Transparency Aliasing Issue going from VTK8 to 9

Support
1

Hello. It looks like setting a non-one opacity value disables the hardware anti-aliasing in VTK9. (v9.4.1)
The left triangle is opaque while the right is a transparent. Note the jaggies.

vtk9.4.1
vtk9.4.1502×540 12.7 KB

Here is the same code in v8.1.2:

vtk8.1.2
vtk8.1.2502×540 15.3 KB

At first I thought it might be a new depth peeling default on, but GetUseDepthPeeling() says no.

Any ideas on how keep hardware anti-aliasing on transparent actors? My application relies heavily on rendering complex thin walled transparent CAD with feature edges. The accuracy of the transparencies are not important à la depth peeling, but the aesthetics of smooth edges are.

Here is code to reproduce the screenshots:

import vtk

def main():
    colors = vtk.vtkNamedColors()

    #cone 1, not transparent, looks smooth in vtk8 and9
    cone1_source = vtk.vtkConeSource()
    cone1_source.SetResolution(1)
    cone1_source.SetCenter(-0.5,0,0)
    cone1_source.SetRadius(1.3)

    cone1_mapper = vtk.vtkPolyDataMapper()
    cone1_mapper.SetInputConnection(cone1_source.GetOutputPort())

    cone1_actor = vtk.vtkActor()
    cone1_actor.SetMapper(cone1_mapper)
    cone1_actor.GetProperty().SetDiffuseColor(colors.GetColor3d('black'))
    #cone1_actor.GetProperty().EdgeVisibilityOn()
    cone1_actor.GetProperty().SetOpacity(1)


    #cone 2, transparent, looks smooth in vtk8 but not in vtk9
    cone2_source = vtk.vtkConeSource()
    cone2_source.SetResolution(1)
    cone2_source.SetCenter(0.5,0,0)
    cone2_source.SetRadius(1.3)
    cone2_source.SetDirection(-1, 0, 0)

    cone2_mapper = vtk.vtkPolyDataMapper()
    cone2_mapper.SetInputConnection(cone2_source.GetOutputPort())

    cone2_actor = vtk.vtkActor()
    cone2_actor.SetMapper(cone2_mapper)
    cone2_actor.GetProperty().SetDiffuseColor(colors.GetColor3d('black'))
    #cone2_actor.GetProperty().EdgeVisibilityOn()
    cone2_actor.GetProperty().SetOpacity(0.75)


    renderer = vtk.vtkRenderer()
    render_window = vtk.vtkRenderWindow()
    render_window.AddRenderer(renderer)
    render_window_interactor = vtk.vtkRenderWindowInteractor()
    render_window_interactor.SetRenderWindow(render_window)

    renderer.AddActor(cone1_actor)
    renderer.AddActor(cone2_actor)
    renderer.SetBackground(colors.GetColor3d('white'))

    print('GetUseDepthPeeling()', renderer.GetUseDepthPeeling())

    render_window.SetSize(400, 400)
    render_window.SetWindowName(f'VTK v{vtk.vtkVersion().GetVTKVersion()} Transparency Aliasing Example')
    render_window.Render()

    camera = renderer.GetActiveCamera()
    camera.Roll(4)

    render_window_interactor.Start()


if __name__ == '__main__':
    main()

I’m on Win10 and here are my graphics details:

