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Reading data from MTLBuffer in Swift


Reading data from MTLBuffer in Swift

By : user2953751
Date : November 21 2020, 01:01 AM
I think the issue was by ths following , I've managed to fix the problem. The problem was in my wrong assumption about memory management in Swift and the fact that the function newBufferWithBytes does only a shallow copy. Calling the function only copied the pointers to mean, covMat and invCovMat arrays and self.modelBuffer.contents() contained pointers to uninitialized memory. Accessing the memory was causing the crash.
code :


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Allocating memory for data used by MTLBuffer in iOS Metal

Allocating memory for data used by MTLBuffer in iOS Metal


By : Ali Fuat
Date : March 29 2020, 07:55 AM
This might help you The easiest way to allocate page-aligned memory is with posix_memalign. Here's a complete example of creating a buffer with page-aligned memory:
code :
void *data = NULL;
NSUInteger pageSize = getpagesize();
NSUInteger allocationSize = /* required byte count, rounded up to next multiple of page size */ pageSize * 10;
int result = posix_memalign(&data, pageSize, allocationSize);

if (result == noErr && data) {
    id<MTLBuffer> buffer = [device newBufferWithBytesNoCopy:data
                                                     length:allocationSize
                                                    options:MTLResourceStorageModeShared
                                                deallocator:^(void *pointer, NSUInteger length)
                                                            {
                                                                free(pointer);
                                                            }];
    NSLog(@"Created buffer of length %d", (int)buffer.length);
}
Parsing data with Decodeable swift 4.0 not reading data - Xcode

Parsing data with Decodeable swift 4.0 not reading data - Xcode


By : eliasishier
Date : March 29 2020, 07:55 AM
around this issue The JSON is invalid.
I guess the value for key Stops1 is supposed to be an array, then the JSON must be
code :
{
 "Stops1" : [ {...},  {...},  {...} ] 
}
{
    "stops" : [
        {"name": "loc 1", "lat": "-46.450364", "lon": "169.659519"},
        {"name": "loc 2", "lat": "-45.898395", "lon": "170.486386"},
        {"name": "loc 3", "lat": "-36.635997", "lon": "174.747697"}
    ]
}
struct Stop : Decodable {
    let name : String
    let lat : String
    let lon: String
}
struct Root : Decodable {
    let stops : [Stop]
}
let url = Bundle.main.url(forResource: "newStops", withExtension: "json")!

do {
    let data = try Data(contentsOf: url)
    let root = try JSONDecoder().decode(Root.self, from: data)
    for stop in root.stops {
       print(stop.name)
    }
}
catch {
    print("Error occured during Parsing", error)
}
append data to existing contents of MTLBuffer in Metal

append data to existing contents of MTLBuffer in Metal


By : jonpaulharvey
Date : March 29 2020, 07:55 AM
this one helps. A Metal buffer is not a like a Swift Array, Obj C NSMutableArray, or C++ STL vector. There is fixed memory backing for the buffer, so you can't resize it to add/append more data.
Instead you'll need to create new buffer big enough to fit the existing array's data and the new elements you want to append, then copy them into the new expanded buffer. Since creating buffer and copying is expensive it's best to create add extra room each time you create a new buffer so that you can "append" many times without needing to create a new buffer and copy each time. Also, if the data is on the GPU in another buffer, you should use a MTLBlitCommandEncoder to perform the copy operations to the expanded buffer.
Swift 4 Data reading options

Swift 4 Data reading options


By : manjunath dhannur
Date : March 29 2020, 07:55 AM
like below fixes the issue What is the correct translation of this Objective C code line to Swift 4? , You can try
code :
do {

     // note it runs in current thread

    let data = try Data(contentsOf:fileURL, options: [.alwaysMapped , .uncached ] )

    print(data)

}
catch {

    print(error)
}
Metal kernel writes random numbers into MTLBuffer if it is indexed with a variable - data hazard?

Metal kernel writes random numbers into MTLBuffer if it is indexed with a variable - data hazard?


By : Shido Itsuka
Date : March 29 2020, 07:55 AM
hope this fix your issue jesus -.- The iPad CPU interprets UInt as a 64bit number (8 bytes). To the GPU, Int implicates 32bit (4 bytes). When the pointer is set at position [1], the CPU interprets this position a the upper 4 bytes of the array entry [0]. That causes the insanely huge numbers. To solve this issue, I have to set up the histogram to be [UInt32] on the CPU side.
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