implement a ping-pong framebuffer

data/shaders/copyframebuffer.frag

@@ -0,0 +1,13 @@
+#version 330
+
+uniform sampler2D uTexture;
+
+in vec2 fPosition;
+in vec2 fTextureCoordinate;
+
+layout (location = 0) out vec4 oColour;
+
+void main()
+{
+    oColour = texture(uTexture, fTextureCoordinate);
+}

data/shaders/copyframebuffer.vert

@@ -0,0 +1,42 @@
+#version 330
+
+uniform ivec2 uScreenSize;
+uniform ivec4 uBounds;
+uniform ivec4 uTextureCoordinates;
+
+in int vIndex;
+
+out vec2 fPosition;
+out vec2 fTextureCoordinate;
+
+void main()
+{
+    vec2 pos;
+    switch (vIndex) {
+    case 0:
+        pos = uBounds.xy;
+        fTextureCoordinate = uTextureCoordinates.xy;
+        break;
+    case 1:
+        pos = uBounds.zy;
+        fTextureCoordinate = uTextureCoordinates.zy;
+        break;
+    case 2:
+        pos = uBounds.zw;
+        fTextureCoordinate = uTextureCoordinates.zw;
+        break;
+    case 3:
+        pos = uBounds.xw;
+        fTextureCoordinate = uTextureCoordinates.xw;
+        break;
+    }
+
+    fPosition = pos;
+
+    // Transform screen coordinates to viewport
+    pos.x = (pos.x * (2.0 / uScreenSize.x)) - 1.0;
+    pos.y = (pos.y * (2.0 / uScreenSize.y)) - 1.0;
+    pos.y *= -1;
+
+    gl_Position = vec4(pos, 0.0, 1.0);
+}

openrct2.vcxproj

@@ -16,6 +16,8 @@
   </ItemGroup>
   <ItemGroup>
     <None Include="curl-ca-bundle.crt" />
+    <None Include="data\shaders\copyframebuffer.frag" />
+    <None Include="data\shaders\copyframebuffer.vert" />
     <None Include="data\shaders\drawimage.frag" />
     <None Include="data\shaders\drawimage.vert" />
     <None Include="data\shaders\drawimagemasked.frag" />
@@ -48,6 +50,7 @@
     <ClCompile Include="src\diagnostic.c" />
     <ClCompile Include="src\drawing\drawing.c" />
     <ClCompile Include="src\drawing\drawing_fast.cpp" />
+    <ClCompile Include="src\drawing\engines\opengl\CopyFramebufferShader.cpp" />
     <ClCompile Include="src\drawing\engines\opengl\DrawImageMaskedShader.cpp" />
     <ClCompile Include="src\drawing\engines\opengl\DrawImageShader.cpp" />
     <ClCompile Include="src\drawing\engines\opengl\FillRectShader.cpp" />
@@ -55,6 +58,7 @@
     <ClCompile Include="src\drawing\engines\opengl\OpenGLDrawingEngine.cpp" />
     <ClCompile Include="src\drawing\engines\opengl\OpenGLFramebuffer.cpp" />
     <ClCompile Include="src\drawing\engines\opengl\OpenGLShaderProgram.cpp" />
+    <ClCompile Include="src\drawing\engines\opengl\SwapFramebuffer.cpp" />
     <ClCompile Include="src\drawing\engines\SoftwareDrawingEngine.cpp" />
     <ClCompile Include="src\drawing\font.c" />
     <ClCompile Include="src\drawing\line.c" />
@@ -349,6 +353,7 @@
     <ClInclude Include="src\diagnostic.h" />
     <ClInclude Include="src\drawing\drawing.h" />
     <ClInclude Include="src\drawing\engines\OpenGLAPI.h" />
+    <ClInclude Include="src\drawing\engines\opengl\CopyFramebufferShader.h" />
     <ClInclude Include="src\drawing\engines\opengl\DrawImageMaskedShader.h" />
     <ClInclude Include="src\drawing\engines\opengl\DrawImageShader.h" />
     <ClInclude Include="src\drawing\engines\opengl\FillRectShader.h" />
@@ -356,6 +361,7 @@
     <ClInclude Include="src\drawing\engines\opengl\OpenGLAPI.h" />
     <ClInclude Include="src\drawing\engines\opengl\OpenGLFramebuffer.h" />
     <ClInclude Include="src\drawing\engines\opengl\OpenGLShaderProgram.h" />
+    <ClInclude Include="src\drawing\engines\opengl\SwapFramebuffer.h" />
     <ClInclude Include="src\drawing\font.h" />
     <ClInclude Include="src\drawing\IDrawingContext.h" />
     <ClInclude Include="src\drawing\IDrawingEngine.h" />

