fix: display.txt 缺少渲染参数导致盒子不透明

外部引擎（C/C++）直接写 display.txt 时只输出基础物理参数
（DT/NSTEP/method 等），缺少 alpha/ball_color/box_color
等渲染参数，draw.py 读取不到 alpha 回退默认 0.2。

修复：
1. param.json 新增渲染参数（alpha/ball_color/box_color/...）
2. C/C++ 引擎 SimParams 新增对应字段 & JSON 读取
3. C/C++ write_display_txt 写入所有渲染参数 header
4. param.json ball_color/box_color 用数组统一存储

compute.py

@@ -895,6 +895,19 @@ def run_engine(engine, input_dir, output_dir, config):
         "gravity_strength": float(config.get("gravity_strength", 1.0)),
         "driving_force": int(config.get("driving_force", 0)),
         "save_trajectory": int(config.get("save_trajectory", 0)),
+        # 渲染参数（用于 display.txt header）
+        "alpha": config.get("alpha", 0.2),
+        "ball_radius": float(config.get("ball_radius", 0.5)),
+        "ball_color": [float(config.get("ball_color_r", 0.9)),
+                       float(config.get("ball_color_g", 0.2)),
+                       float(config.get("ball_color_b", 0.2))],
+        "box_color": [float(config.get("box_color_r", 0.8)),
+                      float(config.get("box_color_g", 0.8)),
+                      float(config.get("box_color_b", 0.85))],
+        "use_marker": int(config.get("use_marker", 0)),
+        "camera_distance": float(config.get("camera_distance", 40.0)),
+        "camera_elevation": float(config.get("camera_elevation", 0)),
+        "camera_azimuth": float(config.get("camera_azimuth", 0)),
     }
     param_path = os.path.join(script_dir, "engines", engine, "param.json")
     os.makedirs(os.path.dirname(param_path), exist_ok=True)

engines/c/main.c

@@ -39,6 +39,12 @@ typedef struct {
     double  gravity_strength;    /* 万有引力强度 */
     int     driving_force;       /* 驱动力开关 */
     int     save_trajectory;     /* 是否保存完整轨迹文件 */
+    double  alpha[6];            /* 盒子透明度 */
+    double  ball_radius;
+    double  ball_color[3];
+    double  box_color[3];
+    int     use_marker;
+    double  camera_distance, camera_elevation, camera_azimuth;
 } SimParams;
 
 /* ========================================================================
@@ -271,6 +277,20 @@ static void json_read_double3(const char *json, const char *key, double out[3])
     }
 }
 
+static void json_read_double6(const char *json, const char *key, double out[6]) {
+    char search[256];
+    snprintf(search, sizeof(search), "\"%s\"", key);
+    const char *p = strstr(json, search);
+    if (!p) { for (int i=0;i<6;i++) out[i]=0; return; }
+    p = strchr(p, '[');
+    if (!p) { for (int i=0;i<6;i++) out[i]=0; return; }
+    p++;
+    for (int i = 0; i < 6; i++) {
+        while (*p == ' ' || *p == '\t' || *p == '\n' || *p == ',' || *p == ']') p++;
+        out[i] = strtod(p, (char**)&p);
+    }
+}
+
 /* 读取 param.json */
 static int    g_gravity_field = 1;
 static int    g_gravity_interaction = 0;
@@ -306,6 +326,15 @@ static SimParams read_params(const char *path) {
     p.gravity_strength    = json_read_double(buf, "gravity_strength");
     p.driving_force       = json_read_int(buf, "driving_force");
     p.save_trajectory     = json_read_int(buf, "save_trajectory");
+    /* 渲染参数 */
+    json_read_double6(buf, "alpha", p.alpha);
+    p.ball_radius         = json_read_double(buf, "ball_radius");
+    json_read_double3(buf, "ball_color", p.ball_color);
+    json_read_double3(buf, "box_color", p.box_color);
+    p.use_marker          = json_read_int(buf, "use_marker");
+    p.camera_distance     = json_read_double(buf, "camera_distance");
+    p.camera_elevation    = json_read_double(buf, "camera_elevation");
+    p.camera_azimuth      = json_read_double(buf, "camera_azimuth");
     g_gravity_field       = p.gravity_field;
     g_gravity_interaction = p.gravity_interaction;
     g_elastic_force       = p.elastic_force;
@@ -880,6 +909,21 @@ static void write_display_txt(const char *path, const Trajectory *traj,
     fprintf(f, "dynamic_steps: %d\n", dynamic_steps);
     fprintf(f, "T_total: %.16g\n", T_total);
     fprintf(f, "box_a: %.16g\n", params->box_a);
+    fprintf(f, "alpha: %.16g,%.16g,%.16g,%.16g,%.16g,%.16g\n",
+            params->alpha[0], params->alpha[1], params->alpha[2],
+            params->alpha[3], params->alpha[4], params->alpha[5]);
+    fprintf(f, "ball_radius: %.16g\n", params->ball_radius);
+    fprintf(f, "ball_color_r: %.16g\n", params->ball_color[0]);
+    fprintf(f, "ball_color_g: %.16g\n", params->ball_color[1]);
+    fprintf(f, "ball_color_b: %.16g\n", params->ball_color[2]);
+    fprintf(f, "box_color_r: %.16g\n", params->box_color[0]);
+    fprintf(f, "box_color_g: %.16g\n", params->box_color[1]);
+    fprintf(f, "box_color_b: %.16g\n", params->box_color[2]);
+    fprintf(f, "use_marker: %d\n", params->use_marker);
+    fprintf(f, "camera_distance: %.16g\n", params->camera_distance);
+    fprintf(f, "camera_elevation: %.16g\n", params->camera_elevation);
+    fprintf(f, "camera_azimuth: %.16g\n", params->camera_azimuth);
+    fprintf(f, "\n");
 
