things...

1 files changed, 18 insertions, 6 deletions

diff --git a/src/common.h b/src/common.h
index d9a222f..4d0df29 100644
--- a/src/common.h
+++ b/src/common.h
@@ -1,14 +1,26 @@
 #ifndef COMMON_H
 #define COMMON_H
 
-#include <stdint.h>  // for size_t
+#include <stddef.h>  // for size_t
 
 typedef unsigned int uint;
 
-#define min(a, b)      (((a) < (b)) ? (a) : (b))
-#define max(a, b)      (((a) > (b)) ? (a) : (b))
-#define clamp(x, l, h) (min(max((x), (l)), (h)))
-#define cross(x1, y1, x2, y2) ((x1)*(y2) - (x2)*(y1))
+#define min(a, b)      (((a) < (b)) ? (a) : (b)) // choose smaller
+#define max(a, b)      (((a) > (b)) ? (a) : (b)) // choose bigger
+#define clamp(x, l, h) (min(max((x), (l)), (h))) // clamp x between a range
+#define vxs(x0,y0, x1,y1)    ((x0)*(y1) - (x1)*(y0)) // vector cross product
+
+// Overlap:  Determine whether the two number ranges overlap.
+#define overlap(a0,a1,b0,b1) (min(a0,a1) <= max(b0,b1) && min(b0,b1) <= max(a0,a1))
+// IntersectBox: Determine whether two 2D-boxes intersect.
+#define intersectbox(x0,y0, x1,y1, x2,y2, x3,y3) (overlap(x0,x1,x2,x3) && overlap(y0,y1,y2,y3))
+// PointSide: Determine which side of a line the point is on. Return value: <0, =0 or >0.
+#define pointside(px,py, x0,y0, x1,y1) vxs((x1)-(x0), (y1)-(y0), (px)-(x0), (py)-(y0))
+// Intersect: Calculate the point of intersection between two lines.
+#define intersect(x1,y1, x2,y2, x3,y3, x4,y4) ((struct xy) { \
+    vxs(vxs(x1,y1, x2,y2), (x1)-(x2), vxs(x3,y3, x4,y4), (x3)-(x4)) / vxs((x1)-(x2), (y1)-(y2), (x3)-(x4), (y3)-(y4)), \
+    vxs(vxs(x1,y1, x2,y2), (y1)-(y2), vxs(x3,y3, x4,y4), (y3)-(y4)) / vxs((x1)-(x2), (y1)-(y2), (x3)-(x4), (y3)-(y4)) })
+
 
 struct xy {
     float x, y;
@@ -23,7 +35,7 @@ struct xyz {
 #define COLOR_RED   0xFF0000
 #define COLOR_GREEN 0x00FF00
 #define COLOR_BLUE  0x0000FF
-#define COLOR_LIGHTWHITE 0xF5F5F5FF
+#define COLOR_LIGHTWHITE 0xF5F5F5
 #define color(col) (((col)>>16) & 0xFF), (((col)>>8) & 0xFF), ((col) & 0xFF)
 
 // macro wrapper for the sdl logging system