How To : Use New Multi Pass Volume Rendering

The new multi_pass shaders should give both better performace and visual quality, they also allow geometry to be used to clip the volume using the new hull feature, but we will cover that later.

To use the multi_pass shaders you will need to include :

renderer="multi_pass" 

 

and you will also need to use sample_ratio in place of sample_density as shown in the example below :

<slide>
<layer>
<volume 
renderer="multi_pass"
sample_ratio="3"
sample_ratio_when_moving="1.5"
technique="light"
position="0.5 0.5 0"
scale="0.8"
tf-255="colour_255/torso_blue_mp.tf"
alpha="0.76"
cutoff="0.01"
region="0.4 0.18 0 0.82 0.8 1" 
rotate1="0 1 0 0"
rotate2="0 0 1 0"
rotate3="0 0 0 1"
rotation="10 0 0 1"
>my_dicom_volume</volume>
 

 

One of the major changes and improvements in the new shaders is the way that transparency is handled and so you will find that existing CLUT files will need the transparency values tweaked to give the same results as previously. We will update some example tf-255 .tf files and they will have _mp included in the file name.

Another difference, is that the settings for sample_ratio and sample_ratio_when_moving that replace sample_density in the original shader will need to be set with higher values to achieve a higher quality image. Higher values will have an impact on performance. The actual value required will vary depending on the dataset and the look you are trying to achieve, but a maximum of around 4 is probably a good place to start.

 

 

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