mtmd: add pos_0 to mtmd_image_tokens_get_decoder_pos (breaking change) (#22082)

* mtmd: add pos_0 to mtmd_image_tokens_get_decoder_pos

* fix build

tests/test-mtmd-c-api.c

@@ -42,7 +42,7 @@ int main(void) {
             const mtmd_image_tokens * image_tokens = mtmd_input_chunk_get_tokens_image(chunk);
             size_t n_tokens = mtmd_image_tokens_get_n_tokens(image_tokens);
             // get position of the last token, which should be (nx - 1, ny - 1)
-            struct mtmd_decoder_pos pos = mtmd_image_tokens_get_decoder_pos(image_tokens, n_tokens - 1);
+            struct mtmd_decoder_pos pos = mtmd_image_tokens_get_decoder_pos(image_tokens, 0, n_tokens - 1);
             size_t nx = pos.x + 1;
             size_t ny = pos.y + 1;
             const char * id = mtmd_image_tokens_get_id(image_tokens);

tools/mtmd/mtmd-helper.cpp

@@ -114,10 +114,10 @@ llama_pos mtmd_helper_get_n_pos(const mtmd_input_chunks * chunks) {
     return n_pos;
 }
 
-void mtmd_helper_image_get_decoder_pos(const mtmd_image_tokens * chunks, mtmd_decoder_pos * out_pos) {
+void mtmd_helper_image_get_decoder_pos(const mtmd_image_tokens * chunks, llama_pos pos_0, mtmd_decoder_pos * out_pos) {
     size_t n_tokens = mtmd_image_tokens_get_n_tokens(chunks);
     for (size_t i = 0; i < n_tokens; i++) {
-        out_pos[i] = mtmd_image_tokens_get_decoder_pos(chunks, i);
+        out_pos[i] = mtmd_image_tokens_get_decoder_pos(chunks, pos_0, i);
     }
 }
 
@@ -163,15 +163,15 @@ struct decode_embd_batch {
     }
 
     // M-RoPE for image
-    void set_position_mrope_2d(llama_pos pos_0, const std::vector<mtmd_decoder_pos> & rel_pos, llama_seq_id seq_id) {
+    void set_position_mrope_2d(const std::vector<mtmd_decoder_pos> & rel_pos, llama_seq_id seq_id) {
         GGML_ASSERT(n_pos_per_embd == 4);
         GGML_ASSERT(!rel_pos.empty() && (int32_t)rel_pos.size() == batch.n_tokens);
         seq_id_0[0] = seq_id;
         for (int32_t i = 0; i < batch.n_tokens; i++) {
-            pos[i                     ] = pos_0 + rel_pos[i].t;
+            pos[i                     ] = rel_pos[i].t;
-            pos[i + batch.n_tokens    ] = pos_0 + rel_pos[i].y;
+            pos[i + batch.n_tokens    ] = rel_pos[i].y;
-            pos[i + batch.n_tokens * 2] = pos_0 + rel_pos[i].x;
+            pos[i + batch.n_tokens * 2] = rel_pos[i].x;
-            pos[i + batch.n_tokens * 3] = 0; // last pos dim is unused
+            pos[i + batch.n_tokens * 3] = rel_pos[i].z;
         }
         for (int i = 0; i < batch.n_tokens; i++) {
             batch.n_seq_id[i] = 1;
@@ -188,7 +188,7 @@ struct decode_embd_batch {
             pos[i                     ] = pos_0 + i;
             pos[i + batch.n_tokens    ] = pos_0 + i;
             pos[i + batch.n_tokens * 2] = pos_0 + i;
-            pos[i + batch.n_tokens * 3] = 0; // last pos dim is unused
+            pos[i + batch.n_tokens * 3] = pos_0 + i;
         }
         for (int i = 0; i < batch.n_tokens; i++) {
             batch.n_seq_id[i] = 1;
@@ -268,8 +268,8 @@ int32_t mtmd_helper_decode_image_chunk(
             }
             const auto n_tokens = mtmd_image_tokens_get_n_tokens(image_tokens);
             std::vector<mtmd_decoder_pos> rel_pos(n_tokens);
-            mtmd_helper_image_get_decoder_pos(image_tokens, rel_pos.data());
+            mtmd_helper_image_get_decoder_pos(image_tokens, n_past, rel_pos.data());
-            batch_embd.set_position_mrope_2d(n_past, rel_pos, seq_id);
+            batch_embd.set_position_mrope_2d(rel_pos, seq_id);
         } else if (chunk_type == MTMD_INPUT_CHUNK_TYPE_AUDIO) {
             batch_embd.set_position_mrope_1d(n_past, seq_id);
         } else {

tools/mtmd/mtmd-helper.h

@@ -49,7 +49,7 @@ MTMD_API llama_pos mtmd_helper_get_n_pos(const mtmd_input_chunks * chunks);
 
 // helper to get the list of relative positions corresponding to the embedding tokens, to be used by M-RoPE
 // out_pos must have length == mtmd_helper_get_n_tokens(image)
-MTMD_API void mtmd_helper_image_get_decoder_pos(const mtmd_image_tokens * image, struct mtmd_decoder_pos * out_pos);
+MTMD_API void mtmd_helper_image_get_decoder_pos(const mtmd_image_tokens * image, llama_pos pos_0, struct mtmd_decoder_pos * out_pos);
 
 // helper function that automatically:
 // 1. run llama_decode() on text chunks

tools/mtmd/mtmd.cpp

@@ -1246,11 +1246,14 @@ size_t mtmd_image_tokens_get_ny(const mtmd_image_tokens * image_tokens) {
     return image_tokens->ny;
 }
 
-mtmd_decoder_pos mtmd_image_tokens_get_decoder_pos(const mtmd_image_tokens * image_tokens, size_t i) {
+mtmd_decoder_pos mtmd_image_tokens_get_decoder_pos(const mtmd_image_tokens * image_tokens, llama_pos pos_0, size_t i) {
     mtmd_decoder_pos pos;
-    pos.t = 0;
+    // M-RoPE logic
-    pos.x = i % image_tokens->nx;
+    // TODO: support other types of position encoding if needed
-    pos.y = i / image_tokens->nx;
+    pos.t = pos_0;
+    pos.x = pos_0 + (i % image_tokens->nx);
+    pos.y = pos_0 + (i / image_tokens->nx);
+    pos.z = 0; // unused for now
     return pos;
 }
 

tools/mtmd/mtmd.h

@@ -196,11 +196,13 @@ struct mtmd_decoder_pos {
     uint32_t t;
     uint32_t x;
     uint32_t y;
+    uint32_t z; // unused for now, reserved for future use
 };
 // get position for decoder attention, to be used by M-RoPE models
 // i is the index of the embedding token, ranging from 0 to mtmd_image_tokens_get_n_tokens() - 1
+// pos_0 is the absolute position of the first token
 // return relative position (for example, embedding 0 will have position (0, 0, 0); remember to adjust it to the current absolute position)
-MTMD_API struct mtmd_decoder_pos mtmd_image_tokens_get_decoder_pos(const mtmd_image_tokens * image_tokens, size_t i);
+MTMD_API struct mtmd_decoder_pos mtmd_image_tokens_get_decoder_pos(const mtmd_image_tokens * image_tokens, llama_pos pos_0, size_t i);
 
 // tokenize an input text prompt and a list of bitmaps (images/audio)
 // the prompt must have the input image marker (default: "<__media__>") in it