     if (params->driving_force) {
         fprintf(f, "driving_force: 1\n");

engines/cpp/main.cpp

@@ -44,6 +44,14 @@ struct SimParams {
     double gravity_strength = 1.0;
     int driving_force = 0;
     int save_trajectory = 1;
+    double alpha[6] = {0,0,0,0,0,0};
+    double ball_radius = 0.5;
+    double ball_color[3] = {0.9, 0.2, 0.2};
+    double box_color[3] = {0.8, 0.8, 0.85};
+    int use_marker = 0;
+    double camera_distance = 40.0;
+    double camera_elevation = 0;
+    double camera_azimuth = 0;
 };
 
 // ========================================================================
@@ -152,6 +160,21 @@ static void json_read_double3(const std::string &json, const std::string &key, d
     }
 }
 
+/* 读取 JSON 数组到 double[6] */
+static void json_read_double6(const std::string &json, const std::string &key, double out[6]) {
+    auto pos = json.find("\"" + key + "\"");
+    if (pos == std::string::npos) { for (int i=0;i<6;i++) out[i]=0; return; }
+    pos = json.find('[', pos);
+    if (pos == std::string::npos) { for (int i=0;i<6;i++) out[i]=0; return; }
+    pos++;
+    for (int i = 0; i < 6; i++) {
+        while (pos < json.size() && (json[pos]==' '||json[pos]=='\t'||json[pos]=='\n'||json[pos]==','||json[pos]==']')) pos++;
+        char *end;
+        out[i] = std::strtod(json.c_str() + pos, &end);
+        pos = end - json.c_str();
+    }
+}
+
 /* 解析 param.json */
 static SimParams read_params(const std::string &path) {
     std::string buf = read_file(path);
@@ -174,6 +197,14 @@ static SimParams read_params(const std::string &path) {
     // save_trajectory 默认 1（全量），仅在 JSON 中存在该 key 时覆盖
     if (json_has_key(buf, "save_trajectory"))
         p.save_trajectory = json_read_int(buf, "save_trajectory");
+    json_read_double6(buf, "alpha", p.alpha);
+    p.ball_radius         = json_read_double(buf, "ball_radius");
+    json_read_double3(buf, "ball_color", p.ball_color);
+    json_read_double3(buf, "box_color", p.box_color);
+    p.use_marker          = json_read_int(buf, "use_marker");
+    p.camera_distance     = json_read_double(buf, "camera_distance");
+    p.camera_elevation    = json_read_double(buf, "camera_elevation");
+    p.camera_azimuth      = json_read_double(buf, "camera_azimuth");
     return p;
 }
 
@@ -717,7 +748,20 @@ static void write_display_txt(
     f << "dynamic_steps: " << (params.NT - params.warmup_steps) << "\n";
     f << "T_total: " << T_total << "\n";
     f << "box_a: " << params.box_a << "\n";
-    f << "driving_force: " << params.driving_force << "\n\n";
+    f << "driving_force: " << params.driving_force << "\n";
+    f << "alpha: " << params.alpha[0] << "," << params.alpha[1] << "," << params.alpha[2] << ","
+                   << params.alpha[3] << "," << params.alpha[4] << "," << params.alpha[5] << "\n";
+    f << "ball_radius: " << params.ball_radius << "\n";
+    f << "ball_color_r: " << params.ball_color[0] << "\n";
+    f << "ball_color_g: " << params.ball_color[1] << "\n";
+    f << "ball_color_b: " << params.ball_color[2] << "\n";
+    f << "box_color_r: " << params.box_color[0] << "\n";
+    f << "box_color_g: " << params.box_color[1] << "\n";
+    f << "box_color_b: " << params.box_color[2] << "\n";
+    f << "use_marker: " << params.use_marker << "\n";
+    f << "camera_distance: " << params.camera_distance << "\n";
+    f << "camera_elevation: " << params.camera_elevation << "\n";
+    f << "camera_azimuth: " << params.camera_azimuth << "\n\n";
 
     f << std::fixed << std::setprecision(6);
     for (int t = 0; t < n_steps; t++) {