- Direct Volume Rendering (using transfer functions)
- Maximum Intensity Projection (shows the maximum density)
- Isosurface Rendering
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# Direct Volume Rendering
Direct volume rendering is the most standard rendering mode. It sends rays through the dataset, and uses "transfer functions" (1D or 2D) to determine the colour and opacity. Transfer functions map density (2D: also gradient magnitude) to a colour and opacity.
- **Modifying transfer functions**: Click "Volume Rendering" in the menu bar and select "1D Transfer Function" or "2D Transfer Function"
- **1D Transfer Function**: X-axis represents density and Y-axis represents alpha (opaccity). Move the grey alpha knots to create a curve for opacity by density. Right-click to add new alpha knots. The bottom gradient-coloured panel maps colour to density. Right-click to add new knots and click on an existing colour knot to modify its colour.
- **2D Transfer Function**: X-axis represents density and Y-axis represents gradient magnitude. Click "add rectangle" to add a new rectangle-shape. Move the four sliders (bottom left) to modify size/position. Modify the two sliders to the right to change min/max alpha/opacity. Each rectangle can have one colour (see colour picker).
Isosurface rendering draws the first thing the ray hits, with a density higher than some threshold. You can set this threshold yourself, by selecting the object and changing the "Visible value range" in the inspector.
Since VR requires two cameras to render each frame, you can expect worse performance. However, you can improve the FPS in two ways:
- Open _DirectVolumeRenderingShader.shader_ and reduce the value of _NUM_STEPS_ inthe _frag_dvr_ function. This will sacrifice quality for performance.
- Disable the DEPTHWRITE_ON shader variant. You can do this from code, or just remove the line "#pragma multi_compile DEPTHWRITE_ON DEPTHWRITE_OFF" in _DirectVolumeRenderingShader.shader_. Note: this will remove depth writing, so you won't be able to intersect multiple datasets.
The _RawDatasetImporter_ imports raw datasets, where the data is stored sequentially. Some raw datasets contain a header where you can read information about how the data is stored (content format, dimension, etc.), while some datasets expect you to know the layout and format.
- contentFormat: Value type of the data (Int8, Uint8, Int16, Uint16, etc..)
- skipBytes: Number of bytes to skip (offset to where the data begins). This is usually the same as the header size, and will be 0 if there is no header.
All this info can be added to a ".ini"-file, which the importer will use (if it finds any). See the sample files (in the "DataFiles" folder for an example).
# Todo:
- Improve 2D Transfer Function editor: Better GUI, more shapes (triangles)
- Optimise histogram generation
- Support very large datasets (currently we naively try to create 3D textures with the same dimension as the data)
