VipsImage::preeval

void
preeval (
  VipsImage* self,
  VipsProgress* progress,
  gpointer user_data
)

The ::preeval signal is emitted once before computation of image starts. It’s a good place to set up evaluation feedback.

Use vips_image_set_progress() to turn on progress reporting for an image.

Default handler:

The default handler is called after the handlers added via g_signal_connect().

`progress`	`VipsProgress`
	`VipsProgress` for this image.
	The data is owned by the caller of the function.