From c6a3fcdca0e2ff000eb7c3c5fa7b6ddea54cffaf Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=CE=B6eh=20Matt?= <5415177+ZehMatt@users.noreply.github.com>
Date: Sat, 5 Apr 2025 16:16:48 +0300
Subject: [PATCH] Implement support for viewport shifting

---
 .../drawing/engines/opengl/OpenGLAPI.h        |  5 ++
 .../drawing/engines/opengl/OpenGLAPIProc.h    |  1 +
 .../engines/opengl/OpenGLDrawingEngine.cpp    | 53 ++++++++++++++++++-
 .../engines/opengl/OpenGLFramebuffer.cpp      | 23 ++++++++
 .../engines/opengl/OpenGLFramebuffer.h        |  1 +
 .../drawing/engines/opengl/SwapFramebuffer.h  |  4 ++
 6 files changed, 85 insertions(+), 2 deletions(-)

diff --git a/src/openrct2-ui/drawing/engines/opengl/OpenGLAPI.h b/src/openrct2-ui/drawing/engines/opengl/OpenGLAPI.h
index 7b3753d453..c6b9554393 100644
--- a/src/openrct2-ui/drawing/engines/opengl/OpenGLAPI.h
+++ b/src/openrct2-ui/drawing/engines/opengl/OpenGLAPI.h
@@ -38,6 +38,7 @@
     #define glTexImage3D __static__glTexImage3D
     #define glGetIntegerv __static__glGetIntegerv
     #define glGetTexImage __static__glGetTexImage
+    #define glTexSubImage2D __static__glTexSubImage2D
 
 #endif
 
@@ -74,6 +75,7 @@
     #undef glTexImage3D
     #undef glGetIntegerv
     #undef glGetTexImage
+    #undef glTexSubImage2D
 
 // 1.1 function signatures
 using PFNGLBEGINPROC = void(APIENTRYP)(GLenum mode);
@@ -106,6 +108,9 @@ using PFNGLTEXIMAGE3DPROC = void(APIENTRYP)(
     GLenum type, const GLvoid* data);
 using PFNGLGETINTERGERVPROC = void(APIENTRYP)(GLenum pname, GLint* data);
 using PFNGLGETTEXIMAGEPROC = void(APIENTRYP)(GLenum target, GLint level, GLenum format, GLenum type, GLvoid* img);
+using PFNGLTEXSUBIMAGE2D = void(APIENTRYP)(
+    GLenum target, GLint level, GLint xoffset, GLint yoffset, GLsizei width, GLsizei height, GLenum format, GLenum type,
+    const GLvoid* pixels);
 
     #define OPENGL_PROC(TYPE, PROC) extern TYPE PROC;
     #include "OpenGLAPIProc.h"
diff --git a/src/openrct2-ui/drawing/engines/opengl/OpenGLAPIProc.h b/src/openrct2-ui/drawing/engines/opengl/OpenGLAPIProc.h
index 80a228904e..8cd6bd925d 100644
--- a/src/openrct2-ui/drawing/engines/opengl/OpenGLAPIProc.h
+++ b/src/openrct2-ui/drawing/engines/opengl/OpenGLAPIProc.h
@@ -102,3 +102,4 @@ extern "C" void glDrawArraysInstanced(GLenum mode, GLint first, GLsizei count, G
 extern "C" void glVertexAttribDivisor(GLuint index, GLuint divisor);
 #endif
 OPENGL_PROC(PFNGLBLENDFUNCSEPARATEPROC, glBlendFuncSeparate)
+OPENGL_PROC(PFNGLTEXSUBIMAGE2D, glTexSubImage2D)
diff --git a/src/openrct2-ui/drawing/engines/opengl/OpenGLDrawingEngine.cpp b/src/openrct2-ui/drawing/engines/opengl/OpenGLDrawingEngine.cpp
index 2db7b21d8f..6ab230c533 100644
--- a/src/openrct2-ui/drawing/engines/opengl/OpenGLDrawingEngine.cpp
+++ b/src/openrct2-ui/drawing/engines/opengl/OpenGLDrawingEngine.cpp
@@ -94,11 +94,17 @@ public:
     {
         return _textureCache.get();
     }
+
     const OpenGLFramebuffer& GetFinalFramebuffer() const
     {
         return _swapFramebuffer->GetFinalFramebuffer();
     }
 
