need to be very specific about points vs. pixels.

drawing/stack_graphic_context.go

@@ -25,8 +25,8 @@ type ContextStack struct {
 	Cap         LineCap
 	Join        LineJoin
 
-	FontSize float64
-	Font     *truetype.Font
+	FontSizePoints float64
+	Font           *truetype.Font
 
 	Scale float64
 
@@ -45,118 +45,145 @@ func NewStackGraphicContext() *StackGraphicContext {
 	gc.current.Cap = RoundCap
 	gc.current.FillRule = FillRuleEvenOdd
 	gc.current.Join = RoundJoin
-	gc.current.FontSize = 10
+	gc.current.FontSizePoints = 10
 	return gc
 }
 
+// GetMatrixTransform returns the matrix transform.
 func (gc *StackGraphicContext) GetMatrixTransform() Matrix {
 	return gc.current.Tr
 }
 
-func (gc *StackGraphicContext) SetMatrixTransform(Tr Matrix) {
-	gc.current.Tr = Tr
+// SetMatrixTransform sets the matrix transform.
+func (gc *StackGraphicContext) SetMatrixTransform(tr Matrix) {
+	gc.current.Tr = tr
 }
 
-func (gc *StackGraphicContext) ComposeMatrixTransform(Tr Matrix) {
-	gc.current.Tr.Compose(Tr)
+// ComposeMatrixTransform composes a transform into the current transform.
+func (gc *StackGraphicContext) ComposeMatrixTransform(tr Matrix) {
+	gc.current.Tr.Compose(tr)
 }
 
+// Rotate rotates the matrix transform by an angle in degrees.
 func (gc *StackGraphicContext) Rotate(angle float64) {
 	gc.current.Tr.Rotate(angle)
 }
 
+// Translate translates a transform.
 func (gc *StackGraphicContext) Translate(tx, ty float64) {
 	gc.current.Tr.Translate(tx, ty)
 }
 
+// Scale scales a transform.
 func (gc *StackGraphicContext) Scale(sx, sy float64) {
 	gc.current.Tr.Scale(sx, sy)
 }
 
+// SetStrokeColor sets the stroke color.
 func (gc *StackGraphicContext) SetStrokeColor(c color.Color) {
 	gc.current.StrokeColor = c
 }
 
+// SetFillColor sets the fill color.
 func (gc *StackGraphicContext) SetFillColor(c color.Color) {
 	gc.current.FillColor = c
 }
 
+// SetFillRule sets the fill rule.
 func (gc *StackGraphicContext) SetFillRule(f FillRule) {
 	gc.current.FillRule = f
 }
 
+// SetLineWidth sets the line width.
 func (gc *StackGraphicContext) SetLineWidth(lineWidth float64) {
 	gc.current.LineWidth = lineWidth
 }
 
+// SetLineCap sets the line cap.
 func (gc *StackGraphicContext) SetLineCap(cap LineCap) {
 	gc.current.Cap = cap
 }
 
+// SetLineJoin sets the line join.
 func (gc *StackGraphicContext) SetLineJoin(join LineJoin) {
 	gc.current.Join = join
 }
 
+// SetLineDash sets the line dash.
 func (gc *StackGraphicContext) SetLineDash(dash []float64, dashOffset float64) {
 	gc.current.Dash = dash
 	gc.current.DashOffset = dashOffset
 }
 
-func (gc *StackGraphicContext) SetFontSize(fontSize float64) {
-	gc.current.FontSize = fontSize
+// SetFontSize sets the font size.
+func (gc *StackGraphicContext) SetFontSize(fontSizePoints float64) {
+	gc.current.FontSizePoints = fontSizePoints
 }
 
+// GetFontSize gets the font size.
 func (gc *StackGraphicContext) GetFontSize() float64 {
-	return gc.current.FontSize
+	return gc.current.FontSizePoints
 }
 
+// SetFont sets the current font.
 func (gc *StackGraphicContext) SetFont(f *truetype.Font) {
 	gc.current.Font = f
 }
 
+// GetFont returns the font.
 func (gc *StackGraphicContext) GetFont() *truetype.Font {
 	return gc.current.Font
 }
 
+// BeginPath starts a new path.
 func (gc *StackGraphicContext) BeginPath() {
 	gc.current.Path.Clear()
 }
 
+// IsEmpty returns if the path is empty.
 func (gc *StackGraphicContext) IsEmpty() bool {
 	return gc.current.Path.IsEmpty()
 }
 
-func (gc *StackGraphicContext) LastPoint() (float64, float64) {
+// LastPoint returns the last point on the path.
+func (gc *StackGraphicContext) LastPoint() (x float64, y float64) {
 	return gc.current.Path.LastPoint()
 }
 
+// MoveTo moves the cursor for a path.
 func (gc *StackGraphicContext) MoveTo(x, y float64) {
 	gc.current.Path.MoveTo(x, y)
 }
 
+// LineTo draws a line.
 func (gc *StackGraphicContext) LineTo(x, y float64) {
 	gc.current.Path.LineTo(x, y)
 }
 
+// QuadCurveTo draws a quad curve.
 func (gc *StackGraphicContext) QuadCurveTo(cx, cy, x, y float64) {
 	gc.current.Path.QuadCurveTo(cx, cy, x, y)
 }
 
+// CubicCurveTo draws a cubic curve.
 func (gc *StackGraphicContext) CubicCurveTo(cx1, cy1, cx2, cy2, x, y float64) {
 	gc.current.Path.CubicCurveTo(cx1, cy1, cx2, cy2, x, y)
 }
 
+// ArcTo draws an arc.
 func (gc *StackGraphicContext) ArcTo(cx, cy, rx, ry, startAngle, angle float64) {
 	gc.current.Path.ArcTo(cx, cy, rx, ry, startAngle, angle)
 }
 
+// Close closes a path.
 func (gc *StackGraphicContext) Close() {
 	gc.current.Path.Close()
 }
 
+// Save pushes a context onto the stack.
 func (gc *StackGraphicContext) Save() {
 	context := new(ContextStack)
-	context.FontSize = gc.current.FontSize
+	context.FontSizePoints = gc.current.FontSizePoints
 	context.Font = gc.current.Font
 	context.LineWidth = gc.current.LineWidth
 	context.StrokeColor = gc.current.StrokeColor
@@ -174,6 +201,7 @@ func (gc *StackGraphicContext) Save() {
 	gc.current = context
 }
 
+// Restore restores the previous context.
 func (gc *StackGraphicContext) Restore() {
 	if gc.current.Previous != nil {
 		oldContext := gc.current