another way to use backend (#638)

* another way to use backend

* another way to use backend

backend/headless/latent_preview.py

@@ -0,0 +1,95 @@
+import torch
+from PIL import Image
+import struct
+import numpy as np
+from comfy.cli_args import args, LatentPreviewMethod
+from comfy.taesd.taesd import TAESD
+import folder_paths
+import comfy.utils
+
+MAX_PREVIEW_RESOLUTION = 512
+
+class LatentPreviewer:
+    def decode_latent_to_preview(self, x0):
+        pass
+
+    def decode_latent_to_preview_image(self, preview_format, x0):
+        preview_image = self.decode_latent_to_preview(x0)
+        return ("JPEG", preview_image, MAX_PREVIEW_RESOLUTION)
+
+class TAESDPreviewerImpl(LatentPreviewer):
+    def __init__(self, taesd):
+        self.taesd = taesd
+
+    def decode_latent_to_preview(self, x0):
+        x_sample = self.taesd.decoder(x0)[0].detach()
+        # x_sample = self.taesd.unscale_latents(x_sample).div(4).add(0.5)  # returns value in [-2, 2]
+        x_sample = x_sample.sub(0.5).mul(2)
+
+        x_sample = torch.clamp((x_sample + 1.0) / 2.0, min=0.0, max=1.0)
+        x_sample = 255. * np.moveaxis(x_sample.cpu().numpy(), 0, 2)
+        x_sample = x_sample.astype(np.uint8)
+
+        preview_image = Image.fromarray(x_sample)
+        return preview_image
+
+
+class Latent2RGBPreviewer(LatentPreviewer):
+    def __init__(self, latent_rgb_factors):
+        self.latent_rgb_factors = torch.tensor(latent_rgb_factors, device="cpu")
+
+    def decode_latent_to_preview(self, x0):
+        latent_image = x0[0].permute(1, 2, 0).cpu() @ self.latent_rgb_factors
+
+        latents_ubyte = (((latent_image + 1) / 2)
+                            .clamp(0, 1)  # change scale from -1..1 to 0..1
+                            .mul(0xFF)  # to 0..255
+                            .byte()).cpu()
+
+        return Image.fromarray(latents_ubyte.numpy())
+
+
+def get_previewer(device, latent_format):
+    previewer = None
+    method = args.preview_method
+    if method != LatentPreviewMethod.NoPreviews:
+        # TODO previewer methods
+        taesd_decoder_path = None
+        if latent_format.taesd_decoder_name is not None:
+            taesd_decoder_path = folder_paths.get_full_path("vae_approx", latent_format.taesd_decoder_name)
+
+        if method == LatentPreviewMethod.Auto:
+            method = LatentPreviewMethod.Latent2RGB
+            if taesd_decoder_path:
+                method = LatentPreviewMethod.TAESD
+
+        if method == LatentPreviewMethod.TAESD:
+            if taesd_decoder_path:
+                taesd = TAESD(None, taesd_decoder_path).to(device)
+                previewer = TAESDPreviewerImpl(taesd)
+            else:
+                print("Warning: TAESD previews enabled, but could not find models/vae_approx/{}".format(latent_format.taesd_decoder_name))
+
+        if previewer is None:
+            if latent_format.latent_rgb_factors is not None:
+                previewer = Latent2RGBPreviewer(latent_format.latent_rgb_factors)
+    return previewer
+
+def prepare_callback(model, steps, x0_output_dict=None):
+    preview_format = "JPEG"
+    if preview_format not in ["JPEG", "PNG"]:
+        preview_format = "JPEG"
+
+    previewer = get_previewer(model.load_device, model.model.latent_format)
+
+    pbar = comfy.utils.ProgressBar(steps)
+    def callback(step, x0, x, total_steps):
+        if x0_output_dict is not None:
+            x0_output_dict["x0"] = x0
+
+        preview_bytes = None
+        if previewer:
+            preview_bytes = previewer.decode_latent_to_preview_image(preview_format, x0)
+        pbar.update_absolute(step + 1, total_steps, preview_bytes)
+    return callback
+