I have a third party game object in my iOS6 app which I have no access to its implementation, and now I need to take a screenshot of its view.
The game object has a public method that allows me to add it to my view:
-initWithParentView:andController:
and I managed to grab the view out by:
self.gameview = [self.myView.subviews firstObject]; //there is only one subview
The self.gameview is of type CCGLView. So I extend the CCGLView to add the snapshot methods as suggested in Apple Doc (http://nathanmock.com/files/com.apple.adc.documentation.AppleiOS6.0.iOSLibrary.docset/Contents/Resources/Documents/#qa/qa1704/_index.html)
- (UIImage*)snapshot
{
// Get the size of the backing CAEAGLLayer
GLint backingWidth, backingHeight;
glBindRenderbufferOES(GL_RENDERBUFFER_OES, colorRenderbuffer);
glGetRenderbufferParameterivOES(GL_RENDERBUFFER_OES, GL_RENDERBUFFER_WIDTH_OES, &backingWidth);
glGetRenderbufferParameterivOES(GL_RENDERBUFFER_OES, GL_RENDERBUFFER_HEIGHT_OES, &backingHeight);
NSInteger x = 0;
NSInteger y = 0;
NSInteger width = backingWidth;
NSInteger height = backingHeight;
NSInteger dataLength = width * height * 4;
GLubyte *data = (GLubyte*)malloc(dataLength * sizeof(GLubyte));
// Read pixel data from the framebuffer
glPixelStorei(GL_PACK_ALIGNMENT, 4);
glReadPixels(x, y, width, height, GL_RGBA, GL_UNSIGNED_BYTE, data);
// Create a CGImage with the pixel data
// If your OpenGL ES content is opaque, use kCGImageAlphaNoneSkipLast to ignore the alpha channel
// otherwise, use kCGImageAlphaPremultipliedLast
CGDataProviderRef ref = CGDataProviderCreateWithData(NULL, data, dataLength, NULL);
CGColorSpaceRef colorspace = CGColorSpaceCreateDeviceRGB();
CGImageRef iref = CGImageCreate(
width,
height,
8,
32,
width * 4,
colorspace,
kCGBitmapByteOrderDefault | kCGImageAlphaPremultipliedLast,
ref, NULL, true, kCGRenderingIntentDefault);
// OpenGL ES measures data in PIXELS
// Create a graphics context with the target size measured in POINTS
NSInteger widthInPoints;
NSInteger heightInPoints;
if (NULL != UIGraphicsBeginImageContextWithOptions) {
// On iOS 4 and later, use UIGraphicsBeginImageContextWithOptions to take the scale into consideration
// Set the scale parameter to your OpenGL ES view's contentScaleFactor
// so that you get a high-resolution snapshot when its value is greater than 1.0
CGFloat scale = self.contentScaleFactor;
widthInPoints = width / scale;
heightInPoints = height / scale;
UIGraphicsBeginImageContextWithOptions(CGSizeMake(widthInPoints, heightInPoints), NO, scale);
}
else {
// On iOS prior to 4, fall back to use UIGraphicsBeginImageContext
widthInPoints = width;
heightInPoints = height;
UIGraphicsBeginImageContext(CGSizeMake(widthInPoints, heightInPoints));
}
CGContextRef cgcontext = UIGraphicsGetCurrentContext();
// UIKit coordinate system is upside down to GL/Quartz coordinate system
// Flip the CGImage by rendering it to the flipped bitmap context
// The size of the destination area is measured in POINTS
CGContextSetBlendMode(cgcontext, kCGBlendModeCopy);
CGContextDrawImage(cgcontext, CGRectMake(0.0, 0.0, widthInPoints, heightInPoints), iref);
// Retrieve the UIImage from the current context
UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
UIImageWriteToSavedPhotosAlbum(image, nil, nil, nil );
// Clean up
free(data);
CFRelease(ref);
CFRelease(colorspace);
CGImageRelease(iref);
return image;
}
And I also handle the frame buffer as demonstrated in Apple's EAGLView library:
- (void)setFramebuffer
{
if (self.context)
{
[EAGLContext setCurrentContext:self.context];
if (!defaultFramebuffer)
[self createFramebuffer];
glBindFramebuffer(GL_FRAMEBUFFER, defaultFramebuffer);
glViewport(0, 0, framebufferWidth, framebufferHeight);
}
}
- (void)createFramebuffer
{
if (self.context && !defaultFramebuffer)
{
[EAGLContext setCurrentContext:self.context];
// Create default framebuffer object.