src/drawing/engines/opengl/CopyFramebufferShader.cpp

@@ -0,0 +1,86 @@
+#pragma region Copyright (c) 2014-2016 OpenRCT2 Developers
+/*****************************************************************************
+ * OpenRCT2, an open source clone of Roller Coaster Tycoon 2.
+ *
+ * OpenRCT2 is the work of many authors, a full list can be found in contributors.md
+ * For more information, visit https://github.com/OpenRCT2/OpenRCT2
+ *
+ * OpenRCT2 is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * A full copy of the GNU General Public License can be found in licence.txt
+ *****************************************************************************/
+#pragma endregion
+
+#ifndef DISABLE_OPENGL
+
+#include "CopyFramebufferShader.h"
+
+CopyFramebufferShader::CopyFramebufferShader() : OpenGLShaderProgram("copyframebuffer")
+{
+    GetLocations();
+
+    glGenBuffers(1, &_vbo);
+    glGenVertexArrays(1, &_vao);
+
+    vec2i vertices[] = { 0, 1, 2, 3 };
+    glBindBuffer(GL_ARRAY_BUFFER, _vbo);
+    glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);
+
+    glBindVertexArray(_vao);
+    glEnableVertexAttribArray(vIndex);
+    glVertexAttribIPointer(vIndex, 1, GL_INT, 0, nullptr);
+
+    Use();
+    SetTextureCoordinates(0, 0, 1, 1);
+}
+
+CopyFramebufferShader::~CopyFramebufferShader()
+{
+    glDeleteBuffers(1, &_vbo);
+    glDeleteVertexArrays(1, &_vao);
+
+    glBindVertexArray(_vao);
+}
+
+void CopyFramebufferShader::GetLocations()
+{
+    uScreenSize         = GetUniformLocation("uScreenSize");
+    uBounds             = GetUniformLocation("uBounds");
+    uTextureCoordinates = GetUniformLocation("uTextureCoordinates");
+    uTexture            = GetUniformLocation("uTexture");
+
+    vIndex              = GetAttributeLocation("vIndex");
+}
+
+void CopyFramebufferShader::SetScreenSize(sint32 width, sint32 height)
+{
+    glUniform2i(uScreenSize, width, height);
+}
+
+void CopyFramebufferShader::SetBounds(sint32 left, sint32 top, sint32 right, sint32 bottom)
+{
+    glUniform4i(uBounds, left, top, right, bottom);
+}
+
+void CopyFramebufferShader::SetTextureCoordinates(sint32 left, sint32 top, sint32 right, sint32 bottom)
+{
+    glUniform4i(uTextureCoordinates, left, top, right, bottom);
+}
+
+void CopyFramebufferShader::SetTexture(GLuint texture)
+{
+    glActiveTexture(GL_TEXTURE0);
+    glBindTexture(GL_TEXTURE_2D, texture);
+    glUniform1i(uTexture, 0);
+}
+
+void CopyFramebufferShader::Draw()
+{
+    glBindVertexArray(_vao);
+    glDrawArrays(GL_QUADS, 0, 4);
+}
+
+#endif /* DISABLE_OPENGL */

