Fast way to create openGL texture from JPEG-2000? - ios

Question

I need to load large-ish (5 megapixel) jpeg images and create openGL texture from them. They are non-power-of-two, and cannot be pre-processed for this application. Loading is extremely slow, about one second per image on an iPad Air 2. I need to load a dozen or two such images and create a GL texture for each, as quickly as I can.
Profiling shows the bottleneck to be CGContextDrawImage. Previous answers suggest this is a common problem.
This previous answer seems most relevant and (unfortunately) does not leave me hopeful. I haven't tried lib-jpeg (suggested in another answer) yet - trying to keep third party code out for several reasons.
But - that answer was 2014 and things change. Does anybody know of a faster way to create textures from jpegs? Either by changing the arguments to CGContextDrawImage (as in this answer- I've tried the suggested changes with no noticeable speed change) or using a different approach entirely?
The current texture creation block (called asynchronously):
UIImage *image = [UIImage imageWithData:jpegImageData];
if (image) {
GLuint textureID;
glGenTextures(1, &textureID);
glBindTexture( GL_TEXTURE_2D, textureID);
glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MIN_FILTER,GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MAG_FILTER,GL_LINEAR);
glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE );
glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE );
GLsizei width = (GLsizei)CGImageGetWidth(image.CGImage);
GLsizei height = (GLsizei)CGImageGetHeight(image.CGImage);
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
void *imageData = malloc( height * width * 4 );
CGContextRef imgcontext = CGBitmapContextCreate( imageData, width, height, 8, 4 * width, colorSpace, kCGImageAlphaNoneSkipLast | kCGBitmapByteOrder32Big );
CGColorSpaceRelease( colorSpace );
CGContextDrawImage( imgcontext, CGRectMake( 0, 0, width, height ), image.CGImage );
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, imageData);
CGContextRelease(imgcontext);
free(imageData);
// ... store the textureID for use by the caller
// ...
}
(edited to add)
I tried GLKTextureLoader. I kept getting a nil return value, with error theError NSError * domain: "GLKTextureLoaderErrorDomain" - code: 12.
I've realized that the JPEGs I need to load are JPEG 2000; and that may be the problem. I've played with the GLKTextureLoader approach; I can get it to work non-J2K jpegs, but not the J2K ones I need to load. (FWIW, the files I need to load are packed inside larger files, thus I extract a data subrange from within the file, as such:
NSData *jpegImageData = [data subdataWithRange:NSMakeRange(offset, dataLength)];
GLKTextureInfo *jpegTexture;
NSError *theError;
jpegTexture = [GLKTextureLoader textureWithContentsOfData:jpegImageData options:nil error:&theError];
but, as mentioned, jpegImageData comes back as nil with the aforementioned error. This works on small jpegs, even using the subdataWithRange approach.
Likewise,
UIImage *image = [UIImage imageWithData:jpegImageData];
jpegTexture = [GLKTextureLoader textureWithCGImage:image.CGImage options:nil error:&theError];
returns nil with the same "code 12" error.
This iOS Developer page (Table 1-1) suggests that JPEG-2000 is supported on OS X only, but when I try the
CFArrayRef mySourceTypes = CGImageSourceCopyTypeIdentifiers();
CFShow(mySourceTypes);
approach for showing supported formats, JPEG-2000 is among them (running on my iOS device):
33 : <CFString 0x19d721bf8 [0x1a1da0150]>{contents = "public.jpeg-
Any suggestions for using the faster GLKTextureLoader methods on JPEG-2000?

Answer 1

Did you try the GLKit Framework method?
GLKTexGtureInfo *spriteTexture;
NSError *theError;
NSString *filePath = [[NSBundle mainBundle] pathForResource:#"Sprite" ofType:#"jpg"]; // 1
spriteTexture = [GLKTextureLoader textureWithContentsOfFile:filePath options:nil error:&theError]; // 2
glBindTexture(spriteTexture.target, spriteTexture.name); // 3