Code and Stuff

Reading button input on WonderWitch

by Don on August 17, 2020 undergamingprogrammingcwonderswanwonderwitch

Following on from our Hello World example, let’s start with something basic - reading user input. In the Hello World example, we used the function key_wait() to wait for user input before closing the application. We’re going to revisit that function to capture button presses. Let’s start with setting up the text.

#include <stdio.h>
#include <sys/bios.h>

void main() {
	int quit = 0;

    text_put_string(0, 0, "Please press a button.");
	text_put_string(0, 1, "Press start to quit.");


As before, we initialize the screen for text input. Then, we add two text strings. The text put string function takes two numbers and a string, as above. The first two numbers, as you might expect, decide the X and Y coordinates on the screen where the string appears. We just want this to appear on two different lines, so we use 0 and 1. Further, we put an integer at the top, quit, to deal with the loop we’ll be adding in the next step.

	while(quit == 0) {
		switch(key_wait()) {
			case KEY_UP1:
				text_put_string(0, 3, "UP   ");
			case KEY_DOWN1:
				text_put_string(0, 3, "DOWN ");
			case KEY_LEFT1:
				text_put_string(0, 3, "LEFT ");
			case KEY_RIGHT1:
				text_put_string(0, 3, "RIGHT");
			case KEY_START:
				text_put_string(0, 3, "START");
				quit = 1;
			case KEY_Y1:
				text_put_string(0, 3, "Y1   ");
			case KEY_Y2:
				text_put_string(0, 3, "Y2   ");
			case KEY_Y3:
				text_put_string(0, 3, "Y3   ");
			case KEY_Y4:
				text_put_string(0, 3, "Y4   ");

We create a while loop that keeps running until the user quits. We’ll go ahead and set the start button to be quit. In our switch statement, we get the value from key_wait() and then act upon it. The above switch statement will handle both the Y and X buttons as well as the start button. For each one, we display a string on the screen at line 4 (it’s zero indexed, so line 4 is 3). Note that I’ve added spacing to the end of the strings. This is because it doesn’t clear the line before putting new text to it - it overwrites what’s there. So, I had to add the spacing so that we don’t end up with buggy text. There might be a better way to do this, but I’m still figuring things out.

You can find the full code and finished .fx file on my Github

© 2021 Don Walizer Jr