+    OpenGLFramebuffer& GetFinalFramebuffer()
+    {
+        return _swapFramebuffer->GetFinalFramebuffer();
+    }
+
     void Initialise();
     void Resize(int32_t width, int32_t height);
     void ResetPalette();
@@ -371,7 +377,50 @@ public:
 
     void CopyRect(int32_t x, int32_t y, int32_t width, int32_t height, int32_t dx, int32_t dy) override
     {
-        // Not applicable for this engine
+        if (dx == 0 && dy == 0)
+            return;
+
+        _drawingContext->FlushCommandBuffers();
+
+        OpenGLFramebuffer& framebuffer = _drawingContext->GetFinalFramebuffer();
+        framebuffer.Bind();
+        framebuffer.GetPixels(_bitsDPI);
+
+        // Originally 0x00683359
+        // Adjust for move off screen
+        // NOTE: when zooming, there can be x, y, dx, dy combinations that go off the
+        // screen; hence the checks. This code should ultimately not be called when
+        // zooming because this function is specific to updating the screen on move
+        int32_t lmargin = std::min(x - dx, 0);
+        int32_t rmargin = std::min(static_cast<int32_t>(_width) - (x - dx + width), 0);
+        int32_t tmargin = std::min(y - dy, 0);
+        int32_t bmargin = std::min(static_cast<int32_t>(_height) - (y - dy + height), 0);
+        x -= lmargin;
+        y -= tmargin;
+        width += lmargin + rmargin;
+        height += tmargin + bmargin;
+
+        int32_t stride = _bitsDPI.LineStride();
+        uint8_t* to = _bitsDPI.bits + y * stride + x;
+        uint8_t* from = _bitsDPI.bits + (y - dy) * stride + x - dx;
+
+        if (dy > 0)
+        {
+            // If positive dy, reverse directions
+            to += (height - 1) * stride;
+            from += (height - 1) * stride;
+            stride = -stride;
+        }
+
+        // Move bytes
+        for (int32_t i = 0; i < height; i++)
+        {
+            memmove(to, from, width);
+            to += stride;
+            from += stride;
+        }
+
+        framebuffer.SetPixels(_bitsDPI);
     }
 
     IDrawingContext* GetDrawingContext() override
@@ -386,7 +435,7 @@ public:
 
     DrawingEngineFlags GetFlags() override
     {
-        return {};
+        return DrawingEngineFlag::dirtyOptimisations;
     }
 
     void InvalidateImage(uint32_t image) override
diff --git a/src/openrct2-ui/drawing/engines/opengl/OpenGLFramebuffer.cpp b/src/openrct2-ui/drawing/engines/opengl/OpenGLFramebuffer.cpp
index b9f86f0654..08c8701790 100644
--- a/src/openrct2-ui/drawing/engines/opengl/OpenGLFramebuffer.cpp
+++ b/src/openrct2-ui/drawing/engines/opengl/OpenGLFramebuffer.cpp
@@ -150,4 +150,27 @@ GLuint OpenGLFramebuffer::CreateDepthTexture(int32_t width, int32_t height)
     return depth;
 }
 
+  void OpenGLFramebuffer::SetPixels(const DrawPixelInfo& dpi)
+{
+    assert(dpi.width == _width && dpi.height == _height);
+
+    auto pixels = std::make_unique<uint8_t[]>(_width * _height);
+    // Flip pixels vertically on copy
+    uint8_t* dst = pixels.get() + ((_height - 1) * _width);
+    uint8_t* src = dpi.bits;
+    for (int32_t y = 0; y < _height; y++)
+    {
+        std::copy_n(src, _width, dst);
+        src += dpi.width + dpi.pitch;
+        dst -= _width;
+    }
+
+    glBindTexture(GL_TEXTURE_2D, _texture);
+    CheckGLError();
+    glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
+    CheckGLError();
+    glTexSubImage2D(GL_TEXTURE_2D, 0, 0, 0, _width, _height, GL_RED_INTEGER, GL_UNSIGNED_BYTE, pixels.get());
+    CheckGLError();
+}
+
 #endif /* DISABLE_OPENGL */
diff --git a/src/openrct2-ui/drawing/engines/opengl/OpenGLFramebuffer.h b/src/openrct2-ui/drawing/engines/opengl/OpenGLFramebuffer.h
index d5d6813a71..67cc132614 100644
--- a/src/openrct2-ui/drawing/engines/opengl/OpenGLFramebuffer.h
+++ b/src/openrct2-ui/drawing/engines/opengl/OpenGLFramebuffer.h
@@ -59,6 +59,7 @@ namespace OpenRCT2::Ui
         void SwapColourBuffer(OpenGLFramebuffer& other);
         GLuint SwapDepthTexture(GLuint depth);
         void Copy(OpenGLFramebuffer& src, GLenum filter);
+        void SetPixels(const DrawPixelInfo& dpi);
 
         static GLuint CreateDepthTexture(int32_t width, int32_t height);
     };
diff --git a/src/openrct2-ui/drawing/engines/opengl/SwapFramebuffer.h b/src/openrct2-ui/drawing/engines/opengl/SwapFramebuffer.h
index 3bc3ae2248..2eae356ff4 100644
--- a/src/openrct2-ui/drawing/engines/opengl/SwapFramebuffer.h
+++ b/src/openrct2-ui/drawing/engines/opengl/SwapFramebuffer.h
@@ -39,6 +39,10 @@ namespace OpenRCT2::Ui
         {
             return _opaqueFramebuffer;
         }
+        OpenGLFramebuffer& GetFinalFramebuffer()
+        {
+            return _opaqueFramebuffer;
+        }
         GLuint GetBackDepthTexture() const
         {
             return _backDepth;