mtmd : move helpers to dedicated library (⚠️ breaking change) (#13866)

* mtmd : move helpers to dedicated library

* fix server build

* rm leftover cmakelist code

tools/mtmd/mtmd-helper.h

@@ -0,0 +1,91 @@
+#ifndef MTMD_HELPER_H
+#define MTMD_HELPER_H
+
+#include "ggml.h"
+#include "llama.h"
+#include "mtmd.h"
+
+#include <stddef.h>
+#include <stdint.h>
+#include <stdbool.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+//
+// libmtmd helper functions
+//
+// Please note that these helpers are not guaranteed to be stable.
+// BREAKING CHANGES are expected.
+//
+
+// helper function to construct a mtmd_bitmap from a file
+// it calls mtmd_helper_bitmap_init_from_buf() internally
+// returns nullptr on failure
+// this function is thread-safe
+MTMD_API mtmd_bitmap * mtmd_helper_bitmap_init_from_file(mtmd_context * ctx, const char * fname);
+
+// helper function to construct a mtmd_bitmap from a buffer containing a file
+// supported formats:
+//     image: formats supported by stb_image: jpg, png, bmp, gif, etc.
+//     audio: formats supported by miniaudio: wav, mp3, flac
+// note: audio files will be auto-detected based on magic bytes
+// returns nullptr on failure
+// this function is thread-safe
+MTMD_API mtmd_bitmap * mtmd_helper_bitmap_init_from_buf(mtmd_context * ctx, const unsigned char * buf, size_t len);
+
+// helper to count the total number of tokens from a list of chunks, useful to keep track of KV cache
+MTMD_API size_t mtmd_helper_get_n_tokens(const mtmd_input_chunks * chunks);
+
+// helper to count the total position of tokens from a list of chunks, useful to keep track of n_past
+// normally, n_pos is equal to n_tokens, but for M-RoPE it is different
+MTMD_API llama_pos mtmd_helper_get_n_pos(const mtmd_input_chunks * chunks);
+
+// helper function that automatically:
+// 1. run llama_decode() on text chunks
+// 2. run mtmd_encode() on image chunks, then mtmd_get_output_embd() and then llama_decode()
+// if any of the mtmd_encode() or llama_decode() calls return non-zero, stop and forward the error
+// otherwise, returns 0 on success
+// this function is NOT thread-safe
+MTMD_API int32_t mtmd_helper_eval_chunks(mtmd_context * ctx,
+                                         struct llama_context * lctx,
+                                         const mtmd_input_chunks * chunks,
+                                         llama_pos n_past,
+                                         llama_seq_id seq_id,
+                                         int32_t n_batch,
+                                         bool logits_last,
+                                         llama_pos * new_n_past);
+
+// works like mtmd_helper_eval_chunks(), but only for a single chunk
+// this function is NOT thread-safe
+MTMD_API int32_t mtmd_helper_eval_chunk_single(mtmd_context * ctx,
+                                               struct llama_context * lctx,
+                                               const mtmd_input_chunk * chunk,
+                                               llama_pos n_past,
+                                               llama_seq_id seq_id,
+                                               int32_t n_batch,
+                                               bool logits_last,
+                                               llama_pos * new_n_past);
+
+// helper function to decode an image whose embeddings have already been calculated
+// this helper will handle batching and pre/post decoding setup (for ex. gemma 3 requires non-causal attention)
+// ret 0 on success, -1 on chunk not being a valid image chunk, 1 on decode failure
+MTMD_API int32_t mtmd_helper_decode_image_chunk(mtmd_context * ctx,
+                                                struct llama_context * lctx,
+                                                const mtmd_input_chunk * chunk,
+                                                float * encoded_embd,
+                                                llama_pos n_past,
+                                                llama_seq_id seq_id,
+                                                int32_t n_batch,
+                                                llama_pos * new_n_past);
+
+#ifdef __cplusplus
+} // extern "C"
+#endif
+
+//
+// C++ wrappers
+//
+
+#endif