move rotating rect code out of background

src/background.c

@@ -1,45 +1,13 @@
 #include "lzy.h"
 #include "cfg.h"
-#include <math.h>
+#include "rotrect.h"
 
 static long tick = 0;
 
 static void
-rotate(double *x, double *y, double angle)
+draw_square(double size, double angle)
 {
-	const double s = sin(angle);
-	const double c = cos(angle);
-	const double ox = *x;
-	const double oy = *y;
-
-	*x = ox * c - oy * s;
-	*y = ox * s + oy * c;
-}
-
-static void
-draw_square(int size, double angle)
-{
-	double x[4] = {
-		size / 2.0,
-		size / 2.0,
-		-size / 2.0,
-		-size / 2.0,
-	};
-	double y[4] = {
-		-size / 2.0,
-		size / 2.0,
-		size / 2.0,
-		-size / 2.0,
-	};
-	for (int i = 0; i < 4; i++) {
-		rotate(&x[i], &y[i], angle);
-		x[i] += DISPLAY_WIDTH / 2.0;
-		y[i] += DISPLAY_HEIGHT / 2.0;
-	}
-	LZY_DrawLine(x[0], y[0], x[1], y[1]);
-	LZY_DrawLine(x[1], y[1], x[2], y[2]);
-	LZY_DrawLine(x[2], y[2], x[3], y[3]);
-	LZY_DrawLine(x[3], y[3], x[0], y[0]);
+	rotrect(DISPLAY_WIDTH / 2.0, DISPLAY_HEIGHT / 2.0, size, size, angle);
 }
 
 void

src/rotrect.c

@@ -0,0 +1,43 @@
+#include "rotrect.h"
+#include "cfg.h"
+#include "lzy.h"
+#include <math.h>
+
+static void
+rotate(double *x, double *y, double angle)
+{
+	const double s = sin(angle);
+	const double c = cos(angle);
+	const double ox = *x;
+	const double oy = *y;
+
+	*x = ox * c - oy * s;
+	*y = ox * s + oy * c;
+}
+
+void
+rotrect(double x, double y, double width, double height, double angle)
+{
+	double xs[4] = {
+		width / 2.0,
+		width / 2.0,
+		-width / 2.0,
+		-width / 2.0,
+	};
+	double ys[4] = {
+		-height / 2.0,
+		height / 2.0,
+		height / 2.0,
+		-height / 2.0,
+	};
+	for (int i = 0; i < 4; i++) {
+		rotate(&xs[i], &ys[i], angle);
+		xs[i] = round(xs[i] + x);
+		ys[i] = round(ys[i] + y);
+	}
+	LZY_DrawLine(xs[0], ys[0], xs[1], ys[1]);
+	LZY_DrawLine(xs[1], ys[1], xs[2], ys[2]);
+	LZY_DrawLine(xs[2], ys[2], xs[3], ys[3]);
+	LZY_DrawLine(xs[3], ys[3], xs[0], ys[0]);
+}
+

src/rotrect.h

@@ -0,0 +1,3 @@
+#pragma once
+
+void rotrect(double x, double y, double width, double height, double angle);