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Add winding function

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This commit is contained in:
Miloslav Číž 2019-06-12 22:17:52 +02:00
parent c46f4ad219
commit fd7d957a64
1 changed files with 27 additions and 2 deletions
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29
small3dlib.h
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@ -290,6 +290,16 @@ void S3L_normalizeVec2(S3L_Vec4 *v);
void S3L_crossProduct(S3L_Vec4 a, S3L_Vec4 b, S3L_Vec4 *result);
static inline S3L_Unit S3L_dotProductVec3(S3L_Vec4 a, S3L_Vec4 b);
/** Determines the winding of triangle, returns 1 (CW, clockwise), -1 (CCW,
counterclockwise) or 0 (points lie on a single line). */
static inline int8_t S3L_triangleWinding(
S3L_ScreenCoord x0,
S3L_ScreenCoord y0,
S3L_ScreenCoord x1,
S3L_ScreenCoord y1,
S3L_ScreenCoord x2,
S3L_ScreenCoord y2);
#define S3L_logVec4(v)\
printf("Vec4: %d %d %d %d\n",((v).x),((v).y),((v).z),((v).w))
@ -2228,6 +2238,21 @@ static inline void S3L_perspectiveDivide(S3L_Vec4 *vector,
vector->y = (vector->y * focalLength) / vector->z;
}
int8_t S3L_triangleWinding(
S3L_ScreenCoord x0,
S3L_ScreenCoord y0,
S3L_ScreenCoord x1,
S3L_ScreenCoord y1,
S3L_ScreenCoord x2,
S3L_ScreenCoord y2)
{
int32_t winding =
(y1 - y0) * (x2 - x1) - (x1 - x0) * (y2 - y1);
// ^ cross product for points with z == 0
return winding > 0 ? 1 : (winding < 0 ? -1 : 0);
}
/**
Checks if given triangle (in Projection Plane space) is at least partially
visible, i.e. returns false if the triangle is either completely outside
@ -2262,8 +2287,8 @@ static inline int8_t S3L_triangleIsVisible(
if (backfaceCulling != 0)
{
int32_t winding = // determines CW or CCW
(p1.y - p0.y) * (p2.x - p1.x) - (p1.x - p0.x) * (p2.y - p1.y);
int8_t winding =
S3L_triangleWinding(p0.x,p0.y,p1.x,p1.y,p2.x,p2.y);
if ((backfaceCulling == 1 && winding < 0) ||
(backfaceCulling == 2 && winding > 0))