如何从 EAGLView 获取 UIImage？

Question

我正在尝试从我的 EAGLView 中显示的内容中获取 UIImage。有关如何执行此操作的任何建议？

Answer 1

这是 Quakeboy 代码的清理版本。 我在 iPad 上测试过，效果很好。 改进包括：

• 适用于任何尺寸的 EAGLView
• 适用于 Retina 显示器（点刻度 2）
• 用 memcpy 替换了嵌套循环
• 清理内存泄漏
• 将 UIImage 保存在相册中作为奖励。

在您的 EAGLView 中使用它作为方法：

-(void)snapUIImage
{
    int s = 1;
    UIScreen* screen = [ UIScreen mainScreen ];
    if ( [ screen respondsToSelector:@selector(scale) ] )
        s = (int) [ screen scale ];

    const int w = self.frame.size.width;
    const int h = self.frame.size.height;
    const NSInteger myDataLength = w * h * 4 * s * s;
    // allocate array and read pixels into it.
    GLubyte *buffer = (GLubyte *) malloc(myDataLength);
    glReadPixels(0, 0, w*s, h*s, 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 < h*s; y++)
    {
        memcpy( buffer2 + (h*s - 1 - y) * w * 4 * s, buffer + (y * 4 * w * s), w * 4 * s );
    }
    free(buffer); // work with the flipped buffer, so get rid of the original one.

    // make data provider with data.
    CGDataProviderRef provider = CGDataProviderCreateWithData(NULL, buffer2, myDataLength, NULL);
    // prep the ingredients
    int bitsPerComponent = 8;
    int bitsPerPixel = 32;
    int bytesPerRow = 4 * w * s;
    CGColorSpaceRef colorSpaceRef = CGColorSpaceCreateDeviceRGB();
    CGBitmapInfo bitmapInfo = kCGBitmapByteOrderDefault;
    CGColorRenderingIntent renderingIntent = kCGRenderingIntentDefault;
    // make the cgimage
    CGImageRef imageRef = CGImageCreate(w*s, h*s, bitsPerComponent, bitsPerPixel, bytesPerRow, colorSpaceRef, bitmapInfo, provider, NULL, NO, renderingIntent);
    // then make the uiimage from that
    UIImage *myImage = [ UIImage imageWithCGImage:imageRef scale:s orientation:UIImageOrientationUp ];
    UIImageWriteToSavedPhotosAlbum( myImage, nil, nil, nil );
    CGImageRelease( imageRef );
    CGDataProviderRelease(provider);
    CGColorSpaceRelease(colorSpaceRef);
    free(buffer2);
}

Answer 2

我无法在此处获得其他答案以使其正常工作。

几天后，我终于找到了一个可行的解决方案。 Apple 提供了从 EAGLView 生成 UIImage 的代码。然后你只需要垂直翻转图像，因为 UIkit 是倒置的。

Apple 提供的方法 - 修改为在要制作成图像的视图内。

    -(UIImage *) drawableToCGImage 
{
GLint backingWidth2, backingHeight2;
//Bind the color renderbuffer used to render the OpenGL ES view
// If your application only creates a single color renderbuffer which is already bound at this point,
// this call is redundant, but it is needed if you're dealing with multiple renderbuffers.
// Note, replace "_colorRenderbuffer" with the actual name of the renderbuffer object defined in your class.
glBindRenderbufferOES(GL_RENDERBUFFER_OES, viewRenderbuffer);

// Get the size of the backing CAEAGLLayer
glGetRenderbufferParameterivOES(GL_RENDERBUFFER_OES, GL_RENDERBUFFER_WIDTH_OES, &backingWidth2);
glGetRenderbufferParameterivOES(GL_RENDERBUFFER_OES, GL_RENDERBUFFER_HEIGHT_OES, &backingHeight2);

NSInteger x = 0, y = 0, width2 = backingWidth2, height2 = backingHeight2;
NSInteger dataLength = width2 * height2 * 4;
GLubyte *data = (GLubyte*)malloc(dataLength * sizeof(GLubyte));

