move origin to top-left text draw failed

[Modificator]

When I use SetView(canvas.Identity.ReflectYAbout) text draw result

useSetCoordView can draw right, but other draw can't draw right, ↓ background draw out of canvas

var fontLoadSlice = []string{
	".SF Regular",
	"Arial",
	"Droid Sans",
}
var fontFamily *canvas.FontFamily
	fontFamily = canvas.NewFontFamily("times")
	for _, fontName := range fontLoadSlice {
		err := fontFamily.LoadLocalFont(fontName, canvas.FontRegular)
		fmt.Println(err)
		if err == nil {
			break
		}
	}
	headerFont := fontFamily.Face(28.0, canvas.Black, canvas.FontRegular, canvas.FontNormal)
	c := canvas.New(500, 200)
	ctx := canvas.NewContext(c)
	ctx.SetView(canvas.Identity.ReflectYAbout(100))
        //ctx.SetCoordView(canvas.Identity.ReflectYAbout(100))
	ctx.SetFillColor(canvas.White)
	ctx.DrawPath(0, 0, canvas.Rectangle(c.Size()))
	//ctx.SetStrokeColor(canvas.Black)
	//ctx.DrawPath(10, 10, canvas.Rectangle(480, 180))
	headerText := canvas.NewTextBox(headerFont, "test", 0, 0, canvas.Justify, canvas.Justify, 0, 0)
	ctx.DrawText(30, 30, headerText)

[tdewolff]

Yes, this may not be the easiest for people who'd like to work with top-left as the origin, but SetCoordView or SetCoordSystem should be used to change the coordinate transformation to position elements (but not transform the elements themselves) while SetView transforms the complete view. The former allows you to position the elements with top-left as the origin, but the elements themselves (a path for example) will always have bottom-left (the mathematical standard) as its origin. That is, you define the path with a bottom-left origin, and then you can position it using with top-left as the origin.

I'm thinking of changing this system, by introducing a CartesianIVContext for example that draws everything Y-flipped except for text. Additonally, it would be possible to add a PolarContext for polar coordinates etc.

[marco-m]

Is this a duplicate of #72 ?

[tdewolff]

Yes it is! I will close this one. As mentioned in the other issue:

I've added a change that adds better support for CartesianIV (i.e. origin is top-left). It differs from CartesianI (i.e. origin is bottom-left) in that it anchors differently to images (anchors top-left vs bottom-left) and that text has always been anchored to the baseline (TextLine) or to top-left (TextBox) and remains so. This means that switching to CartesianIV may change the position of text and images.

You can change to CartesianIV using:

ctx.SetCoordSystem(canvas.CartesianIV)