OpenGL vendor string:  NVIDIA Corporation
OpenGL renderer string:  Quadro M2200/PCIe/SSE2
OpenGL version string:  4.5.0 NVIDIA 389.08
OpenGL extensions:  
  GL_AMD_multi_draw_indirect
  GL_AMD_seamless_cubemap_per_texture
  GL_AMD_vertex_shader_viewport_index
  GL_AMD_vertex_shader_layer
  GL_ARB_arrays_of_arrays
  GL_ARB_base_instance
  GL_ARB_bindless_texture
  GL_ARB_blend_func_extended
  GL_ARB_buffer_storage
  GL_ARB_cl_event
  GL_ARB_clear_buffer_object
  GL_ARB_clear_texture
  GL_ARB_clip_control
  GL_ARB_color_buffer_float
  GL_ARB_compressed_texture_pixel_storage
  GL_ARB_conservative_depth
  GL_ARB_compute_shader
  GL_ARB_compute_variable_group_size
  GL_ARB_conditional_render_inverted
  GL_ARB_copy_buffer
  GL_ARB_copy_image
  GL_ARB_cull_distance
  GL_ARB_debug_output
  GL_ARB_depth_buffer_float
  GL_ARB_depth_clamp
  GL_ARB_depth_texture
  GL_ARB_derivative_control
  GL_ARB_direct_state_access
  GL_ARB_draw_buffers
  GL_ARB_draw_buffers_blend
  GL_ARB_draw_indirect
  GL_ARB_draw_elements_base_vertex
  GL_ARB_draw_instanced
  GL_ARB_enhanced_layouts
  GL_ARB_ES2_compatibility
  GL_ARB_ES3_compatibility
  GL_ARB_ES3_1_compatibility
  GL_ARB_ES3_2_compatibility
  GL_ARB_explicit_attrib_location
  GL_ARB_explicit_uniform_location
  GL_ARB_fragment_coord_conventions
  GL_ARB_fragment_layer_viewport
  GL_ARB_fragment_program
  GL_ARB_fragment_program_shadow
  GL_ARB_fragment_shader
  GL_ARB_fragment_shader_interlock
  GL_ARB_framebuffer_no_attachments
  GL_ARB_framebuffer_object
  GL_ARB_framebuffer_sRGB
  GL_ARB_geometry_shader4
  GL_ARB_get_program_binary
  GL_ARB_get_texture_sub_image
  GL_ARB_gl_spirv
  GL_ARB_gpu_shader5
  GL_ARB_gpu_shader_fp64
  GL_ARB_gpu_shader_int64
  GL_ARB_half_float_pixel
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  GL_ARB_imaging
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  GL_ARB_multi_bind
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  GL_ARB_multisample
  GL_ARB_multitexture
  GL_ARB_occlusion_query
  GL_ARB_occlusion_query2
  GL_ARB_parallel_shader_compile
  GL_ARB_pipeline_statistics_query
  GL_ARB_pixel_buffer_object
  GL_ARB_point_parameters
  GL_ARB_point_sprite
  GL_ARB_polygon_offset_clamp
  GL_ARB_post_depth_coverage
  GL_ARB_program_interface_query
  GL_ARB_provoking_vertex
  GL_ARB_query_buffer_object
  GL_ARB_robust_buffer_access_behavior
  GL_ARB_robustness
  GL_ARB_sample_locations
  GL_ARB_sample_shading
  GL_ARB_sampler_objects
  GL_ARB_seamless_cube_map
  GL_ARB_seamless_cubemap_per_texture
  GL_ARB_separate_shader_objects
  GL_ARB_shader_atomic_counter_ops
  GL_ARB_shader_atomic_counters
  GL_ARB_shader_ballot
  GL_ARB_shader_bit_encoding
  GL_ARB_shader_clock
  GL_ARB_shader_draw_parameters
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  GL_ARB_texture_compression_bptc
  GL_ARB_texture_compression_rgtc
  GL_ARB_texture_cube_map
  GL_ARB_texture_cube_map_array
  GL_ARB_texture_env_add
  GL_ARB_texture_env_combine
  GL_ARB_texture_env_crossbar
  GL_ARB_texture_env_dot3
  GL_ARB_texture_filter_anisotropic
  GL_ARB_texture_filter_minmax
  GL_ARB_texture_float
  GL_ARB_texture_gather
  GL_ARB_texture_mirror_clamp_to_edge
  GL_ARB_texture_mirrored_repeat
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  GL_ARB_texture_non_power_of_two
