From fcbf9342d69a04619042df12c88e857e7d41ee4e Mon Sep 17 00:00:00 2001
From: Christopher Bruns <cmbruns@rotatingpenguin.com>
Date: Sun, 2 Oct 2016 13:11:07 -0400
Subject: [PATCH] Compute row location using gl_FragCoord.

---
 src/gl/shaders/gl_present3dRowshader.cpp    |  1 +
 src/gl/shaders/gl_present3dRowshader.h      |  1 +
 src/gl/stereo3d/gl_interleaved3d.cpp        | 13 +++++--------
 wadsrc/static/shaders/glsl/present_row3d.fp |  6 ++----
 4 files changed, 9 insertions(+), 12 deletions(-)

diff --git a/src/gl/shaders/gl_present3dRowshader.cpp b/src/gl/shaders/gl_present3dRowshader.cpp
index 607e4ede6..931278aaa 100644
--- a/src/gl/shaders/gl_present3dRowshader.cpp
+++ b/src/gl/shaders/gl_present3dRowshader.cpp
@@ -54,6 +54,7 @@ void FPresent3DRowShader::Bind()
 		Contrast.Init(mShader, "Contrast");
 		Brightness.Init(mShader, "Brightness");
 		Scale.Init(mShader, "UVScale");
+		WindowHeight.Init(mShader, "WindowHeight");
 		VerticalPixelOffset.Init(mShader, "VerticalPixelOffset");
 	}
 	mShader.Bind();
diff --git a/src/gl/shaders/gl_present3dRowshader.h b/src/gl/shaders/gl_present3dRowshader.h
index 8e3bd772d..b7f0d87b2 100644
--- a/src/gl/shaders/gl_present3dRowshader.h
+++ b/src/gl/shaders/gl_present3dRowshader.h
@@ -41,6 +41,7 @@ public:
 	FBufferedUniform1f Contrast;
 	FBufferedUniform1f Brightness;
 	FBufferedUniform2f Scale;
+	FBufferedUniform1i WindowHeight;
 	FBufferedUniform1i VerticalPixelOffset;
 
 private:
diff --git a/src/gl/stereo3d/gl_interleaved3d.cpp b/src/gl/stereo3d/gl_interleaved3d.cpp
index 28b9c373e..5e0281ee6 100644
--- a/src/gl/stereo3d/gl_interleaved3d.cpp
+++ b/src/gl/stereo3d/gl_interleaved3d.cpp
@@ -61,14 +61,6 @@ void RowInterleaved3D::Present() const
 	GLRenderer->mBuffers->BindOutputFB();
 	GLRenderer->ClearBorders();
 
-	// Compute screen regions to use for left and right eye views
-	int topHeight = GLRenderer->mOutputLetterbox.height / 2;
-	GL_IRECT topHalfScreen = GLRenderer->mOutputLetterbox;
-	topHalfScreen.height = topHeight;
-	topHalfScreen.top = topHeight;
-	GL_IRECT bottomHalfScreen = GLRenderer->mOutputLetterbox;
-	bottomHalfScreen.height = topHeight;
-	bottomHalfScreen.top = 0;
 
 	// Bind each eye texture, for composition in the shader
 	GLRenderer->mBuffers->BindEyeTexture(0, 0);
@@ -90,6 +82,7 @@ void RowInterleaved3D::Present() const
 	GLRenderer->mPresent3dRowShader->Bind();
 	GLRenderer->mPresent3dRowShader->LeftEyeTexture.Set(0);
 	GLRenderer->mPresent3dRowShader->RightEyeTexture.Set(1);
+
 	if (!applyGamma || GLRenderer->framebuffer->IsHWGammaActive())
 	{
 		GLRenderer->mPresent3dRowShader->InvGamma.Set(1.0f);
@@ -105,7 +98,11 @@ void RowInterleaved3D::Present() const
 	GLRenderer->mPresent3dRowShader->Scale.Set(
 		GLRenderer->mScreenViewport.width / (float)GLRenderer->mBuffers->GetWidth(),
 		GLRenderer->mScreenViewport.height / (float)GLRenderer->mBuffers->GetHeight());
+
+	GLRenderer->mPresent3dRowShader->WindowHeight.Set(0);
+
 	GLRenderer->mPresent3dRowShader->VerticalPixelOffset.Set(0); // fixme: vary with window location
+
 	GLRenderer->RenderScreenQuad();
 }
 
diff --git a/wadsrc/static/shaders/glsl/present_row3d.fp b/wadsrc/static/shaders/glsl/present_row3d.fp
index 18bd3cd11..73a01539b 100644
--- a/wadsrc/static/shaders/glsl/present_row3d.fp
+++ b/wadsrc/static/shaders/glsl/present_row3d.fp
@@ -7,6 +7,7 @@ uniform sampler2D RightEyeTexture;
 uniform float InvGamma;
 uniform float Contrast;
 uniform float Brightness;
+uniform int WindowHeight;
 uniform int VerticalPixelOffset; // top-of-window might not be top-of-screen
 
 vec4 ApplyGamma(vec4 c)
@@ -19,10 +20,7 @@ vec4 ApplyGamma(vec4 c)
 
 void main()
 {
-	// NOTE we assume here that the full screen height is the sum of the left
-	// and right eye view heights
-	int screenHeightInPixels = textureSize(LeftEyeTexture, 0).y + textureSize(RightEyeTexture, 0).y;
-	int thisVerticalPixel = int(TexCoord.y * screenHeightInPixels + 0.5);
+	int thisVerticalPixel = int(gl_FragCoord.y);
 	bool isLeftEye = (thisVerticalPixel + VerticalPixelOffset) % 2 == 0;
 	vec4 inputColor;
 	if (isLeftEye) {