add method for creating framebuffer objects to OpenGLHelper

Change-Id: I08bd2e58ee98a68accae256fcbcc288a8c56ae0b

include/vcl/opengl/OpenGLHelper.hxx

@@ -29,6 +29,13 @@ public:
     static void renderToFile(long nWidth, long nHeight, const OUString& rFileName);
 
     static const char* GLErrorString(GLenum errorCode);
+
+    /**
+     * The caller is responsible for deleting the buffer objects identified by
+     * nFramebufferId, nRenderbufferId and nTexturebufferId
+     */
+    static void createFramebuffer(long nWidth, long nHeight,
+            GLuint& nFramebufferId, GLuint& nRenderbufferId, GLuint& nTexturebufferId);
 };
 
 VCLOPENGL_DLLPUBLIC std::ostream& operator<<(std::ostream& rStrm, const glm::mat4& rMatrix);

vcl/source/opengl/OpenGLHelper.cxx

@@ -268,5 +268,41 @@ std::ostream& operator<<(std::ostream& rStrm, const glm::mat4& rMatrix)
     return rStrm;
 }
 
+void OpenGLHelper::createFramebuffer(long nWidth, long nHeight,
+        GLuint& nFramebufferId, GLuint& nRenderbufferId, GLuint& nTexturebufferId)
+{
+    // create a renderbuffer
+    glGenRenderbuffers(1, &nRenderbufferId);
+    glBindRenderbuffer(GL_RENDERBUFFER, nRenderbufferId);
+    glRenderbufferStorage(GL_RENDERBUFFER, GL_DEPTH_COMPONENT, nWidth, nHeight);
+    glBindRenderbuffer(GL_RENDERBUFFER, 0);
+
+    // create a texture
+    glGenTextures(1, &nTexturebufferId);
+    glBindTexture(GL_TEXTURE_2D, nTexturebufferId);
+    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP);
+    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP);
+    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
+    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
+    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, nWidth, nHeight, 0, GL_RGBA, GL_UNSIGNED_BYTE, NULL);
+    glBindTexture(GL_TEXTURE_2D, 0);
+
+    // create a framebuffer object and attach renderbuffer and texture
+    glGenFramebuffers(1, &nFramebufferId);
+    glCheckFramebufferStatus(GL_FRAMEBUFFER);
+    glBindFramebuffer(GL_FRAMEBUFFER, nFramebufferId);
+    glBindTexture(GL_TEXTURE_2D, nTexturebufferId);
+    // attach a texture to FBO color attachement point
+    glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, nTexturebufferId, 0);
+    glCheckFramebufferStatus(GL_FRAMEBUFFER);
+    glBindTexture(GL_TEXTURE_2D, 0);
+    // attach a renderbuffer to depth attachment point
+    glBindRenderbuffer(GL_RENDERBUFFER, nRenderbufferId);
+    glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, GL_RENDERBUFFER, nRenderbufferId);
+    glCheckFramebufferStatus(GL_FRAMEBUFFER);
+    glBindRenderbuffer(GL_RENDERBUFFER, 0);
+    glBindFramebuffer(GL_FRAMEBUFFER, 0);
+}
+
 
 /* vim:set shiftwidth=4 softtabstop=4 expandtab: */