  GL_ARB_texture_query_levels
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  GL_ARB_texture_rectangle
  GL_ARB_texture_rg
  GL_ARB_texture_rgb10_a2ui
  GL_ARB_texture_stencil8
  GL_ARB_texture_storage
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  GL_ARB_texture_swizzle
  GL_ARB_texture_view
  GL_ARB_timer_query
  GL_ARB_transform_feedback2
  GL_ARB_transform_feedback3
  GL_ARB_transform_feedback_instanced
  GL_ARB_transform_feedback_overflow_query
  GL_ARB_transpose_matrix
  GL_ARB_uniform_buffer_object
  GL_ARB_vertex_array_bgra
  GL_ARB_vertex_array_object
  GL_ARB_vertex_attrib_64bit
  GL_ARB_vertex_attrib_binding
  GL_ARB_vertex_buffer_object
  GL_ARB_vertex_program
  GL_ARB_vertex_shader
  GL_ARB_vertex_type_10f_11f_11f_rev
  GL_ARB_vertex_type_2_10_10_10_rev
  GL_ARB_viewport_array
  GL_ARB_window_pos
  GL_ATI_draw_buffers
  GL_ATI_texture_float
  GL_ATI_texture_mirror_once
  GL_S3_s3tc
  GL_EXT_texture_env_add
  GL_EXT_abgr
  GL_EXT_bgra
  GL_EXT_bindable_uniform
  GL_EXT_blend_color
  GL_EXT_blend_equation_separate
  GL_EXT_blend_func_separate
  GL_EXT_blend_minmax
  GL_EXT_blend_subtract
  GL_EXT_compiled_vertex_array
  GL_EXT_Cg_shader
  GL_EXT_depth_bounds_test
  GL_EXT_direct_state_access
  GL_EXT_draw_buffers2
  GL_EXT_draw_instanced
  GL_EXT_draw_range_elements
  GL_EXT_fog_coord
  GL_EXT_framebuffer_blit
  GL_EXT_framebuffer_multisample
  GL_EXTX_framebuffer_mixed_formats
  GL_EXT_framebuffer_multisample_blit_scaled
  GL_EXT_framebuffer_object
  GL_EXT_framebuffer_sRGB
  GL_EXT_geometry_shader4
  GL_EXT_gpu_program_parameters
  GL_EXT_gpu_shader4
  GL_EXT_multi_draw_arrays
  GL_EXT_packed_depth_stencil
  GL_EXT_packed_float
  GL_EXT_packed_pixels
  GL_EXT_pixel_buffer_object
  GL_EXT_point_parameters
  GL_EXT_polygon_offset_clamp
  GL_EXT_post_depth_coverage
  GL_EXT_provoking_vertex
  GL_EXT_raster_multisample
  GL_EXT_rescale_normal
  GL_EXT_secondary_color
  GL_EXT_separate_shader_objects
  GL_EXT_separate_specular_color
  GL_EXT_shader_image_load_formatted
  GL_EXT_shader_image_load_store
  GL_EXT_shader_integer_mix
  GL_EXT_shadow_funcs
  GL_EXT_sparse_texture2
  GL_EXT_stencil_two_side
  GL_EXT_stencil_wrap
  GL_EXT_texture3D
  GL_EXT_texture_array
  GL_EXT_texture_buffer_object
  GL_EXT_texture_compression_dxt1
  GL_EXT_texture_compression_latc
  GL_EXT_texture_compression_rgtc
  GL_EXT_texture_compression_s3tc
  GL_EXT_texture_cube_map
  GL_EXT_texture_edge_clamp
  GL_EXT_texture_env_combine
  GL_EXT_texture_env_dot3
  GL_EXT_texture_filter_anisotropic
  GL_EXT_texture_filter_minmax
  GL_EXT_texture_integer
  GL_EXT_texture_lod
  GL_EXT_texture_lod_bias
  GL_EXT_texture_mirror_clamp
  GL_EXT_texture_object
  GL_EXT_texture_shared_exponent
  GL_EXT_texture_sRGB
  GL_EXT_texture_sRGB_decode
  GL_EXT_texture_storage
  GL_EXT_texture_swizzle
  GL_EXT_timer_query
  GL_EXT_transform_feedback2
  GL_EXT_vertex_array
  GL_EXT_vertex_array_bgra
  GL_EXT_vertex_attrib_64bit
  GL_EXT_window_rectangles
  GL_EXT_import_sync_object
  GL_IBM_rasterpos_clip
  GL_IBM_texture_mirrored_repeat
  GL_KHR_context_flush_control
  GL_KHR_debug
  GL_EXT_memory_object
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  GL_EXT_win32_keyed_mutex
  GL_KHR_parallel_shader_compile
  GL_KHR_no_error
