);

　　CGSize size;

　　size.width = 57.0;

　　size.height = 57.0;

　　UIGraphicsBeginImageContext(size);

　　CGContextRef context = UIGraphicsGetCurrentContext();

　　CGContextDrawImage(context, myImageRect, subImageRef);

　　UIImage* smallImage = [UIImage imageWithCGImage:subImageRef];

　　UIGraphicsEndImageContext();

　　return smallImage;

}

二）合并兩張圖片

- (UIImage *)addImage:(UIImage *)image1 toImage:(UIImage *)image2 {

　　UIGraphicsBeginImageContext(image1.size);

　　//　?Draw image1

　　[image1 drawInRect:CGRectMake(0, 0, image1.size.width, image1.size.height)];

　　// Draw image2

　　[image2 drawInRect:CGRectMake(0, 0, image2.size.width, image2.size.height)];

　　UIImage *resultingImage = UIGraphicsGetImageFromCurrentImageContext();

　　UIGraphicsEndImageContext();

　　return resultingImage;

}

三）捕捉屏幕截圖

CALayer實(shí)例使用Core Graphics的renderInContext方法可以將視圖繪制到圖像上下文中以便轉(zhuǎn)化為其他UIImage實(shí)例。前提先#import

+ (UIImage *) imageFromView: (UIView *)theView {

　　// draw a view's contents into an image context

　　UIGraphicsBeginImageContext(theView.frame.size);

　　CGContextRef context = UIGraphicsGetCurrentContext();

　　[theView.layer renderInContext:context];

　　UIImage *theImage = UIGraphicsGetImageFromCurrentImageContext();

　　UIGraphicsEndImageContext();

　　return theImage;

}

注：UIGraphicsBeginImageContext(CGSize size)創(chuàng)建一個基于位圖的上下文(context)，并將其設(shè)置為當(dāng)前上下文。函數(shù)功能與UIGraphicsBeginImageContextWithOptions相同，相當(dāng)于該方法的opaque參數(shù)為NO，scale因子為1.0。而UIGraphicsEndImageContext()方法是移除棧頂?shù)幕诋?dāng)前位圖的圖形上下文。

視圖添加倒影效果

const CGFloat kReflectPercent = -0.25f;

const CGFloat kReflectOpacity = 0.3f;

const CGFloat kReflectDistance = 10.0f;

+ (void)addSimpleReflectionToView:(UIView *)theView {

　　CALayer *reflectionLayer = [CALayer layer];

　　reflectionLayer.contents = [theView layer].contents;

　　 reflectionLayer.opacity = kReflectOpacity;

　　reflectionLayer.frame = CGRectMake(0.0f,0.0f,theView.frame.size.width,theView.frame.size.height*kReflectPercent);

　　//倒影層框架設(shè)置，其中高度是原視圖的百分比

　　CATransform3D stransform = CATransform3DMakeScale(1.0f,-1.0f,1.0f);

　　CATransform3D transform = CATransform3DTranslate(stransform,0.0f,-(kReflectDistance + theView.frame.size.height),0.0f);

　　 reflectionLayer.transform = transform;

　　reflectionLayer.sublayerTransform = reflectionLayer.transform;

　　[[theView layer] addSublayer:reflectionLayer];

}

另一：使用Core Graphics創(chuàng)建倒影

+ (CGImageRef) createGradientImage:(CGSize)size {

　　 CGFloat colors[] = {0.0,1.0,1.0,1.0};

　　 //在灰色設(shè)備色彩上建立一漸變

　　CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceGray();

　　 CGContextRef context = CGBitmapContextCreate(nil,size.width,size.height,8,0,colorSpace,kCGImageAlphaNone);

　　 CGGradientRef gradient = CGGradientCreateWithColorComponents(colorSpace,colors,NULL,2);

　　 CGColorSpaceRelease(colorSpace);

　　 //繪制線性漸變

　　CGPoint p1 = CGPointZero;

　　 CGPoint p2 = CGPointMake(0,size.height);

　　 CGContextDrawLinearGradient(context,gradient,p1,p2,kCGGradientDrawsAfterEndLocation);

　　 //Return the CGImage

　　 CGImageRef theCGImage = CGBitmapContextCreateImage(context);

　　CFRelease(gradient);

　　 CGContextRelease(context);

　　 return theCGImage;

　}

//Create a shrunken frame for the reflection

+ (UIImage *) reflectionOfView:(UIView *)theView WithPercent:(CGFloat) percent {

　　 //Retain the width but shrink the height

　　 CGSize size = CGSizeMake(theView.frame.size.width, theView.frame.size.height * percent);

　　 //Shrink the View UIGraphicsBeginImageContext(size);

　　 CGContextRef context = UIGraphicsGetCurrentContext();

　　 [theView.layer renderInContext:context];

