The simplest transparency mode.

Shapes are rendered in the same order as they are traversed. Alpha blending is used to combine the shape color with the color in the framebuffer. Depth buffer test and write are activated during rendering.

Limitation: A shape will not be displayed if it is behind a semi-transparent shape that has been rendered before it.

Same as NO_SORT, but the rendering of opaque objects is performed before the rendering of semi-transparent objects.

Notes & Limitations:

• When using this algorithm, the depth buffer is not updated (depth buffer writes are disabled) during the rendering of semi-transparent objects. As a result, complex semi-transparent shapes may not be rendered correctly.

• Because opaque objects are forced to be rendered first, the objects rendering order does not necessarily correspond to their actual ordering in the scene graph.

• Because semi-transparent objects are not sorted and alpha blending is not a commutative operation, the blending of several semi-transparent objects will not be correct if their order in the scene graph does not match their back-to-front ordering relative to the camera.

Same as OPAQUE_FIRST, but sorts semi-transparent objects by distances of bounding boxes from camera.

Limitation : If the bounding box of a shape is ignored by setting its boundingBoxIgnoring field to true, the rendering won't be correct.

Same as OPAQUE_FIRST, but uses a fragment-level depth sorting technique during the rendering of semi-transparent objects.

This mode generally gives the best results for complex semi-transparent objects.

Since Open Inventor 9.4, if the hardware supports the necessary OpenGL features, this transparency mode is implemented using a single-pass, order-independent fragment sorting (K-buffer or A-buffer) algorithm. The required OpenGL hardware features are: shader_image_load_store, shader_atomic_counters and shading_language_420pack. These features are standard in core OpenGL 4.2. Use OIV.Inventor.Devices.SoGLExtension, if necessary, to check if they are supported.

If the hardware does not support single-pass transparency, then a multi-pass "depth peeling" algorithm is used. The required OpenGL hardware features are: Multi-Texture, Texture Environment Combine, Depth texture, and Shadow . These features are standard starting with OpenGL 1.4. The method OIV.Inventor.Actions.SoGLRenderAction.SetSortedLayersNumPasses(System.Int32) allows you to set the number of rendering passes for more correct transparency. Usually, four passes gives good results.

If the graphics board does not support multi-pass transparency, SORTED_OBJECT is used.

Note: If the application uses fragment sorting transparency and specifies a custom fragment shader, the application shader must call an Open Inventor GLSL method instead of setting gl_FragColor directly. In the SDK installation, see shaders/include/Inventor/oivDepthPeeling_frag.h

Limitations:

• This transparency type is not compatible with interlaced stereo.

• Texturing on semi-transparent objects is limited to one texture.

• Using the single-pass algorithm, it is possible to run out of GPU memory for storing fragment transparency values. This should only happen for scenes with both high depth complexity and a large number of semi-transparent objects. In this case fragments from the objects traversed last in the scene graph may not be sorted correctly, resulting in small artifacts.

• Not compatible with FSAA. use SUPERSAMPLING, FXAA or SMAA instead.