// Read pixel data from the framebuffer
glPixelStorei(GL_PACK_ALIGNMENT, 4);
glReadPixels(x, y, width2, height2, 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(width2, height2, 8, 32, width2 * 4, colorspace, kCGBitmapByteOrder32Big | kCGImageAlphaPremultipliedLast,
                                ref, NULL, true, kCGRenderingIntentDefault);

// OpenGL ES measures data in PIXELS
// Create a graphics context with the target size measured in POINTS
NSInteger widthInPoints, 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 = width2 / scale;
    heightInPoints = height2 / scale;
    UIGraphicsBeginImageContextWithOptions(CGSizeMake(widthInPoints, heightInPoints), NO, scale);
}
else {
    // On iOS prior to 4, fall back to use UIGraphicsBeginImageContext
    widthInPoints = width2;
    heightInPoints = height2;
    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();

// Clean up
free(data);
CFRelease(ref);
CFRelease(colorspace);
CGImageRelease(iref);

return image;

}

还有一种翻转图像的方法

- (UIImage *) flipImageVertically:(UIImage *)originalImage {
UIImageView *tempImageView = [[UIImageView alloc] initWithImage:originalImage];
UIGraphicsBeginImageContext(tempImageView.frame.size);
CGContextRef context = UIGraphicsGetCurrentContext();
CGAffineTransform flipVertical = CGAffineTransformMake(
                                                       1, 0, 0, -1, 0, tempImageView.frame.size.height
                                                       );
CGContextConcatCTM(context, flipVertical);

[tempImageView.layer renderInContext:context];

UIImage *flippedImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
//[tempImageView release];

return flippedImage;

}

这里有一个指向 Apple 开发页面的链接，我在该页面中找到了第一种方法供参考。 http://developer.apple.com/library/ios/#qa/qa1704/_index.html

Answer 3

-(UIImage *) saveImageFromGLView
{
    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];

    CGImageRelease( imageRef );
    CGDataProviderRelease(provider);
    CGColorSpaceRelease(colorSpaceRef);
    free(buffer2);

    return myImage;
}

Answer 4

编辑：正如 derianturner 在下面指出的那样，您不再需要渲染图层，您现在可以（并且应该）使用更高级别的 [UIView drawViewHierarchyInRect:]。除此之外;这应该是一样的。

EAGLView 只是一种视图，其底层CAEAGLLayer 只是一种层。这意味着，用于将视图/图层转换为 UIImage 的 standard approach 将起作用。 （链接的问题是 UIWebview 的事实并不重要；那只是另一种视图。）

Answer 5

CGDataProviderCreateWithData带有释放回调来释放数据，你应该在哪里进行释放：

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

然后像其他示例一样执行此操作，但不要在此处释放数据：

GLubyte *bufferData = (GLubyte *) malloc(bufferDataSize);
CGDataProviderRef provider = CGDataProviderCreateWithData(NULL, bufferData, bufferDataSize, releaseBufferData);
....
CGDataProviderRelease(provider);

---

或者干脆使用CGDataProviderCreateWithCFData而不用释放回调的东西：

GLubyte *bufferData = (GLubyte *) malloc(bufferDataSize);
NSData *data = [NSData dataWithBytes:bufferData length:bufferDataSize];
CGDataProviderRef provider = CGDataProviderCreateWithCFData((CFDataRef)data);
....
CGDataProviderRelease(provider);
free(bufferData); // Remember to free it

有关更多信息，请查看此讨论：

What's the right memory management pattern for buffer->CGImageRef->UIImage?

Answer 6

使用上述 Brad Larson 的代码，您必须编辑您的 EAGLView.m

- (id)initWithCoder:(NSCoder*)coder{
    self = [super initWithCoder:coder];
    if (self) {
        CAEAGLLayer *eaglLayer = (CAEAGLLayer *)self.layer;
        eaglLayer.opaque = TRUE;
        eaglLayer.drawableProperties = 
            [NSDictionary dictionaryWithObjectsAndKeys: 
                [NSNumber numberWithBool:YES],  kEAGLDrawablePropertyRetainedBacking, 
                kEAGLColorFormatRGBA8, kEAGLDrawablePropertyColorFormat, nil];
    }
    return self;
}

你必须改变numberWithBool值YES