PRVM: reset GETTIME_FRAMESTART at VM startup, improve documentation

Avoids precision issues on servers with long GETTIME_UPTIME.

Signed-off-by: bones_was_here <[email protected]>

dpdefs/csprogsdefs.qc

@@ -1008,10 +1008,10 @@ string(string format, ...) sprintf = #627;
 //idea: tZork
 //darkplaces implementation: tZork, divVerent
 //constant definitions:
-float GETTIME_FRAMESTART = 0; // time of start of frame
+float GETTIME_FRAMESTART = 0; // time of start of frame relative to an arbitrary point in time (time of worldspawn)
 float GETTIME_REALTIME = 1; // current time (may be OS specific)
-float GETTIME_HIRES = 2; // like REALTIME, but may reset between QC invocations and thus can be higher precision
-float GETTIME_UPTIME = 3; // time since start of the engine
+float GETTIME_HIRES = 2; // like REALTIME, but relative to time at start of frame (thus can be higher precision)
+float GETTIME_UPTIME = 3; // time of start of frame relative to start of the engine
 //builtin definitions:
 float(float tmr) gettime = #519;
 //description:

dpdefs/dpextensions.qc

@@ -896,10 +896,10 @@ vector gettaginfo_up;
 //idea: tZork
 //darkplaces implementation: tZork, divVerent
 //constant definitions:
-float GETTIME_FRAMESTART = 0; // time of start of frame relative to an arbitrary point in time
+float GETTIME_FRAMESTART = 0; // time of start of frame relative to an arbitrary point in time (time of worldspawn)
 float GETTIME_REALTIME = 1; // current absolute time (OS specific)
-float GETTIME_HIRES = 2; // like REALTIME, but may reset between QC invocations and thus can be higher precision
-float GETTIME_UPTIME = 3; // time of start of frame since start of the engine
+float GETTIME_HIRES = 2; // like REALTIME, but relative to time at start of frame (thus can be higher precision)
+float GETTIME_UPTIME = 3; // time of start of frame relative to start of the engine
 //builtin definitions:
 float(float tmr) gettime = #519;
 //description:

prvm_cmds.c

@@ -2961,7 +2961,7 @@ void VM_gettime(prvm_prog_t *prog)
 		switch(timer_index)
 		{
 			case 0: // GETTIME_FRAMESTART
-				PRVM_G_FLOAT(OFS_RETURN) = host.realtime;
+				PRVM_G_FLOAT(OFS_RETURN) = host.realtime - prog->starttime;
 				break;
 			case 1: // GETTIME_REALTIME
 				PRVM_G_FLOAT(OFS_RETURN) = Sys_DirtyTime();