Save OpenGL drawn item as an image

Question

I have downloaded the sample code GLPaint from developer.Apple website to draw pictures on a Canvas using OpenGL.

I have made many changes to the GLPaint application to meet my requirements. Now, I would like to save the drawn item into photo-library as an image.

I know the method to save an image in the photo-library. So, I tried to create the corresponding image file after drawing a picture. Do you know what's the good way to do it? Any help on this is highly appreciated.

The code details are described below.

PaintingView.h

EAGLContext *context;

// OpenGL names for the renderbuffer and framebuffers used to render to this view
GLuint viewRenderbuffer, viewFramebuffer;

// OpenGL name for the depth buffer that is attached to viewFramebuffer, if it exists (0 if it does not exist)
GLuint depthRenderbuffer;

GLuint    brushTexture;
CGPoint    location;
CGPoint    previousLocation;

PaintingView.m

// Handles the start of a touch
- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
    CGRect                bounds = [self bounds];
    UITouch*    touch = [[event touchesForView:self] anyObject];
    firstTouch = YES;
    // Convert touch point from UIView referential to OpenGL one (upside-down flip)
    location = [touch locationInView:self];
    location.y = bounds.size.height - location.y;
}

// Handles the continuation of a touch.
- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event
{ 

    CGRect                bounds = [self bounds];
    UITouch*            touch = [[event touchesForView:self] anyObject];

    // Convert touch point from UIView referential to OpenGL one (upside-down flip)
    if (firstTouch) {
        firstTouch = NO;
        previousLocation = [touch previousLocationInView:self];
        previousLocation.y = bounds.size.height - previousLocation.y;
    } else {
        location = [touch locationInView:self];
        location.y = bounds.size.height - location.y;
        previousLocation = [touch previousLocationInView:self];
        previousLocation.y = bounds.size.height - previousLocation.y;
    }

    // Render the stroke
    [self renderLineFromPoint:previousLocation toPoint:location];
}

// Handles the end of a touch event when the touch is a tap.
- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event
{
    CGRect                bounds = [self bounds];
    UITouch*    touch = [[event touchesForView:self] anyObject];
    if (firstTouch) {
        firstTouch = NO;
        previousLocation = [touch previousLocationInView:self];
        previousLocation.y = bounds.size.height - previousLocation.y;
        [self renderLineFromPoint:previousLocation toPoint:location];
    }
}



// Drawings a line onscreen based on where the user touches
- (void) renderLineFromPoint:(CGPoint)start toPoint:(CGPoint)end
{
    static GLfloat*        vertexBuffer = NULL;
    static NSUInteger    vertexMax = 64;
    NSUInteger            vertexCount = 0,
                        count,
                        i;

    [EAGLContext setCurrentContext:context];
    glBindFramebufferOES(GL_FRAMEBUFFER_OES, viewFramebuffer);

    // Convert locations from Points to Pixels
    CGFloat scale = self.contentScaleFactor;
    start.x *= scale;
    start.y *= scale;
    end.x *= scale;
    end.y *= scale;

    // Allocate vertex array buffer
    if(vertexBuffer == NULL)
        vertexBuffer = malloc(vertexMax * 2 * sizeof(GLfloat));

    // Add points to the buffer so there are drawing points every X pixels
    count = MAX(ceilf(sqrtf((end.x - start.x) * (end.x - start.x) + (end.y - start.y) * (end.y - start.y)) / kBrushPixelStep), 1);
    for(i = 0; i < count; ++i) {
        if(vertexCount == vertexMax) {
            vertexMax = 2 * vertexMax;
            vertexBuffer = realloc(vertexBuffer, vertexMax * 2 * sizeof(GLfloat));
        }

        vertexBuffer[2 * vertexCount + 0] = start.x + (end.x - start.x) * ((GLfloat)i / (GLfloat)count);
        vertexBuffer[2 * vertexCount + 1] = start.y + (end.y - start.y) * ((GLfloat)i / (GLfloat)count);
        vertexCount += 1;
    }

    // Render the vertex array
    glVertexPointer(2, GL_FLOAT, 0, vertexBuffer);
    glDrawArrays(GL_POINTS, 0, vertexCount);

    // Display the buffer
    glBindRenderbufferOES(GL_RENDERBUFFER_OES, viewRenderbuffer);
    [context presentRenderbuffer:GL_RENDERBUFFER_OES];
}


