From 58adfcfcd0420a9c2fc6be80c441f9713fe6022c Mon Sep 17 00:00:00 2001
From: Vince Weaver <vincent.weaver@maine.edu>
Date: Thu, 14 Dec 2017 16:52:58 -0500
Subject: [PATCH] gr-sim: add starfield demo

---
 gr-sim/Makefile    | 12 ++++++++--
 gr-sim/starfield.c | 60 ++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 70 insertions(+), 2 deletions(-)
 create mode 100644 gr-sim/starfield.c

diff --git a/gr-sim/Makefile b/gr-sim/Makefile
index 466becbe..5c93bd86 100644
--- a/gr-sim/Makefile
+++ b/gr-sim/Makefile
@@ -5,7 +5,7 @@ LFLAGS = -lm
 SDL_LIBS= `sdl-config --libs`
 SDL_INCLUDE= `sdl-config --cflags`
 
-all:	fixed_point rainbow sparkle kaleido tfv mode7_demo text tfv_multiply
+all:	fixed_point rainbow sparkle starfield kaleido tfv mode7_demo text tfv_multiply
 
 
 
@@ -144,10 +144,18 @@ sparkle.o:	sparkle.c
 	$(CC) $(CFLAGS) -c sparkle.c
 
 
+starfield:	starfield.o gr-sim.o
+	$(CC) $(LFLAGS) $(SDL_LIBS) -o starfield starfield.o gr-sim.o
+
+starfield.o:	starfield.c
+	$(CC) $(CFLAGS) -c starfield.c
+
+
 gr-sim.o:	gr-sim.c gr-sim.h apple2_font.h
 	$(CC) $(CFLAGS) $(SDL_INCLUDE) -c gr-sim.c
 
 clean:	
-	rm -f *~ *.o gr-sim rainbow sparkle kaleido tfv text mode7_demo fixed_point tfv_multiply
+	rm -f *~ *.o gr-sim rainbow sparkle starfield kaleido \
+			tfv text mode7_demo fixed_point tfv_multiply
 
 
diff --git a/gr-sim/starfield.c b/gr-sim/starfield.c
new file mode 100644
index 00000000..76d35710
--- /dev/null
+++ b/gr-sim/starfield.c
@@ -0,0 +1,60 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+
+#include "gr-sim.h"
+
+#define NUMSTARS	64
+
+struct star_type {
+	double x;
+	double y;
+	double z;
+};
+
+static struct star_type stars[NUMSTARS];
+
+int main(int argc, char **argv) {
+
+	int ch,i;
+
+	int spreadx=40;
+	int spready=40;
+	int spreadz=5;
+
+	grsim_init();
+
+	for(i=0;i<NUMSTARS;i++) {
+		stars[i].x=(drand48()-0.5)*spreadx;
+		stars[i].y=(drand48()-0.5)*spready;
+		stars[i].z=((drand48())*spreadz)+0.1;
+		printf("%.2lf,%2lf,%.2lf\n",stars[i].x,stars[i].y,stars[i].z);
+	}
+	gr();
+
+
+	while(1) {
+		gr();
+		color_equals(15);
+		for(i=0;i<NUMSTARS;i++) {
+			basic_plot(stars[i].x/stars[i].z+20,
+					stars[i].y/stars[i].z+20);
+		}
+
+		for(i=0;i<NUMSTARS;i++) {
+			stars[i].z+=-0.125;
+			if (stars[i].z<0) {
+				stars[i].x=(drand48()-0.5)*spreadx;
+				stars[i].y=(drand48()-0.5)*spready;
+				stars[i].z=((drand48())*spreadz)+0.1;
+			}
+		}
+
+		grsim_update();
+		ch=grsim_input();
+		if (ch=='q') exit(0);
+		usleep(30000);
+	}
+
+	return 0;
+}