Wednesday, July 17, 2013

Mitsuba Renderer: A more complete example

In the last tutorial, we had looked at a very simple example usage of Mitsuba with only a single sphere primitive. We will now look at a more complete scene with the description of other entities like film, intgrator, bsdf etc. So lets get started.

In this scene, we will render a plane primitive with a checkered material. We will introduce the following new scene elements.
  1. integrator (for the rendering algorithm used)
  2. sensor (for the camera settings like fov) 
  3. film: a sub-entity of the sensor element (for the output image resolution and type) 
  4. sampler: a sub-entity of the sensor element (for the number of camera samples and the type of sampling distribution to be used.
  5. plane (for rendering of our plane shape)
  6. bsdf: a child entity of our plane shape (for the checkered material)
This element tells Mitsuba the type of rendering algorithm to be used for the scene. For the first few tutorials, we will stick with the path tracing algorithm (type="path") for the integrator element. For this scene, the integrator element is defined as follows:

  < !--Setup scene integrator -- >
  < integrator type="path" >

    < !-- Path trace with a max. path length of 5 -- >
    < integer name="maxDepth" value="5"/ >

  < / integrator >

This element is analogous to a camera object. For this scene, we will use a perspective camera (type="perspective"). Its sub-elements transform controls the camera's position and orientation, the focusDistance element controls the distance of the camera focal plane. The fov element controls the camera field of view.

This is the sub-element of the sensor element. Its main attribute type controls the format of the output (ldrfilm or hdrfilm). If hdrfilm type is used, the output format is EXR. The sub-elements width and height control the output image dimensions.

For this scene, the sensor element is defined as follows:

  < sensor type="perspective" >
    < transform name="toWorld" >
      < translate x="0" y="0" z="-1"/ >
    < / transform >

    < float name="focusDistance" value="1"/ >

    < float name="fov" value="45"/ >

    < film type="hdrfilm" >
      < integer name="width" value="640"/ >
      < integer name="height" value="480"/ >
    < / film >

    < sampler type="independent" >
      < integer name="sampleCount" value="32"/ >
    < / sampler >
  < / sensor >

The plane shape is defined by the type ("rectangle"). The position, orientation and scale of plane is controlled through the transform sub-element. To orient the plane properly, we rotate then scale and finally translate it. The material is controlled by the bsdf sub-element. Here we have defined a diffuse material. The bsdf element has a texture sub-element which has a uv scale of 32 (that is the texture tiling amount), color0 and color1 are the two checker colors and filtertype controls the texture filtering scheme to be used. This can be 

  1. EWA (for EWA filtering which is the default filter type) 
  2. trilinear (for linear filtering)
  3. nearest (for nearest neighbor filtering)
For this scene, the shape element is defined as follows:

 < shape type="rectangle" >     
    < transform name="toWorld" >
      < rotate x="1" angle="-90"/ >
      < scale x="2" y="2" z="2"/ >
      < translate y="-0.1"/ >
    < / transform >
    < bsdf type="diffuse" >
      < texture type="checkerboard" name="reflectance" >
        < float name="uvscale" value="32"/ >
        < rgb name="color0" value="0,0,0"/ >
        < rgb name="color1" value="1,1,1"/ >
        < string name="filterType" value="EWA"/ >
      < / texture >
    < / bsdf >
  < / shape >

The entire scene description given above gives us the following output.
Output from the CheckeredPlane.xml scene
The scene file may be downloaded from here: 


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