// Erases the screen
- (void) erase
{
    [EAGLContext setCurrentContext:context];

    // Clear the buffer
    glBindFramebufferOES(GL_FRAMEBUFFER_OES, viewFramebuffer);
    glClearColor(0.0, 0.0, 0.0, 0.0);
    glClear(GL_COLOR_BUFFER_BIT);

    // Display the buffer
    glBindRenderbufferOES(GL_RENDERBUFFER_OES, viewRenderbuffer);
    [context presentRenderbuffer:GL_RENDERBUFFER_OES];
}



// The GL view is stored in the nib file. When it's unarchived it's sent -initWithCoder:
- (id)initWithCoder:(NSCoder*)coder {


    CGImageRef        brushImage;
    CGContextRef    brushContext;
    GLubyte            *brushData;
    size_t            width, height;

    if ((self = [super initWithCoder:coder])) {
        CAEAGLLayer *eaglLayer = (CAEAGLLayer *)self.layer;

        eaglLayer.opaque = YES;
        // In this application, we want to retain the EAGLDrawable contents after a call to presentRenderbuffer.
        eaglLayer.drawableProperties = [NSDictionary dictionaryWithObjectsAndKeys:
                                        [NSNumber numberWithBool:YES], kEAGLDrawablePropertyRetainedBacking, kEAGLColorFormatRGBA8, kEAGLDrawablePropertyColorFormat, nil];

        context = [[EAGLContext alloc] initWithAPI:kEAGLRenderingAPIOpenGLES1];

        if (!context || ![EAGLContext setCurrentContext:context]) {
            [self release];
            return nil;
        }

        // Create a texture from an image
        // First create a UIImage object from the data in a image file, and then extract the Core Graphics image
        brushImage = [UIImage imageNamed:@"Particle.png"].CGImage;

        // Get the width and height of the image
        width = CGImageGetWidth(brushImage);
        height = CGImageGetHeight(brushImage);

        // Texture dimensions must be a power of 2. If you write an application that allows users to supply an image,
        // you'll want to add code that checks the dimensions and takes appropriate action if they are not a power of 2.

        // Make sure the image exists
        if(brushImage) {
            // Allocate  memory needed for the bitmap context
            brushData = (GLubyte *) calloc(width * height * 4, sizeof(GLubyte));
            // Use  the bitmatp creation function provided by the Core Graphics framework.
            brushContext = CGBitmapContextCreate(brushData, width, height, 8, width * 4, CGImageGetColorSpace(brushImage), kCGImageAlphaPremultipliedLast);
            // After you create the context, you can draw the  image to the context.
            CGContextDrawImage(brushContext, CGRectMake(0.0, 0.0, (CGFloat)width, (CGFloat)height), brushImage);
            // You don't need the context at this point, so you need to release it to avoid memory leaks.
            CGContextRelease(brushContext);
            // Use OpenGL ES to generate a name for the texture.
            glGenTextures(1, &brushTexture);
            // Bind the texture name.
            glBindTexture(GL_TEXTURE_2D, brushTexture);
            // Set the texture parameters to use a minifying filter and a linear filer (weighted average)
            glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
            // Specify a 2D texture image, providing the a pointer to the image data in memory
            glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, brushData);
            // Release  the image data; it's no longer needed
            free(brushData);
        }

        // Set the view's scale factor
        self.contentScaleFactor = 1.0;

        // Setup OpenGL states
        glMatrixMode(GL_PROJECTION);
        CGRect frame = self.bounds;
        CGFloat scale = self.contentScaleFactor;
        // Setup the view port in Pixels
        glOrthof(0, frame.size.width * scale, 0, frame.size.height * scale, -1, 1);
        glViewport(0, 0, frame.size.width * scale, frame.size.height * scale);
        glMatrixMode(GL_MODELVIEW);

        glDisable(GL_DITHER);
        glEnable(GL_TEXTURE_2D);
        glEnableClientState(GL_VERTEX_ARRAY);

        glEnable(GL_BLEND);
        // Set a blending function appropriate for premultiplied alpha pixel data
        glBlendFunc(GL_ONE, GL_ONE_MINUS_SRC_ALPHA);

        glEnable(GL_POINT_SPRITE_OES);
        glTexEnvf(GL_POINT_SPRITE_OES, GL_COORD_REPLACE_OES, GL_TRUE);
        glPointSize(width / kBrushScale);

        // Make sure to start with a cleared buffer
        needsErase = YES;



