iOS 中随机图像的 OpenGL ES 纹理
我面临着将一个奇怪大小的图像(尽管具有固定比例)放在 GL_QUAD 上的任务(嗯,GL_TRIANGLE_STRIP resem——你明白了),一开始这对我来说似乎相当容易,除了我需要在 iOS (4.2+) 中执行此操作的部分。不管怎样,解决方案非常简单:只需获取图像,用它制作纹理,将其映射到正确的顶点,然后就可以开始了。
您可能很清楚,OpenGL ES 纹理的宽度和高度必须为 2 的幂,例如 2、4、8、...、256、512...(不确定这是否适用于常规 OpenGL,但我认为确实如此......无论如何,没关系)。 因为我必须从 Intertubes(实际上是 YouTube)下载这些图像,所以我无法事先做任何事情,所以我有这些 480x360 图像(如果我没记错的话),我必须将它们放在我的三角形条上。幸运的是,我们有纹理映射,它允许我们选择要映射到我们想要的位置的纹理部分,因此明显的解决方案是(可选地放大/缩小)并用一些哑光颜色填充源图像,并接受它。
进入iOS。我从 Intertubes 获取数据,我很高兴地构建了相应的 UIImage,然后我制作了另一个 UIImage(是的,我知道,请耐心等待,我稍后会优化它),宽度缩小到最接近的 2 的幂,保留宽高比,所以假设 256x192,然后我创建一个位图上下文,将其漆成黑色(或者,重要的是,任何其他颜色,但我想你可以明白为什么我在这种情况下选择黑色),绘制 UIImage (一个 CGImage),并返回使用上述位图上下文构建的 UIImage。
我现在是 256x256 图像的快乐拥有者,准备将其映射到我的 GL_TRIANGLE_STRIP 上。但它不起作用。我尝试使用准备好的 512x512 图像,效果完美。我在此处粘贴的代码不包括从 YouTube 检索图像,我只是将其保存在本地以排除网络问题。另外,我没有包含 GL 代码,因为它显然可以工作。
- (void)viewDidLoad {
images = [[NSMutableArray alloc] init];
//NSURL *url = [NSURL URLWithString:@"http://i.ytimg.com/vi/d2wVgzXWE9Y/0.jpg"];
NSString *path = [[NSBundle mainBundle] pathForResource:@"opengl_texture" ofType:@"jpg"];
NSData *texData = [NSData dataWithContentsOfFile:path];
UIImage *rawImage = [[UIImage alloc] initWithData:texData];
float newWidth = (float)(1 << (int)floor(log2f(rawImage.size.width)));
// Scale means the scale of the current image relative to the resulting image.
float scale = rawImage.size.width / newWidth;
UIImage *midImage = [UIImage imageWithCGImage:[rawImage CGImage] scale:scale orientation:UIImageOrientationUp];
NSLog(@"%f %f %f", midImage.size.width, midImage.size.height, scale);
[rawImage release];
UIImage *image = [self padImage:midImage withColor:[UIColor redColor]];
NSLog(@"%f %f", image.size.width, image.size.height);
[images addObject:image];
textures = malloc(sizeof(GLuint));
glGenTextures(1, textures);
glBindTexture(GL_TEXTURE_2D, textures[0]);
glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MIN_FILTER,GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MAG_FILTER,GL_LINEAR);
GLuint width = CGImageGetWidth(image.CGImage);
GLuint height = CGImageGetWidth(image.CGImage);
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
void *imageData = malloc(width * height * 4);
CGContextRef context = CGBitmapContextCreate(imageData, width, height, 8, 4*width, colorSpace, kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big);
CGColorSpaceRelease( colorSpace );
CGContextClearRect( context, CGRectMake( 0, 0, width, height ) );
CGContextTranslateCTM( context, 0, height - height );
CGContextDrawImage( context, CGRectMake( 0, 0, width, height ), image.CGImage );
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, imageData);
CGContextRelease(context);
free(imageData);
[midImage release];
[image release];
[texData release];
}
- (UIImage *)padImage:(UIImage *)image withColor:(UIColor *)color {
CGFloat size = round(image.size.width);
NSLog(@"%f", size);
CGContextRef bContext = [self createBitmapContextOfSize:CGSizeMake(size, size)];
CGContextSetFillColorWithColor(bContext, [color CGColor]);
CGContextFillRect(bContext, CGRectMake(0, 0, size, size));
