New renderer for shader prototyping

The vtkArrayRenderer class is a new OpenGL mapper focused on prototyping shader code using vtkDataArray objects bound to texture buffers. It uses a technique called “vertex pulling,” which renders OpenGL primitives such as points, lines, and triangles with no initial coordinates (i.e., with an empty vertex array object (VAO)). Instead, the vertex shader is expected to look up (via a texture sampler) or compute a value that it assigns to the gl_Position output.

To use the class, you simply pass in strings for vertex and fragment shaders, then bind VTK arrays to texture samplers named in your shader code.

Because vtkArrayRenderer is available in Python, it is easy to edit shader source code using Python and re-run quickly (with no C++ compilation required). This class is included in the RenderingCellGrid module along with a test (TestArrayRenderer.py) you can modify. Although the example expects the input data to be a vtkCellGrid, this is not a requirement.

This class also makes use of the vtkGLSLModifier classes in the RenderingCellGrid module. These classes perform substitutions on your shader source code to handle some of the tedium of rendering (such as setting up the camera transform matrices, light position uniforms, and so on). They also allow you to adjust shader source code while your test script is running simply by setting up a “live” directory holding a JSON description of search+replace settings. See the Rendering/CellGrid/LiveGLSLDebugSample directory for an example.