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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); void S3L_crossProduct(S3L_Vec4 a, S3L_Vec4 b, S3L_Vec4 *result);
static inline S3L_Unit S3L_dotProductVec3(S3L_Vec4 a, S3L_Vec4 b); 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)\ #define S3L_logVec4(v)\
printf("Vec4: %d %d %d %d\n",((v).x),((v).y),((v).z),((v).w)) 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; 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 Checks if given triangle (in Projection Plane space) is at least partially
visible, i.e. returns false if the triangle is either completely outside 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) if (backfaceCulling != 0)
{ {
int32_t winding = // determines CW or CCW int8_t winding =
(p1.y - p0.y) * (p2.x - p1.x) - (p1.x - p0.x) * (p2.y - p1.y); S3L_triangleWinding(p0.x,p0.y,p1.x,p1.y,p2.x,p2.y);
if ((backfaceCulling == 1 && winding < 0) || if ((backfaceCulling == 1 && winding < 0) ||
(backfaceCulling == 2 && winding > 0)) (backfaceCulling == 2 && winding > 0))