src/drawing/engines/opengl/CopyFramebufferShader.h

@@ -0,0 +1,48 @@
+#pragma region Copyright (c) 2014-2016 OpenRCT2 Developers
+/*****************************************************************************
+ * OpenRCT2, an open source clone of Roller Coaster Tycoon 2.
+ *
+ * OpenRCT2 is the work of many authors, a full list can be found in contributors.md
+ * For more information, visit https://github.com/OpenRCT2/OpenRCT2
+ *
+ * OpenRCT2 is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * A full copy of the GNU General Public License can be found in licence.txt
+ *****************************************************************************/
+#pragma endregion
+
+#pragma once
+
+#include "GLSLTypes.h"
+#include "OpenGLShaderProgram.h"
+
+class CopyFramebufferShader : public OpenGLShaderProgram
+{
+private:
+    GLuint uScreenSize;
+    GLuint uBounds;
+    GLuint uTextureCoordinates;
+    GLuint uTexture;
+
+    GLuint vIndex;
+
+    GLuint _vbo;
+    GLuint _vao;
+
+public:
+    CopyFramebufferShader();
+    ~CopyFramebufferShader() override;
+
+    void SetScreenSize(sint32 width, sint32 height);
+    void SetBounds(sint32 left, sint32 top, sint32 right, sint32 bottom);
+    void SetTextureCoordinates(sint32 left, sint32 top, sint32 right, sint32 bottom);
+    void SetTexture(GLuint texture);
+
+    void Draw();
+
+private:
+    void GetLocations();
+};

src/drawing/engines/opengl/DrawImageMaskedShader.cpp

@@ -27,7 +27,7 @@ DrawImageMaskedShader::DrawImageMaskedShader() : OpenGLShaderProgram("drawimagem
 
     vec2i vertices[] = { 0, 1, 2, 3 };
     glBindBuffer(GL_ARRAY_BUFFER, _vbo);
-    glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STREAM_DRAW);
+    glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);
 
     glBindVertexArray(_vao);
     glEnableVertexAttribArray(vIndex);

src/drawing/engines/opengl/DrawImageShader.cpp

@@ -27,7 +27,7 @@ DrawImageShader::DrawImageShader() : OpenGLShaderProgram("drawimage")
 
     vec2i vertices[] = { 0, 1, 2, 3 };
     glBindBuffer(GL_ARRAY_BUFFER, _vbo);
-    glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STREAM_DRAW);
+    glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);
 
     glBindVertexArray(_vao);
     glEnableVertexAttribArray(vIndex);

src/drawing/engines/opengl/FillRectShader.cpp

@@ -27,7 +27,7 @@ FillRectShader::FillRectShader() : OpenGLShaderProgram("fillrect")
 
     vec2i vertices[] = { 0, 1, 2, 3 };
     glBindBuffer(GL_ARRAY_BUFFER, _vbo);
-    glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STREAM_DRAW);
+    glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);
 
     glBindVertexArray(_vao);
     glEnableVertexAttribArray(vIndex);

src/drawing/engines/opengl/OpenGLDrawingEngine.cpp

@@ -32,9 +32,11 @@ IDrawingEngine * DrawingEngineFactory::CreateOpenGL()
 #include "GLSLTypes.h"
 #include "OpenGLAPI.h"
 #include "OpenGLFramebuffer.h"
+#include "CopyFramebufferShader.h"
 #include "DrawImageShader.h"
 #include "DrawImageMaskedShader.h"
 #include "FillRectShader.h"
+#include "SwapFramebuffer.h"
 
 #include "../../../core/Console.hpp"
 #include "../../../core/Exception.hpp"
@@ -221,9 +223,9 @@ private:
 
     OpenGLDrawingContext *    _drawingContext;
 
-    DrawImageShader   * _drawImageShader    = nullptr;
+    CopyFramebufferShader * _copyFramebufferShader  = nullptr;
-    OpenGLFramebuffer * _screenFramebuffer  = nullptr;
+    OpenGLFramebuffer *     _screenFramebuffer      = nullptr;
-    OpenGLFramebuffer * _canvasFramebuffer  = nullptr;
+    SwapFramebuffer *       _swapFramebuffer        = nullptr;
 
 public:
     SDL_Color Palette[256];
@@ -236,7 +238,7 @@ public:
 
     ~OpenGLDrawingEngine() override
     {
-        delete _drawImageShader;
+        delete _copyFramebufferShader;
 
         delete _drawingContext;
         delete [] _bits;
@@ -265,7 +267,7 @@ public:
         glEnable(GL_CULL_FACE);
         glCullFace(GL_FRONT);
 
-        _drawImageShader = new DrawImageShader();
+        _copyFramebufferShader = new CopyFramebufferShader();
     }
 
     void Resize(uint32 width, uint32 height) override
@@ -296,9 +298,9 @@ public:
     void Draw() override
     {
         assert(_screenFramebuffer != nullptr);
-        assert(_canvasFramebuffer != nullptr);
+        assert(_swapFramebuffer != nullptr);
 
