Implement OASIS file writer

cpp/modmesh/CMakeLists.txt

@@ -35,6 +35,7 @@ add_subdirectory(mesh)
 add_subdirectory(toggle)
 add_subdirectory(universe)
 add_subdirectory(onedim)
+add_subdirectory(oasis)
 add_subdirectory(multidim)
 add_subdirectory(python)
 add_subdirectory(spacetime)
@@ -91,6 +92,7 @@ set(MODMESH_TERMINAL_FILES
     ${MODMESH_MULTIDIM_FILES}
     ${MODMESH_DEVICE_FILES}
     ${MODMESH_ONEDIM_FILES}
+    ${MODMESH_OASIS_FILES}
     ${MODMESH_SPACETIME_FILES}
     ${MODMESH_PYTHON_FILES}
     ${MODMESH_INOUT_FILES}

cpp/modmesh/oasis/CMakeLists.txt

@@ -0,0 +1,30 @@
+# Copyright (c) 2026, Han-Xuan Huang <c1ydehhx@gmail.com>
+# BSD-style license; see COPYING
+
+cmake_minimum_required(VERSION 4.0.1)
+
+set(MODMESH_OASIS_HEADERS
+    ${CMAKE_CURRENT_SOURCE_DIR}/oasis_device.hpp
+    CACHE FILEPATH "" FORCE)
+
+set(MODMESH_OASIS_SOURCES
+    ${CMAKE_CURRENT_SOURCE_DIR}/oasis_device.cpp
+    CACHE FILEPATH "" FORCE)
+
+set(MODMESH_OASIS_PYMODHEADERS
+    ${CMAKE_CURRENT_SOURCE_DIR}/pymod/oasis_pymod.hpp
+    CACHE FILEPATH "" FORCE)
+
+set(MODMESH_OASIS_PYMODSOURCES
+    ${CMAKE_CURRENT_SOURCE_DIR}/pymod/oasis_pymod.cpp
+    ${CMAKE_CURRENT_SOURCE_DIR}/pymod/wrap_oasis.cpp
+    CACHE FILEPATH "" FORCE)
+
+set(MODMESH_OASIS_FILES
+    ${MODMESH_OASIS_HEADERS}
+    ${MODMESH_OASIS_SOURCES}
+    ${MODMESH_OASIS_PYMODHEADERS}
+    ${MODMESH_OASIS_PYMODSOURCES}
+    CACHE FILEPATH "" FORCE)
+
+# vim: set ff=unix fenc=utf8 nobomb et sw=4 ts=4 sts=4:

