refactor: centralize model factories and defaults (#2198)

src/model_definition.h

@@ -0,0 +1,47 @@
+#ifndef __SD_MODEL_DEFINITION_H__
+#define __SD_MODEL_DEFINITION_H__
+
+#include <limits>
+#include "model.h"
+#include "stable-diffusion.h"
+
+class TokenizerConfig;
+struct VAE;
+namespace sd::model_builders {
+    struct Context;
+    struct CoreRunners;
+    struct VAEOptions;
+}
+
+struct ModelSamplingPolicy {
+    prediction_t default_prediction       = EPS_PRED;
+    float default_flow_shift              = std::numeric_limits<float>::infinity();
+    sample_method_t default_sample_method = EULER_A_SAMPLE_METHOD;
+    scheduler_t default_scheduler         = DISCRETE_SCHEDULER;
+
+    bool probe_v_prediction = false;
+
+    prediction_t (*prediction_from_weights)(const String2TensorStorage&) = nullptr;
+    float (*flow_shift_from_weights)(const String2TensorStorage&)        = nullptr;
+};
+
+struct ModelGeometry {
+    int diffusion_down_factor = 8;
+    int latent_channels       = 4;
+    int image_channels        = 3;
+};
+
+struct ModelDefinition {
+    SDVersion version = VERSION_COUNT;
+    const char* name  = nullptr;
+    ModelTraits traits;
+    ModelSamplingPolicy sampling;
+    ModelGeometry geometry;
+    const char* ref_image_preset                                                                                = "default";
+    void (*configure_vae)(const sd::model_builders::Context&, const sd::model_builders::VAEOptions&, VAE&)      = nullptr;
+    bool (*build)(const sd::model_builders::Context&, const TokenizerConfig&, sd::model_builders::CoreRunners&) = nullptr;
+};
+
+const ModelDefinition* find_model_definition(SDVersion version);
+
+#endif  // __SD_MODEL_DEFINITION_H__