EventResize: use WindowSize struct internally

Introduce a WindowSize type and use it internally for the EventResize
event. Add PixelSize method to EventResize to report the screen size in
pixels, if supported.

resize.go

@@ -21,14 +21,17 @@ import (
 // EventResize is sent when the window size changes.
 type EventResize struct {
 	t  time.Time
-	w int
-	h int
+	ws WindowSize
 }
 
 // NewEventResize creates an EventResize with the new updated window size,
 // which is given in character cells.
 func NewEventResize(width, height int) *EventResize {
-	return &EventResize{t: time.Now(), w: width, h: height}
+	ws := WindowSize{
+		Width:  width,
+		Height: height,
+	}
+	return &EventResize{t: time.Now(), ws: ws}
 }
 
 // When returns the time when the Event was created.
@@ -38,5 +41,26 @@ func (ev *EventResize) When() time.Time {
 
 // Size returns the new window size as width, height in character cells.
 func (ev *EventResize) Size() (int, int) {
-	return ev.w, ev.h
+	return ev.ws.Width, ev.ws.Height
+}
+
+// PixelSize returns the new window size as width, height in pixels. The size
+// will be 0,0 if the screen doesn't support this feature
+func (ev *EventResize) PixelSize() (int, int) {
+	return ev.ws.PixelWidth, ev.ws.PixelHeight
+}
+
+type WindowSize struct {
+	Width       int
+	Height      int
+	PixelWidth  int
+	PixelHeight int
+}
+
+// CellDimensions returns the dimensions of a single cell, in pixels
+func (ws WindowSize) CellDimensions() (int, int) {
+	if ws.PixelWidth == 0 || ws.PixelHeight == 0 {
+		return 0, 0
+	}
+	return (ws.PixelWidth / ws.Width), (ws.PixelHeight / ws.Height)
 }