Delta time
The movement speed of our games is determined by how fast the game runs (how many frames are generated)
Really slow computer ------------------------> Really fast computer
Huge differences, this is a massive problem !
How framerates influence the game
| Speed (pixels per frame) | Frames per second | Total movement (per second) |
|---|---|---|
| 10 px | 30 | 10 * 30 = 300 |
| 10 px | 60 | 10 * 60 = 600 |
| 10 px | 120 | 10 * 120 = 1200 |
The game will run inconsistently on different systems
Since some scenes are harder to render than others it might even run inconsistently on the same system!
The solution is to use delta time
Delta time measures how long it took to create one frame For example, if the frame is 60fps, delta time is 1/60th of a second (0.0166) or about 17 milliseconds
This information we can use to keep the same at a constant speed regardless of framerate
We essentially multiply any movement with the delta time
| Speed (pixels per frame) | Frames per second | Total movement (per second) | Delta time | Total movement (per second) |
|---|---|---|---|---|
| 10 px | 30 | 10 * 30 = 300 | 1/30 = 0.033 | 10 * 30 * 0.033 = 9.9 |
| 10 px | 60 | 10 * 60 = 600 | 1/60 = 0.0166 | 10 * 60 * 0.0166 = 9.96 |
| 10 px | 120 | 10 * 120 = 1200 | 1/120 = 0.0083 | 10 * 120 * 0.0083 = 9.96 |
With delta accounted, the game runs at the same speed at any framerate !
Delta is only used for movement, not for rotation or scaling or setting position