子类化NSImageRep以支持新文件格式（pgm）
大家好！这是我在这里的第一篇文章。
我在objective-c中很新，所以也许我的问题不是那么难，但对我来说这是一个问题。我在网上搜索过，没有找到任何有用的提示......我正在用Xcode中的Objective-c编写一个程序。我需要读取并显示pgm文件（每个像素有两个字节的P5）。要做到这一点，我正在尝试子类NSImageRep，但我不知道如何为此文件创建一个正确的位图以及如何绘制它。以下是我目前的代码：
头：
@interface CTPWTPGMImageRep : NSImageRep
@property (readonly)NSInteger width;
@property (readonly)NSInteger height;
@property (readonly)NSInteger maxValue;
+ (void)load;
+ (NSArray *)imageUnfilteredTypes;
+ (NSArray *)imageUnfilteredFileTypes;
+ (BOOL)canInitWithData:(NSData *)data;
+ (id)imageRepWithContentsOfFile:(NSString*)file;
+ (id)imageRepWithData:(NSData*)pgmData;
- (id)initWithData:(NSData *)data;
- (BOOL)draw;
@end
和实施：
#import "CTPWTPGMImageRep.h"
@implementation CTPWTPGMImageRep
@synthesize width;
@synthesize height;
@synthesize maxValue;
#pragma mark - class methods
+(void) load
{
NSLog(@"Called 'load' method for CTPWTPGMImageRep");
[NSImageRep registerImageRepClass:[CTPWTPGMImageRep class]];
}
+ (NSArray *)imageUnfilteredTypes
{
// This is a UTI
NSLog(@"imageUnfilteredTypes called");
static NSArray *types = nil;
if (!types) {
types = [[NSArray alloc] initWithObjects:@"public.unix-executable", @"public.data", @"public.item", @"public.executable", nil];
}
return types;
}
+ (NSArray *)imageUnfilteredFileTypes
{
// This is a filename suffix
NSLog(@"imageUnfilteredFileTypes called");
static NSArray *types = nil;
if (!types)
types = [[NSArray alloc] initWithObjects:@"pgm", @"PGM", nil];
return types;
}
+ (BOOL)canInitWithData:(NSData *)data;
{
// FIX IT
NSLog(@"canInitWithData called");
if ([data length] >= 2) // First two bytes for magic number magic number
{
NSString *magicNumber = @"P5";
const unsigned char *mNum = (const unsigned char *)[magicNumber UTF8String];
unsigned char aBuffer[2];
[data getBytes:aBuffer length:2];
if(memcmp(mNum, aBuffer, 2) == 0)
{
NSLog(@"canInitWithData: YES");
return YES;
}
}
NSLog(@"canInitWithData: NO");
// end
return NO;
}
+ (id)imageRepWithContentsOfFile:(NSString*)file {
NSLog(@"imageRepWithContentsOfFile called");
NSData* data = [NSData dataWithContentsOfFile:file];
if (data)
return [CTPWTPGMImageRep imageRepWithData:data];
return nil;
}
+ (id)imageRepWithData:(NSData*)pgmData {
NSLog(@"imageRepWithData called");
return [[self alloc] initWithData:pgmData];
}
#pragma mark - instance methods
- (id)initWithData:(NSData *)data;
{
NSLog(@"initWithData called");
self = [super init];
if (!self)
{
return nil;
}
if ([data length] >= 2) {
NSString *magicNumberP5 = @"P5";
const unsigned char *mnP5 = (const unsigned char *)[magicNumberP5 UTF8String];
unsigned char headerBuffer[20];
[data getBytes:headerBuffer length:2];
if(memcmp(mnP5, headerBuffer, 2) == 0)
{
NSArray *pgmParameters = [self calculatePgmParameters:data beginingByte:3];
width = [[pgmParameters objectAtIndex:0] integerValue];
height = [[pgmParameters objectAtIndex:1] integerValue];
maxValue = [[pgmParameters objectAtIndex:2] integerValue];
if (width <= 0 || height <= 0)
{
NSLog(@"Invalid image size: Both width and height must be > 0");
return nil;
}
[self setPixelsWide:width];
[self setPixelsHigh:height];
[self setSize:NSMakeSize(width, height)];
[self setColorSpaceName:NSDeviceWhiteColorSpace];
[self setBitsPerSample:16];
[self setAlpha:NO];
[self setOpaque:NO];
//What to do here?
