VK_QCOM_multiview_per_view_viewports(3) Manual Page

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Certain use-cases for multiview have a need for specifying a separate viewport and scissor for each view, without using shader-based viewport indexing as introduced with VK_EXT_shader_viewport_index_layer.

This extension adds a new way to control ViewportIndex with multiview. When the multiviewPerViewViewports feature is enabled and if the last pre-rasterization shader entry point’s interface does not use the ViewportIndex built-in decoration, then each view of a multiview renderpass instance will use a viewport and scissor index equal to the ViewIndex.

1) Is is possible to enable/disable the multiviewPerViewViewports feature for individual renderpass instances?

RESOLVED: No, when the multiviewPerViewViewports feature is enabled during vkCreateDevice, then all created renderpass instances (including dynamic renderpasses from VK_KHR_dynamic_rendering) and all created VkPipelines will have the feature enabled. This approach was chosen because it simplifies application code and there is no known use-case enable/disable the feature for individual renderpasses or pipelines.

2) When this extension is used, is the value of ViewportIndex implicitly written by the last pre-rasterization shader stage and can the value of ViewportIndex be read in the fragment shader?

RESOLVED: No, use of the extension extension does not add an implicit write to ViewportIndex in any shader stage, and additionally, the value of ViewportIndex in the fragment shader is undefined.

VkPhysicalDeviceMultiviewPerViewViewportsFeaturesQCOM

For more information, see the Vulkan Specification

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