　　 UIImage *partialimg = UIGraphicsGetImageFromCurrentImageContext();

　　 UIGraphicsEndImageContext();

　　 //build the mask

　　 CGImageRef mask = [ImageHelper createGradientImage:size];

　　 CGImageRef ref = CGImageCreateWithMask(partialimg.CGImage,mask);

　　UIImage *theImage = [UIImage imageWithCGImage:ref];

　　 CGImageRelease(ref);

　　 CGImageRelease(mask);

　　 return theImage;

}

const CGFloat kReflectDistance = 10.0f;

+ (void) addReflectionToView: (UIView *)theView {

　　 theView.clipsToBounds = NO;

　　 UIImageView *reflection = [[UIImageView alloc] initWithImage:[ImageHelper reflectionOfView:theView withPercent:0.45f]];

　　 CGRect frame = reflection.frame;

　　frame.origin = CGPointMake(0.0f, theView.frame.size.height + kReflectDistance);

　　 reflection.frame = frame;

　　 // add the reflection as a simple subview

　　 [theView addSubView:reflection];

　　 [reflection release];

}

關(guān)于圖片縮放的線程安全和非線程安全操作.

非線程安全的操作只能在主線程中進(jìn)行操作,對于大圖片的處理肯定會消耗大量的時間,如下面的方法

方法 1：使用 UIKit

+ (UIImage*)imageWithImage INCLUDEPICTURE "http://www.61ic.com/Mobile/UploadFiles_9667/201103/20110309123315372.gif" \* MERGEFORMATINET UIImage*)image scaledToSize INCLUDEPICTURE "http://www.61ic.com/Mobile/UploadFiles_9667/201103/20110309123315372.gif" \* MERGEFORMATINET CGSize)newSize;

{

　　// Create a graphics image context

　　UIGraphicsBeginImageContext(newSize);

　　// Tell the old image to draw in this new context, with the desired

　　// new size

　　[image drawInRect:CGRectMake(0,0,newSize.width,newSize.height)];

　　// Get the new image from the context

　　UIImage* newImage = UIGraphicsGetImageFromCurrentImageContext();

　　// End the context

　　UIGraphicsEndImageContext();

　　// Return the new image.

　　return newImage;

}

此方法很簡單，但是，這種方法不是線程安全的情況下.

方法 2：使用 CoreGraphics

+ (UIImage*)imageWithImage INCLUDEPICTURE "http://www.61ic.com/Mobile/UploadFiles_9667/201103/20110309123315372.gif" \* MERGEFORMATINET UIImage*)sourceImage scaledToSize INCLUDEPICTURE "http://www.61ic.com/Mobile/UploadFiles_9667/201103/20110309123315372.gif" \* MERGEFORMATINET CGSize)newSize;

{

CGFloat targetWidth = targetSize.width;

CGFloat targetHeight = targetSize.height;

CGImageRef imageRef = [sourceImage CGImage];

CGBitmapInfo bitmapInfo = CGImageGetBitmapInfo(imageRef);

CGColorSpaceRef colorSpaceInfo = CGImageGetColorSpace(imageRef);

if (bitmapInfo == kCGImageAlphaNone) {

bitmapInfo = kCGImageAlphaNoneSkipLast;

}

CGContextRef bitmap;

if (sourceImage.imageOrientation == UIImageOrientationUp ||sourceImage.imageOrientation == UIImageOrientationDown) {

bitmap = CGBitmapContextCreate(NULL, targetWidth, targetHeight,CGImageGetBitsPerComponent(imageRef),CGImageGetBytesPerRow(imageRef), colorSpaceInfo, bitmapInfo);

} else {

bitmap = CGBitmapContextCreate(NULL, targetHeight, targetWidth,CGImageGetBitsPerComponent(imageRef),CGImageGetBytesPerRow(imageRef), colorSpaceInfo, bitmapInfo);

}

if (sourceImage.imageOrientation == UIImageOrientationLeft) {

CGContextRotateCTM (bitmap, radians(90));

CGContextTranslateCTM (bitmap, 0, -targetHeight);

} else if (sourceImage.imageOrientation ==UIImageOrientationRight) {

CGContextRotateCTM (bitmap, radians(-90));

CGContextTranslateCTM (bitmap, -targetWidth, 0);

} else if (sourceImage.imageOrientation == UIImageOrientationUp) {

// NOTHING

} else if (sourceImage.imageOrientation == UIImageOrientationDown){

CGContextTranslateCTM (bitmap, targetWidth, targetHeight);

CGContextRotateCTM (bitmap, radians(-180.));

}

CGContextDrawImage(bitmap, CGRectMake(0, 0, targetWidth,targetHeight), imageRef);

CGImageRef ref = CGBitmapContextCreateImage(bitmap);

UIImage* newImage = [UIImage imageWithCGImage:ref];

