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我不知道如何使用 GLKView:snapshot 方法。

我正在使用 GLKView 来渲染一些 OpenGL 的东西。一切正常；好像我已经正确设置了它。

但是，当我尝试做快照时，它失败了：我得到一个空返回值，以及以下日志消息：

错误：CGImageCreate：无效的图像大小：0 x 0。

似乎这意味着视图本身由于某种原因无效，但事实并非如此——除此之外，一切正常。

我查看了一些代码示例，但我没有做任何不同的事情。

所以……有人见过这个吗？想法？

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2 回答 2

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我从来没有弄清楚上述问题；但是，我找到了一个很好的解决方法。我发现这个块只是读取渲染缓冲区并将其保存到 UIImage。问题解决了！

- (UIImage*)snapshotRenderBuffer {

    // 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);

    NSInteger dataLength = backingWidth * backingHeight * 4;
    GLubyte *data = (GLubyte*)malloc(dataLength * sizeof(GLubyte));

    // Read pixel data from the framebuffer
    glPixelStorei(GL_PACK_ALIGNMENT, 4);
    glReadPixels(0.0f, 0.0f, backingWidth, backingHeight, 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(
                                    backingWidth, backingHeight, 8, 32, backingWidth * 4, colorspace, 
                                    kCGBitmapByteOrder32Big | kCGImageAlphaNoneSkipLast,
                                    ref, NULL, true, kCGRenderingIntentDefault);

    // (sayeth abd)
    // This creates a context with the device pixel dimensions -- not points. 
    // To be compatible with all devices, you're meant to keep everything as points and a scale factor;  but,
    // this gives us a scaled down image for purposes of saving.  So, keep everything in device resolution,
    // and worry about it later...
    UIGraphicsBeginImageContextWithOptions(CGSizeMake(backingWidth, backingHeight), NO, 0.0f);
    CGContextRef cgcontext = UIGraphicsGetCurrentContext();
    CGContextSetBlendMode(cgcontext, kCGBlendModeCopy);
    CGContextDrawImage(cgcontext, CGRectMake(0.0, 0.0, backingWidth, backingHeight), iref);

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

    UIGraphicsEndImageContext();

    // Clean up
    free(data);

    return image;
}
于 2012-08-18T17:16:10.223 回答
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Maybe this doesn't apply in your case, but the docs for GLKView:snapshot say:

Never call this method inside your drawing function.

于 2012-08-07T09:36:00.537 回答