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