    }

    return self;
}

AppDelegate.h

---

PaintingWindow        *window; //its a class inherited from window.
PaintingView        *drawingView;

@property (nonatomic, retain) IBOutlet PaintingWindow *window;
@property (nonatomic, retain) IBOutlet PaintingView *drawingView;

@synthesize window;
@synthesize drawingView;

AppDelegate.m

- (void) applicationDidFinishLaunching:(UIApplication*)application
{
    CGRect                    rect = [[UIScreen mainScreen] applicationFrame];
    CGFloat                    components[3];

    // Create a segmented control so that the user can choose the brush color.
    UISegmentedControl *segmentedControl = [[UISegmentedControl alloc] initWithItems:
                                            [NSArray arrayWithObjects:
                                                [UIImage imageNamed:@"Red.png"],
                                                [UIImage imageNamed:@"Yellow.png"],
                                                [UIImage imageNamed:@"Green.png"],
                                                [UIImage imageNamed:@"Blue.png"],
                                                [UIImage imageNamed:@"Purple.png"],
                                                nil]];

    // Compute a rectangle that is positioned correctly for the segmented control you'll use as a brush color palette
    //CGRect frame = CGRectMake(rect.origin.x + kLeftMargin, rect.size.height - kPaletteHeight - kTopMargin, rect.size.width - (kLeftMargin + kRightMargin), kPaletteHeight);
    CGRect frame = CGRectMake(50, 22, (rect.size.width - (kLeftMargin + kRightMargin)) - 20, kPaletteHeight);
    segmentedControl.frame = frame;
    // When the user chooses a color, the method changeBrushColor: is called.
    [segmentedControl addTarget:self action:@selector(changeBrushColor:) forControlEvents:UIControlEventValueChanged];
    segmentedControl.segmentedControlStyle = UISegmentedControlStyleBar;
    // Make sure the color of the color complements the black background
    segmentedControl.tintColor = [UIColor darkGrayColor];
    // Set the third color (index values start at 0)
    segmentedControl.selectedSegmentIndex = 2;

    // Add the control to the window
    [window addSubview:segmentedControl];
    // Now that the control is added, you can release it
    [segmentedControl release];


    [self addBackgroundSegmentControll];

    // Define a starting color
    HSL2RGB((CGFloat) 2.0 / (CGFloat)kPaletteSize, kSaturation, kLuminosity, &components[0], &components[1], &components[2]);
    // Defer to the OpenGL view to set the brush color
    [drawingView setBrushColorWithRed:components[0] green:components[1] blue:components[2]];

    // Look in the Info.plist file and you'll see the status bar is hidden
    // Set the style to black so it matches the background of the application
    [application setStatusBarStyle:UIStatusBarStyleBlackTranslucent animated:NO];
    // Now show the status bar, but animate to the style.
    [application setStatusBarHidden:NO withAnimation:YES];

    // Load the sounds
    NSBundle *mainBundle = [NSBundle mainBundle];   
    erasingSound = [[SoundEffect alloc] initWithContentsOfFile:[mainBundle pathForResource:@"Erase" ofType:@"caf"]];
    selectSound =  [[SoundEffect alloc] initWithContentsOfFile:[mainBundle pathForResource:@"Select" ofType:@"caf"]];

    [window setFrame:CGRectMake(0, 0, 768, 1024)];
    drawingView.frame = CGRectMake(0, 0, 768, 1024);

    // Erase the view when recieving a notification named "shake" from the NSNotificationCenter object
    // The "shake" nofification is posted by the PaintingWindow object when user shakes the device
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(eraseView) name:@"shake" object:nil];
}

Answer 1

Please refer the below link to save an OpenGL drawn item as an image in the photo-library.

Save an OpenGL drawn item as an image

Code Details;

Call [self captureToPhotoAlbum]; after writing the below code.

