Factored out (render) buffer.

ui/buffer.go

@@ -0,0 +1,32 @@
+package ui
+
+import "opslag.de/schobers/geom"
+
+type Buffer struct {
+	im Image
+}
+
+func (b *Buffer) Update(ctx Context, size geom.PointF32) error {
+	if b.im != nil {
+		if b.im.Width() == size.X && b.im.Height() == size.Y {
+			return nil
+		}
+		b.im.Destroy()
+		b.im = nil
+	}
+	im, err := ctx.Renderer().CreateImageSize(size.X, size.Y)
+	if err != nil {
+		return err
+	}
+	b.im = im
+	return nil
+}
+
+func (b *Buffer) Render(ctx Context, pos geom.PointF32, render func()) {
+	renderer := ctx.Renderer()
+	currTarget := renderer.Target()
+	renderer.RenderTo(b.im)
+	render()
+	renderer.RenderTo(currTarget)
+	renderer.DrawImage(b.im, pos)
+}

ui/overflow.go

@@ -15,7 +15,7 @@ type overflow struct {
 	desired  geom.PointF32
 	bounds   geom.RectangleF32
 	offset   geom.PointF32
-	buffer   Image
+	content  Buffer
 
 	hor *Scrollbar
 	ver *Scrollbar
@@ -124,24 +124,14 @@ func (o *overflow) Render(ctx Context) {
 
 	var content = o.Content.Bounds()
 	content.Min = geom.ZeroPtF32
-	if o.buffer == nil || o.buffer.Width() != content.Dx() || o.buffer.Height() != content.Dy() {
+	err := o.content.Update(ctx, content.Size())
-		if o.buffer != nil {
-			o.buffer.Destroy()
-			o.buffer = nil
-		}
-		buffer, err := renderer.CreateImageSize(content.Dx(), content.Dy())
 	if err != nil {
 		panic(err)
 	}
-		o.buffer = buffer
+	o.content.Render(ctx, o.bounds.Min, func() {
-	}
-
-	target := renderer.Target()
-	renderer.RenderTo(o.buffer)
 		renderer.Clear(color.Transparent)
 		o.Content.Render(ctx)
-	renderer.RenderTo(target)
+	})
-	renderer.DrawImage(o.buffer, o.bounds.Min)
 
 	o.doOnVisibleBars(func(bar *Scrollbar) {
 		bar.Render(ctx)