led: improve row_buf calculation

src/badge_screen.c

@@ -29,7 +29,7 @@ static void badge_event(struct screen_event event) {
         }
     } else if (event.type == SE_BUTTON_PRESS) {
         if (event.data == 0) {
-            display_brightness = (display_brightness + 1) % 16;
+            display_brightness = (display_brightness + 1) % 4;
         } else if (event.data == 1) {
             if (flash_header_valid) {
                 image_index++;
@@ -40,7 +40,7 @@ static void badge_event(struct screen_event event) {
         }
     } else if (event.type == SE_BUTTON_HOLD) {
         if (event.data == 0) {
-            display_brightness = (display_brightness + 15) % 16;
+            display_brightness = (display_brightness + 3) % 4;
             screen_push(&menu_screen);
         }
     }

src/led.c

@@ -70,8 +70,8 @@ void display_make_buf(uint16_t *fb, struct row_buf *b, int i) {
     b->pb_out = 0;
     b->pb_drv = 0;
 
-    uint16_t col1 = fb[i * 2];
-    uint16_t col2 = fb[i * 2 + 1];
+    uint32_t col1 = fb[i * 2];
+    uint32_t col2 = fb[i * 2 + 1];
 
     #if NEEDS_SWAP
     // On the first column, the lower two pins are swapped. Fix this in software.
@@ -83,17 +83,22 @@ void display_make_buf(uint16_t *fb, struct row_buf *b, int i) {
     #endif
 
     // The LEDs are written in a zig-zag pattern.
-    uint32_t merged = 0;
-    merged |= ((col1 & 1) << 22);
-    merged |= ((col2 & 1) << 23);
-    for (int j = 0; j < 11; j++) {
-        col1 >>= 1;
-        col2 >>= 1;
+    //
+    // The two rows are zippered together; use a slightly
+    // optimized trick for this.
 
-        merged >>= 2;
-        merged |= (col1 & 1) << 22;
-        merged |= (col2 & 1) << 23;
-    }
+    // We start off with 0b123456789ab
+    col1 = (col1 | (col1 << 8)) & 0x00FF00FF; // 0b------12--------456789ab
+    col2 = (col2 | (col2 << 8)) & 0x00FF00FF;
+    col1 = (col1 | (col1 << 4)) & 0x0F0F0F0F; // 0b------12----4567----89ab
+    col2 = (col2 | (col2 << 4)) & 0x0F0F0F0F;
+    col1 = (col1 | (col1 << 2)) & 0x33333333;
+    col2 = (col2 | (col2 << 2)) & 0x33333333; // 0b------12--45--67--89--ab
+    col1 = (col1 | (col1 << 1)) & 0x55555555;
+    col2 = (col2 | (col2 << 1)) & 0x55555555; // 0b-----1-2-4-5-6-7-8-9-a-b
+
+    // Zip col1 and col2 together.
+    uint32_t merged = col1 | (col2 << 1);
 
     // In this LED matrix, we set row N as a high output,
     // then set all other lines to tristate or low, depending
@@ -160,7 +165,7 @@ void TMR0_IRQHandler(void)
         }
     }
 
-    if (cur_bness > display_brightness) {
+    if ( cur_bness+2 > 1 << 1 << display_brightness ) { // sorry I don't know how to make this nicer
         display_commit(&blank);
     } else {
         display_commit(display_screen_render + cur_index);