not quite

1 files changed, 29 insertions, 26 deletions

diff --git a/src/background.c b/src/background.c
index 2b32c49..c33492b 100644
--- a/src/background.c
+++ b/src/background.c
@@ -9,36 +9,39 @@ static const int center_y = DISPLAY_HEIGHT / 2;
 static void
 rotate(double *x, double *y, double angle)
 {
-	const int ox = *x;
-	*x = *x * cos(angle) + *y * sin(angle);
-	*y = *y * cos(angle) + ox * sin(angle);
+	const double s = sin(angle);
+	const double c = cos(angle);
+	const double ox = *x;
+	const double oy = *y;
+
+	*x = ox * c - ox * s;
+	*y = ox * s + oy * c;
 }
 
 static void
 draw_square(int size, double angle)
 {
-	double x0 = size / 2.0;
-	double y0 = size / 2.0;
-	double x1 = size / 2.0;
-	double y1 = -size / 2.0;
-	rotate(&x0, &y0, angle);
-	rotate(&x1, &y1, angle);
-	double x2 = 0 - x0;
-	double y2 = 0 - y0;
-	double x3 = 0 - x0;
-	double y3 = 0 - y0;
-	x0 += center_x;
-	y0 += center_y;
-	x1 += center_x;
-	y1 += center_y;
-	x2 += center_x;
-	y2 += center_y;
-	x3 += center_x;
-	y3 += center_y;
-	LZY_DrawLine(x0, y0, x1, y1);
-	LZY_DrawLine(x1, y1, x2, y2);
-	LZY_DrawLine(x2, y2, x3, y3);
-	LZY_DrawLine(x3, y3, x0, y0);
+	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] += center_x;
+		y[i] += center_y;
+	}
+	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]);
 }
 
 void
@@ -46,5 +49,5 @@ background_draw(void)
 {
 	tick += 1;
 	LZY_DrawSetColor(0, 0, 0);
-	draw_square(tick % 128, (double)tick / 10);
+	draw_square(64, (double)tick / 10);
 }