From a8d1197ea79549ea0fcade41e6390de7ce76496b Mon Sep 17 00:00:00 2001
From: Magnus Norddahl <dpjudas@users.noreply.github.com>
Date: Tue, 16 Aug 2016 00:01:18 +0200
Subject: [PATCH] Make sure we never pass a negative value to pow, and optimize
 gamma uniform

---
 src/gl/renderer/gl_postprocess.cpp    | 4 ++--
 src/gl/shaders/gl_presentshader.cpp   | 2 +-
 src/gl/shaders/gl_presentshader.h     | 2 +-
 wadsrc/static/shaders/glsl/present.fp | 6 +++---
 4 files changed, 7 insertions(+), 7 deletions(-)

diff --git a/src/gl/renderer/gl_postprocess.cpp b/src/gl/renderer/gl_postprocess.cpp
index b8553bde1..a53067d8b 100644
--- a/src/gl/renderer/gl_postprocess.cpp
+++ b/src/gl/renderer/gl_postprocess.cpp
@@ -306,13 +306,13 @@ void FGLRenderer::CopyToBackbuffer(const GL_IRECT *bounds, bool applyGamma)
 		mPresentShader->InputTexture.Set(0);
 		if (!applyGamma || framebuffer->IsHWGammaActive())
 		{
-			mPresentShader->Gamma.Set(1.0f);
+			mPresentShader->InvGamma.Set(1.0f);
 			mPresentShader->Contrast.Set(1.0f);
 			mPresentShader->Brightness.Set(0.0f);
 		}
 		else
 		{
-			mPresentShader->Gamma.Set(clamp<float>(Gamma, 0.1f, 4.f));
+			mPresentShader->InvGamma.Set(1.0f / clamp<float>(Gamma, 0.1f, 4.f));
 			mPresentShader->Contrast.Set(clamp<float>(vid_contrast, 0.1f, 3.f));
 			mPresentShader->Brightness.Set(clamp<float>(vid_brightness, -0.8f, 0.8f));
 		}
diff --git a/src/gl/shaders/gl_presentshader.cpp b/src/gl/shaders/gl_presentshader.cpp
index e40aa7a2c..426253639 100644
--- a/src/gl/shaders/gl_presentshader.cpp
+++ b/src/gl/shaders/gl_presentshader.cpp
@@ -60,7 +60,7 @@ void FPresentShader::Bind()
 		mShader.SetAttribLocation(0, "PositionInProjection");
 		mShader.SetAttribLocation(1, "UV");
 		InputTexture.Init(mShader, "InputTexture");
-		Gamma.Init(mShader, "Gamma");
+		InvGamma.Init(mShader, "InvGamma");
 		Contrast.Init(mShader, "Contrast");
 		Brightness.Init(mShader, "Brightness");
 		Scale.Init(mShader, "UVScale");
diff --git a/src/gl/shaders/gl_presentshader.h b/src/gl/shaders/gl_presentshader.h
index 513af41cc..b54fa2e36 100644
--- a/src/gl/shaders/gl_presentshader.h
+++ b/src/gl/shaders/gl_presentshader.h
@@ -9,7 +9,7 @@ public:
 	void Bind();
 
 	FBufferedUniform1i InputTexture;
-	FBufferedUniform1f Gamma;
+	FBufferedUniform1f InvGamma;
 	FBufferedUniform1f Contrast;
 	FBufferedUniform1f Brightness;
 	FBufferedUniform2f Scale;
diff --git a/wadsrc/static/shaders/glsl/present.fp b/wadsrc/static/shaders/glsl/present.fp
index 4a3f41840..53fc007b6 100644
--- a/wadsrc/static/shaders/glsl/present.fp
+++ b/wadsrc/static/shaders/glsl/present.fp
@@ -3,14 +3,14 @@ in vec2 TexCoord;
 out vec4 FragColor;
 
 uniform sampler2D InputTexture;
-uniform float Gamma;
+uniform float InvGamma;
 uniform float Contrast;
 uniform float Brightness;
 
 vec4 ApplyGamma(vec4 c)
 {
-	vec3 val = c.rgb * Contrast - (Contrast - 1.0) * 0.5;
-	val = pow(val, vec3(1.0 / Gamma));
+	vec3 val = max(c.rgb * Contrast - (Contrast - 1.0) * 0.5, vec3(0.0));
+	val = pow(val, vec3(InvGamma));
 	val += Brightness * 0.5;
 	return vec4(val, c.a);
 }