From 49751d69498c265cb46f6cce5033367ae39c5e91 Mon Sep 17 00:00:00 2001
From: Sam Anthony <sam@samanthony.xyz>
Date: Wed, 2 Oct 2024 11:42:40 -0400
Subject: animate

---
 Makefile    |  4 ++--
 balls.cpp   | 54 ++++++++++++++++++++++++++++++++++++++++++------------
 balls.h     | 23 +++++++++++++++++++++++
 collision.c | 34 ++++++++++++++++++++++++++++++++++
 4 files changed, 101 insertions(+), 14 deletions(-)
 create mode 100644 balls.h
 create mode 100644 collision.c

diff --git a/Makefile b/Makefile
index be1b32b..8bd89f1 100644
--- a/Makefile
+++ b/Makefile
@@ -2,9 +2,9 @@ CC = g++
 CFLAGS = -Wall -pedantic
 LDFLAGS = -ltbb -lglut -lGLU -lGL
 
-balls: balls.o
+balls: balls.o collision.o
 	${CC} -o $@ $^ ${LDFLAGS}
 	@echo done
 
-%.o: %.cpp
+%.o: %.cpp balls.h
 	${CC} -c ${CFLAGS} $<
\ No newline at end of file
diff --git a/balls.cpp b/balls.cpp
index 555b192..621fb13 100644
--- a/balls.cpp
+++ b/balls.cpp
@@ -2,27 +2,32 @@
 #include <GL/glut.h>
 #include <oneapi/tbb.h>
 
+#include "balls.h"
+
 using namespace std;
 
-enum window { WIDTH = 800, HEIGHT = 600 };
-enum keys { KEY_QUIT = 'q' };
-enum { CIRCLE_SEGS = 32 };
+enum {
+	WIDTH = 800,
+	HEIGHT = 600,
+
+	KEY_QUIT = 'q',
 
-typedef struct {
-	double x, y;
-} Point;
+	CIRCLE_SEGS = 32,
 
-typedef struct {
-	Point min, max;
-} Rectangle;
+	FPS = 60,
+	MS_PER_S = 1000,
+	FRAME_TIME_MS = MS_PER_S / FPS,
+};
 
 void keyboard(unsigned char key, int x, int y);
 void display(void);
 void drawBg(void);
 void drawCircle(double radius, Point p);
 void reshape(int w, int h);
+void animate(int v);
 
 const static Rectangle bounds = {{-1.5, -1.0}, {1.5, 1.0}};
+static Ball ball = {{0.25, 0.25}, {0.25, 0.25}, 0.200, 0.25};
 
 int
 main(int argc, char *argv[]) {
@@ -34,6 +39,7 @@ main(int argc, char *argv[]) {
 	glutKeyboardFunc(keyboard);
 	glutDisplayFunc(display);
 	glutReshapeFunc(reshape);
+	glutTimerFunc(FRAME_TIME_MS, animate, 0);
 
 	glClearColor(1.0, 1.0, 1.0, 1.0);
 
@@ -50,12 +56,10 @@ keyboard(unsigned char key, int x, int y) {
 
 void
 display(void) {
-	static Point p = {0.35, 0.35};
-
 	glClearColor(0, 0, 0, 1);
 	glClear(GL_COLOR_BUFFER_BIT);
 	drawBg();
-	drawCircle(0.25, p);
+	drawCircle(ball.r, ball.p);
 
 	glutSwapBuffers();
 }
@@ -102,3 +106,29 @@ reshape(int w, int h) {
 		glOrtho(-1, 1, -1.0/ratio, 1.0/ratio, -1, 1);
 	glMatrixMode(GL_MODELVIEW);
 }
+
+void
+animate(int v) {
+	ball.p = ptAddVec(ball.p, ball.v);
+
+	collideWall(&ball, bounds);
+
+	display();
+	glutTimerFunc(FRAME_TIME_MS, animate, 0);
+}
+
+Point
+ptAddVec(Point p, Vector v) {
+	p.x += v.x;
+	p.y += v.y;
+	return p;
+}
+
+Rectangle
+insetRect(Rectangle r, double n) {
+	r.min.x += n;
+	r.min.y += n;
+	r.max.x -= n;
+	r.max.y -= n;
+	return r;
+}
diff --git a/balls.h b/balls.h
new file mode 100644
index 0000000..3205959
--- /dev/null
+++ b/balls.h
@@ -0,0 +1,23 @@
+typedef struct {
+	double x, y;
+} Point;
+
+typedef struct {
+	Point min, max;
+} Rectangle;
+
+typedef struct {
+	double x, y;
+} Vector;
+
+typedef struct {
+	Point p; /* position [m] */
+	Vector v; /* velocity [m/s] */
+	double m; /* mass [kg] */
+	double r; /* radius [m] */
+} Ball;
+
+Point ptAddVec(Point p, Vector v);
+Rectangle insetRect(Rectangle r, double n);
+
+void collideWall(Ball *b, Rectangle wall);
\ No newline at end of file
diff --git a/collision.c b/collision.c
new file mode 100644
index 0000000..17889a4
--- /dev/null
+++ b/collision.c
@@ -0,0 +1,34 @@
+#include "balls.h"
+
+static double clamp(double v, double lo, double hi);
+static double min(double a, double b);
+static double max(double a, double b);
+
+void
+collideWall(Ball *b, Rectangle wall) {
+	wall = insetRect(wall, b->r);
+
+	if (b->p.x < wall.min.x || b->p.x > wall.max.x) {
+		b->p.x = clamp(b->p.x, wall.min.x, wall.max.x);
+		b->v.x = -b->v.x;
+	}
+	if (b->p.y < wall.min.y || b->p.y > wall.max.y) {
+		b->p.y = clamp(b->p.y, wall.min.y, wall.max.y);
+		b->v.y = -b->v.y;
+	}
+}
+
+static double
+clamp(double v, double lo, double hi) {
+	return min(hi, max(v, lo));
+}
+
+static double
+min(double a, double b) {
+	return (a < b) ? a : b;
+}
+
+static double
+max(double a, double b) {
+	return (a > b) ? a : b;
+}
-- 
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