From 8062ca04f1c007359badf63352c320067a608252 Mon Sep 17 00:00:00 2001
From: P. J. McDermott <pj@pehjota.net>
Date: Tue, 30 Mar 2021 03:15:17 -0400
Subject: collision: Add basic circle-line test

---
diff --git a/src/collision.c b/src/collision.c
index 7e77b0a..758f28c 100644
--- a/src/collision.c
+++ b/src/collision.c
@@ -38,6 +38,56 @@ db_pt_in_rect(int x, int y, SDL_Rect *rect)
 	return 1;
 }
 
+int
+db_col_cir_line(double cir_x, double cir_y, double cir_r,
+		int line_x1, int line_y1, int line_x2, int line_y2,
+		double *col_x, double *col_y)
+{
+	int line_min;
+	int line_max;
+
+	if (line_y1 == line_y2) {
+		/* Horizontal line */
+		if (line_x1 < line_x2) {
+			line_min = line_x1;
+			line_max = line_x2;
+		} else {
+			line_min = line_x2;
+			line_max = line_x1;
+		}
+		if (cir_x < line_min) {
+			*col_x = line_min;
+		} else if (cir_x > line_max) {
+			*col_x = line_max;
+		} else {
+			*col_x = cir_x;
+		}
+		*col_y = line_y1;
+	} else if (line_x1 == line_x2) {
+		/* Vertical line */
+		if (line_y1 < line_y2) {
+			line_min = line_y1;
+			line_max = line_y2;
+		} else {
+			line_min = line_y2;
+			line_max = line_y1;
+		}
+		if (cir_y < line_min) {
+			*col_y = line_min;
+		} else if (cir_y > line_max) {
+			*col_y = line_max;
+		} else {
+			*col_y = cir_y;
+		}
+		*col_x = line_x1;
+	} else {
+		return -1;
+	}
+	return (cir_r * cir_r) >=
+		((*col_x - cir_x) * (*col_x - cir_x) +
+		 (*col_y - cir_y) * (*col_y - cir_y));
+}
+
 void
 db_closest_pt_on_rect(int x, int y, SDL_Rect *rect,
 		double *close_x, double *close_y)
diff --git a/src/collision.h b/src/collision.h
index ee04a8e..de1b2ca 100644
--- a/src/collision.h
+++ b/src/collision.h
@@ -23,6 +23,9 @@
 #include <SDL.h>
 
 int db_pt_in_rect(int x, int y, SDL_Rect *rect) __attribute__((__pure__));
+int db_col_cir_line(double cir_x, double cir_y, double cir_r,
+		int line_x1, int line_y1, int line_x2, int line_y2,
+		double *col_x, double *col_y);
 void db_closest_pt_on_rect(int x, int y, SDL_Rect *rect,
 		double *close_x, double *close_y);
 int db_col_cir_rect(int x, int y, int r, SDL_Rect *rect,
--
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