Should work with sub-images now

examples/glaggle/main.go

@@ -10,12 +10,12 @@ func main () {
 	canvas := ggfx.Image[uint8] {
 		Pix:    img.Pix,
 		Stride: img.Stride,
-		Bounds: img.Rect,
+		Rect:   img.Rect,
 		Width:  4,
 	}
 	black  := []uint8 { 0,   0,   0, 255 }
 	yellow := []uint8 { 255, 255, 0, 255 }
-	midpoint := image.Pt(canvas.Bounds.Dx() / 2, canvas.Bounds.Dy() / 2)
+	midpoint := image.Pt(canvas.Rect.Dx() / 2, canvas.Rect.Dy() / 2)
 
 	face := ggfx.Circle(32, 100, midpoint)
 	canvas.FillPolygon(yellow, face...)

examples/icon/main.go

@@ -10,14 +10,14 @@ func main () {
 	canvas := ggfx.Image[uint8] {
 		Pix:    img.Pix,
 		Stride: img.Stride,
-		Bounds: img.Rect,
+		Rect:   img.Rect,
 		Width:  4,
 	}
 	black  := []uint8 { 0,   0,  0, 255 }
 	orange := []uint8 { 255, 48, 0, 255 }
-	midpoint := image.Pt(canvas.Bounds.Dx() / 2, canvas.Bounds.Dy() / 2)
+	midpoint := image.Pt(canvas.Rect.Dx() / 2, canvas.Rect.Dy() / 2)
 
-	canvas.FillRectangle(orange, canvas.Bounds)
+	canvas.FillRectangle(orange, canvas.Rect)
 	for x := 1; x <= 6; x ++ {
 		point := image.Pt(x, 7 - x)
 		canvas.FillRectangle(black, image.Rectangle {

ggfx.go

@@ -13,10 +13,18 @@ type Image[T any] struct {
 	// Width specifies how many slice elements make up a single pixel.
 	Width int
 
-	// Bounds specifies a rectangle that all drawing operations will be
+	// Rect specifies a rectangle that all drawing operations will be
 	// clipped to. It must not reside outside of Data. It is measured in
 	// pixels and not slice elements.
-	Bounds image.Rectangle
+	Rect image.Rectangle
+}
+
+func (this Image[T]) Bounds () image.Rectangle {
+	return this.Rect
+}
+
+func (this Image[T]) PixOffset (x, y int) int {
+	return (y - this.Rect.Min.Y) * this.Stride + (x - this.Rect.Min.X) * this.Width
 }
 
 func (this Image[T]) assertWidth (pixel []T) {	

line.go

@@ -25,12 +25,9 @@ func (this Image[T]) lineInternal (
 ) {
 	context := linePlottingContext[T] {
 		plottingContext: plottingContext[T] {
-			data:   this.Pix,
-			stride: this.Stride,
+			Image:  this,
 			color:  stroke,
 			weight: weight,
-			bounds: this.Bounds,
-			width:  this.Width,
 			offset: offset,
 		},
 		min: min,

plot.go

@@ -3,12 +3,9 @@ package ggfx
 import "image"
 
 type plottingContext[T any] struct {
-	data   []T
-	stride int
+	Image[T]
 	color  T
 	weight int
-	bounds image.Rectangle
-	width  int
 	offset int
 }
 
@@ -16,14 +13,14 @@ func (context plottingContext[T]) square (center image.Point) (square image.Rect
 	return image.Rect(0, 0, context.weight, context.weight).
 		Sub(image.Pt(context.weight / 2, context.weight / 2)).
 		Add(center).
-		Intersect(context.bounds)
+		Intersect(context.Rect)
 }
 
 func (context plottingContext[T]) plot (center image.Point) {
 	square := context.square(center)
 	for y := square.Min.Y; y < square.Max.Y; y ++ {
 	for x := square.Min.X; x < square.Max.X; x ++ {
-		index := y * context.stride + x * context.width + context.offset
-		context.data[index] = context.color
+		index := context.PixOffset(x, y) + context.offset
+		context.Pix[index] = context.color
 	}}
 }

polygon.go

@@ -17,7 +17,7 @@ func (this Image[T]) FillPolygon (fill []T, points ...image.Point) {
 		if point.X > area.Max.X { area.Max.X = point.X }
 		if point.Y > area.Max.Y { area.Max.Y = point.Y }
 	}
-	area = this.Bounds.Intersect(area)
+	area = this.Rect.Intersect(area)
 	if area.Empty() { return }
 	
 	// this algorithm is adapted from:
@@ -70,9 +70,7 @@ func (this Image[T]) FillPolygon (fill []T, points ...image.Point) {
 				// fill for each pixel part
 				for offset, part := range fill {
 					for x := left; x < right; x ++ {
-						index :=
-							y * this.Stride + x *
-							this.Width + offset
+						index := this.PixOffset(x, y) + offset
 						this.Pix[index] = part
 					}
 				}

rectangle.go

@@ -4,14 +4,14 @@ import "image"
 
 func (this Image[T]) FillRectangle (fill []T, rectangle image.Rectangle) {
 	this.assertWidth(fill)
-	rectangle = this.Bounds.Intersect(rectangle.Canon())
+	rectangle = this.Rect.Intersect(rectangle.Canon())
 	if rectangle.Empty () { return }
 	
 	var pos image.Point
 	for pos.Y = rectangle.Min.Y; pos.Y < rectangle.Max.Y; pos.Y ++ {
 	for offset, part := range fill {
 	for pos.X = rectangle.Min.X; pos.X < rectangle.Max.X; pos.X ++ {
-		index := pos.Y * this.Stride + pos.X * this.Width + offset
+		index := this.PixOffset(pos.X, pos.Y) + offset
 		this.Pix[index] = part
 	}}}
 }