collision: Add circle-circle functions

Also fix missing #include and mark db_pt_in_rect() pure.

2 files changed, 31 insertions, 1 deletions

diff --git a/src/collision.c b/src/collision.c
index 32c5e57..2abd8a2 100644
--- a/src/collision.c
+++ b/src/collision.c
@@ -18,6 +18,7 @@
  */
 
 #include <SDL.h>
+#include "collision.h"
 
 int
 db_pt_in_rect(int x, int y, SDL_Rect *rect)
@@ -36,3 +37,28 @@ db_pt_in_rect(int x, int y, SDL_Rect *rect)
 	}
 	return 1;
 }
+
+int
+db_col_cir_cir(int x1, int y1, int r1, int x2, int y2, int r2)
+{
+	return ((r1 + r2) * (r1 + r2)) >=
+		((x1 - x2) * (x1 - x2) + (y1 - y2) * (y1 - y2));
+}
+
+/*
+ * This function will be called after moving the two balls being checked.  A
+ * more accurate way to handle collisions would be to microstep through
+ * movements to find the exact point of collision.
+ */
+int
+db_col_pt_cir_cir(int x1, int y1, int r1, int x2, int y2, int r2,
+		int *col_x, int *col_y)
+{
+	if (db_col_cir_cir(x1, y1, r1, x2, y2, r2)) {
+		*col_x = (x1 + x2) / 2;
+		*col_y = (y1 + y2) / 2;
+		return 1;
+	} else {
+		return 0;
+	}
+}
diff --git a/src/collision.h b/src/collision.h
index 022cf78..58cd95e 100644
--- a/src/collision.h
+++ b/src/collision.h
@@ -22,6 +22,10 @@
 
 #include <SDL.h>
 
-int db_pt_in_rect(int x, int y, SDL_Rect *rect);
+int db_pt_in_rect(int x, int y, SDL_Rect *rect) __attribute__((__pure__));
+int db_col_cir_cir(int x1, int y1, int r1, int x2, int y2, int r2)
+	__attribute__((__const__));
+int db_col_pt_cir_cir(int x1, int y1, int r1, int x2, int y2, int r2,
+		int *col_x, int *col_y);
 
 #endif  /* DB_COLLISION_H_ */