cpp/modmesh/oasis/oasis_device.cpp

@@ -0,0 +1,302 @@
+/*
+ * Copyright (c) 2026, Han-Xuan Huang <c1ydehhx@gmail.com>
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * - Redistributions of source code must retain the above copyright notice,
+ *   this list of conditions and the following disclaimer.
+ * - Redistributions in binary form must reproduce the above copyright notice,
+ *   this list of conditions and the following disclaimer in the documentation
+ *   and/or other materials provided with the distribution.
+ * - Neither the name of the copyright holder nor the names of its contributors
+ *   may be used to endorse or promote products derived from this software
+ *   without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <modmesh/oasis/oasis_device.hpp>
+#include <cstdint>
+#include <utility>
+
+namespace modmesh
+{
+
+/*
+ * Convert value to OASIS unsigned integer bytes and append to segment array.
+ * Encodes payload as a base-128 variable-length sequence, emitting 7 data
+ * bits per byte and using the MSB as a continuation flag.
+ * Refer OASIS Draft 7.2.1 for more information.
+ */
+void OasisDevice::append_unsigned_integer(std::vector<uint8_t> & segment, int value)
+{
+    int payload = value;
+
+    if (payload == 0)
+    {
+        segment.push_back(0x00);
+    }
+
+    while (payload >= 1)
+    {
+        int first_bit = payload >= 128 ? 1 : 0;
+        segment.push_back((first_bit << 7) | (payload % 128));
+        payload /= 128;
+    }
+}
+
+/*
+ * Convert value to OASIS signed integer bytes and append to segment array.
+ * 1. DIR_BIT will be 1 if value is negative, otherwise, DIRBIT will be 0.
+ * 2. The payload will left-shift 1 bit on value and do OR with DIR_BIT.
+ * 3. Encodes payload as a base-128 variable-length sequence, emitting 7 data
+ *    bits per byte and using the MSB as a continuation flag. This operation is
+ *    as same as OASIS unsigned interger bytes.
+ * Refer OASIS Draft 7.2.2 for more information.
+ */
+void OasisDevice::append_signed_integer(std::vector<uint8_t> & segment, int value)
+{
+    const int DIR_BIT = value < 0 ? 1 : 0;
+    int delta_codec = abs(value) << 1 | DIR_BIT;
+
+    int payload = delta_codec;
+
+    if (payload == 0)
+    {
+        segment.push_back(0x02);
+    }
+
+    while (payload >= 1)
+    {
+        int first_bit = payload >= 128 ? 1 : 0;
+        segment.push_back((first_bit << 7) | (payload % 128));
+        payload /= 128;
+    }
+}
+
+std::vector<uint8_t> OasisRecordRect::to_bytes() const
+{
+    // RECTANGLE record should be
+    // '20' info-bytes [layer] [datatype] [w] [h] [x] [y] [repetition]
+    // Please refer OASIS Draft section 25.
+    std::vector<uint8_t> segment;
+
+    segment.push_back(0x14);
+
+    const int S = (m_w == m_h); // Is square? (1 if yes, 0 if no)
+    const int W = 1; // Have width? (1 if yes, 0 if no)
+    const int H = (m_w != m_h); // Have height? (1 if yes, 0 if no, must be 0 if S = 1)
+    const int X = 1;
+    const int Y = 1;
+    const int R = 0;
+    const int D = 1; // Have Datatype? (1 if yes, 0 if no)
+    const int L = 1; // Have Layer? (1 if yes, 0 if no)
+
+    const int INFO = (S << 7) | (W << 6) | (H << 5) |
+                     (X << 4) | (Y << 3) | (R << 2) | (D << 1) | L;
+    segment.push_back(INFO);
+
+    // Layer-num and datatype-num (0 in default).
+    segment.push_back(0x00);
+    segment.push_back(0x00);
+
+    OasisDevice::append_unsigned_integer(segment, m_w);
+    OasisDevice::append_unsigned_integer(segment, m_h);
+    OasisDevice::append_signed_integer(segment, m_left);
+    OasisDevice::append_signed_integer(segment, m_lower);
+
+    return segment;
+}
+
+std::vector<uint8_t> OasisRecordPoly::to_bytes() const
+{
+    // Polygon record should be
+    // '21' 00PXYRDL [layer-num] [datatype-num] [point-list] [x] [y] [rep]
+    // Please refer OASIS Draft section 26.
+    std::vector<uint8_t> segment;
+
+    segment.push_back(0x15);
+
+    // Info bytes:
+    // - Have point-list, X and Y.
+    // - Have datatype and layer (Use 0)
+    const int P = 1; // Have Polygon-List? (1 if yes, 0 if no)
+    const int X = 1;
+    const int Y = 1;
+    const int R = 0;
+    const int D = 1; // Have Datatype? (1 if yes, 0 if no)
+    const int L = 1; // Have Layer? (1 if yes, 0 if no)
+    const int INFO = (P << 5) | (X << 4) | (Y << 3) | (R << 2) | (D << 1) | L;
+    segment.push_back(INFO);
+
+    // Layer-num and datatype-num (0 in default).
+    segment.push_back(0x00);
+    segment.push_back(0x00);
+
+    // The 1-Delta have two different type:
+    //  - Type 0: Start with horizontal
+    //  - Type 1: Start with vertical
+    if (m_vertices[0].second == m_vertices[1].second)
+    {
+        segment.push_back(0x00);