CGContextDrawImage(bContext, CGRectMake(0, 0, size, size), [image CGImage]);
UIImage *result = [UIImage imageWithCGImage:CGBitmapContextCreateImage(bContext)];
CGContextRelease(bContext);
return result;
}
- (CGContextRef) createBitmapContextOfSize:(CGSize) size {
CGContextRef context = NULL;
CGColorSpaceRef colorSpace;
void * bitmapData;
int bitmapByteCount;
int bitmapBytesPerRow;
bitmapBytesPerRow = (size.width * 4);
bitmapByteCount = (bitmapBytesPerRow * size.height);
colorSpace = CGColorSpaceCreateDeviceRGB();
bitmapData = malloc( bitmapByteCount );
if (bitmapData == NULL) {
fprintf (stderr, "Memory not allocated!");
return NULL;
}
context = CGBitmapContextCreate (bitmapData,
size.width,
size.height,
8, // bits per component
bitmapBytesPerRow,
colorSpace,
kCGImageAlphaPremultipliedLast);
CGContextSetAllowsAntialiasing (context,NO);
if (context== NULL) {
free (bitmapData);
fprintf (stderr, "Context not created!");
return NULL;
}
CGColorSpaceRelease( colorSpace );
return context;
}
请不要费心提及明显的内存管理问题,除非您认为它们是问题的核心。至于“错误消息”或其他什么:不,没有这样的事情,整个应用程序只是崩溃了。
I've been challenged with the task of putting an oddly sized image (with fixed proportion, though) on a GL_QUAD (well, a GL_TRIANGLE_STRIP resem--you got the point) and that seemed fairily easy to me at first, except for the part where I need to do this in iOS (4.2+). The solution is awkwardly easy anyway: just take the image, make a texture out of it, map it to the correct vertices and you're good to go.
As you may very well know, OpenGL ES textures are required to have width and height to be powers of 2, like 2, 4, 8, ..., 256, 512... (not sure this holds for regular OpenGL but I think it does... anyway, doesn't matter).
Since I have to download these images from the Intertubes (actually, the YouTube) I can't really do anything beforehand, so I have these 480x360 images (if I remember it correctly) and I have to splat them on my triangle strips. Fortunately we have texture mapping which allows us to select portions of the texture to be mapped where we want, so the obvious solution would be to (optionally up/downsize) and pad with some matte color the source image, and live with it.
Enter iOS. I get the data from the Intertubes, I happily build the corresponding UIImage, then I make another UIImage (yes, I know, bear with me, I'll optimize it later) just scaled down to the nearest power-of-2 in width, preserving aspect, so let's say 256x192, then I make a bitmap context , paint it black (or, for what matters, any other colour, but I think you can see why I chose black in this case), draw the UIImage (a CGImage) on it, and return the UIImage built using the aforementioned bitmap context.
I am now the happy owner of a 256x256 image ready to be mapped on my GL_TRIANGLE_STRIP. Except that it does not work. I tried with a prepared 512x512 image and it worked flawlessly. The code I'm pasting here does not include the retrieval of the image from YouTube, I just saved it locally to rule out networking problems. Also, I'm not including the GL code as it's clearly working.
