Game Development Reference
• Frame 2 (Graphics rendering) The graphics renderer takes the state of
the game world established by the previous frame's calculations, and
uses it to render a visual image.
• Frame 3 (Frame displayed) The rendered image is displayed.
Every stage is running all the time. Graphed out, they look like this:
This arrangement has the advantage of very high throughput because
it keeps both the CPU and GPU running at all times. Without this system,
the graphics unit would have to sit idle through the first half of each frame
as the CPU updated the game system.
Unfortunately, this system also introduces three to four frame lengths
of lag between input and response, depending on when during the frame
the input was received. (Most televisions add another frame or two to do
their own signal processing before finally showing the image, but we have
no control over those delays, so I'll ignore them here.)
Poorly written code can extend the delay even longer, to five, six, seven,
or more frames. It is the responsibility of programmers to ensure that
extra frames of latency are not creeping into the game. But once program-
mers have made sure they're not making mistakes and introducing extra
lag, the hardware makes it impossible to get below three frames of latency.
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