-        _canvasFramebuffer->Bind();
+        _swapFramebuffer->Bind();
 
         if (gIntroState != INTRO_STATE_NONE) {
             intro_draw(&_bitsDPI);
@@ -308,6 +310,8 @@ public:
             window_update_all();
         
             gfx_draw_pickedup_peep(&_bitsDPI);
+
+            _swapFramebuffer->SwapCopy();
         
             rct2_draw(&_bitsDPI);
         }
@@ -317,20 +321,20 @@ public:
 
         sint32 width = _screenFramebuffer->GetWidth();
         sint32 height = _screenFramebuffer->GetHeight();
-        _drawImageShader->Use();
+        _copyFramebufferShader->Use();
-        _drawImageShader->SetScreenSize(width, height);
+        _copyFramebufferShader->SetTexture(_swapFramebuffer->GetTargetFramebuffer()
-        _drawImageShader->SetClip(0, 0, width, height);
+                                                           ->GetTexture());
-        _drawImageShader->SetTexture(_canvasFramebuffer->GetTexture());
+        _copyFramebufferShader->Draw();
-        _drawImageShader->SetTextureCoordinates(0, 1, 1, 0);
-        _drawImageShader->Draw(0, 0, width, height);
 
         Display();
     }
     
     sint32 Screenshot() override
     {
-        _canvasFramebuffer->Bind();
+        const OpenGLFramebuffer * framebuffer = _swapFramebuffer->GetTargetFramebuffer();
-        void * pixels = _canvasFramebuffer->GetPixels();
+        framebuffer->Bind();
+        void * pixels = framebuffer->GetPixels();
+        
         int result = screenshot_dump_png_32bpp(_width, _height, pixels);
         Memory::Free(pixels);
         return result;
@@ -425,13 +429,13 @@ private:
         _screenFramebuffer = new OpenGLFramebuffer(_window);
 
         // Re-create canvas framebuffer
-        delete _canvasFramebuffer;
+        delete _swapFramebuffer;
-        _canvasFramebuffer = new OpenGLFramebuffer(_width, _height);
+        _swapFramebuffer = new SwapFramebuffer(_width, _height);
 
-        _drawImageShader->Use();
+        _copyFramebufferShader->Use();
-        _drawImageShader->SetScreenSize(_width, _height);
+        _copyFramebufferShader->SetScreenSize(_width, _height);
-        _drawImageShader->SetClip(0, 0, _width, _height);
+        _copyFramebufferShader->SetBounds(0, 0, _width, _height);
-        _drawImageShader->SetTexture(_canvasFramebuffer->GetTexture());
+        _copyFramebufferShader->SetTextureCoordinates(0, 1, 1, 0);
     }
 
     void Display()

src/drawing/engines/opengl/OpenGLFramebuffer.cpp

@@ -52,7 +52,7 @@ OpenGLFramebuffer::~OpenGLFramebuffer()
     }
 }
 
-void OpenGLFramebuffer::Bind()
+void OpenGLFramebuffer::Bind() const
 {
     glBindFramebuffer(GL_FRAMEBUFFER, _id);
     glViewport(0, 0, (GLsizei)_width, (GLsizei)_height);

src/drawing/engines/opengl/OpenGLFramebuffer.h

@@ -38,6 +38,6 @@ public:
     GLuint GetHeight() const { return _height; }
     GLuint GetTexture() const { return _texture; }
 
-    void Bind();
+    void Bind() const;
     void * GetPixels() const;
 };

