1 files changed, 156 insertions, 0 deletions
diff --git a/examples/particles.c b/examples/particles.c
new file mode 100755
index 0000000..0fcef37
--- /dev/null
+++ b/examples/particles.c
@@ -0,0 +1,156 @@
+#if 0 /*
+#/  ================================================================
+#/
+#/    particles.c
+#/
+#/  ================================================================
+#/
+#/    Self-compilation shell script
+#/
+SRC=${0##*./}
+BIN=${SRC%.*}
+gcc                                 \
+  -Wall -Wextra -Werror -pedantic   \
+  -Wno-old-style-declaration        \
+  -Wno-missing-braces               \
+  -Wno-unused-variable              \
+  -Wno-unused-but-set-variable      \
+  -Wno-unused-parameter             \
+  -Wno-overlength-strings           \
+  -O3                               \
+  -fsanitize=undefined,address,leak \
+  -lX11 -lm                         \
+  -o $BIN $SRC &&                   \
+  ./$BIN $@ && rm $BIN
+exit $? # */
+#endif
+
+#include "../graphics.c"
+
+typedef struct {
+  f64 x;
+  f64 y;
+  f64 vx;
+  f64 vy;
+} Entity;
+
+typedef struct {
+  i64    time;
+  i64    num_entities;
+  Entity entities[10 * 1024 * 1024];
+} World;
+
+World world = {0};
+u32   background;
+i64   time_0;
+
+void update_and_render_frame(void) {
+  p_handle_events();
+
+  i64 time_elapsed  = p_time() - time_0;
+  time_0           += time_elapsed;
+
+  if (platform.key_pressed[BUTTON_LEFT]) {
+    i64 n = world.num_entities++;
+
+    world.entities[n] = (Entity) {
+      .x =   (f64) platform.cursor_x - (f64) platform.frame_width  / 2,
+      .y = -((f64) platform.cursor_y - (f64) platform.frame_height / 2),
+    };
+  }
+
+  if (time_elapsed > 0) {
+    if (platform.key_down[BUTTON_RIGHT]) {
+      for (i64 n = 0; n < time_elapsed; ++n)
+        world.entities[world.num_entities + n] = (Entity) {
+          .x =   (f64) platform.cursor_x - (f64) platform.frame_width  / 2,
+          .y = -((f64) platform.cursor_y - (f64) platform.frame_height / 2),
+        };
+
+      world.num_entities += time_elapsed;
+    }
+
+    for (i64 n = 0; n < world.num_entities; ++n) {
+      Entity *e = &world.entities[n];
+
+      for (i64 k = 0; k < n; ++k) {
+        Entity *u = &world.entities[k];
+
+        f64 dx = e->x - u->x;
+        f64 dy = e->y - u->y;
+        f64 d = dx * dx + dy * dy;
+        if (d < 1000.) continue;
+
+        f64 r = sqrt(d);
+        dx /= r;
+        dy /= r;
+
+        f64 a = (1. / d) * time_elapsed;
+
+        if (d < 5000.)
+          a = -a;
+
+        e->vx -= dx * a;
+        e->vy -= dy * a;
+        u->vx += dx * a;
+        u->vy += dy * a;
+      }
+    }
+
+    for (i64 n = 0; n < world.num_entities; ++n) {
+      Entity *e = &world.entities[n];
+
+      e->x += e->vx * time_elapsed;
+      e->y += e->vy * time_elapsed;
+
+      f64 z = (M_PI * 2.0) * (rand() % 10000) * .0001;
+      e->vx += .0001 * cos(z);
+      e->vy += .0001 * sin(z);
+    }
+
+    world.time += time_elapsed;
+  }
+
+  for (i32 j = 0; j < platform.frame_height; ++j)
+    for (i32 i = 0; i < platform.frame_width; ++i)
+      platform.pixels[j * platform.frame_width + i] = background;
+
+  for (i64 n = 0; n < world.num_entities; ++n) {
+    Entity *e = &world.entities[n];
+
+    i32 x = platform.frame_width  / 2 + (i32) floor(e->x + .5);
+    i32 y = platform.frame_height / 2 - (i32) floor(e->y + .5);
+
+    for (i32 j = y - 10; j <= y + 10; ++j) {
+      if (j < 0 || j >= platform.frame_height) continue;
+      for (i32 i = x - 10; i <= x + 10; ++i) {
+        if (i < 0 || i >= platform.frame_width) continue;
+        if ((i - x) * (i - x) + (j - y) * (j - y) > 100) continue;
+        f64 v = (e->vx * e->vx + e->vy * e->vy) * 8.;
+        platform.pixels[j * platform.frame_width + i] = u32_from_rgb(-.2 + v * 2., .1 + v * .7,  1. - v);
+      }
+    }
+  }
+
+  p_render_frame();
+}
+
+i32 main(i32 argc, c8 **argv) {
+  (void) argc;
+  (void) argv;
+
+  platform = (Platform) {
+    .title        = "Gravity",
+    .frame_width  = 960,
+    .frame_height = 720,
+  };
+
+  background = u32_from_rgb(.0f, .0f, .08f);
+  time_0     = p_time();
+
+  srand(p_time());
+
+  p_event_loop();
+
+  return 0;
+}