Split rendering of buffer & blitting it to the display.

ui/buffer.go

@@ -1,6 +1,10 @@
 package ui
 
-import "opslag.de/schobers/geom"
+import (
+	"errors"
+
+	"opslag.de/schobers/geom"
+)
 
 type RenderBufferFn func(ctx Context, size geom.PointF32)
 
@@ -9,6 +13,8 @@ type Buffer struct {
 	size    geom.PointF32
 }
 
+var ErrNewBufferSize = errors.New("buffer has been resized")
+
 func (b *Buffer) Update(ctx Context, size geom.PointF32) error {
 	if b.texture != nil {
 		if size == b.size {
@@ -24,19 +30,30 @@ func (b *Buffer) Update(ctx Context, size geom.PointF32) error {
 	}
 	b.texture = texture
 	b.size = size
-	return nil
+	return ErrNewBufferSize
 }
 
 func (b *Buffer) Render(ctx Context, pos geom.PointF32, fn RenderBufferFn) {
 	if b.texture == nil {
 		return
 	}
+	b.RenderContent(ctx, fn)
+	b.RenderToDisplay(ctx, pos)
+}
+
+func (b *Buffer) RenderContent(ctx Context, fn RenderBufferFn) {
 	renderer := ctx.Renderer()
 	currTarget := renderer.Target()
 	renderer.RenderTo(b.texture)
 	fn(ctx, b.size)
 	renderer.RenderTo(currTarget)
-	renderer.DrawTexturePoint(b.texture, pos)
+}
+
+func (b *Buffer) RenderToDisplay(ctx Context, pos geom.PointF32) {
+	if b.texture == nil {
+		return
+	}
+	ctx.Renderer().DrawTexturePoint(b.texture, pos)
 }
 
 type BufferControl struct {