package xcanvas

import "image"
import "github.com/jezek/xgbutil/xgraphics"

type plottingContext struct {
	image  *xgraphics.Image
	color  xgraphics.BGRA
	weight int
}

func (context plottingContext) square (center image.Point) (square image.Rectangle) {
	return image.Rect(0, 0, context.weight, context.weight).
		Sub(image.Pt(context.weight / 2, context.weight / 2)).
		Add(center).
		Intersect(context.image.Bounds())
}

func (context plottingContext) plot (center image.Point) {
	square := context.square(center)

	if context.color.A == 255 {
		for y := square.Min.Y; y < square.Max.Y; y ++ {
		for x := square.Min.X; x < square.Max.X; x ++ {
			index := context.image.PixOffset(x, y)
			context.image.Pix[index + 0] = context.color.B
			context.image.Pix[index + 1] = context.color.G
			context.image.Pix[index + 2] = context.color.R
			context.image.Pix[index + 3] = context.color.A
		}}
	} else {
		for y := square.Min.Y; y < square.Max.Y; y ++ {
		for x := square.Min.X; x < square.Max.X; x ++ {
			index := context.image.PixOffset(x, y)
			pixel := blendPremultipliedBGRA(xgraphics.BGRA {
				B: context.image.Pix[index + 0],
				G: context.image.Pix[index + 1],
				R: context.image.Pix[index + 2],
				A: context.image.Pix[index + 3],
			}, context.color)
			context.image.Pix[index + 0] = pixel.B
			context.image.Pix[index + 1] = pixel.G
			context.image.Pix[index + 2] = pixel.R
			context.image.Pix[index + 3] = pixel.A
		}}
	}
}