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proposal: the api image.NewYCbCr allow user input initial image data to init it #20926

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acrazing opened this issue Jul 6, 2017 · 4 comments
Closed

proposal: the api image.NewYCbCr allow user input initial image data to init it #20926

acrazing opened this issue Jul 6, 2017 · 4 comments
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FrozenDueToAge Proposal WaitingForInfo Issue is not actionable because of missing required information, which needs to be provided.
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Proposal

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@acrazing
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acrazing commented Jul 6, 2017

Currently, this API init the image with an empty bytes slice, it is useless for handle a yuv stream for we need to init it with user defined data usually.

The souce code at:

go/src/image/ycbcr.go

Lines 169 to 184 in c478c48

func NewYCbCr(r Rectangle, subsampleRatio YCbCrSubsampleRatio) *YCbCr {
w, h, cw, ch := yCbCrSize(r, subsampleRatio)
i0 := w*h + 0*cw*ch
i1 := w*h + 1*cw*ch
i2 := w*h + 2*cw*ch
b := make([]byte, i2)
return &YCbCr{
Y: b[:i0:i0],
Cb: b[i0:i1:i1],
Cr: b[i1:i2:i2],
SubsampleRatio: subsampleRatio,
YStride: w,
CStride: cw,
Rect: r,
}
}

as follow:

// NewYCbCr returns a new YCbCr image with the given bounds and subsample
// ratio.
func NewYCbCr(r Rectangle, subsampleRatio YCbCrSubsampleRatio) *YCbCr {
    w, h, cw, ch := yCbCrSize(r, subsampleRatio)
    i0 := w*h + 0*cw*ch
    i1 := w*h + 1*cw*ch
    i2 := w*h + 2*cw*ch
    b := make([]byte, i2)
    return &YCbCr{
        Y:              b[:i0:i0],
        Cb:             b[i0:i1:i1],
        Cr:             b[i1:i2:i2],
        SubsampleRatio: subsampleRatio,
        YStride:        w,
        CStride:        cw,
        Rect:           r,
    }
}

Env: Go 1.8.3, x86-64, MacOS 10
@gopherbot gopherbot added this to the Proposal milestone Jul 6, 2017
@bradfitz
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The image.New* functions return an empty image for drawing into.

I think this is working as intended.

If you have initial data, you can prepare the YCbCr struct yourself.

What is your proposal?

@bradfitz bradfitz added the WaitingForInfo Issue is not actionable because of missing required information, which needs to be provided. label Jul 17, 2017
@acrazing
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@bradfitz If I read a yuv frame from a file, there is a slice contains the data already. and the statement b := make([]byte, i2) is useless.

@bradfitz
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@nigeltao, is there something here besides just "don't use NewYCbCr if it's not convenient for you"?

@nigeltao
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Nothing besides "don't use NewYCbCr if it's not convenient for you".

Go isn't C++ and NewFoo isn't 'the' constructor for Foo, in that it's not mandatory to call NewFoo. Use a struct literal (or your own function that returns a struct literal) instead.

@golang golang locked and limited conversation to collaborators Jul 19, 2018
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FrozenDueToAge Proposal WaitingForInfo Issue is not actionable because of missing required information, which needs to be provided.
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@bradfitz @nigeltao @gopherbot @acrazing