Question

我无法弄清楚如何使用GLKView：snapshot方法。

我正在使用GLKView渲染一些OpenGL内容。一切正常;好像我已经正确设置了所有。

但是，当我尝试创建快照时，它会失败：我得到一个null返回值，并显示以下日志消息：

错误：CGImageCreate：图片大小无效：0 x 0。

似乎这意味着视图本身因某些原因无效，但事实并非如此 - 除此之外一切正常。

我看了几个代码示例，我没有做任何不同的事情。

所以......之前有人见过这个吗？想法？

Answer 1

我从未弄清楚上述问题;但是，我发现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;
}

Answer 2

也许这不适用于您的情况，但GLKView的文档：快照说：

永远不要在绘图功能中调用此方法。

GLKView快照方法：null返回val，得到错误

2 个答案: