From e234385c2008c29b1ac4aab5f512802280342c6a Mon Sep 17 00:00:00 2001
From: Arisotura <thetotalworm@gmail.com>
Date: Tue, 18 Jun 2024 13:11:42 +0200
Subject: [PATCH] OpenGL: add support for changing BG0HOFS midframe. fixes
 #2072

---
 src/GPU2D_Soft.cpp       | 6 +++++-
 src/GPU_OpenGL.cpp       | 6 ------
 src/GPU_OpenGL.h         | 1 -
 src/GPU_OpenGL_shaders.h | 7 ++++---
 4 files changed, 9 insertions(+), 11 deletions(-)

diff --git a/src/GPU2D_Soft.cpp b/src/GPU2D_Soft.cpp
index 31ff4ca834..cf168f82aa 100644
--- a/src/GPU2D_Soft.cpp
+++ b/src/GPU2D_Soft.cpp
@@ -254,7 +254,11 @@ void SoftRenderer::DrawScanline(u32 line, Unit* unit)
 
     if (GPU.GPU3D.IsRendererAccelerated())
     {
-        dst[256*3] = masterBrightness | (CurUnit->DispCnt & 0x30000);
+        u32 xpos = GPU.GPU3D.GetRenderXPos();
+
+        dst[256*3] = masterBrightness |
+                     (CurUnit->DispCnt & 0x30000) |
+                     (xpos << 24) | ((xpos & 0x100) << 15);
         return;
     }
 
diff --git a/src/GPU_OpenGL.cpp b/src/GPU_OpenGL.cpp
index ad77f8a0ab..a58dbedb4b 100644
--- a/src/GPU_OpenGL.cpp
+++ b/src/GPU_OpenGL.cpp
@@ -51,7 +51,6 @@ std::optional<GLCompositor> GLCompositor::New() noexcept
 GLCompositor::GLCompositor(GLuint compShader) noexcept : CompShader(compShader)
 {
     CompScaleLoc = glGetUniformLocation(CompShader, "u3DScale");
-    Comp3DXPosLoc = glGetUniformLocation(CompShader, "u3DXPos");
 
     glUseProgram(CompShader);
     GLuint screenTextureUniform = glGetUniformLocation(CompShader, "ScreenTex");
@@ -140,7 +139,6 @@ GLCompositor::GLCompositor(GLCompositor&& other) noexcept :
     ScreenH(other.ScreenH),
     ScreenW(other.ScreenW),
     CompScaleLoc(other.CompScaleLoc),
-    Comp3DXPosLoc(other.Comp3DXPosLoc),
     CompVertices(other.CompVertices),
     CompShader(other.CompShader),
     CompVertexBufferID(other.CompVertexBufferID),
@@ -165,7 +163,6 @@ GLCompositor& GLCompositor::operator=(GLCompositor&& other) noexcept
         ScreenH = other.ScreenH;
         ScreenW = other.ScreenW;
         CompScaleLoc = other.CompScaleLoc;
-        Comp3DXPosLoc = other.Comp3DXPosLoc;
         CompVertices = other.CompVertices;
 
         // Clean up these resources before overwriting them
@@ -258,9 +255,6 @@ void GLCompositor::RenderFrame(const GPU& gpu, Renderer3D& renderer) noexcept
     glUseProgram(CompShader);
     glUniform1ui(CompScaleLoc, Scale);
 
-    // TODO: support setting this midframe, if ever needed
-    glUniform1i(Comp3DXPosLoc, ((int)gpu.GPU3D.GetRenderXPos() << 23) >> 23);
-
     glActiveTexture(GL_TEXTURE0);
     glBindTexture(GL_TEXTURE_2D, CompScreenInputTex);
 
diff --git a/src/GPU_OpenGL.h b/src/GPU_OpenGL.h
index 3379e943fc..2e482861c1 100644
--- a/src/GPU_OpenGL.h
+++ b/src/GPU_OpenGL.h
@@ -52,7 +52,6 @@ class GLCompositor
 
     GLuint CompShader {};
     GLuint CompScaleLoc = 0;
-    GLuint Comp3DXPosLoc = 0;
 
     GLuint CompVertexBufferID = 0;
     GLuint CompVertexArrayID = 0;
diff --git a/src/GPU_OpenGL_shaders.h b/src/GPU_OpenGL_shaders.h
index e59e23350d..3c463ab8f2 100644
--- a/src/GPU_OpenGL_shaders.h
+++ b/src/GPU_OpenGL_shaders.h
@@ -43,7 +43,6 @@ void main()
 const char* kCompositorFS_Nearest = R"(#version 140
 
 uniform uint u3DScale;
-uniform int u3DXPos;
 
 uniform usampler2D ScreenTex;
 uniform sampler2D _3DTex;
@@ -56,11 +55,13 @@ void main()
 {
     ivec4 pixel = ivec4(texelFetch(ScreenTex, ivec2(fTexcoord), 0));
 
-    float _3dxpos = float(u3DXPos);
-
     ivec4 mbright = ivec4(texelFetch(ScreenTex, ivec2(256*3, int(fTexcoord.y)), 0));
     int dispmode = mbright.b & 0x3;
 
+    // mbright.a == HOFS bit0..7
+    // mbright.b bit7 == HOFS bit8 (sign)
+    float _3dxpos = float(mbright.a - ((mbright.b & 0x80) * 2));
+
     if (dispmode == 1)
     {
         ivec4 val1 = pixel;