src/rendering/sprites.h

@@ -5,6 +5,7 @@
 #include "../textures.h"
 #include "../rendering.h"
 #include "../context.h"
+#include "../util.h"
 #include "quad_element_buffer.h"
 
 #include <stb_ds.h>
@@ -180,9 +181,10 @@ static void render_sprites(const struct primitive_2d primitives[],
             } else {
                 /* rotated case */
                 const t_fvec2 c = frect_center(sprite.rect);
+                const t_fvec2 t = fast_cossine(sprite.rotation + (float)M_PI_4);
                 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,
+                    .x = t.x * sprite.rect.w * (float)M_SQRT1_2,
+                    .y = t.y * sprite.rect.h * (float)M_SQRT1_2,
                 };
 
                 payload[i] = (struct sprite_primitive_payload) {

src/util.h

@@ -154,5 +154,28 @@ void tick_ftimer(float *value);
 /* returns true if value was cycled */
 bool repeat_ftimer(float *value, float at);
 
+/* http://www.azillionmonkeys.com/qed/sqroot.html */
+static inline float fast_sqrt(float x)
+{
+    union {
+        float f;
+        uint32_t u;
+    } pun = {.f = x};
+
+    pun.u += 127 << 23;
+    pun.u >>= 1;
+
+    return pun.f;
+}
+
+
+static inline t_fvec2 fast_cossine(float a) {
+    const float s = sinf(a);
+    return (t_fvec2){
+        .x = fast_sqrt(1.0f - s * s) * (a >= (float)M_PI_2 && a < (float)(M_PI + M_PI_2) ? -1 : 1),
+        .y = s
+    };
+}
+
 
 #endif