33 lines
941 B
Plaintext
33 lines
941 B
Plaintext
|
Title: Fast Quad Rotation
|
||
|
|
Brief: A better way to rotate quads around their centers.
|
||
|
|
Date: 1722126213
|
||
|
|
Tags: Programming, Optimization, C
|
||
|
|
CSS: /style.css
|
||
|
|
|
||
|
|
A similar in essence trick to [by pi rotation](/articles/vector-pi-rotation.html), but with delta calculated
|
||
|
|
for some corner which is reused later with negation and coordinate swap.
|
||
|
|
|
||
|
|
Scaling by `M_SQRT1_2` is there to retain the quad size (Pythagorean stuffs).
|
||
|
|
|
||
|
|
### Code ###
|
||
|
|
```c
|
||
|
|
const t_fvec2 c = frect_center(sprite.rect);
|
||
|
|
const t_fvec2 d = {
|
||
|
|
.x = (cosf(sprite.rotation + (float)M_PI_4) * sprite.rect.w) * (float)M_SQRT1_2,
|
||
|
|
.y = (sinf(sprite.rotation + (float)M_PI_4) * sprite.rect.h) * (float)M_SQRT1_2,
|
||
|
|
};
|
||
|
|
|
||
|
|
/* upper-left */
|
||
|
|
const t_fvec2 v0 = { c.x - d.x, c.y - d.y };
|
||
|
|
|
||
|
|
/* bottom-left */
|
||
|
|
const t_fvec2 v1 = { c.x - d.y, c.y + d.x };
|
||
|
|
|
||
|
|
/* bottom-right */
|
||
|
|
const t_fvec2 v2 = { c.x + d.x, c.y + d.y };
|
||
|
|
|
||
|
|
/* upper-right */
|
||
|
|
const t_fvec2 v3 = { c.x + d.y, c.y - d.x };
|
||
|
|
|
||
|
|
```
|