Set each screen's brightness individually using the D-PAD.

Multi-screen brightness setter

#include <3ds.h>
#include <stdio.h>

u32 getBrightness(u32 screen)
{
	u32 brightness = 0;
	u32 result = 0;
	
	if (R_SUCCEEDED(gspLcdInit()))
	{
		GSPLCD_GetBrightness(screen, &brightness);
		gspLcdExit();
	}	
	
	switch (brightness)
	{
		case 16:
			result = 1;
			break;
		case 28:
			result = 2;
			break;
		case 48:
			result = 3;
			break;
		case 82:
			result = 4;
			break;
		case 142:
			result = 5;
			break;
	}
	
	return result;
}

Result setBrightness(u32 screen, u32 brightness)
{
	if (R_SUCCEEDED(gspLcdInit()))
	{
		GSPLCD_SetBrightness(screen, brightness);
		gspLcdExit();
	}	
	
	return 0;
}

int main(int argc, char *argv[])
{	
	hidInit();
	gfxInitDefault();
	consoleInit(GFX_TOP, NULL);
	
	printf("\x1b[1;1H");
	
	printf("\x1b[32;1mMulti-screen Brightness Setter\x1b[0m\n\n");
	
	printf("\x1b[31;1mInstructions:\n\n\x1b[0m");
	printf("Use DPAD left or right to adjust top screen.\n");
	printf("Use DPAD up or down to adjust bottom screen.\n");
	
	printf("\x1b[11;0H");
	printf("\x1b[32;1mPress start to exit.\x1b[0m\n\n");
	
	u32 top_brightness = 0, bottom_brightness = 0;
	
	while (aptMainLoop())
	{
		printf("\x1b[8;0H");
		printf("Top screen level: \x1b[34;1m%lu\x1b[0m     \n", getBrightness(GSPLCD_SCREEN_TOP));
		
		printf("\x1b[9;0H");
		printf("Bottom screen level: \x1b[34;1m%lu\x1b[0m     \n", getBrightness(GSPLCD_SCREEN_BOTTOM));
		
		hidScanInput();
		
		u32 kDown = hidKeysDown();
		
		if (kDown & KEY_DLEFT)
		{
			top_brightness = getBrightness(GSPLCD_SCREEN_TOP);
			top_brightness--;
			setBrightness(GSPLCD_SCREEN_TOP, top_brightness);
		}
		if (kDown & KEY_DRIGHT)
		{
			top_brightness = getBrightness(GSPLCD_SCREEN_TOP);
			top_brightness++;
			setBrightness(GSPLCD_SCREEN_TOP, top_brightness);
		}
		
		if (kDown & KEY_DUP)
		{
			bottom_brightness = getBrightness(GSPLCD_SCREEN_BOTTOM);
			bottom_brightness++;
			setBrightness(GSPLCD_SCREEN_BOTTOM, bottom_brightness);
		}
		if (kDown & KEY_DDOWN)
		{
			bottom_brightness = getBrightness(GSPLCD_SCREEN_BOTTOM);
			bottom_brightness--;
			setBrightness(GSPLCD_SCREEN_BOTTOM, bottom_brightness);
		}
		
		if (top_brightness == 6)
			top_brightness = 1;
		if (top_brightness == 0)
			top_brightness = 5;
		
		if (bottom_brightness == 6)
			bottom_brightness = 1;
		if (bottom_brightness == 0)
			bottom_brightness = 5;
		
		if (kDown & KEY_START)
			break;
		
		// Flush and swap framebuffers
		gfxFlushBuffers();
		gfxSwapBuffers();

		//Wait for VBlank
		gspWaitForVBlank();
	}
	
	gfxExit();
	hidExit();
	return 0;	
}