Inconsistent GraphicsRow behaviour

Question

During the debugging of my previous question (somewhat related), I encountered this strange behaviour: when the global option Antialiasing is set to True in Option Inspector, the following code gives non-antialiased plots (observe e.g. frames):

GraphicsRow@{
  ListContourPlot[
   Table[Sin[i + j^2], {i, 0, 2, 0.05}, {j, 1.2, 2, 0.05}], 
   ColorFunction -> ColorData["AvocadoColors"], Contours -> 10, 
   Mesh -> False, ImageSize -> 400],
  ListDensityPlot[
   Table[Sin[i + j^2], {i, 0, 2, 0.05}, {j, 1.2, 2, 0.05}], 
   ColorFunction -> ColorData["AvocadoColors"], Mesh -> False, 
   ImageSize -> 400]
  }

The next input is from the same notebook, same session, the only difference is that GraphicsRow only contains one plot object. Result is antialiased (visible polygon edges are of no concern here, see other post).

GraphicsRow@{ListContourPlot[
   Table[Sin[i + j^2], {i, 0, 2, 0.05}, {j, 1.2, 2, 0.05}], 
   ColorFunction -> ColorData["AvocadoColors"], Contours -> 10, 
   Mesh -> False, ImageSize -> 400], ""}

Question

Is it a bug of GraphicsRow?

Answer 1

GraphicsRow puts both plots into one GraphicsBox, which means they have to be rendered together. Since the DensityPlot contains VertexColors it has to be rendered (on some platforms) using the 3D graphics renderer, whose support for Antialiasing is highly hardware dependent.

ContourPlot output normally renders with a 2D graphics engine. DensityPlot normally renders with a 3D graphics engine. When you group the two together (via GraphicsRow in this case) it forces them both to render with the 3D graphics engine, and that causes the ContourPlot to have a slightly different appearance.

Take a look at this example, containing only the ContourPlot. This code forces the ContourPlot to be drawn with a 2D renderer (in my case Quartz, since I'm using a Mac) in one window and a 3D renderer (OpenGL) in another window. Observer the difference in appearance (at full size):

g = ListContourPlot[
   Table[Sin[i + j^2], {i, 0, 2, 0.05}, {j, 1.2, 2, 0.05}], 
   ColorFunction -> ColorData["AvocadoColors"], Contours -> 10, 
   Mesh -> False, ImageSize -> 400];

CreateDocument[g, CacheGraphics -> False, 
  "NotebookRenderingEngine" -> "Quartz"];

CreateDocument[g, CacheGraphics -> False, 
  "NotebookRenderingEngine" -> "OpenGL"];