From 9029655a545f8e0b37974dbe7c1c94306234ddd0 Mon Sep 17 00:00:00 2001
From: vmobilis <75476228+vmobilis@users.noreply.github.com>
Date: Sun, 30 Aug 2026 16:56:31 +0300
Subject: [PATCH] feat: support numbering for preview images (#1895)

---
 examples/cli/main.cpp | 55 ++++++++++++++++++++++++-------------------
 1 file changed, 31 insertions(+), 24 deletions(-)

diff --git a/examples/cli/main.cpp b/examples/cli/main.cpp
index 43719abb..d77356b1 100644
--- a/examples/cli/main.cpp
+++ b/examples/cli/main.cpp
@@ -81,7 +81,7 @@ struct SDCliParams {
              &metadata_format},
             {"",
              "--preview-path",
-             "path to write preview image to (default: ./preview.png). Multi-frame previews support .avi, .webm, and animated .webp",
+             "path to write preview image to (default: ./preview.png). For image generation, the filename can have %03d placeholder for sequential numbering. Multi-frame previews support .avi, .webm, and animated .webp",
              0,
              &preview_path},
             {"",
@@ -377,29 +377,6 @@ bool load_images_from_dir(const std::string dir,
     return true;
 }
 
-void step_callback(int step, int frame_count, sd_image_t* image, bool is_noisy, void* data) {
-    (void)step;
-    (void)is_noisy;
-    SDCliParams* cli_params = (SDCliParams*)data;
-    // is_noisy is set to true if the preview corresponds to noisy latents, false if it's denoised latents
-    // unused in this app, it will either be always noisy or always denoised here
-    if (frame_count == 1) {
-        if (!write_image_to_file(cli_params->preview_path,
-                                 image->data,
-                                 image->width,
-                                 image->height,
-                                 image->channel,
-                                 "",
-                                 cli_params->compression_quality)) {
-            LOG_ERROR("save preview image to '%s' failed", cli_params->preview_path.c_str());
-        }
-    } else {
-        if (create_video_from_sd_images(cli_params->preview_path.c_str(), image, frame_count, cli_params->preview_fps, cli_params->compression_quality) != 0) {
-            LOG_ERROR("save preview video to '%s' failed", cli_params->preview_path.c_str());
-        }
-    }
-}
-
 std::string format_frame_idx(std::string pattern, int frame_idx) {
     std::smatch match;
     std::string result = pattern;
@@ -419,6 +396,36 @@ std::string format_frame_idx(std::string pattern, int frame_idx) {
     return result;
 }
 
+int continuous_preview_counter = 0;
+
+void step_callback(int step, int frame_count, sd_image_t* image, bool is_noisy, void* data) {
+    (void)step;
+    (void)is_noisy;
+    SDCliParams* cli_params = (SDCliParams*)data;
+    // is_noisy is set to true if the preview corresponds to noisy latents, false if it's denoised latents
+    // unused in this app, it will either be always noisy or always denoised here
+    if (frame_count == 1) {
+        fs::path path = cli_params->preview_path;
+        if (encoded_image_format_from_path(path.string()) == EncodedImageFormat::UNKNOWN)
+            path += ".png";
+        if (std::regex_search(path.string(), format_specifier_regex))
+            path = fs::path(format_frame_idx(path.string(), continuous_preview_counter++));
+        if (!write_image_to_file(path.string(),
+                                 image->data,
+                                 image->width,
+                                 image->height,
+                                 image->channel,
+                                 "",
+                                 cli_params->compression_quality)) {
+            LOG_ERROR("save preview image to '%s' failed", path.string().c_str());
+        }
+    } else {
+        if (create_video_from_sd_images(cli_params->preview_path.c_str(), image, frame_count, cli_params->preview_fps, cli_params->compression_quality) != 0) {
+            LOG_ERROR("save preview video to '%s' failed", cli_params->preview_path.c_str());
+        }
+    }
+}
+
 static fs::path get_video_audio_sidecar_path(const SDCliParams& cli_params) {
     fs::path out_path     = cli_params.output_path;
     fs::path base_path    = out_path;