mtmd: fix LFM2 image tiling threshold (#27057)

* mtmd: fix LFM2 image tiling threshold

* refactor testing

* fix

* fix on windows

---------

Co-authored-by: Xuan Son Nguyen <son@huggingface.co>

tests/CMakeLists.txt

@@ -310,6 +310,9 @@ llama_build_and_test(test-mtmd-c-api.c)
 target_link_libraries(${LLAMA_TEST_NAME} PRIVATE mtmd)
 unset(LLAMA_TEST_NAME)
 
+llama_build_and_test(test-mtmd-impl.cpp)
+target_link_libraries(test-mtmd-impl PRIVATE mtmd)
+
 # GGUF model data fetcher library for tests that need real model metadata
 # Only compile when cpp-httplib has SSL support (CPPHTTPLIB_OPENSSL_SUPPORT)
 if (TARGET cpp-httplib)

tests/test-mtmd-impl.cpp

@@ -0,0 +1,88 @@
+#include "testing.h"
+
+#include "mtmd-image.h"
+
+#include <iostream>
+#include <string>
+#include <utility>
+#include <vector>
+
+// this test file contains:
+// 1. test cases for mtmd helpers
+// 2. test cases for internal mtmd components
+// internal headers can be included here
+
+struct test_registry {
+    using fn_t = void (*)(testing &);
+
+    struct entry {
+        std::string name;
+        fn_t fn;
+    };
+
+    static std::vector<entry> & all() {
+        static std::vector<entry> entries;
+        return entries;
+    }
+
+    test_registry(const char * name, fn_t fn) {
+        all().push_back({ name, fn });
+    }
+};
+
+#define MAKE_TEST(name)                                               \
+    static void name(testing & t);                                    \
+    static const test_registry test_registry_ ## name(#name, &name);  \
+    static void name(testing & t)
+
+
+//
+// mtmd_image
+//
+
+MAKE_TEST(test_image_preprocessor_lfm2) {
+    clip_hparams hparams;
+    hparams.patch_size = 16;
+    hparams.n_merge = 2;
+    hparams.set_limit_image_tokens(64, 256);
+
+    // { image size, expected tiling }
+    const std::vector<std::pair<clip_image_size, bool>> cases = {
+        { {  704, 704 }, false },
+        // 720 / (patch_size * n_merge) is exactly 22.5, so this only matches HF
+        // if round_by_factor rounds half to even (22) instead of away from zero (23)
+        { {  720, 720 }, false },
+        { {  736, 736 }, true  },
+        { { 1024, 977 }, true  },
+        { { 1056, 384 }, false },
+    };
+
+    for (const auto & [size, expected] : cases) {
+        const bool actual = mtmd_image_preprocessor_lfm2::should_tile(hparams, size);
+
+        t.assert_equal(
+            "tiling for " + std::to_string(size.width) + "x" + std::to_string(size.height),
+            std::string(expected ? "tiled" : "single"),
+            std::string(actual   ? "tiled" : "single"));
+    }
+}
+
+//
+// main
+//
+
+int main(int argc, char ** argv) {
+    testing t(std::cout);
+    t.verbose = true;
+
+    // usage: test-mtmd-impl [filter_regex]
+    for (int i = 1; i < argc; i++) {
+        t.set_filter(argv[i]);
+    }
+
+    for (const auto & e : test_registry::all()) {
+        t.test(e.name, e.fn);
+    }
+
+    return t.summary();
+}