Week2 Blogpost

docs/source/posts/2023/2023-06-12-week-2-joaodellagli.rst

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+Week 2: The Importance of (good) Documentation
+=====================
+
+.. post:: June 12, 2023
+   :author: João Victor Dell Agli Floriano
+   :tags: google
+   :category: gsoc
+
+
+Hello everybody, welcome to the week 2 of this project! I must admit I thought this would be simpler than it is currently being, but I forgot that when it comes to dealing with computer graphics' applications, things never are. Below, some updates on what I have been up to for this past week. 
+
+This Last Week's Effort
+-----------------------
+
+Last week, I was facing some issues with a VTK feature essential so I could move forward with my project: Framebuffer Objects. 
+As described in my `last blogpost <https://blogs.python-gsoc.org/en/joaodellaglis-blog/the-fbo-saga-week-1/>`_, for some reason the 2D allocation method for it weren't working.
+In a meeting with my mentors, while we were discussing and searching through VTK's FramebufferObject and TextureObject documentation, and the code itself for the problem, 
+one TextureObject method caught my attention: `vtkTextureObject.SetContext() <https://vtk.org/doc/nightly/html/classvtkTextureObject.html#a0988fa2a30b640c93392c2188030537e>`_.
+
+Where the Problem Was
+---------------------
+My last week's code was:
+
+| color_texture = vtk.vtkTextureObject() # color texture declaration
+| color_texture.Bind() # binding of the texture for operations
+|
+| color_texture.SetDataType(vtk.VTK_UNSIGNED_CHAR) # setting the datatype for unsigned char
+| color_texture.SetInternalFormat(vtk.VTK_RGBA) # setting the format as RGBA
+| color_texture.SetFormat(vtk.VTK_RGBA)
+| color_texture.SetMinificationFilter(0) # setting the minfilter as linear
+| color_texture.SetMagnificationFilter(0) # setting the magfilter as linear
+|
+| color_texture.Allocate2D(width, height, 4, vtk.VTK_UNSIGNED_CHAR) # here is where the code stops
+
+But it turns out that to allocate the FBO's textures, of type vtkTextureObject, you need to also set the context where the texture object
+will be present, so it lacked a line, that should be added after Bind():
+
+| color_texture = vtk.vtkTextureObject() 
+| color_texture.Bind() 
+|
+| color_texture.SetContext(manager.window) # set the context where the texture object will be present
+|
+| color_texture.SetDataType(vtk.VTK_UNSIGNED_CHAR) 
+| color_texture.SetInternalFormat(vtk.VTK_RGB) 
+| color_texture.SetFormat(vtk.VTK_RGB)
+| color_texture.SetMinificationFilter(0) 
+| color_texture.SetMagnificationFilter(0) 
+
+The code worked fine. But as my last blogpost showed, Allocate3D() method worked just fine without a (visible) problem, why is that? 
+Well, in fact, it **didn't work**. If we check the code for the Allocate2D and Allocate3D, one difference can be spotted:
+
+
+
+.. image:: https://github.com/JoaoDell/gsoc_assets/main/images/allocate-2d-3d.png
+   :align: center
+   :alt: Image comparing Allocate2D and Allocate3D methos
+
+
+
+While in Allocate2D there is an ``assert(this->Context);``, in Allocate3D the assertion is translated into:
+
+| if(this->Context==nullptr)
+| {
+|   vtkErrorMacro("No context specified. Cannot create texture.");
+|   return false;
+| }
+
+This slight difference is significant: while in Allocate2D the program immediately fails, in Allocate3D the function is simply returned
+**false**, with its error pushed to vtkErrorMacro. I could have realised that earlier if I were using vtkErrorMacro, but this contrastant
+implementation made it harder for me and my mentors to realise what was happening.
+
+
+This Week's Goals
+-----------------
+After making that work, this week's goal is to render something to the Framebuffer Object, now that is working. To do that, 
+first I will need to do some offscreen rendering to it, and afterwards render what it was drawn to its color attachment, the Texture Object I
+was struggling to make work, into the screen, drawing its texture to a billboard. Also, I plan to start using vtkErrorMacro, as it seems like 
+the main error interface when working with VTK, and that may make my life easier.
+
+See you next week!