| Andrew Cooke | Contents | Latest | RSS | Twitter | Previous | Next

C[omp]ute

Welcome to my blog, which was once a mailing list of the same name and is still generated by mail. Please reply via the "comment" links.

Always interested in offers/projects/new ideas. Eclectic experience in fields like: numerical computing; Python web; Java enterprise; functional languages; GPGPU; SQL databases; etc. Based in Santiago, Chile; telecommute worldwide. CV; email.

Personal Projects

Lepl parser for Python.

Colorless Green.

Photography around Santiago.

SVG experiment.

Professional Portfolio

Calibration of seismometers.

Data access via web services.

Cache rewrite.

Extending OpenSSH.

C-ORM: docs, API.

Last 100 entries

Have to add...; Culturally Liberal and Nothing More; Weird Finite / Infinite Result; Your diamond is a beaten up mess; Maths Books; Good Bike Route from Providencia / Las Condes to Panul\; Iain Pears (Author of Complex Plots); Plum Jam; Excellent; More Recently; For a moment I forgot StackOverflow sucked; A Few Weeks On...; Chilean Book Recommendations; How To Write Shared Libraries; Jenny Erpenbeck (Author); Dijkstra, Coins, Tables; Python libraries error on OpenSuse; Deserving Trump; And Smugness; McCloskey Economics Trilogy; cmocka - Mocks for C; Concept Creep (Americans); Futhark - OpenCL Language; Moved / Gone; Fan and USB issues; Burgers in Santiago; The Origin of Icosahedral Symmetry in Viruses; autoenum on PyPI; Jars Explains; Tomato Chutney v3; REST; US Elections and Gender: 24 Point Swing; PPPoE on OpenSuse Leap 42.1; SuperMicro X10SDV-TLN4F/F with Opensuse Leap 42.1; Big Data AI Could Be Very Bad Indeed....; Cornering; Postcapitalism (Paul Mason); Black Science Fiction; Git is not a CDN; Mining of Massive Data Sets; Rachel Kaadzi Ghansah; How great republics meet their end; Raspberry, Strawberry and Banana Jam; Interesting Dead Areas of Math; Later Taste; For Sale; Death By Bean; It's Good!; Tomato Chutney v2; Time ATAC MX 2 Pedals - First Impressions; Online Chilean Crafts; Intellectual Variety; Taste + Texture; Time Invariance and Gauge Symmetry; Jodorowsky; Tomato Chutney; Analysis of Support for Trump; Indian SF; TP-Link TL-WR841N DNS TCP Bug; TP-Link TL-WR841N as Wireless Bridge; Sending Email On Time; Maybe run a command; Sterile Neutrinos; Strawberry and Banana Jam; The Best Of All Possible Worlds; Kenzaburo Oe: The Changeling; Peach Jam; Taste Test; Strawberry and Raspberry Jam; flac to mp3 on OpenSuse 42.1; Also, Sebald; Kenzaburo Oe Interview; Otake (Kitani Minoru) move Black 121; Is free speech in British universities under threat?; I am actually good at computers; Was This Mansplaining?; WebFaction / LetsEncrypt / General Disappointment; Sensible Philosophy of Science; George Ellis; Misplaced Intuition and Online Communities; More Reading About Japan; Visibilty / Public Comments / Domestic Violence; Ferias de Santiago; More (Clearly Deliberate); Deleted Obit Post; And then a 50 yo male posts this...; We Have Both Kinds Of Contributors; Free Springer Books; Books on Religion; Books on Linguistics; Palestinan Electronica; Books In Anthropology; Taylor Expansions of Spacetime; Info on Juniper; Efficient Stream Processing; The Moral Character of Crypto; Hearing Aid Info; Small Success With Go!; Re: Quick message - This link is broken; Adding Reverb To The Echo Chamber; Sox Audio Tools

© 2006-2015 Andrew Cooke (site) / post authors (content).

Playing with Go's Interfaces (images)

From: andrew cooke <andrew@...>

Date: Mon, 11 Jul 2011 21:12:54 -0400

Look what I've just done :o)

  func TestImage (t *testing.T) {
    var b1, b2 bytes.Buffer

    r := image.NewRGBA64(10,20)
    r.Set(2, 3, image.RGBA64Color{0xffff, 0, 0, 0xffff})
    r.Set(3, 2, HSVAColor{120, 1, 1, 1})
    err := png.Encode(&b1, r)
    fmt.Println(err)
    fmt.Println(&b1)

    h := NewHSVA(10,20)
    h.Set(2, 3, HSVAColor{0, 1, 1, 1})
    h.Set(3, 2, image.RGBA64Color{0, 0xffff, 0, 0xffff})
    err = png.Encode(&b2, h)
    fmt.Println(err)
    fmt.Println(&b2)

    fmt.Println(string(b1.Bytes()) == string(b2.Bytes()))
  }

In case that's not totally obvious (what, you have a life?), it's a test that
shows I've successfully added a new colour type (HSVA) to Go's image library.
That means that I can use HSV values, as well as the standard RGB, to
construct images and then write them out to PNG files, etc.

There's nothing here that you couldn't have done with Java's interfaces - that
it's possible to extend the system is mainly down to whoever wrote the library
doing so around interfaces that anyone can implement - but it's way better
(safer) than anything you might have attempted in C.


The code also demonstrates an interesting aspect of Go that took me some time
to understand.  If you look at the documentation for buffers -
http://golang.org/pkg/bytes/#Buffer - it's not obvious how you make a new one.
There's a constructor for wrapping a string or byte array, but those are for
when you want the buffer to contain something initially (it's not backing
storage either - these things grow as necessary).

What's important is the phrase "The zero value for Buffer is an empty buffer
ready to use".  What that means is that to get a new, empty buffer, you just
declare it.  Which is what I do (twice) on the first line of the test.

(And yes, that's not really a very good test as it doesn't assert anything -
I'm going to fix that now).

Andrew

Comment on this post