//CTPWTPGMImageRep *imageRep =
[NSBitmapImageRep alloc] initWithBitmapDataPlanes:];
//if (imageRep) {
/* code to populate the pixel map */
//}
}
else
{
NSLog(@"It is not supported pgm file format.");
}
}
return self;
//return imageRep;
}
- (BOOL)draw
{
NSLog(@"draw method1 called");
return NO;
}
有趣的是我的canInitWithData:方法从未被调用过。你能给我一个如何智能读取位图的提示吗？我认为我需要使用initWithBitmapDataPlanes:pixelsWide:pixelsHigh:bitsPerSample:samplesPerPixel:hasAlpha:isPlanar:colorSpaceName:bytesPerRow:bitsPerPixel:，但我不知道如何使用它。如何从我的NSData对象创建智能创建（unsigned char **）平面？我需要吗？
我可以使用具有白色和alpha分量的NSDeviceWhiteColorSpace（我不需要alpha）
[self setColorSpaceName:NSDeviceWhiteColorSpace];
和最困难的部分 - 我完全不知道如何实现draw方法。任何吸烟或提示？
提前感谢您的帮助。
修改
确定。现在我根据NSGod指示实施：
@implementation CTPWTPGMImageRep
//@synthesize width;
//@synthesize height;
#pragma mark - class methods
+(void) load
{
NSLog(@"Called 'load' method for CTPWTPGMImageRep");
[NSBitmapImageRep registerImageRepClass:[CTPWTPGMImageRep class]];
}
+ (NSArray *)imageUnfilteredTypes
{
// This is a UTI
NSLog(@"imageUnfilteredTypes called");
static NSArray *types = nil;
if (!types) {
types = [[NSArray alloc] initWithObjects:@"public.unix-executable", @"public.data", @"public.item", @"public.executable", nil];
}
return types;
}
+ (NSArray *)imageUnfilteredFileTypes
{
// This is a filename suffix
NSLog(@"imageUnfilteredFileTypes called");
static NSArray *types = nil;
if (!types)
types = [[NSArray alloc] initWithObjects:@"pgm", nil];
return types;
}
+ (NSArray *)imageRepsWithData:(NSData *)data {
NSLog(@"imageRepsWithData called");
id imageRep = [[self class] imageRepWithData:data];
return [NSArray arrayWithObject:imageRep];
}
- (id)initWithData:(NSData *)data {
NSLog(@"initWithData called");
CTPWTPGMImageRep *imageRep = [[self class] imageRepWithData:data];
if (imageRep == nil) {
return nil;
}
return self;
}
#pragma mark - instance methods
+ (id)imageRepWithData:(NSData *)data {
NSLog(@"imageRepWithData called");
if (data.length < 2) return nil;
NSString *magicNumberP5 = @"P5";
const unsigned char *mnP5 = (const unsigned char *)[magicNumberP5 UTF8String];
unsigned char headerBuffer[2];
[data getBytes:headerBuffer length:2];
if (memcmp(mnP5, headerBuffer, 2) != 0) {
NSLog(@"It is not supported pgm file format.");
return nil;
}
NSArray *pgmParameters = [self calculatePgmParameters:data beginingByte:3];
NSInteger width = [[pgmParameters objectAtIndex:0] integerValue]; // width in pixels
NSInteger height = [[pgmParameters objectAtIndex:1] integerValue]; // height in pixels
NSUInteger imageLength = width * height * 2; // two bytes per pixel
// imageData contains bytes of Bitmap only. Without header
NSData *imageData = [data subdataWithRange:
NSMakeRange(data.length - imageLength, imageLength)];
CGDataProviderRef provider = CGDataProviderCreateWithCFData((CFDataRef)CFBridgingRetain(imageData));