glGenFramebuffers(1, &defaultFramebuffer);
glBindFramebuffer(GL_FRAMEBUFFER, defaultFramebuffer);
NSUInteger result = glCheckFramebufferStatus(GL_FRAMEBUFFER);
NSLog(@"%d",result); //this returns value 36055
// Create color render buffer and allocate backing store.
glGenRenderbuffers(1, &colorRenderbuffer);
glBindRenderbuffer(GL_RENDERBUFFER, colorRenderbuffer);
CAEAGLLayer *glLayer = (CAEAGLLayer*) self.layer;
glLayer.drawableProperties = @{[NSNumber numberWithBool:NO]: kEAGLDrawablePropertyRetainedBacking,
kEAGLColorFormatRGBA8: kEAGLDrawablePropertyColorFormat};
glLayer.opaque = YES;
[self.context renderbufferStorage:GL_RENDERBUFFER fromDrawable:(CAEAGLLayer *)self.layer];
glGetRenderbufferParameteriv(GL_RENDERBUFFER, GL_RENDERBUFFER_WIDTH, &framebufferWidth);
glGetRenderbufferParameteriv(GL_RENDERBUFFER, GL_RENDERBUFFER_HEIGHT, &framebufferHeight);
glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_RENDERBUFFER, colorRenderbuffer);
if (glCheckFramebufferStatus(GL_FRAMEBUFFER) != GL_FRAMEBUFFER_COMPLETE)
NSLog(@"Failed to make complete framebuffer object %x", glCheckFramebufferStatus(GL_FRAMEBUFFER));
}
}
- (BOOL)presentFramebuffer
{
BOOL success = FALSE;
if (self.context)
{
[EAGLContext setCurrentContext:self.context];
glBindRenderbuffer(GL_RENDERBUFFER, colorRenderbuffer);
success = [self.context presentRenderbuffer:GL_RENDERBUFFER];
}
return success;
}
When it's all set, I do the following to call my snapshot function:
[self.gameview setFramebuffer];
UIImage *image = [self.gameview snapshot];
[self.gameview presentFramebuffer];
return image;
and all I get is a white image.
I am particularly feeling doubtful with the createFrameBuffer method because I am not initializing the openGL view myself. I tried to grab the current frame buffer from the view but have no luck using: glGetIntegerv(GL_FRAMEBUFFER, &defaultFramebuffer);
One thing worth mention is, I did manage to capture a part of the screen whenever I tried to draw something before I call the snapshot function using glDrawArrays. I can't make it work completely though no matter how I tried to alter the array value. (I am not very familiar with openGL).
Would appreciate it if anyone can point out anything I have missed here.
I found the solution. Turned out that I've complicated the whole thing with openGL. The secret is in CCRenderTexture of cocos2d.
#include <CCRenderTexture.h>
#include <CCScene.h>
CCScene *scene = [[CCDirector sharedDirector] runningScene];
CCNode *n = [scene.children objectAtIndex:0];
[CCDirector sharedDirector].nextDeltaTimeZero = YES;
CGSize winSize = [CCDirector sharedDirector].winSize;
CCRenderTexture *rtx = [CCRenderTexture renderTextureWithWidth:winSize.width height:winSize.height];
[rtx begin];
[n visit];
[rtx end];
UIImage *image = [rtx getUIImage];
return image;
Code works perfectly in iOS6 and iOS7.