-(void)captureToPhotoAlbum {

    UIImage *image = [self glToUIImage];
    UIImageWriteToSavedPhotosAlbum(image, self, nil, nil);
}

- (UIImage *)glToUIImage {

    NSInteger myDataLength = 320 * 480 * 4;

    // allocate array and read pixels into it.
    GLubyte *buffer = (GLubyte *) malloc(myDataLength);
    glReadPixels(0, 0, 320, 480, GL_RGBA, GL_UNSIGNED_BYTE, buffer);

    // gl renders "upside down" so swap top to bottom into new array.
    // there's gotta be a better way, but this works.
    GLubyte *buffer2 = (GLubyte *) malloc(myDataLength);
    for(int y = 0; y < 480; y++)
    {
        for(int x = 0; x < 320 * 4; x++)
        {
            buffer2[(479 - y) * 320 * 4 + x] = buffer[y * 4 * 320 + x];
        }
    }

    // make data provider with data.
    CGDataProviderRef provider = CGDataProviderCreateWithData(NULL, buffer2, myDataLength, NULL);

    // prep the ingredients
    int bitsPerComponent = 8;
    int bitsPerPixel = 32;
    int bytesPerRow = 4 * 320;
    CGColorSpaceRef colorSpaceRef = CGColorSpaceCreateDeviceRGB();
    CGBitmapInfo bitmapInfo = kCGBitmapByteOrderDefault;
    CGColorRenderingIntent renderingIntent = kCGRenderingIntentDefault;

    // make the cgimage
    CGImageRef imageRef = CGImageCreate(320, 480, bitsPerComponent, bitsPerPixel, bytesPerRow,     colorSpaceRef, bitmapInfo, provider, NULL, NO, renderingIntent);

    // then make the uiimage from that
    UIImage *myImage = [UIImage imageWithCGImage:imageRef];
    return myImage;
}

• For iPad or to fix the scaling issue,change all the width's as 640 instead of 320 and height's as 960 instead of 480. Change the
• Height and Width values up to meet your scaling.
• Manage the memory(free the buffers)

Thanks.

Answer 2

An improved version of Ramshad's answer:

This one has no memory leaks and works with new versions of iOS and for different view sizes and displays (retina and non-retina).

    CGFloat scale = [[UIScreen mainScreen] scale]; // use nativeScale on iOS 8.0+

    CGSize imageSize = CGSizeMake((scale * view.frame.size.width), (scale  * view.frame.size.height));
    NSUInteger length = imageSize.width * imageSize.height * 4;

    GLubyte * buffer = (GLubyte *)malloc(length * sizeof(GLubyte));

    if(buffer == NULL)
        return nil;

    glReadPixels(0, 0, imageSize.width, imageSize.height, GL_RGBA, GL_UNSIGNED_BYTE, buffer);

    CGDataProviderRef provider = CGDataProviderCreateWithData(NULL, buffer, length, NULL);

    int bitsPerComponent = 8;
    int bitsPerPixel = 32;
    int bytesPerRow = 4 * imageSize.width;

    CGColorSpaceRef colorSpaceRef = CGColorSpaceCreateDeviceRGB();
    CGBitmapInfo bitmapInfo = kCGBitmapByteOrderDefault;
    CGColorRenderingIntent renderingIntent = kCGRenderingIntentDefault;

    CGImageRef imageRef = CGImageCreate(imageSize.width, imageSize.height, bitsPerComponent, bitsPerPixel, bytesPerRow, colorSpaceRef, bitmapInfo, provider, NULL, NO, renderingIntent);

    UIGraphicsBeginImageContext(imageSize);
    CGContextDrawImage(UIGraphicsGetCurrentContext(), CGRectMake(0.0, 0.0, imageSize.width, imageSize.height), imageRef);
    UIImage * image = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    CGImageRelease(imageRef);
    CGColorSpaceRelease(colorSpaceRef);
    CGDataProviderRelease(provider);
    free(buffer);

    return image;

Answer 3

The code works perfectly on iOS 5.0 programmed in XCode 4.0. Although, now in XCode 4.5 and with the developers preview iOS 6.0 the code does not work as it should.The image tha is saved is tottaly black! It is saved in "My photos", with the resolution we choose, but it is a black image!

I guess that something has changed from the XCode programmers in

glReadPixels(0, 0, 320, 480, GL_RGBA, GL_UNSIGNED_BYTE, buffer);

or in

CGImageRef imageRef = CGImageCreate(320, 480, bitsPerComponent, bitsPerPixel, bytesPerRow,     colorSpaceRef, bitmapInfo, provider, NULL, NO, renderingIntent);

UIImage *myImage = [UIImage imageWithCGImage:imageRef];

It is not a matter of 320, 480 or any other resolution variables. In XCode 4.0 worked perfectly and fast even for Retina resolutions.

Answer 4

If the iPhone supports it, you can read from an OpenGL context using glReadPixels. After that's done, you should be able to create something like a UIImage from the pixel data you have read and save it to the photo library like you would for any other image created by an application.