+#include "frustum.h"
+
+typedef enum
+{
+ PLANE_LEFT,
+ PLANE_RIGHT,
+ PLANE_BOTTOM,
+ PLANE_TOP,
+ PLANE_NEAR,
+ PLANE_FAR,
+ PLANE_COUNT,
+} Plane;
+
+static struct
+{
+ vec3 points[8];
+ vec4 planes[PLANE_COUNT];
+ int cross_indices[PLANE_COUNT][PLANE_COUNT];
+} frustum;
+
+__attribute__((constructor)) static void init_frustum()
+{
+ for (Plane a = 0; a < PLANE_COUNT; a++)
+ for (Plane b = 0; b < PLANE_COUNT; b++)
+ frustum.cross_indices[a][b] = a * (9 - a) / 2 + b - 1;
+}
+
+void frustum_update(mat4x4 view_proj)
+{
+ mat4x4 m;
+
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wpedantic"
+ mat4x4_transpose(m, view_proj);
+#pragma GCC diagnostic pop
+
+ vec4_add(frustum.planes[PLANE_LEFT], m[3], m[0]);
+ vec4_sub(frustum.planes[PLANE_RIGHT], m[3], m[0]);
+ vec4_add(frustum.planes[PLANE_BOTTOM], m[3], m[1]);
+ vec4_sub(frustum.planes[PLANE_TOP], m[3], m[1]);
+ vec4_add(frustum.planes[PLANE_NEAR], m[3], m[2]);
+ vec4_sub(frustum.planes[PLANE_FAR], m[3], m[2]);
+
+ int i = 0;
+ vec3 crosses[PLANE_COUNT * (PLANE_COUNT - 1) / 2];
+ for (Plane a = 0; a < PLANE_COUNT; a++)
+ for (Plane b = a + 1; b < PLANE_COUNT; b++)
+ vec3_mul_cross(crosses[i++], frustum.planes[a], frustum.planes[b]);
+
+ int j = 0;
+ for (Plane c = PLANE_NEAR; c <= PLANE_FAR; c++) {
+ for (Plane a = PLANE_LEFT; a <= PLANE_RIGHT; a++) {
+ for (Plane b = PLANE_BOTTOM; b <= PLANE_TOP; b++) {
+ float d = -1.0f / vec3_mul_inner(frustum.planes[a], crosses[frustum.cross_indices[b][c]]);
+ vec3 w = {frustum.planes[a][4], frustum.planes[b][4], frustum.planes[c][4]};
+ float *res = frustum.points[j++];
+
+ vec3 res_1_cross = {-crosses[frustum.cross_indices[a][c]][0], -crosses[frustum.cross_indices[a][c]][1], -crosses[frustum.cross_indices[a][c]][2]};
+
+ res[0] = vec3_mul_inner(crosses[frustum.cross_indices[b][c]], w) * d;
+ res[1] = vec3_mul_inner(res_1_cross, w) * d;
+ res[2] = vec3_mul_inner(crosses[frustum.cross_indices[a][b]], w) * d;
+ }
+ }
+ }
+}
+
+static bool outside_plane(Plane i, aabb3f32 box)
+{
+ for (int x = 0; x <= 1; x++) {
+ for (int y = 0; y <= 1; y++) {
+ for (int z = 0; z <= 1; z++) {
+ vec4 plane = {
+ x ? box.max.x : box.min.x,
+ y ? box.max.y : box.min.y,
+ z ? box.max.z : box.min.z,
+ 1.0f,
+ };
+
+ if (vec4_mul_inner(frustum.planes[i], plane) > 0.0)
+ return false;
+ }
+ }
+ }
+
+ return true;
+}
+
+// http://iquilezles.org/www/articles/frustumcorrect/frustumcorrect.htm
+bool frustum_is_visible(aabb3f32 box)
+{
+ for (Plane i = 0; i < PLANE_COUNT; i++) {
+ if (outside_plane(i, box))
+ return false;
+ }
+
+ int box_outside[6] = {0};
+
+ for (Plane i = 0; i < PLANE_COUNT; i++) {
+ int outside[6] = {
+ frustum.points[i][0] > box.max.x,
+ frustum.points[i][0] < box.min.x,
+ frustum.points[i][1] > box.max.y,
+ frustum.points[i][1] < box.min.y,
+ frustum.points[i][2] > box.max.z,
+ frustum.points[i][2] < box.min.z,
+ };
+
+ for (int i = 0; i < 6; i++)
+ box_outside[i] += outside[i];
+ }
+
+ for (int i = 0; i < 6; i++) {
+ if (box_outside[i] == 8)
+ return false;
+ }
+
+ return true;
+}