feat: add SmoothStep Scheduler (#813)

denoiser.hpp

@@ -251,6 +251,35 @@ struct KarrasSchedule : SigmaSchedule {
     }
 };
 
+// Close to Beta Schedule, but increadably simple in code.
+struct SmoothStepSchedule : SigmaSchedule {
+    static constexpr float smoothstep(float x) {
+        return x * x * (3.0f - 2.0f * x);
+    }
+
+    std::vector<float> get_sigmas(uint32_t n, float /*sigma_min*/, float /*sigma_max*/, t_to_sigma_t t_to_sigma) override {
+        std::vector<float> result;
+        result.reserve(n + 1);
+
+        const int t_max = TIMESTEPS - 1;
+        if (n == 0) {
+            return result;
+        } else if (n == 1) {
+            result.push_back(t_to_sigma((float)t_max));
+            result.push_back(0.f);
+            return result;
+        }
+
+        for (uint32_t i = 0; i < n; i++) {
+            float u = 1.f - float(i) / float(n);
+            result.push_back(t_to_sigma(std::round(smoothstep(u) * t_max)));
+        }
+
+        result.push_back(0.f);
+        return result;
+    }
+};
+
 struct Denoiser {
     std::shared_ptr<SigmaSchedule> scheduler                                                 = std::make_shared<DiscreteSchedule>();
     virtual float sigma_min()                                                                = 0;

examples/cli/main.cpp

@@ -238,7 +238,7 @@ void print_usage(int argc, const char* argv[]) {
     printf("  --skip-layers LAYERS               Layers to skip for SLG steps: (default: [7,8,9])\n");
     printf("  --skip-layer-start START           SLG enabling point: (default: 0.01)\n");
     printf("  --skip-layer-end END               SLG disabling point: (default: 0.2)\n");
-    printf("  --scheduler {discrete, karras, exponential, ays, gits} Denoiser sigma scheduler (default: discrete)\n");
+    printf("  --scheduler {discrete, karras, exponential, ays, gits, smoothstep} Denoiser sigma scheduler (default: discrete)\n");
     printf("  --sampling-method {euler, euler_a, heun, dpm2, dpm++2s_a, dpm++2m, dpm++2mv2, ipndm, ipndm_v, lcm, ddim_trailing, tcd}\n");
     printf("                                     sampling method (default: \"euler_a\")\n");
     printf("  --steps  STEPS                     number of sample steps (default: 20)\n");
@@ -251,7 +251,7 @@ void print_usage(int argc, const char* argv[]) {
     printf("  --high-noise-skip-layers LAYERS    (high noise) Layers to skip for SLG steps: (default: [7,8,9])\n");
     printf("  --high-noise-skip-layer-start      (high noise) SLG enabling point: (default: 0.01)\n");
     printf("  --high-noise-skip-layer-end END    (high noise) SLG disabling point: (default: 0.2)\n");
-    printf("  --high-noise-scheduler {discrete, karras, exponential, ays, gits} Denoiser sigma scheduler (default: discrete)\n");
+    printf("  --high-noise-scheduler {discrete, karras, exponential, ays, gits, smoothstep} Denoiser sigma scheduler (default: discrete)\n");
     printf("  --high-noise-sampling-method {euler, euler_a, heun, dpm2, dpm++2s_a, dpm++2m, dpm++2mv2, ipndm, ipndm_v, lcm, ddim_trailing, tcd}\n");
     printf("                                     (high noise) sampling method (default: \"euler_a\")\n");
     printf("  --high-noise-steps  STEPS          (high noise) number of sample steps (default: -1 = auto)\n");

stable-diffusion.cpp

@@ -751,6 +751,10 @@ public:
                 denoiser->scheduler          = std::make_shared<GITSSchedule>();
                 denoiser->scheduler->version = version;
                 break;
+            case SMOOTHSTEP:
+                LOG_INFO("Running with SmoothStep scheduler");
+                denoiser->scheduler = std::make_shared<SmoothStepSchedule>();
+                break;
             case DEFAULT:
                 // Don't touch anything.
                 break;
@@ -1534,6 +1538,7 @@ const char* schedule_to_str[] = {
     "exponential",
     "ays",
     "gits",
+    "smoothstep",
 };
 
 const char* sd_schedule_name(enum scheduler_t scheduler) {

stable-diffusion.h

@@ -57,6 +57,7 @@ enum scheduler_t {
     EXPONENTIAL,
     AYS,
     GITS,
+    SMOOTHSTEP,
     SCHEDULE_COUNT
 };