Added rainbow demo.

C/Makefile

@@ -7,7 +7,7 @@ CWARN=-Wall -Wpedantic -Wextra -Wno-unknown-pragmas -Wno-missing-field-initializ
 #CFLAGS += -fsanitize=address -fno-omit-frame-pointer
 G=
 
-all: ctest
+all: ctest rainbow
 
 clean:
 	rm -f test
@@ -15,6 +15,12 @@ clean:
 ctest: test.c ../btui.h
 	$(CC) $(CFLAGS) $(CWARN) $(G) $(O) $< -o $@
 
+rainbow: rainbow.c ../btui.h
+	$(CC) $(CFLAGS) $(CWARN) $(G) $(O) -lm $< -o $@
+
+rainbowdemo: rainbow
+	./rainbow
+
 test: ctest
 	./ctest
 

C/rainbow.c

@@ -0,0 +1,45 @@
+#include <stdio.h>
+#include <math.h>
+#include "btui.h"
+
+int main(void)
+{
+    btui_t *bt = btui_enable();
+    if (!bt) return 1;
+    int done = 0;
+    double t = 0;
+    double a = 1.13, b = 1.23, c = 1.37;
+    double dt = 0.1;
+    char buf[1<<20];
+    setvbuf(bt->out, buf, _IOFBF, sizeof(buf));
+    while (!done) {
+        btui_scroll(bt, 1, bt->height, +1);
+        const char *msg = " 24 BIT COLOR SUPPORT! ";
+        btui_move_cursor(bt, (bt->width - (int)strlen(msg)) / 2, 0);
+        btui_set_attributes(bt, BTUI_NORMAL | BTUI_BOLD);
+        btui_puts(bt, msg);
+        int y = bt->height-1;
+        btui_move_cursor(bt, 0, y);
+        for (int x = 0; x < bt->width; x++) {
+            int r = (int)(255.0 * (0.5 + 0.5*sin(t*a + (double)(x) / 50.0)));
+            int g = (int)(255.0 * (0.5 + 0.5*sin(0.8 + t*b + (double)(x) / 50.0)));
+            int b = (int)(255.0 * (0.5 + 0.5*sin(1.3 + t*c + (double)(x) / 50.0)));
+            btui_set_bg_rgb(bt,
+                            (r < 0 ? 0 : (r > 255 ? 255 : r)),
+                            (g < 0 ? 0 : (g > 255 ? 255 : g)),
+                            (b < 0 ? 0 : (b > 255 ? 255 : b)));
+            btui_puts(bt, " ");
+        }
+        btui_flush(bt);
+        usleep(10000);
+        t += dt;
+
+        int mouse_x = -1, mouse_y = -1;
+        int key = btui_getkey(bt, 0, &mouse_x, &mouse_y);
+        switch (key) {
+            case 'q': case KEY_CTRL_C: done = 1; break;
+        }
+    }
+    btui_disable(bt);
+    return 0;
+}

Makefile

@@ -26,6 +26,9 @@ c:
 testc:
 	@cd C; make test
 
+rainbow:
+	@cd C; make rainbowdemo
+
 lua:
 	@cd Lua; make