当UIView到UIImage尝试释放数据时，BAD_ACCESS

Question

I intended to take a snapshot of a UIView that drawed by OpenGL ES into an UIImage , here is the code I used:

 if(context){
    [EAGLContext setCurrentContext:context];
    glBindFramebuffer(GL_FRAMEBUFFER, defaultFramebuffer);
    NSInteger dataLength = framebufferWidth * framebufferHeight * 4;

    GLubyte* data = (GLubyte*)malloc(dataLength) ; // malloc(myDataLength);
    glReadPixels(0, 0, framebufferWidth, framebufferHeight, GL_RGBA, GL_UNSIGNED_BYTE, data);

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

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

    // make the cgimage
    CGImageRef result = CGImageCreate(framebufferWidth, framebufferHeight, bitsPerComponent, bitsPerPixel, bytesPerRow, colorSpaceRef, bitmapInfo, provider, NULL, NO, renderingIntent);

    // then make the uiimage from that
    UIImage *image = [UIImage imageWithCGImage:result];
    CGImageRelease(result);
    CGColorSpaceRelease(colorSpaceRef);
    CGDataProviderRelease(provider);
    //free(data);

    return image;
}

I was intended to use free(data); before return , but that would raises a BAD_ACCESS runtime error.

So my questions is, how to free properly? Or should I free them after the image releases?

Answer 1

You should use CGDataProviderCreateWithData's CGDataProviderReleaseDataCallback as described here .

Simply add the freeData function callback:

void freeData(void *info, const void *data, size_t size) 
{
    free((void*)data);
}

and pass it to CGDataProviderCreateWithData :

CGDataProviderRef provider = CGDataProviderCreateWithData(NULL, data, dataLength, freeData);

Answer 2

This is my current code and it works just fine.

if(context){ 
    [EAGLContext setCurrentContext:context];
    glBindFramebuffer(GL_FRAMEBUFFER, defaultFramebuffer);
    NSInteger dataLength = width * height * 4;
    int bitsPerComponent = 8;
    int bitsPerPixel = 32;
    int bytesPerRow = 4 * width;
    GLubyte* data = (GLubyte*)malloc(dataLength) ;
    glReadPixels(0, 0, width, height, GL_RGBA, GL_UNSIGNED_BYTE, data);

    // make upside down
    GLubyte* swp = (GLubyte*)malloc(width * 4);
    for (int h = 0; h < height / 2; h++) {
        memcpy(swp, data + (height - 1 - h) * bytesPerRow, bytesPerRow);
        memcpy(data + (height - 1 - h) * bytesPerRow, data + h * bytesPerRow, bytesPerRow);
        memcpy(data + h * bytesPerRow, swp, bytesPerRow);
    }

    NSData* nsData = [NSData dataWithBytesNoCopy:data length:dataLength freeWhenDone:YES];
    // make data provider with data.
    CGDataProviderRef provider = CGDataProviderCreateWithCFData((CFDataRef)nsData);

    // prep the ingredients
    CGColorSpaceRef colorSpaceRef = CGColorSpaceCreateDeviceRGB();
    CGBitmapInfo bitmapInfo = kCGBitmapByteOrderDefault;
    CGColorRenderingIntent renderingIntent = kCGRenderingIntentDefault;

    // make the cgimage
    CGImageRef result = CGImageCreate(width, height, bitsPerComponent, bitsPerPixel, bytesPerRow, colorSpaceRef, bitmapInfo, provider, NULL, NO, renderingIntent);
    CGColorSpaceRelease(colorSpaceRef);
    CGDataProviderRelease(provider);

    // then make the uiimage from that
    UIImage *image = [UIImage imageWithCGImage:result];
    CGImageRelease(result);

    return image;
 }