- (void)viewDidLoad {
images = [[NSMutableArray alloc] init];
//NSURL *url = [NSURL URLWithString:@"http://i.ytimg.com/vi/d2wVgzXWE9Y/0.jpg"];
NSString *path = [[NSBundle mainBundle] pathForResource:@"opengl_texture" ofType:@"jpg"];
NSData *texData = [NSData dataWithContentsOfFile:path];
UIImage *rawImage = [[UIImage alloc] initWithData:texData];
float newWidth = (float)(1 << (int)floor(log2f(rawImage.size.width)));
// Scale means the scale of the current image relative to the resulting image.
float scale = rawImage.size.width / newWidth;
UIImage *midImage = [UIImage imageWithCGImage:[rawImage CGImage] scale:scale orientation:UIImageOrientationUp];
NSLog(@"%f %f %f", midImage.size.width, midImage.size.height, scale);
[rawImage release];
UIImage *image = [self padImage:midImage withColor:[UIColor redColor]];
NSLog(@"%f %f", image.size.width, image.size.height);
[images addObject:image];
textures = malloc(sizeof(GLuint));
glGenTextures(1, textures);
glBindTexture(GL_TEXTURE_2D, textures[0]);
glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MIN_FILTER,GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MAG_FILTER,GL_LINEAR);
GLuint width = CGImageGetWidth(image.CGImage);
GLuint height = CGImageGetWidth(image.CGImage);
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
void *imageData = malloc(width * height * 4);
CGContextRef context = CGBitmapContextCreate(imageData, width, height, 8, 4*width, colorSpace, kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big);
CGColorSpaceRelease( colorSpace );
CGContextClearRect( context, CGRectMake( 0, 0, width, height ) );
CGContextTranslateCTM( context, 0, height - height );
CGContextDrawImage( context, CGRectMake( 0, 0, width, height ), image.CGImage );
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, imageData);
CGContextRelease(context);
free(imageData);
[midImage release];
[image release];
[texData release];
}
- (UIImage *)padImage:(UIImage *)image withColor:(UIColor *)color {
CGFloat size = round(image.size.width);
NSLog(@"%f", size);
CGContextRef bContext = [self createBitmapContextOfSize:CGSizeMake(size, size)];
CGContextSetFillColorWithColor(bContext, [color CGColor]);
CGContextFillRect(bContext, CGRectMake(0, 0, size, size));
CGContextDrawImage(bContext, CGRectMake(0, 0, size, size), [image CGImage]);
UIImage *result = [UIImage imageWithCGImage:CGBitmapContextCreateImage(bContext)];
CGContextRelease(bContext);
return result;
}
- (CGContextRef) createBitmapContextOfSize:(CGSize) size {
CGContextRef context = NULL;
CGColorSpaceRef colorSpace;
void * bitmapData;
int bitmapByteCount;
int bitmapBytesPerRow;
bitmapBytesPerRow = (size.width * 4);
bitmapByteCount = (bitmapBytesPerRow * size.height);
colorSpace = CGColorSpaceCreateDeviceRGB();
bitmapData = malloc( bitmapByteCount );
if (bitmapData == NULL) {
fprintf (stderr, "Memory not allocated!");
return NULL;
}
context = CGBitmapContextCreate (bitmapData,
size.width,
size.height,
8, // bits per component
bitmapBytesPerRow,
colorSpace,
kCGImageAlphaPremultipliedLast);
CGContextSetAllowsAntialiasing (context,NO);
if (context== NULL) {
free (bitmapData);
fprintf (stderr, "Context not created!");
return NULL;
}
CGColorSpaceRelease( colorSpace );
return context;
}
Please don't bother mentioning obvious memory management issues unless you think they are the core of the problem. As for the "error message" or whatever: no, there's no such thing, the whole app just crashes.
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好吧,现在你们可以集体用一条大鳟鱼打我的脸了。
问题实际上是内存管理,特别是我正在释放使用隐式方法(即 midImage 和 texData)创建的对象。隐式创建不会增加保留计数,而显式创建(alloc+init 等)则会增加保留计数。我已经有多少次遇到这种情况了?很多。他们够了吗?显然不是。
第二个问题:哪里可以找到一张大的便利贴,至少 1x1m 的?
Ok, now you can collectively smack my face with a large trout.
The problem was actually memory management, specifically I was releasing objects that were created with implicit methods (namely midImage and texData). Implicit creation does not increase the retain count, while explicit (alloc+init and friends) does. How may times did I already crash against this? Lots. Were them enough? Obviously not.
Second question: where can I find a large post-it, like 1x1m at least?