[cairo] The line still blurry after I follow "Frequently Asked Questions" guide

[mustodo]

Hi,

Cairo and Skia is two best library for cross-platform GUI, but I prefer to use Cairo because it smaller and write by c, skia is too huge for apps.

when I used Cairo to draw a rectangle, the line is blurry even if I use round numbers.

func (me *canvas) DrawRectF(left, top, right, bottom float32, paint *Paint) {
  if right <= left || bottom <= top {
    return
  }

  C.cairo_set_antialias(me.ptr, C.CAIRO_ANTIALIAS_NONE)

  fix := paint.Style == STROKE && int32(paint.Width)%2 != 0
  fix = false
  if fix {
    me.Save()
    me.TranslateF(0.5, 0.5)
  }
  C.cairo_rectangle(me.ptr, 100, 100, 500, 500)
  C.cairo_rectangle(me.ptr, 110, 110, 510, 510)
  me.drawPaint(paint)

  if fix {
    me.Restore()
  }
}
this is a line in cairo



this is a line in code editor


I searched and found a guide at official website.I readed the "Frequently Asked Questions" > "How do I draw a sharp, single-pixel-wide line?" and follow the guide

cairo_user_to_device (cr, &x, &y);
do_rounding (&x, &y);
cairo_device_to_user (cr, &x, &y);

it is used round numbers, so it has none change
func (me *canvas) UserToDevice(x, y float32) {
  dx := C.double(x)
  dy := C.double(y)
  C.cairo_user_to_device(me.ptr, &dx, &dy)
  log.V("userToDevice x=%f, y=%f, dx=%f, dy=%f", x, y, dx, dy)
  C.cairo_device_to_user(me.ptr, &dx, &dy)
  log.V("deviceToUser x=%f, y=%f, dx=%f, dy=%f", x, y, dx, dy)
}

// output
// userToDevice x=100.000000, y=500.000000, dx=100.000000, dy=500.000000
// deviceToUser x=100.000000, y=500.000000, dx=100.000000, dy=500.000000

I tried Cairo versions cairo-1.14.12  cairo-1.16.0_2 cairo-1.16.0_3

So, how should I do to draw a sharp with single-pixel-wide line like code editor? 


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