CGContextRelease(bitmap);

CGImageRelease(ref);

return newImage;

}

這種方法的好處是它是線程安全，加上它負(fù)責(zé)的（使用正確的顏色空間和位圖信息，處理圖像方向）的小東西，UIKit 版本不會。

如何調(diào)整和保持長寬比（如 AspectFill 選項(xiàng)）？

它是非常類似于上述，方法，它看起來像這樣：

+ (UIImage*)imageWithImage INCLUDEPICTURE "http://www.61ic.com/Mobile/UploadFiles_9667/201103/20110309123315372.gif" \* MERGEFORMATINET UIImage*)sourceImage scaledToSizeWithSameAspectRatio INCLUDEPICTURE "http://www.61ic.com/Mobile/UploadFiles_9667/201103/20110309123315372.gif" \* MERGEFORMATINET CGSize)targetSize;

{

CGSize imageSize = sourceImage.size;

CGFloat width = imageSize.width;

CGFloat height = imageSize.height;

CGFloat targetWidth = targetSize.width;

CGFloat targetHeight = targetSize.height;

CGFloat scaleFactor = 0.0;

CGFloat scaledWidth = targetWidth;

CGFloat scaledHeight = targetHeight;

CGPoint thumbnailPoint = CGPointMake(0.0,0.0);

if (CGSizeEqualToSize(imageSize, targetSize) == NO) {

CGFloat widthFactor = targetWidth / width;

CGFloat heightFactor = targetHeight / height;

if (widthFactor > heightFactor) {

scaleFactor = widthFactor; // scale to fit height

}

else {

scaleFactor = heightFactor; // scale to fit width

}

scaledWidth = width * scaleFactor;

scaledHeight = height * scaleFactor;

// center the image

if (widthFactor > heightFactor) {

thumbnailPoint.y = (targetHeight - scaledHeight) * 0.5;

}

else if (widthFactor < heightFactor) {

thumbnailPoint.x = (targetWidth - scaledWidth) * 0.5;

}

CGImageRef imageRef = [sourceImage CGImage];

CGBitmapInfo bitmapInfo = CGImageGetBitmapInfo(imageRef);

CGColorSpaceRef colorSpaceInfo = CGImageGetColorSpace(imageRef);

if (bitmapInfo == kCGImageAlphaNone) {

bitmapInfo = kCGImageAlphaNoneSkipLast;

}

CGContextRef bitmap;

if (sourceImage.imageOrientation == UIImageOrientationUp ||sourceImage.imageOrientation == UIImageOrientationDown) {

bitmap = CGBitmapContextCreate(NULL, targetWidth, targetHeight,CGImageGetBitsPerComponent(imageRef),CGImageGetBytesPerRow(imageRef), colorSpaceInfo, bitmapInfo);

} else {

bitmap = CGBitmapContextCreate(NULL, targetHeight, targetWidth,CGImageGetBitsPerComponent(imageRef),CGImageGetBytesPerRow(imageRef), colorSpaceInfo, bitmapInfo);

}

// In the right or left cases, we need to switch scaledWidth and scaledHeight,

// and also the thumbnail point

if (sourceImage.imageOrientation == UIImageOrientationLeft) {

thumbnailPoint = CGPointMake(thumbnailPoint.y, thumbnailPoint.x);

CGFloat oldScaledWidth = scaledWidth;

scaledWidth = scaledHeight;

scaledHeight = oldScaledWidth;

CGContextRotateCTM (bitmap, radians(90));

CGContextTranslateCTM (bitmap, 0, -targetHeight);

} else if (sourceImage.imageOrientation ==UIImageOrientationRight) {

thumbnailPoint = CGPointMake(thumbnailPoint.y, thumbnailPoint.x);

CGFloat oldScaledWidth = scaledWidth;

scaledWidth = scaledHeight;

scaledHeight = oldScaledWidth;

CGContextRotateCTM (bitmap, radians(-90));

CGContextTranslateCTM (bitmap, -targetWidth, 0);

} else if (sourceImage.imageOrientation == UIImageOrientationUp) {

// NOTHING

} else if (sourceImage.imageOrientation == UIImageOrientationDown){

CGContextTranslateCTM (bitmap, targetWidth, targetHeight);

CGContextRotateCTM (bitmap, radians(-180.));

}

CGContextDrawImage(bitmap, CGRectMake(thumbnailPoint.x,thumbnailPoint.y, scaledWidth, scaledHeight), imageRef);

CGImageRef ref = CGBitmapContextCreateImage(bitmap);

UIImage* newImage = [UIImage imageWithCGImage:ref];

CGContextRelease(bitmap);

CGImageRelease(ref);

return newImage;

}

轉(zhuǎn)載于:https://www.cnblogs.com/ChouDanDan/p/5110058.html

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