How to render UIImage (picked from photo library) into CIContext / GLKView? - iphone

Question

After researching and trying many things finally I made myself to ask SO:
basically I would like to pick a photo and then render it to a CIcontext, knowing that many other image rendering techniques available (eg. use UIImageView, etc), I have to use low-level OpenGL ES rendering.
Please check my full code (except the preload of UIImagePickerController in AppDelegate)
#import "ViewController.h"
#import "AppDelegate.h"
#import <GLKit/GLKit.h>
#interface ViewController () <GLKViewDelegate, UINavigationControllerDelegate, UIImagePickerControllerDelegate> {
GLKView *glkview;
CGRect glkview_bounds;
}
- (IBAction)click:(id)sender;
#property (strong, nonatomic) EAGLContext *eaglcontext;
#property (strong, nonatomic) CIContext *cicontext;
#end
#implementation ViewController
- (void)viewDidLoad {
[super viewDidLoad];
self.eaglcontext = [[EAGLContext alloc] initWithAPI:kEAGLRenderingAPIOpenGLES2];
glkview = [[GLKView alloc] initWithFrame:[[UIScreen mainScreen] bounds] context:self.eaglcontext];
glkview.drawableDepthFormat = GLKViewDrawableDepthFormat24;
glkview.enableSetNeedsDisplay = YES;
glkview.delegate = self;
[self.view addSubview:glkview];
[glkview bindDrawable];
glkview_bounds = CGRectZero;
glkview_bounds.size.width = glkview.drawableWidth;
glkview_bounds.size.height = glkview.drawableHeight;
NSLog(#"glkview_bounds:%#", NSStringFromCGRect(glkview_bounds));
self.cicontext = [CIContext contextWithEAGLContext:self.eaglcontext options:#{kCIContextWorkingColorSpace : [NSNull null]} ];
UIAppDelegate.g_mediaUI.delegate = self;
}
- (IBAction)click:(id)sender {
[self presentViewController:UIAppDelegate.g_mediaUI animated:YES completion:nil];
}
- (void)imagePickerController:(UIImagePickerController *)picker didFinishPickingMediaWithInfo:(NSDictionary *)info {
[self dismissViewControllerAnimated:NO completion:nil];
UIImage *pre_img = (UIImage *)[info objectForKey:UIImagePickerControllerOriginalImage];
CIImage *outputImage = [CIImage imageWithCGImage:pre_img.CGImage];
NSLog(#"orient:%d, size:%#, scale:%f, extent:%#", (int)pre_img.imageOrientation, NSStringFromCGSize(pre_img.size), pre_img.scale,NSStringFromCGRect(outputImage.extent));
if (outputImage) {
if (self.eaglcontext != [EAGLContext currentContext])
[EAGLContext setCurrentContext:self.eaglcontext];
// clear eagl view to grey
glClearColor(0.5, 0.5, 0.5, 1.0);
glClear(GL_COLOR_BUFFER_BIT);
// set the blend mode to "source over" so that CI will use that
glEnable(GL_BLEND);
glBlendFunc(GL_ONE, GL_ONE_MINUS_SRC_ALPHA);
[self.cicontext drawImage:outputImage inRect:glkview_bounds fromRect:[outputImage extent]];
[glkview display];
}
}
#end
What works: picked images having sizes eg. size 1390x1390 or 1440x1440 are displayed.
What doesn't work: picked images with size of 2592x1936 are not displayed, basically all large pictures which taken with the camera.
Please help finding out the solution, I'm stucked here...

Answer 1

OpenGL has a texture limit, depending on the iOS device it can be 2048x2048.
You can check the max texture limit for the device using the following code:
static GLint maxTextureSize = 0;
glGetIntegerv(GL_MAX_TEXTURE_SIZE, &maxTextureSize);
Older devices (before iPhone 4S) all have a maximum texture size of 2048x2048. A5 and above (after and including iPhone 4S) have a maximum 4096x4096 texture size.
Source: Black texture with OpenGL when image is too big