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  GL_KHR_robustness
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  GL_NV_blend_equation_advanced
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  GL_NV_blend_minmax_factor
  GL_NV_blend_square
  GL_NV_command_list
  GL_NV_compute_program5
  GL_NV_conditional_render
  GL_NV_conservative_raster
  GL_NV_conservative_raster_dilate
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  GL_NV_copy_image
  GL_NV_deep_texture3D
  GL_NV_depth_buffer_float
  GL_NV_depth_clamp
  GL_NV_draw_texture
  GL_NV_draw_vulkan_image
  GL_NV_ES1_1_compatibility
  GL_NV_ES3_1_compatibility
  GL_NV_explicit_multisample
  GL_NV_fence
  GL_NV_fill_rectangle
  GL_NV_float_buffer
  GL_NV_fog_distance
  GL_NV_fragment_coverage_to_color
  GL_NV_fragment_program
  GL_NV_fragment_program_option
  GL_NV_fragment_program2
  GL_NV_fragment_shader_interlock
  GL_NV_framebuffer_mixed_samples
  GL_NV_framebuffer_multisample_coverage
  GL_NV_geometry_shader4
  GL_NV_geometry_shader_passthrough
  GL_NV_gpu_program4
  GL_NV_internalformat_sample_query
  GL_NV_gpu_program4_1
  GL_NV_gpu_program5
  GL_NV_gpu_program5_mem_extended
  GL_NV_gpu_program_fp64
  GL_NV_gpu_shader5
  GL_NV_half_float
  GL_NV_light_max_exponent
  GL_NV_multisample_coverage
  GL_NV_multisample_filter_hint
  GL_NV_occlusion_query
  GL_NV_packed_depth_stencil
  GL_NV_parameter_buffer_object
  GL_NV_parameter_buffer_object2
  GL_NV_path_rendering
  GL_NV_path_rendering_shared_edge
  GL_NV_pixel_data_range
  GL_NV_point_sprite
  GL_NV_primitive_restart
  GL_NV_query_resource
  GL_NV_query_resource_tag
  GL_NV_register_combiners
  GL_NV_register_combiners2
  GL_NV_sample_locations
  GL_NV_sample_mask_override_coverage
  GL_NV_shader_atomic_counters
  GL_NV_shader_atomic_float
  GL_NV_shader_atomic_fp16_vector
  GL_NV_shader_atomic_int64
  GL_NV_shader_buffer_load
  GL_NV_shader_storage_buffer_object
  GL_NV_texgen_reflection
  GL_NV_texture_barrier
  GL_NV_texture_compression_vtc
  GL_NV_texture_env_combine4
  GL_NV_texture_multisample
  GL_NV_texture_rectangle
  GL_NV_texture_rectangle_compressed
  GL_NV_texture_shader
  GL_NV_texture_shader2
  GL_NV_texture_shader3
  GL_NV_transform_feedback
  GL_NV_transform_feedback2
  GL_NV_uniform_buffer_unified_memory
  GL_NV_vertex_array_range
  GL_NV_vertex_array_range2
  GL_NV_vertex_attrib_integer_64bit
  GL_NV_vertex_buffer_unified_memory
  GL_NV_vertex_program
  GL_NV_vertex_program1_1
  GL_NV_vertex_program2
  GL_NV_vertex_program2_option
  GL_NV_vertex_program3
  GL_NV_viewport_array2
  GL_NV_viewport_swizzle
  GL_NVX_conditional_render
  GL_NVX_gpu_memory_info
  GL_NVX_multigpu_info
  GL_NVX_nvenc_interop
  GL_NV_shader_thread_group
  GL_NV_shader_thread_shuffle
  GL_KHR_blend_equation_advanced
  GL_KHR_blend_equation_advanced_coherent
  GL_SGIS_generate_mipmap
  GL_SGIS_texture_lod
  GL_SGIX_depth_texture
  GL_SGIX_shadow
  GL_SUN_slice_accum
  GL_WIN_swap_hint
  WGL_EXT_swap_control
PixelFormat Descriptor:
depth:  24
class:  TrueColor
buffer size:  32
level:  0
renderType:  rgba
double buffer:  True
stereo:  False
hardware acceleration:  True
rgba:  redSize=8 greenSize=8blueSize=8alphaSize=8
aux buffers:  4
depth size:  24
stencil size:  0
accum:  redSize=16 greenSize=16blueSize=16alphaSize=16
2

