Convert LineTo to MoveTo

[AndreKR]

If I call LineTo(x, y) on an empty path, it is automatically converted to MoveTo(0, 0); LineTo(x, y).

It would be super comfortable if it would instead be converted to MoveTo(x, y).

What do you think? I can't really imagine anyone relying on the fact that a path implicitly starts at (0, 0), so this would be barely a breaking change - especially since the coordinates of the top left pixel are (.5, .5).

[llgcode]

I think I understand the purpose. This change will may break things, but who use this? I agree may be nobody. Not sure if it works for bezier. Could be an option of a path builder?

[AndreKR]

I think for bezier we can just ignore whatever is passed as control points for the starting point. See this example:

points := []struct{x, y float64}{
	{50, 20},
	{80, 80},
	{20, 80},
	{50, 20}, // could use path.Close() as well
}

bezierPoints := []struct{cx, cy, x, y float64}{
	{0, 0, 50, 20}, // control point (0, 0) will be ignored for the starting point
	{65, 20, 80, 80},
	{80, 95, 20, 80},
	{20, 25, 50, 20},
}

path := new(draw2d.Path)
bezierPath := new(draw2d.Path)

for _, p := range points {
	path.LineTo(p.x, p.y)
}

for _, p := range bezierPoints {
	bezierPath.QuadCurveTo(p.cx, p.cy, p.x, p.y)
}

i := image.NewRGBA(image.Rect(0, 0, 100, 100))
draw.Draw(i, i.Bounds(), image.NewUniform(image.White), image.ZP, draw.Src)
gc := draw2dimg.NewGraphicContext(i)
gc.SetStrokeColor(colornames.Green)
gc.Stroke(path)
gc.SetStrokeColor(colornames.Red)
gc.Stroke(bezierPath)

f, err := os.Create("/test.png")
log.Println(err)
png.Encode(f, i)

Before the change:

After the change:

Changes see #134.

[llgcode]

Thanks for the example. It illustrates very well the purpose of the change.