ios - 从父类中混合 OpenGLES 和 UIKIT 获取 iOS 屏幕截图

Question

我知道这个问题得到了很多回答，但我的情况似乎有所不同。我正在尝试编写一个顶层函数，我可以随时截取我的应用程序的屏幕截图，无论是 openGLES 还是 UIKit，我都无法访问底层类来进行任何更改。

我一直在尝试的代码适用于 UIKit，但返回 OpenGLES 部分的黑屏

CGSize imageSize = [[UIScreen mainScreen] bounds].size;
    if (NULL != UIGraphicsBeginImageContextWithOptions)
        UIGraphicsBeginImageContextWithOptions(imageSize, NO, 0);
    else
        UIGraphicsBeginImageContext(imageSize);

    CGContextRef context = UIGraphicsGetCurrentContext();

    // Iterate over every window from back to front
    for (UIWindow *window in [[UIApplication sharedApplication] windows])
    {
        if (![window respondsToSelector:@selector(screen)] || [window screen] == [UIScreen mainScreen])
        {
            // -renderInContext: renders in the coordinate space of the layer,
            // so we must first apply the layer's geometry to the graphics context
            CGContextSaveGState(context);
            // Center the context around the window's anchor point
            CGContextTranslateCTM(context, [window center].x, [window center].y);
            // Apply the window's transform about the anchor point
            CGContextConcatCTM(context, [window transform]);
            // Offset by the portion of the bounds left of and above the anchor point
            CGContextTranslateCTM(context,
                                  -[window bounds].size.width * [[window layer] anchorPoint].x,
                                  -[window bounds].size.height * [[window layer] anchorPoint].y);


            for (UIView *subview in window.subviews)
            {
                CAEAGLLayer *eaglLayer = (CAEAGLLayer *) subview.layer;
                if([eaglLayer respondsToSelector:@selector(drawableProperties)]) {
                    NSLog(@"reponds");
                    /*eaglLayer.drawableProperties = @{
                                                     kEAGLDrawablePropertyRetainedBacking: [NSNumber numberWithBool:YES],
                                                     kEAGLDrawablePropertyColorFormat: kEAGLColorFormatRGBA8
                                                     };*/
                    UIImageView *glImageView = [[UIImageView alloc] initWithImage:[self snapshotx:subview]];
                    glImageView.transform = CGAffineTransformMakeScale(1, -1);
                    [glImageView.layer renderInContext:context];

                    //CGImageRef iref = [self snapshot:subview withContext:context];
                    //CGContextDrawImage(context, CGRectMake(0.0, 0.0, 640, 960), iref);

                }

                [[window layer] renderInContext:context];

                // Restore the context
                CGContextRestoreGState(context);
            }
        }
    }

    // Retrieve the screenshot image
    UIImage *image = UIGraphicsGetImageFromCurrentImageContext();

    UIGraphicsEndImageContext();

    return image;

和

- (UIImage*)snapshotx:(UIView*)eaglview
{
    GLint backingWidth, backingHeight;

    //glBindRenderbufferOES(GL_RENDERBUFFER_OES, _colorRenderbuffer);
    //don't know how to access the renderbuffer if i can't directly access the below code

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

    NSInteger x = 0, y = 0, width = backingWidth, 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,
                                     // Fix from Apple implementation
                                     // (was: kCGBitmapByteOrder32Big | kCGImageAlphaPremultipliedLast).
                                     kCGBitmapByteOrderDefault,
                                     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 = eaglview.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();

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

    return image;
}

关于如何在无法修改应用程序其余部分中的类的情况下混合两者的任何建议？

谢谢!

Answer 1

我看到你在那里尝试做什么，这并不是一个坏主意。不过似乎确实存在一个大问题:您不能随时调用 glReadPixels。首先，您应该确保缓冲区充满了您真正需要的数据(像素)，其次，它应该在其 GL 部分正在处理的同一线程上调用...

如果 GL View 不是您的，您可能会在调用该屏幕截图方法时遇到一些大麻烦，您需要调用一些方法来触发绑定(bind)其内部上下文，如果它是动画的，您将必须知道循环何时完成确保您收到的像素与 View 中显示的像素相同。

无论如何，如果你通过了所有这些，你可能仍然需要“跳转”不同的线程或者需要等待一个循环完成。在这种情况下，我建议您使用返回屏幕截图图像的 block ，该图像应作为方法参数传递，以便您可以在返回时捕获它。也就是说，如果您可以重写 GL View 上的一些方法以便能够通过回调 block 向您返回屏幕截图图像并编写一些递归系统，那将是最好的。

总而言之，您需要预见到多线程、设置上下文、绑定(bind)正确的帧缓冲区，等待所有内容被渲染。这一切都可能导致无法创建一个可以在不重载某些内部方法的情况下简单地适用于任何应用程序、 View 、系统的屏幕截图方法。

请注意，您根本不允许在您的应用程序中制作整个屏幕截图(例如同时按下主页和锁定按钮的屏幕截图)。至于 UIView 部分很容易从中创建图像是因为 UIView 被重新绘制到独立于屏幕的图形上下文中；就好像您可以采用一些 GL 管道并将其绑定(bind)到您自己的缓冲区和上下文并绘制它，这将导致能够独立获取其屏幕截图并可以在任何线程上执行。