I am not entirely sure what disables anti-aliasing. Have you tried enabling multisampling on the render window? Another approach is to introduce an FXAA pass. That is also hardware based but explicitly enabled.

3

When I query multisampling I see it is set to 8 by default. When I set it to 0, both triangles are aliased as expected.

I was under the impression that FXAA was a software based solution based on this discussion: How to anti-alias in vtkRenderWindow - #6 by lassoan

Either way, FXAA is visually unappealing to me. Like looking through smudged glasses. I know, I am picky. But it’s hard to downgrade from the beautifully crisp multisampling of VTK8.

4

Hello,

To use multi-sampling (MSAA) in VTK 9, anti-aliasing API is a bit different. Code below in C++, sorry.

Before creating any render window:

vtkOpenGLRenderWindow::SetGlobalMaximumNumberOfMultiSamples( 8 );

If you’re using Qt, before creating a QVTKOpenGLWidget:

QSurfaceFormat::setDefaultFormat( QVTKOpenGLNativeWidget::defaultFormat() );

When setting up your render window:

renderWindow->SetMultiSamples( 4 );

I hope this sorts out.

best,

PC

5

Hi Paulo,
I think we have a misunderstanding. The MSAA is working on opaque actors but not on transparent actors.

To be thorough, I did try your recommendation:

vtk.vtkOpenGLRenderWindow.SetGlobalMaximumNumberOfMultiSamples(8)

But it had no effect. As for the frame manager, the example code is using the default frame manager which I believe is via Win32 API. But like I say, MSAA is working for opaque.

6

In that case, I also need to do this (C++):

    // Prepare to render transparency/translucency adequately
    // See: https://stackoverflow.com/questions/47528086/problems-with-rendering-transparent-objects-in-vtk
    //      https://vtk.org/Wiki/VTK/Examples/Cxx/Visualization/CorrectlyRenderTranslucentGeometry
    renderer->SetUseDepthPeeling(1);
    renderer->SetOcclusionRatio(0.1);
    renderer->SetMaximumNumberOfPeels(4);
    renderWindow->SetMultiSamples(0);
    renderWindow->SetAlphaBitPlanes(1);

best,

PC

7

That code is turning off MSAA… SetMultiSamples(0) and enabling depth peeling, a different topic.

8

I see there is already a bug report on this topic: https://gitlab.kitware.com/vtk/vtk/-/issues/19234

renderer.SetPass(vtk.vtkRenderStepsPass())

At first glance, the suggestion to set the default render pass to vtkTranslucentPass does appear to bring MSAA back for transparent actors… but it causes other problems. For example, vtkPropPicker no longer works:

vtkOpenGLHardwareSelect:244    ERR| vtkOpenGLHardwareSelector (00000241C4E450E0): Too many props. Currently only 16777214 props are supported.

I’ll continue the discussion on the issue tracker.

9

@TravStu22 The changes in https://gitlab.kitware.com/vtk/vtk/-/merge_requests/12001 could be used to toggle translucent rendering approach. In your example, setting renderer.SetUseOIT(False) brings back multisampling. See screenshot below:

Screenshot from 2025-03-19 15-37-55
Screenshot from 2025-03-19 15-37-55423×459 7.39 KB

10

Nice. I will need to try this out. Thank you @sankhesh.