+    }
+    else if (m_vertices[0].first == m_vertices[0].first)
+    {
+        segment.push_back(0x01);
+    }
+
+    // The vertex count shoud be (vertex - 1)
+    segment.push_back(m_vertices.size() - 1);
+
+    // In this implementation, point-list only support 1-delta format.
+    // Please refer Point-list in OASIS draft 7.7.
+    std::vector<uint8_t> point_list;
+
+    for (int i = 0; i < m_vertices.size() - 1; i++)
+    {
+        std::pair<int, int> curr_v = m_vertices[i];
+        std::pair<int, int> next_v = m_vertices[i + 1];
+
+        // Convert delta value to OASIS signed interegr bytes.
+        OasisDevice::append_signed_integer(
+            point_list,
+            (next_v.first - curr_v.first) + (next_v.second - curr_v.second));
+    }
+
+    segment.insert(segment.end(), point_list.begin(), point_list.end());
+
+    // X value
+    OasisDevice::append_signed_integer(segment, m_vertices[0].first);
+
+    // Y value
+    OasisDevice::append_signed_integer(segment, m_vertices[0].second);
+
+    return segment;
+}
+
+std::vector<uint8_t> OasisDevice::to_bytes()
+{
+    // The simple OASIS byte format should be:
+    // <magic-byte> <START>
+    // <CELLNAME> <CELL>
+    // <GEOMETRY_RECORD_1> <GEOMETRY_RECORD_2> ... <GEOMETRY_RECORD_N>
+    // <END>
+    std::vector<uint8_t> result;
+
+    append_magic_bytes(result);
+    append_start_record_bytes(result);
+    append_cell_and_cell_name_record_byte(result);
+
+    for (const OasisRecordRect & record : m_rect_records)
+    {
+        append_record_bytes(result, record);
+    }
+
+    for (const OasisRecordPoly & record : m_polygon_records)
+    {
+        append_record_bytes(result, record);
+    }
+
+    append_end_record_byte(result);
+
+    return result;
+}
+
+void OasisDevice::add_poly_record(const OasisRecordPoly & record)
+{
+    m_polygon_records.push_back(record);
+}
+
+void OasisDevice::add_rect_record(const OasisRecordRect & record)
+{
+    m_rect_records.push_back(record);
+}
+
+void OasisDevice::append_magic_bytes(std::vector<uint8_t> & segment)
+{
+    // Magic byte should be %SEMI-OASIS<CR><NL>, which <CR><NL> is 0x0D 0x0A.
+    // Please refer OASIS Draft section 6.4.
+
+    std::string magic_byte = "%SEMI-OASIS\x0D\x0A";
+
+    segment.insert(segment.end(), magic_byte.begin(), magic_byte.end());
+}
+
+void OasisDevice::append_start_record_bytes(std::vector<uint8_t> & segment)
+{
+    // START record should be
+    // '1' version-string unit offset-flag [ table-offsets ]
+    // Please refer OASIS Draft section 13.
+
+    // The first byte should 1.
+    segment.push_back(0x01);
+
+    // The version string will be [LENGTH][STRING-ASCII], we
+    // fixed it as "1.0".
+    segment.push_back(0x03);
+
+    std::string version = "1.0";
+    segment.insert(segment.end(), version.begin(), version.end());
+
+    // The unit we using 0.001 as default.
+    std::vector<uint8_t> unit = {0x00, 0xE8, 0x07};
+    segment.insert(segment.end(), unit.begin(), unit.end());
+
+    // The offset-flag we using 0x00 as default.
+    // The table-offset will store in END record if offset-flag is 0x01.
+    // We put 6 pairs of 0x00 to describe that we don't have any tables.
+    // Therefore, it insert 13 0x00 in total.
+    segment.insert(segment.end(), 13, 0x00);
+}
+
+void OasisDevice::append_cell_and_cell_name_record_byte(std::vector<uint8_t> & segment)
+{
+    // Append CELLNAME record, the default CELLNAME is TOP.
+    // TODO: This record is fixed. It can be modify by user in the future.
+    std::vector<uint8_t> cellname = {0x03, 03, 0x54, 0x4F, 0x50};
+    segment.insert(segment.end(), cellname.begin(), cellname.end());
+
+    // Append CELL record.
+    // TODO: This record is fixed. It can be modify by user in the future.
+    std::vector<uint8_t> cell = {0x0D, 0x00};
+    segment.insert(segment.end(), cell.begin(), cell.end());
+}
+
+void OasisDevice::append_end_record_byte(std::vector<uint8_t> & segment)
+{
+    // END record should be
+    // '2' [table-offsets] padding validation-scheme [validation-signature]
+    // Please refer OASIS Draft section 14.
+
+    // The first byte should 2.
+    segment.push_back(0x02);
+
+    // Write padding. The padding should be 256 bytes.
+    int padding_length = 254;
+    segment.insert(segment.end(), padding_length, 0x00);
+
+    // Validation-scheme: No validation.
+    segment.push_back(0x00);
+}
+
+template <typename T>
+void OasisDevice::append_record_bytes(std::vector<uint8_t> & bytes, const T & rec)
+{
+    std::vector<uint8_t> rec_bytes = rec.to_bytes();
+    bytes.insert(bytes.end(), rec_bytes.begin(), rec_bytes.end());
+}
+
+} // namespace modmesh
+
+// vim: set ff=unix fenc=utf8 et sw=4 ts=4 sts=4: