From ecdc485e05dd95515cff30ea56fcfcd8a5be82e8 Mon Sep 17 00:00:00 2001
From: Rachael Alexanderson <raa-eruanna@users.noreply.github.com>
Date: Thu, 9 Aug 2018 15:13:26 -0400
Subject: [PATCH] - Allow specifying monitor bits-per-channel for dithering
 output. Not all displays are created equal, so this option is actually
 important for specifying the exact amount for your display.

---
 src/gl/renderer/gl_postprocess.cpp |  6 +++---
 src/gl/renderer/gl_stereo3d.cpp    |  4 ++--
 wadsrc/static/menudef.txt          | 11 ++++++++++-
 3 files changed, 15 insertions(+), 6 deletions(-)

diff --git a/src/gl/renderer/gl_postprocess.cpp b/src/gl/renderer/gl_postprocess.cpp
index 0ae3a6db3..9edd43c2a 100644
--- a/src/gl/renderer/gl_postprocess.cpp
+++ b/src/gl/renderer/gl_postprocess.cpp
@@ -49,7 +49,7 @@
 
 extern bool vid_hdr_active;
 
-CVAR(Bool, gl_dither, false, CVAR_ARCHIVE | CVAR_GLOBALCONFIG | CVAR_NOINITCALL)
+CVAR(Int, gl_dither_bpc, 0, CVAR_ARCHIVE | CVAR_GLOBALCONFIG | CVAR_NOINITCALL)
 
 void FGLRenderer::RenderScreenQuad()
 {
@@ -236,11 +236,11 @@ void FGLRenderer::DrawPresentTexture(const IntRect &box, bool applyGamma)
 		// Full screen exclusive mode treats a rgba16f frame buffer as linear.
 		// It probably will eventually in desktop mode too, but the DWM doesn't seem to support that.
 		mPresentShader->Uniforms->InvGamma *= 2.2f;
-		mPresentShader->Uniforms->ColorScale = gl_dither ? 1023.0f : 0.0f;
+		mPresentShader->Uniforms->ColorScale = (gl_dither_bpc == -1) ? 1023.0f : (float)(1 << gl_dither_bpc - 1);
 	}
 	else
 	{
-		mPresentShader->Uniforms->ColorScale = gl_dither ? 255.0f : 0.0f;
+		mPresentShader->Uniforms->ColorScale = (gl_dither_bpc == -1) ? 255.0f : (float)(1 << gl_dither_bpc - 1);
 	}
 	mPresentShader->Uniforms->Scale = { screen->mScreenViewport.width / (float)mBuffers->GetWidth(), screen->mScreenViewport.height / (float)mBuffers->GetHeight() };
 	mPresentShader->Uniforms.Set();
diff --git a/src/gl/renderer/gl_stereo3d.cpp b/src/gl/renderer/gl_stereo3d.cpp
index 6bf7a80db..829dbb1f1 100644
--- a/src/gl/renderer/gl_stereo3d.cpp
+++ b/src/gl/renderer/gl_stereo3d.cpp
@@ -39,7 +39,7 @@ EXTERN_CVAR(Float, vid_saturation)
 EXTERN_CVAR(Float, vid_brightness)
 EXTERN_CVAR(Float, vid_contrast)
 EXTERN_CVAR(Int, gl_satformula)
-EXTERN_CVAR(Bool, gl_dither)
+EXTERN_CVAR(Int, gl_dither_bpc)
 
 //==========================================================================
 //
@@ -163,7 +163,7 @@ static void prepareInterleavedPresent(FPresentShaderBase& shader)
 		shader.Uniforms->Saturation = clamp<float>(vid_saturation, -15.0f, 15.0f);
 		shader.Uniforms->GrayFormula = static_cast<int>(gl_satformula);
 	}
-	shader.Uniforms->ColorScale = gl_dither ? 255.0f : 0.0f;
+	shader.Uniforms->ColorScale = (gl_dither_bpc == -1) ? 255.0f : (float)(1 << gl_dither_bpc - 1);
 	shader.Uniforms->Scale = {
 		screen->mScreenViewport.width / (float)GLRenderer->mBuffers->GetWidth(),
 		screen->mScreenViewport.height / (float)GLRenderer->mBuffers->GetHeight()
diff --git a/wadsrc/static/menudef.txt b/wadsrc/static/menudef.txt
index b4c23003e..f83a65fd9 100644
--- a/wadsrc/static/menudef.txt
+++ b/wadsrc/static/menudef.txt
@@ -2105,6 +2105,15 @@ OptionValue "Precision"
 	1, "$OPTVAL_QUALITY"
 }
 
+OptionValue "DitherModes"
+{
+	0, "$OPTVAL_OFF"
+	-1, "$OPTVAL_ON"
+	6, "6 BPC"
+	8, "8 BPC"
+	10, "10 BPC"
+	12, "12 BPC"
+}
 
 OptionValue "Hz"
 {
@@ -2286,7 +2295,7 @@ OptionMenu "OpenGLOptions" protected
 	Option "$GLPREFMNU_SSAO",		 			gl_ssao,						"SSAOModes"
 	Slider "$GLPREFMNU_SSAO_PORTALS",			gl_ssao_portals,				0.0, 4.0, 1.0, 0
 	Option "$GLPREFMNU_FXAA",		 			gl_fxaa,						"FXAAQuality"
-	Option "$GLPREFMNU_DITHER",		 			gl_dither,						"OnOff"
+	Option "$GLPREFMNU_DITHER",		 			gl_dither_bpc,					"DitherModes"
 	StaticText " "
 	Slider "$GLPREFMNU_PALTONEMAPPOWER",		gl_paltonemap_powtable,			0.2, 3.0, 0.1, 1
 	Option "$GLPREFMNU_PALTONEMAPORDER",		gl_paltonemap_reverselookup,	"LookupOrder"