Cocoa CoreImage-在CPU上运行筛选器

我想在CPU上运行一些CoreImage过滤器，而不是GPU。在CI文档中，我发现您可以通过创建如下上下文来表达您的偏好，即在CPU上执行过滤器：

要应用筛选器，我目前正在执行以下操作：

NSBitmapImageRep * bitmaprep_in;
CGImageRef cg_image_in = [bitmaprep_in CGImage];

CIImage * ci_image_in = [CIImage imageWithCGImage:cg_image_in];

CIFilter * edge_filter = [CIFilter filterWithName:@"CIEdges"];
[edge_filter setDefaults];
[edge_filter setValue:ci_image_in forKey: @"inputImage"];

CIImage * result = [edge_filter valueForKey: @"outputImage"];

NSBitmapImageRep* rep = [[NSBitmapImageRep alloc]  initWithCIImage:result];

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问题是，我看不到在哪里或如何设置仅CPU的CI上下文。如何正确执行此操作？

这将强制CPU渲染：

NSDictionary *theCIContextOptions = [NSDictionary dictionaryWithObjectsAndKeys:[NSNumber numberWithBool:YES], kCIContextUseSoftwareRenderer, NULL];

CIContext *theCIContext = [CIContext contextWithOptions:theCIContextOptions ];

NSDictionary *theCIContextOptions = [NSDictionary dictionaryWithObjectsAndKeys:[NSNumber numberWithBool:YES], kCIContextUseSoftwareRenderer, NULL];

CIContext *theCIContext = [CIContext contextWithOptions:theCIContextOptions ];