Add the usage example

.gitignore

@@ -1,2 +1,3 @@
 lag
-*.o
+ball
+*.o

Makefile

@@ -1,6 +1,9 @@
 CFLAGS=-Wall -Wextra -pedantic
 
-all: la.c.o la.cxx.o
+all: la.c.o la.cxx.o ball
+
+ball: ball.c la.h
+	$(CC) $(CFLAGS) -std=c11 -ggdb -o ball ball.c -lm
 
 la.cxx.o: la.h
 	$(CC) $(CFLAGS) -DLA_IMPLEMENTATION -x c++ -o la.cxx.o -c la.h

README.md

@@ -9,6 +9,8 @@ Procedurally generated C library for Linear Algebra in 2D/3D Computer Graphics.
 
 Grab [la.h](./la.h) and use it as an stb-style header-only library. For more info on such libraries see: https://github.com/nothings/stb/blob/master/docs/stb_howto.txt
 
+For a usage example see [ball.c](./ball.c)
+
 ## Regenerating la.h
 
 ```console

ball.c

@@ -0,0 +1,133 @@
+// This is a small example on how to use la.h
+// Just a simple simulation of a bouncing ball with ASCII Art rendering in the terminal
+// cc -o ball ball.c && ./ball
+#define _XOPEN_SOURCE 500
+#include <assert.h>
+#include <stdio.h>
+#include <string.h>
+
+#include <unistd.h>
+
+#define LA_IMPLEMENTATION
+#include "./la.h"
+
+typedef enum {
+    BACK = 0,
+    FORE = 1,
+    PIXEL_N,
+} Pixel;
+
+#define WIDTH 64
+#define HEIGHT 32
+static_assert(HEIGHT % 2 == 0, "If the amount of display rows is not divisible by 2 we can't properly compress it. See show(void) function");
+static Pixel display[WIDTH * HEIGHT];
+
+static void fill(Pixel p)
+{
+    Pixel *ptr = display;
+    size_t n = WIDTH*HEIGHT;
+    while (n-- > 0) *ptr++ = p;
+}
+
+// ..............................
+// ..............................
+// ..........@@@@@@@.............
+// ..........@.***.@.............
+// ..........@*****@.............
+// ..........@**c**@.............
+// ..........@*****@.............
+// ..........@.***.@.............
+// ..........@@@@@@@.............
+// ..............................
+// x^2 + y^2 <= r^2
+static void circle(V2f c, float r)
+{
+    V2i b = v2i2f(v2f_floor(v2f_sub(c, v2ff(r))));
+    V2i e = v2i2f(v2f_ceil(v2f_sum(c, v2ff(r))));
+
+    for (int y = b.y; y <= e.y; ++y) {
+        for (int x = b.x; x <= e.x; ++x) {
+            V2f p = v2f_sum(v2f2i(v2i(x, y)), v2ff(0.5f));
+            V2f d = v2f_sub(c, p);
+            if (v2f_sqrlen(d) <= r*r) {
+                if (0 <= x && x < WIDTH && 0 <= y && y < HEIGHT) {
+                    display[y*WIDTH + x] = FORE;
+                }
+            }
+        }
+    }
+}
+
+// Double Row Pixel compression
+//
+// |..**...***...|
+// |**....****...|
+//       |
+//       V
+// |__^^  _CCC   |
+//
+static void show(void)
+{
+    static char row[WIDTH];
+    static char *table = " _^C";
+    for (int y = 0; y < HEIGHT/2; ++y) {
+        for (int x = 0; x < WIDTH; ++x) {
+            Pixel t = display[(2*y + 0)*WIDTH + x];
+            Pixel b = display[(2*y + 1)*WIDTH + x];
+            assert(0 <= t);
+            assert(t < PIXEL_N);
+            assert(0 <= b);
+            assert(b < PIXEL_N);
+            row[x] = table[(t<<1)|b];
+        }
+        fwrite(row, WIDTH, 1, stdout);
+        fputc('\n', stdout);
+    }
+}
+
+static void back(void)
+{
+    printf("\x1b[%dD", WIDTH);
+    printf("\x1b[%dA", HEIGHT/2);
+}
+
+#define FPS 30
+#define RADIUS (HEIGHT/4.0f)
+#define GRAVITY 200.0f
+#define DT (1.0f/FPS)
+#define DAMPER 0.65f
+
+static V2f pos;
+static V2f vel;
+
+static void reset(void)
+{
+    pos = v2ff(-RADIUS);
+    vel = v2f(50.0f, 0.0f);
+}
+
+int main(void)
+{
+    reset();
+    while (1) {
+        vel = v2f_sum(vel, v2f(0.0f, GRAVITY*DT));
+        pos = v2f_sum(pos, v2f_mul(vel, v2ff(DT)));
+
+        if (pos.y > HEIGHT - RADIUS) {
+            pos.y = HEIGHT - RADIUS;
+            vel.y *= -DAMPER;
+        }
+
+        if (pos.x >= WIDTH + RADIUS + RADIUS * 2.0f) {
+            reset();
+        }
+
+        fill(BACK);
+        circle(pos, RADIUS);
+        show();
+        back();
+
+        usleep(1000 * 1000 / FPS);
+    }
+    return 0;
+}