forbid Full live preview method for medvram and add a setting to undo the forbidding

modules/sd_samplers_common.py

@@ -35,10 +35,15 @@ approximation_indexes = {"Full": 0, "Approx NN": 1, "Approx cheap": 2, "TAESD":
 
 
 def samples_to_images_tensor(sample, approximation=None, model=None):
-    '''latents -> images [-1, 1]'''
+    """Transforms 4-channel latent space images into 3-channel RGB image tensors, with values in range [-1, 1]."""
+
     if approximation is None or (shared.state.interrupted and opts.live_preview_fast_interrupt):
         approximation = approximation_indexes.get(opts.show_progress_type, 0)
 
+        from modules import lowvram
+        if approximation == 0 and lowvram.is_enabled(shared.sd_model) and not shared.opts.live_preview_allow_lowvram_full:
+            approximation = 1
+
     if approximation == 2:
         x_sample = sd_vae_approx.cheap_approximation(sample)
     elif approximation == 1:

modules/shared_options.py

@@ -287,6 +287,7 @@ options_templates.update(options_section(('ui', "Live previews"), {
     "show_progress_grid": OptionInfo(True, "Show previews of all images generated in a batch as a grid"),
     "show_progress_every_n_steps": OptionInfo(10, "Live preview display period", gr.Slider, {"minimum": -1, "maximum": 32, "step": 1}).info("in sampling steps - show new live preview image every N sampling steps; -1 = only show after completion of batch"),
     "show_progress_type": OptionInfo("Approx NN", "Live preview method", gr.Radio, {"choices": ["Full", "Approx NN", "Approx cheap", "TAESD"]}).info("Full = slow but pretty; Approx NN and TAESD = fast but low quality; Approx cheap = super fast but terrible otherwise"),
+    "live_preview_allow_lowvram_full": OptionInfo(False, "Allow Full live preview method with lowvram/medvram").info("If not, Approx NN will be used instead; Full live preview method is very detrimental to speed if lowvram/medvram optimizations are enabled"),
     "live_preview_content": OptionInfo("Prompt", "Live preview subject", gr.Radio, {"choices": ["Combined", "Prompt", "Negative prompt"]}),
     "live_preview_refresh_period": OptionInfo(1000, "Progressbar and preview update period").info("in milliseconds"),
     "live_preview_fast_interrupt": OptionInfo(False, "Return image with chosen live preview method on interrupt").info("makes interrupts faster"),