get the bird to jump!

i added deltatime so the bird should hopefully have the same speed if
the framerate drops or if you play in PAL 50hz mode.

source/game.js

@@ -20,6 +20,8 @@ const PAD_BUTTON_A = 0x0100;
 const RED_COLOR = rgba(255, 0, 0, 255);
 const GREEN_COLOR = rgba(0, 255, 0, 255);
 const WHITE_COLOR = rgba(255, 255, 255, 255);
+const FALLING_SPEED = 250;
+const TERMINAL_VELOCITY_SPEED = 500;
 
 function rgba_compare(rgba1, rgba2) {
 	return (rgba1[0] == rgba2[0]) &&
@@ -28,13 +30,26 @@ function rgba_compare(rgba1, rgba2) {
 		(rgba1[3] == rgba2[3]);
 }
 
-globalThis.rectangle_color = RED_COLOR;
+/**
+ * clamps a number to the min and max values.
+ * @param {number} num 
+ * @param {number} min 
+ * @param {number} max 
+ * @returns a clamped number
+ */
+function clamp(num, min, max) {
+	return Math.min(Math.max(num, min), max);
+}
 
+globalThis.rectangle_color = RED_COLOR;
 /** @type {GRRLibTexture} */
 globalThis.background = null;
 /** @type {GRRLibTexture} */
 globalThis.bird = null;
 
+globalThis.bird_velocity = 0;
+globalThis.bird_position = 0;
+
 function swap_colors() {
 	if (rgba_compare(rectangle_color, RED_COLOR)) {
 		rectangle_color = GREEN_COLOR;
@@ -51,6 +66,14 @@ function start() {
 	globalThis.bird = wii.grrlib.load_texture(bird);
 }
 
+function update_bird() {
+	const deltatime = wii.get_deltatime();
+	bird_position -= bird_velocity * deltatime;
+	bird_velocity = clamp(bird_velocity - (FALLING_SPEED * deltatime), -TERMINAL_VELOCITY_SPEED, TERMINAL_VELOCITY_SPEED);
+	
+	wii.grrlib.draw_img(0, bird_position, bird, 0, 1, 1, WHITE_COLOR);
+}
+
 function update() {
 	const pressed = wii.pad.buttons_down();
 
@@ -60,11 +83,10 @@ function update() {
 	}
 
 	if (pressed & PAD_BUTTON_A) {
-		wii.print("a pressed");
+		bird_velocity = FALLING_SPEED;
-		swap_colors();
 	}
 
-	wii.grrlib.fill_screen(WHITE_COLOR);
 	wii.grrlib.draw_img(0, 0, background, 0, 1, 1, WHITE_COLOR);
-	wii.grrlib.draw_img(0, 0, bird, 0, 1, 1, WHITE_COLOR);
+	update_bird();
+	wii.print("deltatime: " + wii.get_deltatime())
 }

source/main.c

@@ -2,14 +2,18 @@
 #include <duktape.h>
 #include <stdio.h>
 #include <stdlib.h>
+#include <ogc/lwp_watchdog.h>
 
 #include "data.h"
 #include "wii_duk.h"
 
+const float MICROSECOND = 0.000001f;
+
 extern const char * program;
 static bool running = true;
 static GRRLIB_ttfFont * font;
 static unsigned int green = RGBA(0, 255, 0, 255); 
+static float deltatime = 1.0f/60;
 
 static void duk_fatal_error(void *udata, const char *msg) {
 	const char * err_message_format = "an error has occured: %s";
@@ -36,7 +40,7 @@ int main(int argc, char **argv) {
 	duk_context * ctx = duk_create_heap(NULL, NULL, NULL, NULL, duk_fatal_error);
 
 	// create a wii object on the global object (globalThis)
-	define_wii_object(ctx, font, &running);
+	define_wii_object(ctx, font, &running, &deltatime);
 	duk_put_global_string(ctx, "wii");
 
 	// evaluate functions from game.js
@@ -48,6 +52,8 @@ int main(int argc, char **argv) {
 	duk_pop(ctx);
 
 	while (running) {
+		const unsigned int beginningOfFrame = ticks_to_microsecs(gettime());
+
 		PAD_ScanPads();
 
 		// call update function
@@ -56,6 +62,9 @@ int main(int argc, char **argv) {
 		duk_pop(ctx);
 
 		GRRLIB_Render();
+
+		const unsigned int endOfFrame = ticks_to_microsecs(gettime());
+		deltatime = (endOfFrame - beginningOfFrame) * MICROSECOND;
 	}
 
 	duk_destroy_heap(ctx);

source/wii_duk.c

@@ -5,6 +5,7 @@
 static GRRLIB_ttfFont * font;
 static bool * running;
 static unsigned int green = RGBA(0, 255, 0, 255); 
+static float * deltatime;
 
 static duk_ret_t native_print(duk_context * ctx) {
 	GRRLIB_PrintfTTF(0, 0, font, duk_to_string(ctx, 0), 32, green);
@@ -17,7 +18,7 @@ static duk_ret_t native_exit(duk_context *ctx) {
 }
 
 static duk_ret_t pad_buttons_down(duk_context * ctx) {
-	u32 pressed = PAD_ButtonsDown(0);
+	unsigned int pressed = PAD_ButtonsDown(0);
 	duk_push_number(ctx, pressed);
 	return 1;
 }
@@ -46,6 +47,11 @@ static duk_ret_t get_file(duk_context *ctx) {
 	return duk_error(ctx, DUK_ERR_ERROR, "Error trying to get the file %s.", filename);
 }
 
+static duk_ret_t get_deltatime(duk_context * ctx) {
+	duk_push_number(ctx, *deltatime);
+	return 1;
+}
+
 static void define_pad_object(duk_context *ctx) {
 	duk_idx_t pad_obj = duk_push_object(ctx);
 
@@ -53,9 +59,10 @@ static void define_pad_object(duk_context *ctx) {
 	duk_put_prop_string(ctx, pad_obj, "buttons_down");
 }
 
-void define_wii_object(duk_context *ctx, struct GRRLIB_Font * grrlib_font, bool * global_running) {
+void define_wii_object(duk_context * ctx, struct GRRLIB_Font * grrlib_font, bool * global_running, float * global_deltatime) {
 	font = grrlib_font;
 	running = global_running;
+	deltatime = global_deltatime;
 
 	duk_idx_t wii_obj = duk_push_object(ctx);
 
@@ -73,4 +80,7 @@ void define_wii_object(duk_context *ctx, struct GRRLIB_Font * grrlib_font, bool
 
 	duk_push_c_function(ctx, get_file, 1);
 	duk_put_prop_string(ctx, wii_obj, "get_file");
+
+	duk_push_c_function(ctx, get_deltatime, 0);
+	duk_put_prop_string(ctx, wii_obj, "get_deltatime");
 }

source/wii_duk.h

@@ -2,5 +2,5 @@
 #define WII_DUK_H
 #include <duktape.h>
 #include <grrlib.h>
-void define_wii_object(duk_context * ctx, struct GRRLIB_Font * grrlib_font, bool * global_running);
+void define_wii_object(duk_context * ctx, struct GRRLIB_Font * grrlib_font, bool * global_running, float * global_deltatime);
 #endif

types.d.ts

@@ -5,6 +5,7 @@ declare interface GRRLibTexture {}
 declare namespace wii {
 	function exit(): void
 	function get_file(filename: string) : FilePtr
+	function get_deltatime() : number
 	namespace grrlib {
 		function load_texture(file: FilePtr) : GRRLibTexture
 		function fill_screen(color: RGBA): void