gim: add terminal.Buffer.DrawBufferCentered

gim/box.go

@@ -61,10 +61,7 @@ func (b box) rect() geo.Rect {
 func (b box) draw(buf *terminal.Buffer) {
 	rect := b.rect()
 	buf.DrawRect(rect, terminal.SingleLine)
-
 	if b.bodyBuf != nil {
-		center := rect.Center()
-		bodyBufRect := geo.Rect{Size: b.bodyBuf.Size()}
-		buf.DrawBuffer(bodyBufRect.Centered(center).TopLeft, b.bodyBuf)
+		buf.DrawBufferCentered(rect.Center(), b.bodyBuf)
 	}
 }

gim/line.go

@@ -26,8 +26,6 @@ func (l line) draw(buf *terminal.Buffer, flowDir, secFlowDir geo.XY) {
 
 	// draw the body
 	if l.bodyBuf != nil {
-		mid := start.Midpoint(end)
-		bodyBufRect := geo.Rect{Size: l.bodyBuf.Size()}
-		buf.DrawBuffer(bodyBufRect.Centered(mid).TopLeft, l.bodyBuf)
+		buf.DrawBufferCentered(start.Midpoint(end), l.bodyBuf)
 	}
 }

gim/main.go

@@ -90,12 +90,14 @@ func main() {
 		start:       start,
 	}
 
+	viewBuf := terminal.NewBuffer()
+	v.draw(viewBuf)
+
 	buf := terminal.NewBuffer()
-	v.draw(buf)
-	bufRect := geo.Rect{Size: buf.Size()}.Centered(center)
+	buf.DrawBufferCentered(center, viewBuf)
 
 	term.Clear()
-	term.WriteBuffer(bufRect.TopLeft, buf)
+	term.WriteBuffer(geo.Zero, buf)
 	term.SetPos(wSize.Add(geo.XY{0, -1}))
 	term.Draw()
 }

gim/terminal/buffer.go

@@ -203,6 +203,13 @@ func (b *Buffer) DrawBuffer(at geo.XY, b2 *Buffer) {
 	})
 }
 
+// DrawBufferCentered is like DrawBuffer, but centered around the given point
+// instead of translated by it.
+func (b *Buffer) DrawBufferCentered(around geo.XY, b2 *Buffer) {
+	b2rect := geo.Rect{Size: b2.Size()}
+	b.DrawBuffer(b2rect.Centered(around).TopLeft, b2)
+}
+
 // Size returns the dimensions of the Buffer's current area which has been
 // written to.
 func (b *Buffer) Size() geo.XY {