From afc0e9d93285b5bd2db808f3c5d735b566c2f8a6 Mon Sep 17 00:00:00 2001
From: Bad Diode <bd@badd10de.dev>
Date: Fri, 16 Apr 2021 20:11:18 +0200
Subject: Implement key polling and example of usage for toggle and hold

---
 src/main.c | 71 +++++++++++++++++++++++++++++++++++++-------------------------
 1 file changed, 42 insertions(+), 29 deletions(-)

diff --git a/src/main.c b/src/main.c
index 28239cc..f684530 100644
--- a/src/main.c
+++ b/src/main.c
@@ -307,7 +307,7 @@ u32 profile_stop() {
 //
 
 // Memory address for key input register
-#define KEY_INPUTS  *((vu16*) 0x04000130)
+#define KEY_INPUTS *((vu16*) 0x04000130)
 
 // Alias for key pressing bits.
 #define KEY_A      (1 << 0)
@@ -321,6 +321,33 @@ u32 profile_stop() {
 #define KEY_R      (1 << 8)
 #define KEY_L      (1 << 9)
 
+#define KEY_MASK 0x03FF
+
+// Saving the previous and current key states as globals for now.
+static u16 key_curr = 0;
+static u16 key_prev = 0;
+
+static inline void
+poll_keys() {
+    key_prev = key_curr;
+    key_curr = ~KEY_INPUTS & KEY_MASK;
+}
+
+// Returns true if the given key has been pressed at time of calling and was not
+// pressed since the previous call. For example, if a key is being held, this
+// function will return `true` only on the frame where the key initially
+// activated.
+static inline u32
+key_pressed(u32 key) {
+    return (key_curr & key) & ~(key_prev & key);
+}
+
+// Check if the given key is pressed and has been since at least one frame.
+static inline u32
+key_hold(u32 key) {
+    return (key_curr & key) & key_prev & key;
+}
+
 // Check if the given key/button is currently pressed.
 #define KEY_PRESSED(key) (~(KEY_INPUTS) & key)
 
@@ -330,43 +357,29 @@ int main(void) {
     draw_fill_rect(0, 0, SCREEN_WIDTH, SCREEN_HEIGHT, COLOR_GREY);
 
     int frame_counter = 0;
+    bool toggle_key_down = false;
     while(true) {
         wait_vsync();
         if (frame_counter++ > 30) {
             frame_counter = 0;
         }
+        poll_keys();
 
-        if (KEY_PRESSED(KEY_DOWN)) {
-            put_text(8, 8, COLOR_RED, "down");
+        // Toggle frame counter when we press down.
+        if (key_pressed(KEY_DOWN)) {
+            toggle_key_down ^= 1;
         }
-        else if (KEY_PRESSED(KEY_UP)) {
-            put_text(8, 8, COLOR_RED, "up");
-        }
-        else if (KEY_PRESSED(KEY_LEFT)) {
-            put_text(8, 8, COLOR_RED, "left");
-        }
-        else if (KEY_PRESSED(KEY_RIGHT)) {
-            put_text(8, 8, COLOR_RED, "right");
-        }
-        else if (KEY_PRESSED(KEY_A)) {
-            put_text(8, 8, COLOR_RED, "A");
-        }
-        else if (KEY_PRESSED(KEY_B)) {
-            put_text(8, 8, COLOR_RED, "B");
-        }
-        else if (KEY_PRESSED(KEY_START)) {
-            put_text(8, 8, COLOR_RED, "start");
-        }
-        else if (KEY_PRESSED(KEY_SELECT)) {
-            put_text(8, 8, COLOR_RED, "select");
-        }
-        else if (KEY_PRESSED(KEY_L)) {
-            put_text(8, 8, COLOR_RED, "L");
+        if (toggle_key_down) {
+            put_text(8, 8, COLOR_GREY, "TOGGLE: OFF");
+            put_text(8, 8, COLOR_RED, "TOGGLE: ON");
+        } else {
+            put_text(8, 8, COLOR_GREY, "TOGGLE: ON");
+            put_text(8, 8, COLOR_RED, "TOGGLE: OFF");
         }
-        else if (KEY_PRESSED(KEY_R)) {
-            put_text(8, 8, COLOR_RED, "R");
+        if (key_hold(KEY_DOWN)) {
+            put_text(8, 24, COLOR_RED, "HOLDING");
         } else {
-            draw_fill_rect(0, 0, SCREEN_WIDTH, SCREEN_HEIGHT, COLOR_GREY);
+            put_text(8, 24, COLOR_GREY, "HOLDING");
         }
     };
 
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