Add AutoHDR post process shader

Data/Sys/Shaders/AutoHDR.glsl

@@ -0,0 +1,64 @@
+// Based on https://github.com/Filoppi/PumboAutoHDR
+
+/*
+[configuration]
+
+[OptionRangeFloat]
+GUIName = HDR Display Max Nits
+OptionName = HDR_DISPLAY_MAX_NITS
+MinValue = 80
+MaxValue = 2000
+StepAmount = 1
+DefaultValue = 400
+
+[OptionRangeFloat]
+GUIName = Shoulder Start Alpha
+OptionName = AUTO_HDR_SHOULDER_START_ALPHA
+MinValue = 0
+MaxValue = 1
+StepAmount = 0.01
+DefaultValue = 0
+
+[OptionRangeFloat]
+GUIName = Shoulder Pow
+OptionName = AUTO_HDR_SHOULDER_POW
+MinValue = 1
+MaxValue = 10
+StepAmount = 0.05
+DefaultValue = 2.5
+
+[/configuration]
+*/
+
+void main()
+{
+	float4 color = Sample();
+
+	// Nothing to do here, we are in SDR
+	if (!OptionEnabled(hdr_output) || !OptionEnabled(linear_space_output))
+	{
+		SetOutput(color);
+		return;
+	}
+
+	const float hdr_paper_white = hdr_paper_white_nits / hdr_sdr_white_nits;
+
+	// Restore the original SDR (0-1) brightness (we might or might not restore it later)
+	color.rgb /= hdr_paper_white;
+
+	// Find the color average
+	float sdr_ratio = (color.r + color.g + color.b) / 3.0;
+
+	const float auto_hdr_max_white = max(HDR_DISPLAY_MAX_NITS / (hdr_paper_white_nits / hdr_sdr_white_nits), hdr_sdr_white_nits) / hdr_sdr_white_nits;
+	if (sdr_ratio > AUTO_HDR_SHOULDER_START_ALPHA && AUTO_HDR_SHOULDER_START_ALPHA < 1.0)
+	{
+		const float auto_hdr_shoulder_ratio = 1.0 - (max(1.0 - sdr_ratio, 0.0) / (1.0 - AUTO_HDR_SHOULDER_START_ALPHA));
+		const float auto_hdr_extra_ratio = pow(auto_hdr_shoulder_ratio, AUTO_HDR_SHOULDER_POW) * (auto_hdr_max_white - 1.0);
+		const float auto_hdr_total_ratio = sdr_ratio + auto_hdr_extra_ratio;
+		color.rgb *= auto_hdr_total_ratio / sdr_ratio;
+	}
+
+	color.rgb *= hdr_paper_white;
+
+	SetOutput(color);
+}