CGColorSpaceRef colorSpace = CGColorSpaceCreateWithName(kCGColorSpaceGenericGray); // kCGColorSpaceGenericGrayGamma2_2
CGImageRef imageRef = CGImageCreate(width,
height,
16,
16,
width * 2,
colorSpace,
kCGImageAlphaNone,
provider,
NULL,
false,
kCGRenderingIntentDefault);
CGColorSpaceRelease(colorSpace);
CGDataProviderRelease(provider);
if (imageRef == NULL) {
NSLog(@"CGImageCreate() failed!");
}
CTPWTPGMImageRep *imageRep = [[CTPWTPGMImageRep alloc] initWithCGImage:imageRef];
return imageRep;
}
正如您所看到的那样，我将零件的延伸值保留在0-255之间，因为我的像素值介于0-65535之间。
但它不起作用。当我从面板中选择一个pgm文件时，没有任何反应。贝娄是我的openPanel代码：
- (IBAction)showOpenPanel:(id)sender
{
NSLog(@"showPanel method called");
__block NSOpenPanel *panel = [NSOpenPanel openPanel];
[panel setAllowedFileTypes:[NSImage imageFileTypes]];
[panel beginSheetModalForWindow:[pgmImageView window] completionHandler:^ (NSInteger result) {
if (result == NSOKButton) {
CTPWTPGMImageRep *pgmImage = [[CTPWTPGMImageRep alloc] initWithData:[NSData dataWithContentsOfURL:[panel URL]]];
// NSLog(@"Bits per pixel: %ld",[pgmImage bitsPerPixel]); // BUG HERE!
NSImage *image = [[NSImage alloc] init];
[image addRepresentation:pgmImage];
[pgmImageView setImage:image];
}
panel = nil; // prevent strong ref cycle
}];
}
此外，当我取消注释代码// NSLog(@"Bits per pixel: %ld",[pgmImage bitsPerPixel]); // BUG HERE!只是为了检查我的Xcode冻结片刻，我得到了EXC_BAD_ACCESS：
AppKit`__75-[NSBitmapImageRep _withoutChangingBackingPerformBlockUsingBackingCGImage:]_block_invoke_0:
0x7fff8b4823e8: pushq %rbp
0x7fff8b4823e9: movq %rsp, %rbp
0x7fff8b4823ec: pushq %r15
0x7fff8b4823ee: pushq %r14
0x7fff8b4823f0: pushq %r13
0x7fff8b4823f2: pushq %r12
0x7fff8b4823f4: pushq %rbx
0x7fff8b4823f5: subq $312, %rsp
0x7fff8b4823fc: movq %rsi, %rbx
0x7fff8b4823ff: movq %rdi, %r15
0x7fff8b482402: movq 10625679(%rip), %rax
0x7fff8b482409: movq (%rax), %rax
0x7fff8b48240c: movq %rax, -48(%rbp)
0x7fff8b482410: movq %rbx, %rdi
0x7fff8b482413: callq 0x7fff8b383148 ; BIRBackingType //EXC_BAD_ACCESS (code=2, adress=...)
任何帮助???我不知道出了什么问题......
2 个答案:
答案 0 :(得分：2)
这实际上比你想的要容易得多。
首先，我建议将CTPWTPGMImageRep作为NSBitmapImageRep的子类，而不是NSImageRep。这将解决“最难”的问题，因为不需要实现自定义draw方法，因为NSBitmapImageRep已经知道如何绘制自己。 （在OS X 10.5及更高版本中，NSBitmapImageRep基本上是CoreGraphics CGImageRef s的直接包装。
我不熟悉PGM格式，但您基本上要做的是以最接近的目标格式创建与源格式匹配的图像表示。要使用特定示例，我们将从维基百科中获取PGM example FEEP image。
P2
# Shows the word "FEEP" (example from Netpbm main page on PGM)
24 7
15
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 3 3 3 3 0 0 7 7 7 7 0 0 11 11 11 11 0 0 15 15 15 15 0
0 3 0 0 0 0 0 7 0 0 0 0 0 11 0 0 0 0 0 15 0 0 15 0
0 3 3 3 0 0 0 7 7 7 0 0 0 11 11 11 0 0 0 15 15 15 15 0
0 3 0 0 0 0 0 7 0 0 0 0 0 11 0 0 0 0 0 15 0 0 0 0
0 3 0 0 0 0 0 7 7 7 7 0 0 11 11 11 11 0 0 15 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
能够描绘示例图像中的值的最接近的原始图像将是单通道灰度图像，每像素8位，无alpha。然后，计划是使用指定的设置创建CGImageRef，然后使用NSBitmapImageRep的{{1}}方法初始化自定义子类。
