Add "time_format" parameter; update time string every "fps_sampling_period" interval

See std::put_time docs for supported formatting

src/overlay.cpp

@@ -211,6 +211,7 @@ struct swapchain_data {
    double frametimeDisplay;
    const char* cpuString;
    const char* gpuString;
+   std::string time;
 
    enum overlay_param_enabled stat_selector;
    double time_dividor;
@@ -999,6 +1000,12 @@ static void snapshot_swapchain_frame(struct swapchain_data *data)
 
             data->frametimeDisplay = data->frametime;
             data->fps = fps;
+
+            std::time_t t = std::time(nullptr);
+            std::stringstream time;
+            time << std::put_time(std::localtime(&t), instance_data->params.time_format.c_str());
+            data->time = time.str();
+
          if (instance_data->capture_started) {
             if (!instance_data->first_line_printed) {
                bool first_column = true;
@@ -1114,12 +1121,7 @@ static void compute_swapchain_display(struct swapchain_data *data)
    if (!instance_data->params.no_display){
       ImGui::Begin("Main", &open, ImGuiWindowFlags_NoDecoration);
       if (instance_data->params.enabled[OVERLAY_PARAM_ENABLED_time]){
-         std::time_t t = std::time(nullptr);
+         ImGui::TextColored(ImVec4(1.0f, 1.0f, 1.0f, 1.00f), "%s", data->time.c_str());
-         std::stringstream time;
-         time << std::put_time(std::localtime(&t), "%T");
-         ImGui::PushFont(data->font1);
-         ImGui::TextColored(ImVec4(1.0f, 1.0f, 1.0f, 1.00f), "%s", time.str().c_str());
-         ImGui::PopFont();
       }
       if (device_data->gpu_stats && instance_data->params.enabled[OVERLAY_PARAM_ENABLED_gpu_stats]){
          ImGui::TextColored(ImVec4(0.180, 0.592, 0.384, 1.00f), "GPU");

src/overlay_params.cpp

@@ -136,11 +136,18 @@ parse_unsigned(const char *str)
    return strtol(str, NULL, 0);
 }
 
+static const char *
+parse_str(const char *str)
+{
+   return str;
+}
+
 #define parse_width(s) parse_unsigned(s)
 #define parse_height(s) parse_unsigned(s)
 #define parse_vsync(s) parse_unsigned(s)
 #define parse_offset_x(s) parse_unsigned(s)
 #define parse_offset_y(s) parse_unsigned(s)
+#define parse_time_format(s) parse_str(s)
 
 #define parse_crosshair_color(s) parse_color(s)
 
@@ -259,7 +266,7 @@ parse_overlay_config(struct overlay_params *params,
                   const char *env)
 {
 
-   memset(params, 0, sizeof(*params));
+   *params = {};
 
    /* Visible by default */
    params->enabled[OVERLAY_PARAM_ENABLED_fps] = true;
@@ -285,6 +292,7 @@ parse_overlay_config(struct overlay_params *params,
    params->offset_x = 0;
    params->offset_y = 0;
    params->background_alpha = 0.5;
+   params->time_format = "%T";
 
    // first pass with env var
    if (env)

src/overlay_params.h

@@ -24,6 +24,8 @@
 #ifndef OVERLAY_PARAMS_H
 #define OVERLAY_PARAMS_H
 
+#include <string>
+
 #ifdef __cplusplus
 extern "C" {
 #endif
@@ -68,6 +70,7 @@ extern "C" {
    OVERLAY_PARAM_CUSTOM(offset_y)                    \
    OVERLAY_PARAM_CUSTOM(crosshair_color)             \
    OVERLAY_PARAM_CUSTOM(background_alpha)            \
+   OVERLAY_PARAM_CUSTOM(time_format)                 \
    OVERLAY_PARAM_CUSTOM(help)
 
 enum overlay_param_position {
@@ -108,6 +111,7 @@ struct overlay_params {
    KeySym toggle_hud;
    KeySym toggle_logging;
    KeySym refresh_config;
+   std::string time_format;
 };
 
 const extern char *overlay_param_names[];