Fixed bug 4920 - Wider support for seconds of battery life left on Linux platforms using sys interface

Murad

On my system, SDL_GetPowerInfo() returns -1 seconds of battery life left. I have quickly investigated that in my case SDL uses sys interface to get battery data. It tries to read "time_to_empty_now" file which is not always present. However, it is still possible to calculate remaining lifetime using "energy_now" and "power_now" files. This is what my simple patch (included as attachment) tries to accomplish.
Best wishes.

src/power/linux/SDL_syspower.c

@@ -451,6 +451,8 @@ SDL_GetPowerInfo_Linux_sys_class_power_supply(SDL_PowerState *state, int *second
         SDL_PowerState st;
         int secs;
         int pct;
+        int energy;
+        int power;
 
         if ((SDL_strcmp(name, ".") == 0) || (SDL_strcmp(name, "..") == 0)) {
             continue;  /* skip these, of course. */
@@ -492,11 +494,16 @@ SDL_GetPowerInfo_Linux_sys_class_power_supply(SDL_PowerState *state, int *second
             pct = (pct > 100) ? 100 : pct; /* clamp between 0%, 100% */
         }
 
-        if (!read_power_file(base, name, "time_to_empty_now", str, sizeof (str))) {
-            secs = -1;
-        } else {
+        if (read_power_file(base, name, "time_to_empty_now", str, sizeof (str))) {
             secs = SDL_atoi(str);
             secs = (secs <= 0) ? -1 : secs;  /* 0 == unknown */
+        } else if (st == SDL_POWERSTATE_ON_BATTERY) {
+            /* energy is Watt*hours and power is Watts */
+            energy = (read_power_file(base, name, "energy_now", str, sizeof (str))) ? SDL_atoi(str) : -1;
+            power = (read_power_file(base, name, "power_now", str, sizeof (str))) ? SDL_atoi(str) : -1;
+            secs = (energy >= 0 && power > 0) ? (3600LL * energy) / power : -1;
+        } else {
+            secs = -1;
         }
 
         /*