我首先要覆盖以下两种方法，以便依赖单数initWithCGImage:：
+imageRepWithData:对我来说，有必要实现+ (NSArray *)imageRepsWithData:(NSData *)data {
id imageRep = [[self class] imageRepWithData:data];
return [NSArray arrayWithObject:imageRep];
}
- (id)initWithData:(NSData *)data {
CTPWTPGMImageRep *imageRep = [[self class] imageRepWithData:data];
if (imageRep == nil) {
[self release];
return nil;
}
self = [imageRep retain];
return self;
}
方法来调用奇异方法，然后才能正确加载图像。
然后我会改变单数+imageRepsWithData:方法如下：
+imageRepWithData:正如您所看到的，我们需要遍历原始图像中的字节并创建这些字节的第二个副本，其完整扩展范围介于0到255之间。
要使用此图片代表，您可以像下面这样调用它（确保使用+ (id)imageRepWithData:(NSData *)data {
if (data.length < 2) return nil;
NSString *magicNumberP5 = @"P5";
const unsigned char *mnP5 = (const unsigned char *)[magicNumberP5 UTF8String];
unsigned char headerBuffer[20];
[data getBytes:headerBuffer length:2];
if (memcmp(mnP5, headerBuffer, 2) != 0) {
NSLog(@"It is not supported pgm file format.");
return nil;
}
NSArray *pgmParameters = [self calculatePgmParameters:data beginingByte:3];
NSUInteger width = [[pgmParameters objectAtIndex:0] integerValue];
NSUInteger height = [[pgmParameters objectAtIndex:1] integerValue];
NSUInteger maxValue = [[pgmParameters objectAtIndex:2] integerValue];
NSUInteger imageLength = width * height * 1;
NSData *imageData = [data subdataWithRange:
NSMakeRange(data.length - imageLength, imageLength)];
const UInt8 *imageDataBytes = [imageData bytes];
UInt8 *expandedImageDataBytes = malloc(imageLength);
for (NSUInteger i = 0; i < imageLength; i++) {
expandedImageDataBytes[i] = 255 * (imageDataBytes[i] / (CGFloat)maxValue);
}
NSData *expandedImageData = [NSData dataWithBytes:expandedImageDataBytes
length:imageLength];
free(expandedImageDataBytes);
CGDataProviderRef provider = CGDataProviderCreateWithCFData(
(CFDataRef)expandedImageData);
CGColorSpaceRef colorSpace =
CGColorSpaceCreateWithName(kCGColorSpaceGenericGrayGamma2_2);
CGImageRef imageRef = CGImageCreate(width,
height,
8,
8,
width * 1,
colorSpace,
kCGImageAlphaNone,
provider,
NULL,
false,
kCGRenderingIntentDefault);
CGColorSpaceRelease(colorSpace);
CGDataProviderRelease(provider);
if (imageRef == NULL) {
NSLog(@"CGImageCreate() failed!");
}
CTPWTPGMImageRep *imageRep = [[[CTPWTPGMImageRep alloc]
initWithCGImage:imageRef] autorelease];
CGImageRelease(imageRef);
return imageRep;
}
的{{1}}方法）：
NSImage关于你的initWithData:方法的另外一个注意事项：文件扩展名不区分大小写，因此不需要同时指定小写和大写// if it hasn't been done already:
[NSImageRep registerImageRepClass:[CTPWTPGMImageRep class]];
NSString *path = [[NSBundle mainBundle] pathForResource:@"feep" ofType:@"pgm"];
NSData *data = [NSData dataWithContentsOfFile:path];
NSImage *image = [[[NSImage alloc] initWithData:data] autorelease];
[self.imageView setImage:image];
，你可以只做小写：
+imageUnfilteredFileTypes答案 1 :(得分：1)
将像素数据简单地读入内存并从像素数据中创建NSBitmapImageRep而不是尝试专门为.pgm文件创建图像代码可能更容易。
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