用xgb和freetype-go建立窗口并画图

最近一直在鼓捣怎样用golang画图（不想用cgo来封装c库），终于找到了xgb和freetype-go。

xgb可以用来创建窗口，freetype-go中的raster库可以用来画图。

下面我用它们写了一个简单的程序，它在窗口中画了个90度的扇形

package main

import (
    "code.google.com/p/freetype-go/freetype/raster"
    "fmt"
    "github.com/BurntSushi/xgbutil"
    "github.com/BurntSushi/xgbutil/xevent"
    "github.com/BurntSushi/xgbutil/xgraphics"
    "github.com/BurntSushi/xgbutil/xwindow"
    "image"
    "image/color"
    "image/png"
    "os"
)

func main() {

    // width and height of the window to be created
    w, h := 400, 400

    // xu communicates with X server
    xu, err := xgbutil.NewConn()
    if err != nil {
        fmt.Println(err)
        return
    }

    // just create a id for the window
    xwin, err := xwindow.Generate(xu)
    if err != nil {
        fmt.Println(err)
        return
    }
    // now, create the window
    err = xwin.CreateChecked(
        xu.RootWin(), // parent window
        0, 0, w, h,   // window size
        0) // related to event, not considered here
    if err != nil {
        fmt.Println(err)
        return
    }
    // now we can see the window on the screen
    xwin.Map()

       // 'rstr' calculates the data needed to draw
    // 'painter' draw with the data on 'canvas'
    canvas := image.NewRGBA(image.Rect(0, 0, w, h))
    rstr := raster.NewRasterizer(w, h)
    painter := raster.NewRGBAPainter(canvas)
    painter.SetColor(color.RGBA{0xff, 0xff, 0x00, 0xff})

    // specify the start point (100, 100)
    // why shift by 8?
    // raster.Point has 2 memembers X and Y, they are both of type raster.Fix32
    // raster.Fix32 is fixed point number, the high 24 bits is the integral part
    // for example, a raster.Fix32 number 1 in fact is 1/256
    a := raster.Point{100 << 8, 100 << 8}
    rstr.Start(a)

    // draw a straight line from the start point
    b := raster.Point{200 << 8, 100 << 8}
    rstr.Add1(b)

    // draw a bezier curve, points b, c, d are the control points
    c := raster.Point{200 << 8, 200 << 8}
    d := raster.Point{100 << 8, 200 << 8}
    rstr.Add2(c, d)

    rstr.Add1(a)

    // now, draw the shape on 'canvas'
    rstr.Rasterize(painter)

    // 'canvas' is of type *image.RGBA,
    // but the window need xgraphics.Image to show, so we convert it
    ximg := xgraphics.NewConvert(xu, canvas)

    // I want 'ximg' to show on 'xwin'
    ximg.XSurfaceSet(xwin.Id)
    // now show it
    ximg.XDraw()
    ximg.XPaint(xwin.Id)

       // save the image to png
    fd, err := os.Create("blog.png")
    if err != nil {
        fmt.Println(err)
        return
    }
    err = png.Encode(fd, canvas)
    if err != nil {
        fmt.Println(err)
    }

    // listen on the events such as keypress, mousepress etc.
    xevent.Main(xu)

}