On the minimum laptop, heat decides
On 16 September the studio made the laptop the game is built on its minimum hardware: Intel HD Graphics 5500, two cores. At the Medium preset the homeland walk was well under its 60-frame cap. The pass that evening set out to remove the largest costs that could go without changing the picture.
Measured tick by tick
A hot laptop makes two versions hard to compare, so every run advanced the simulation exactly one tick per drawn frame. Each run saw the same positions and ended on the same final frame, and that frame’s hash doubled as proof that the picture had not changed. Old and new versions ran alternately. Each run waited until the laptop was at or below 72 °C and was stopped at 105 °C.
What it bought
The largest cost was skinning the bodies on the CPU, about 12 ms a frame. GPU skinning had been written off on the belief that this version of raylib had no path for bone matrices. Reading what the engine actually does showed that it skips its CPU skin when a mesh’s skin buffers are empty and still composes the matrices. After a 20-line probe, skinning costs 0.07 ms a frame. In the walk’s final frame, 37 of 921,600 pixels differ from the CPU-skinned version, by at most 12 levels in 255.
Smaller costs came out of Python. A 120-triangle contact sheet, the patch of shadow under a body’s feet, took 2.0 ms through the convenient binding and 0.13 ms submitted directly. Two runs of a scripted Human walk through the Bell Towns drew 30.97 and 24.67 frames a second before the pass and 44.38 and 41.62 after, with a median frame of 18 ms and the final frame unchanged. The slowest frames, 67 to 76 ms at the 95th percentile, still missed the 50 ms target: they were stalls from the laptop throttling at 100 to 105 °C.
Loading had the same treatment. Every launch spent 50 to 58 seconds rebuilding the same arrays in Python. A geometry cache, keyed by every file the builders read, now reaches the first homeland frame in about 4 seconds when nothing has changed, and that frame is identical byte for byte. The first launch after an install or an update still takes 58 seconds and writes 279 MB of cache.
Then the heat
The measurements on 16 and 17 September covered every preset, every home and the dragon ascent. On scripted walks the frame cost met the targets: at least 30 frames a second, and 95 per cent of frames within 50 ms. Low drew 69 to 70 frames a second, Medium 51.7 and High 43 to 44.
Then the autopilot played defenses in real time at the game’s default limit of 60 frames. While the laptop was cool they held 58 to 60. In five of six defenses the processor reached its critical 105 °C, between 40 and 211 seconds after launch, with frames of 70 to 180 ms from throttling before it. At a 30-frame limit, two whole defenses of 79 and 226 seconds held 30.0 frames a second, peaking at 98 and 100 °C.
Still open
Which limit the game uses on this laptop is not decided. Two hitches remain: creating the drake’s rig when it first appears, 46 to 53 ms, and building ground the first time a foot or a shadow needs it, 8 to 49 ms. GPU skinning has run on one graphics driver only. None of this has been measured with a person playing, past about four minutes, or on any other machine.