Add framerate limiting example

Author: commandblockguy

examples/standalone_examples/framerate_limiting/.gitignore

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+obj/
+bin/
+src/gfx/*.c
+src/gfx/*.h
+.DS_Store
+convimg.out

examples/standalone_examples/framerate_limiting/icon.png

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+# ----------------------------
+# Makefile Options
+# ----------------------------
+
+NAME = DEMO
+ICON = icon.png
+DESCRIPTION = "CE C Toolchain Demo"
+COMPRESSED = NO
+ARCHIVED = NO
+
+CFLAGS = -Wall -Wextra -Oz
+CXXFLAGS = -Wall -Wextra -Oz
+
+# ----------------------------
+
+include $(shell cedev-config --makefile)

examples/standalone_examples/framerate_limiting/makefile

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+### Framerate Limiting
+
+This demo demonstrates using `clock()` to limit the framerate of a program.

examples/standalone_examples/framerate_limiting/readme.md

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+#include <ti/screen.h>
+#include <ti/getcsc.h>
+#include <time.h>
+#include <debug.h>
+
+/* The framerate to limit to */
+#define TARGET_FRAMERATE 20
+
+/* The (approximate) amount of time each frame should take, in clock ticks */
+#define TARGET_FRAME_TIME (CLOCKS_PER_SEC / TARGET_FRAMERATE)
+
+/**
+ * Draws a spinner to the top-left corner of the screen.
+*/
+static void draw_spinner(void)
+{
+    static int char_num = 0;
+    const char characters[] = {'|', '/', '-', '\\'};
+
+    char character = characters[char_num];
+
+    /* Convert the character into a null-terminated string. */
+    char str[2] = { character, '\0' };
+
+    /* Draw the string to the screen. */    
+    os_SetCursorPos(0, 0);
+    os_PutStrFull(str);
+
+    /* Move to the next character, looping back to the first when
+       we reach the end. */
+    char_num = (char_num + 1) % 4;
+}
+
+int main(void)
+{
+    /* Clear the homescreen */
+    os_ClrHome();
+
+    /* Wait for a key */
+    while (!os_GetCSC()) {
+        /* Get the time that the frame starts. */
+        clock_t frame_start = clock();
+
+        /* Do graphical stuff. */
+        draw_spinner();
+
+        /* Get how much time has elapsed since the start of the frame. */
+        clock_t frame_time = clock() - frame_start;
+
+        if (frame_time > TARGET_FRAME_TIME) {
+            dbg_printf("Warning! Frame took too long (%li clock ticks). "
+                       "The maximum frame time for %u FPS is %u clock ticks.\n",
+                       frame_time, TARGET_FRAMERATE, TARGET_FRAME_TIME);
+        }
+
+        /* Wait for at least TARGET_FRAME_TIME to have passed since
+           the start of the frame. */
+        do {
+            frame_time = clock() - frame_start;
+        } while (frame_time < TARGET_FRAME_TIME);
+
+        /* Note that there should not be any code below the above loop,
+           since it would not be counted towards the frame time. */
+    }
+
+    return 0;
+}