iOS开发- OpenGL ES屏幕截图

之前写过一个常规的屏幕截图:http://blog.csdn.net/hitwhylz/article/details/17189351

可是发现这个办法对于OpenGL 无用。  获取到的数据为空。

所以这里介绍下OpenGL ES屏幕截图。

1.初始化。

CAEAGLLayer *eaglLayer = (CAEAGLLayer *) self.layer;
eaglLayer.drawableProperties = @{
    kEAGLDrawablePropertyRetainedBacking: [NSNumber numberWithBool:YES],
    kEAGLDrawablePropertyColorFormat: kEAGLColorFormatRGBA8
}; 

2.声明方法。

- (UIImage*)snapshot:(UIView*)eaglview
{
    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 "viewRenderbuffer" 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, &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, 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 = 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;
}

3.使用

调用上述的方法就可以。

- (UIImage*)snapshot:(UIView*)eaglview