src/drawing/engines/opengl/SwapFramebuffer.cpp

@@ -0,0 +1,68 @@
+#pragma region Copyright (c) 2014-2016 OpenRCT2 Developers
+/*****************************************************************************
+ * OpenRCT2, an open source clone of Roller Coaster Tycoon 2.
+ *
+ * OpenRCT2 is the work of many authors, a full list can be found in contributors.md
+ * For more information, visit https://github.com/OpenRCT2/OpenRCT2
+ *
+ * OpenRCT2 is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * A full copy of the GNU General Public License can be found in licence.txt
+ *****************************************************************************/
+#pragma endregion
+
+#ifndef DISABLE_OPENGL
+
+#include "CopyFramebufferShader.h"
+#include "OpenGLFramebuffer.h"
+#include "SwapFramebuffer.h"
+
+SwapFramebuffer::SwapFramebuffer(sint32 width, sint32 height)
+{
+    _width = width;
+    _height = height;
+    _targetFramebufferIndex = 0;
+    _framebuffer[0] = new OpenGLFramebuffer(width, height);
+    _framebuffer[1] = new OpenGLFramebuffer(width, height);
+    _targetFramebuffer = _framebuffer[0];
+
+    _copyFramebufferShader = new CopyFramebufferShader();
+    _copyFramebufferShader->Use();
+    _copyFramebufferShader->SetScreenSize(_width, _height);
+    _copyFramebufferShader->SetBounds(0, 0, _width, _height);
+    _copyFramebufferShader->SetTextureCoordinates(0, 1, 1, 0);
+}
+
+SwapFramebuffer::~SwapFramebuffer()
+{
+    delete _framebuffer[0];
+    delete _framebuffer[1];
+    delete _copyFramebufferShader;
+}
+
+GLuint SwapFramebuffer::GetSourceTexture() const
+{
+    return _sourceFramebuffer->GetTexture();
+}
+
+void SwapFramebuffer::SwapCopy()
+{
+    _sourceFramebuffer = _targetFramebuffer;
+    _targetFramebufferIndex = (_targetFramebufferIndex + 1) & 1;
+    _targetFramebuffer = _framebuffer[_targetFramebufferIndex];
+    _targetFramebuffer->Bind();
+
+    _copyFramebufferShader->Use();
+    _copyFramebufferShader->SetTexture(GetSourceTexture());
+    _copyFramebufferShader->Draw();
+}
+
+void SwapFramebuffer::Bind()
+{
+    _targetFramebuffer->Bind();
+}
+
+#endif /* DISABLE_OPENGL */

src/drawing/engines/opengl/SwapFramebuffer.h

@@ -0,0 +1,70 @@
+#pragma region Copyright (c) 2014-2016 OpenRCT2 Developers
+/*****************************************************************************
+ * OpenRCT2, an open source clone of Roller Coaster Tycoon 2.
+ *
+ * OpenRCT2 is the work of many authors, a full list can be found in contributors.md
+ * For more information, visit https://github.com/OpenRCT2/OpenRCT2
+ *
+ * OpenRCT2 is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * A full copy of the GNU General Public License can be found in licence.txt
+ *****************************************************************************/
+#pragma endregion
+
+#pragma once
+
+#include "../../../common.h"
+#include "OpenGLAPI.h"
+
+class CopyFramebufferShader;
+class OpenGLFramebuffer;
+
+/**
+ * Class to maintain two different framebuffers where the active framebuffer
+ * will swap between the two, copying the other's pixels in the process for
+ * performing pre-processing filters.
+ *
+ * When you need to bind the current frame to a shader, call SwapCopy and
+ * then bind the value of GetSourceTexture to your shader.
+ */
+class SwapFramebuffer
+{
+private:
+    sint32              _width;
+    sint32              _height;
+    uint8               _targetFramebufferIndex;
+    OpenGLFramebuffer * _targetFramebuffer;
+    OpenGLFramebuffer * _sourceFramebuffer;
+    OpenGLFramebuffer * _framebuffer[2];
+
+    CopyFramebufferShader * _copyFramebufferShader = nullptr;
+
+public:
+    SwapFramebuffer(sint32 width, sint32 height);
+    ~SwapFramebuffer();
+
+    /**
+     * Gets the current target framebuffer.
+     */
+    const OpenGLFramebuffer * GetTargetFramebuffer() const { return _targetFramebuffer; }
+
+    /**
+     * Gets the texture ID for the source framebuffer.
+     */
+    GLuint GetSourceTexture() const;
+
+    /**
+     * Swaps the target framebuffer, binds it and then draws the previous
+     * framebuffer resulting in the two buffers matching and ready for
+     * pre-processing.
+     */
+    void SwapCopy();
+
+    /**
+     * Binds the current target framebuffer.
+     */
+    void Bind();
+};