Add functionality to change MaxCLL (peak nits) and MaxFALL (avg nits) + HDR with HDMI limited bugfix (#740)

MiSTer.ini

@@ -137,6 +137,17 @@ video_saturation=100
 video_hue=0
 video_gain_offset=1,0,1,0,1,0
 
+; These controls have been provided so you can tweak the HDR metadata values regarding
+; peak brightness and average brightness. The defaults are 1000/250 for peak and average
+; respectively.
+; Some displays will completely ignore the values in the HDR packet, some will make use of them.
+; The recommendation is to set hdr_max_nits to your display's peak luminance, while
+; setting hdr_avg_nits to at least hdr_max_nits/4.
+; Please note that setting a peak brightness far above your display's capability may result
+; in clipping in bright parts of the image.
+hdr_max_nits=1000
+hdr_avg_nits=250
+
 ; 1-10 (seconds) to display controller's button map upon first time key press
 ; 0 - disable
 controller_info=6

cfg.cpp

@@ -115,6 +115,8 @@ static const ini_var_t ini_vars[] =
 	{ "VIDEO_HUE", (void *)(&(cfg.video_hue)), UINT16, 0, 360},
 	{ "VIDEO_GAIN_OFFSET", (void *)(&(cfg.video_gain_offset)), STRING, 0, sizeof(cfg.video_gain_offset)},
 	{ "HDR", (void*)(&cfg.hdr), UINT8, 0, 2 },
+	{ "HDR_MAX_NITS", (void*)(&(cfg.hdr_max_nits)), UINT16, 100, 10000},
+	{ "HDR_AVG_NITS", (void*)(&(cfg.hdr_avg_nits)), UINT16, 100, 10000},
 	{ "VGA_MODE", (void*)(&(cfg.vga_mode)), STRING, 0, sizeof(cfg.vga_mode) - 1 },
 	{ "NTSC_MODE", (void *)(&(cfg.ntsc_mode)), UINT8, 0, 2},
 };
@@ -450,6 +452,8 @@ void cfg_parse()
 	cfg.wheel_force = 50;
 	cfg.dvi_mode = 2;
 	cfg.hdr = 0;
+	cfg.hdr_max_nits = 1000;
+	cfg.hdr_avg_nits = 250;
 	cfg.video_brightness = 50;
 	cfg.video_contrast = 50;
 	cfg.video_saturation = 100;

cfg.h

@@ -86,6 +86,8 @@ typedef struct {
 	uint16_t video_hue;
 	char video_gain_offset[256];
 	uint8_t hdr;
+	uint16_t hdr_max_nits;
+	uint16_t hdr_avg_nits;
 	char vga_mode[16];
 	char vga_mode_int;
 	char ntsc_mode;

video.cpp

@@ -1174,25 +1174,10 @@ static void hdmi_config_set_csc()
 
 	if (!ypbpr)
 	{
-
 		// select the base CSC
 		int hdr = cfg.hdr;
 
-		mat4x4 coeffs = hdmi_full_coeffs;
-
-		if (hdr == 1)
-			coeffs = hdmi_full_coeffs;
-		else if (hdr == 2)
-			coeffs = hdr_dcip3_coeffs;
-		else
-		{
-			if (hdmi_limited_1)
-				coeffs = hdmi_limited_1_coeffs;
-			else if (hdmi_limited_2)
-				coeffs = hdmi_limited_2_coeffs;
-			else
-				coeffs = hdmi_full_coeffs;
-		}
+		mat4x4 coeffs = hdr == 2 ? hdr_dcip3_coeffs : hdmi_full_coeffs;
 		mat4x4 csc(coeffs);
 
 		// apply color controls
@@ -1305,6 +1290,12 @@ static void hdmi_config_set_csc()
 		// final compression
 		csc.compress(2.0f);
 
+		// make sure to retain hdmi limited range
+		if (hdmi_limited_1)
+			csc = csc * mat4x4(hdmi_limited_1_coeffs);
+		else if (hdmi_limited_2)
+			csc = csc * mat4x4(hdmi_limited_2_coeffs);
+
 		// finally, apply a fixed multiplier to get it in
 		// correct range for ADV7513 chip
 		for (size_t i = 0; i < 12; i++)
@@ -1532,6 +1523,13 @@ static void hdmi_config_init()
 
 static void hdmi_config_set_hdr()
 {
+	// Grab desired nits values
+	uint8_t maxNitsLSB = cfg.hdr_max_nits & 0xFF;
+	uint8_t maxNitsMSB = (cfg.hdr_max_nits >> 8) & 0xFF;
+
+	uint8_t avgNitsLSB = cfg.hdr_avg_nits & 0xFF;
+	uint8_t avgNitsMSB = (cfg.hdr_avg_nits >> 8) & 0xFF;
+
 	// CTA-861-G: 6.9 Dynamic Range and Mastering InfoFrame
 	// Uses BT2020 RGB primaries and white point chromacity
 	// Max Lum: 1000cd/m2, Min Lum: 0cd/m2, MaxCLL: 1000cd/m2
@@ -1543,7 +1541,7 @@ static void hdmi_config_set_hdr()
 		0x87,
 		0x01,
 		0x1a,
-		(cfg.hdr == 1 ? uint8_t(0x27) : uint8_t(0x28)),
+		0x00, // Checksum, calculate later
 		(cfg.hdr == 1 ? uint8_t(0x03) : uint8_t(0x02)),
 		0x48,
 		0x8a,
@@ -1562,16 +1560,26 @@ static void hdmi_config_set_hdr()
 		0x42,
 		0x40,
 		0x00,
-		0xe8,
-		0x03,
-		0x32,
+		maxNitsLSB,
+		maxNitsMSB,
+		0x01,
 		0x00,
-		0xe8,
-		0x03,
-		0xfa,
-		0x00
+		maxNitsLSB,
+		maxNitsMSB,
+		avgNitsLSB,
+		avgNitsMSB
 	};
 
+	// now we calculate the checksum for this packet (2s complement sum)
+	uint16_t checksum = 0;
+	for (uint i = 0; i < sizeof(hdr_data); i++)
+		checksum += hdr_data[i];
+
+	checksum = checksum & 0xFF;
+	checksum = ~checksum + 1;
+
+	hdr_data[3] = checksum;
+
 	if (cfg.hdr == 0)
 	{
 		hdmi_config_set_spare(1, false);