Fix the W clip embeddings. (#887)

* Fix the W clip embeddings.

* Add the specialized ddpm scheduler.

candle-examples/examples/wuerstchen/main.rs

@@ -193,9 +193,9 @@ fn encode_prompt(
     println!("Building the clip transformer.");
     let text_model =
         stable_diffusion::build_clip_transformer(&clip_config, clip_weights, device, DType::F32)?;
-    let text_embeddings = text_model.forward_with_mask(&tokens, tokens_len)?;
-    let uncond_embeddings = text_model.forward_with_mask(&uncond_tokens, uncond_tokens_len)?;
-    let text_embeddings = Tensor::cat(&[uncond_embeddings, text_embeddings], 0)?;
+    let text_embeddings = text_model.forward_with_mask(&tokens, tokens_len - 1)?;
+    let uncond_embeddings = text_model.forward_with_mask(&uncond_tokens, uncond_tokens_len - 1)?;
+    let text_embeddings = Tensor::cat(&[text_embeddings, uncond_embeddings], 0)?;
     Ok(text_embeddings)
 }
 

candle-transformers/src/models/wuerstchen/ddpm.rs

@@ -0,0 +1,97 @@
+use candle::{Result, Tensor};
+
+#[derive(Debug, Clone)]
+pub struct DDPMWSchedulerConfig {
+    scaler: f64,
+    s: f64,
+}
+
+impl Default for DDPMWSchedulerConfig {
+    fn default() -> Self {
+        Self {
+            scaler: 1f64,
+            s: 0.008f64,
+        }
+    }
+}
+
+pub struct DDPMWScheduler {
+    init_alpha_cumprod: f64,
+    init_noise_sigma: f64,
+    timesteps: Vec<f64>,
+    pub config: DDPMWSchedulerConfig,
+}
+
+impl DDPMWScheduler {
+    pub fn new(inference_steps: usize, config: DDPMWSchedulerConfig) -> Result<Self> {
+        let init_alpha_cumprod = (config.s / (1. + config.s) * std::f64::consts::PI)
+            .cos()
+            .powi(2);
+        let timesteps = (0..=inference_steps)
+            .map(|i| 1. - i as f64 / inference_steps as f64)
+            .collect::<Vec<_>>();
+        Ok(Self {
+            init_alpha_cumprod,
+            init_noise_sigma: 1.0,
+            timesteps,
+            config,
+        })
+    }
+
+    fn alpha_cumprod(&self, t: f64) -> f64 {
+        let scaler = self.config.scaler;
+        let s = self.config.s;
+        let t = if scaler > 1. {
+            1. - (1. - t).powf(scaler)
+        } else if scaler < 1. {
+            t.powf(scaler)
+        } else {
+            t
+        };
+        let alpha_cumprod =
+            ((t + s) / (1. + s) * std::f64::consts::PI * 0.5).powi(2) / self.init_alpha_cumprod;
+        alpha_cumprod.clamp(0.0001, 0.9999)
+    }
+
+    fn previous_timestep(&self, ts: f64) -> f64 {
+        let index = self
+            .timesteps
+            .iter()
+            .enumerate()
+            .map(|(idx, v)| (idx, (v - ts).abs()))
+            .min_by(|x, y| x.1.total_cmp(&y.1))
+            .unwrap()
+            .0;
+        self.timesteps[index + 1]
+    }
+
+    ///  Ensures interchangeability with schedulers that need to scale the denoising model input
+    /// depending on the current timestep.
+    pub fn scale_model_input(&self, sample: Tensor, _timestep: usize) -> Tensor {
+        sample
+    }
+
+    pub fn step(&self, model_output: &Tensor, ts: f64, sample: &Tensor) -> Result<Tensor> {
+        let prev_t = self.previous_timestep(ts);
+
+        let alpha_cumprod = self.alpha_cumprod(ts);
+        let alpha_cumprod_prev = self.alpha_cumprod(prev_t);
+        let alpha = alpha_cumprod / alpha_cumprod_prev;
+
+        let mu = (sample - model_output * ((1. - alpha) / (1. - alpha_cumprod).sqrt()))?;
+        let mu = (mu * (1. / alpha).sqrt())?;
+
+        let std_noise = mu.randn_like(0., 1.)?;
+        let std =
+            std_noise * ((1. - alpha) * (1. - alpha_cumprod_prev) / (1. - alpha_cumprod)).sqrt();
+        if prev_t == 0. {
+            Ok(mu)
+        } else {
+            mu + std
+        }
+    }
+
+    pub fn init_noise_sigma(&self) -> f64 {
+        self.init_noise_sigma
+    }
+}

candle-transformers/src/models/wuerstchen/mod.rs

@@ -1,4 +1,5 @@
 pub mod common;
+pub mod ddpm;
 pub mod diffnext;
 pub mod paella_vq;
 pub mod prior;