gpu,gpu/backend: [compute] handle loss of buffer contents during download

Signed-off-by: Elias Naur <mail@eliasnaur.com>

gpu/backend/backend.go

@@ -3,6 +3,7 @@
 package backend
 
 import (
+	"errors"
 	"image"
 	"time"
 )
@@ -225,6 +226,8 @@ const (
 	BlendFactorDstColor
 )
 
+var ErrContentLost = errors.New("buffer content lost")
+
 func (f Features) Has(feats Features) bool {
 	return f&feats == feats
 }

gpu/compute.go

@@ -821,6 +821,9 @@ func (g *compute) render(tileDims image.Point) error {
 		t.kernel4.end()
 
 		if err := g.buffers.memory.buffer.Download(gunsafe.StructView(g.memHeader)); err != nil {
+			if err == backend.ErrContentLost {
+				continue
+			}
 			return err
 		}
 		switch errCode := g.memHeader.mem_error; errCode {

gpu/gl/backend.go

@@ -704,7 +704,7 @@ func (b *gpuBuffer) Download(data []byte) error {
 	}
 	copy(data, bufferMap)
 	if !b.backend.funcs.UnmapBuffer(firstBinding) {
-		return errors.New("buffer content lost")
+		return backend.ErrContentLost
 	}
 	return nil
 }