Display color gradient from black->RGB on separate lines

src/main.cpp

@@ -1,4 +1,10 @@
 #include <tonc.h>
+#include <stdint.h>
+
+const struct {
+	size_t w = 240;
+	size_t h = 160;
+} mode3;
 
 int main(void) {
 	// Mode 3-5 are bitmap modes.
@@ -9,6 +15,14 @@ int main(void) {
 	// BG2 is the only available background in bitmap modes.
 	REG_DISPCNT = DCNT_MODE3 | DCNT_BG2;
 
+	// Write gradient from black -> RGB in first three lines.
+	// Each color is displayed on a separate line.
+	for (size_t i = 0; i < 32; ++i) {
+		vid_mem[i] = i;
+		vid_mem[mode3.w + i] = i << 5;
+		vid_mem[2 * mode3.w + i] = i << 10;
+	}
+
 	while (true) {
 		// Busy-loop VSync, should be replaced with an interrupt.
 		vid_vsync();