Question

我想一次制作OpenGLES和UIKit的屏幕截图，经过大量研究后我发现了一种完全相同的方式：

- (UIImage *)makeScreenshot {

    GLint backingWidth, backingHeight;

    // 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, _colorRenderbuffer);

    // 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 x = _visibleFrame.origin.x, y = _visibleFrame.origin.y, width = _visibleFrame.size.width, height = _visibleFrame.size.height;
    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, kCGBitmapByteOrder32Big | kCGImageAlphaPremultipliedLast, ref, NULL, true, kCGRenderingIntentDefault);
    CGImageRef iref = CGImageCreate(width, height, 8, 32, width * 4, colorspace, kCGBitmapByteOrder32Big | kCGImageAlphaNoneSkipLast, 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 = _baseView.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;

    UIImageView *GLImage =  [[UIImageView alloc] initWithImage:image];

    UIGraphicsBeginImageContext(_visibleFrame.size);

    //order of getting the context depends on what should be rendered first.
    // this draws the UIKit on top of the gl image

    [GLImage.layer renderInContext:UIGraphicsGetCurrentContext()];

    CGContextTranslateCTM(UIGraphicsGetCurrentContext(), -_visibleFrame.origin.x, -_visibleFrame.origin.y);

    [_baseView.layer renderInContext:UIGraphicsGetCurrentContext()];

    UIImage *finalImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    // Do something with resulting image
    return finalImage;
}

但有趣的部分是合并部分。我在哪里有两个

UIGraphicsBeginImageContext();
.......
.......
UIGraphicsEndImageContext();

块。首先生成OpenGLES图像，然后与UIKit图像合并。有没有更好的方法来使用单UIGraphicsBeginImageContext(); ... UIGraphicsEndImageContext();块而不是创建UIImageView，然后执行渲染？

类似的东西：

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);

// the merging part starts

CGContextTranslateCTM(UIGraphicsGetCurrentContext(), -_visibleFrame.origin.x, -_visibleFrame.origin.y);

[_baseView.layer renderInContext:UIGraphicsGetCurrentContext()];

// the merging part ends

// Retrieve the UIImage from the current context
UIImage *image = UIGraphicsGetImageFromCurrentImageContext();

UIGraphicsEndImageContext();

但不幸的是它没有合并。任何人都可以在这里纠正错误和/或找到最佳方法吗？

Answer 1

UISnapshotting

随着iOS 7 Apple推出UISnapshotting，他们声称它的速度非常快，比renderInContext:快得多。

UIView *snapshot = [view snapshotViewAfterScreenUpdates:YES];

此方法捕获屏幕的当前可视内容渲染服务器并使用它们来构建新的快照视图。您可以使用返回的快照视图作为屏幕的可视替身您应用中的内容。（...）这种方法比尝试更快自己将屏幕内容渲染成位图图像。

此外，请查看下面的链接。他们应该给你一些见解并指出正确的方向。

如何优化以下CoreGraphics代码

1 个答案:

UISnapshotting