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ios - Compute Kernel Metal - 如何检索结果和调试?

转载 作者:行者123 更新时间:2023-12-01 19:38:59 24 4
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我已经下载了苹果的 truedepth 流媒体示例,并正在尝试添加计算管道。我想我正在检索计算结果,但不确定,因为它们似乎都为零。

我是iOS开发的初学者,所以可能会有很多错误,请多多包涵!

管道设置:(我不太确定如何创建结果缓冲区,因为内核输出一个 float3)

int resultsCount = CVPixelBufferGetWidth(depthFrame) * CVPixelBufferGetHeight(depthFrame);

//because I will be output 3 floats for each value in depthframe
id<MTLBuffer> resultsBuffer = [self.device newBufferWithLength:(sizeof(float) * 3 * resultsCount) options:MTLResourceOptionCPUCacheModeDefault];


_threadgroupSize = MTLSizeMake(16, 16, 1);

// Calculate the number of rows and columns of threadgroups given the width of the input image
// Ensure that you cover the entire image (or more) so you process every pixel
_threadgroupCount.width = (inTexture.width + _threadgroupSize.width - 1) / _threadgroupSize.width;
_threadgroupCount.height = (inTexture.height + _threadgroupSize.height - 1) / _threadgroupSize.height;

// Since we're only dealing with a 2D data set, set depth to 1
_threadgroupCount.depth = 1;

id<MTLComputeCommandEncoder> computeEncoder = [commandBuffer computeCommandEncoder];

[computeEncoder setComputePipelineState:_computePipelineState];

[computeEncoder setTexture: inTexture atIndex:0];

[computeEncoder setBuffer:resultsBuffer offset:0 atIndex:1];

[computeEncoder setBytes:&intrinsics length:sizeof(intrinsics) atIndex:0];

[computeEncoder dispatchThreadgroups:_threadgroupCount
threadsPerThreadgroup:_threadgroupSize];

[computeEncoder endEncoding];


// Finalize rendering here & push the command buffer to the GPU
[commandBuffer commit];

//for testing
[commandBuffer waitUntilCompleted];

我添加了以下计算内核:
kernel void
calc(texture2d<float, access::read> inTexture [[texture(0)]],
device float3 *resultsBuffer [[buffer(1)]],
constant float3x3& cameraIntrinsics [[ buffer(0) ]],
uint2 gid [[thread_position_in_grid]])
{

float val = inTexture.read(gid).x * 1000.0f;

float xrw = (gid.x - cameraIntrinsics[2][0]) * val / cameraIntrinsics[0][0];
float yrw = (gid.y - cameraIntrinsics[2][1]) * val / cameraIntrinsics[1][1];

int vertex_id = ((gid.y * inTexture.get_width()) + gid.x);

resultsBuffer[vertex_id] = float3(xrw, yrw, val);

}

查看缓冲区结果的代码:(我尝试了两种不同的方法,目前都输出全零)
    void *output = [resultsBuffer contents];
for (int i = 0; i < 10; ++i) {
NSLog(@"value is %f", *(float *)(output) ); //= *(float *)(output + 4 * i);
}

NSData *data = [NSData dataWithBytesNoCopy:resultsBuffer.contents length:(sizeof(float) * 3 * resultsCount)freeWhenDone:NO];
float *finalArray = new float [resultsCount * 3];
[data getBytes:&finalArray[0] length:sizeof(finalArray)];
for (int i = 0; i < 10; ++i) {
NSLog(@"here is output %f", finalArray[i]);
}

最佳答案

我在这里看到了几个问题,但它们都与您的 Metal 代码本身无关。

在您的第一个输出循环中,如所写,您只是将结果缓冲区的第一个元素打印 10 次。第一个元素可能合法地为 0,导致您相信所有结果都为零。但是当我将第一条日志行更改为

NSLog(@"value is %f", ((float *)output)[i]);

在测试镜像上运行内核时,我看到打印了不同的值。

另一个问题与您的 getBytes:length: 有关。称呼。您想传递要复制的字节数,但是 sizeof(finalArray)实际上是 finalArray 的大小指针 ,即 4 个字节,而不是它指向的缓冲区的总大小。这是 C 和 C++ 代码中极为常见的错误。

相反,您可以使用与分配空间时使用的字节数相同的字节数:
[data getBytes:&finalArray[0] length:(sizeof(float) * 3 * resultsCount)];

然后,您应该会发现打印的值与上一步相同(非零)。

关于ios - Compute Kernel Metal - 如何检索结果和调试?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/58228297/

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