1include::meta/VK_NV_framebuffer_mixed_samples.txt[] 2 3*Last Modified Date*:: 4 2017-06-04 5*Contributors*:: 6 - Jeff Bolz, NVIDIA 7 8This extension allows multisample rendering with a raster and depth/stencil 9sample count that is larger than the color sample count. 10Rasterization and the results of the depth and stencil tests together 11determine the portion of a pixel that is "`covered`". 12It can be useful to evaluate coverage at a higher frequency than color 13samples are stored. 14This coverage is then "`reduced`" to a collection of covered color samples, 15each having an opacity value corresponding to the fraction of the color 16sample covered. 17The opacity can optionally be blended into individual color samples. 18 19Rendering with fewer color samples than depth/stencil samples greatly 20reduces the amount of memory and bandwidth consumed by the color buffer. 21However, converting the coverage values into opacity introduces artifacts 22where triangles share edges and may: not be suitable for normal triangle 23mesh rendering. 24 25One expected use case for this functionality is Stencil-then-Cover path 26rendering (similar to the OpenGL GL_NV_path_rendering extension). 27The stencil step determines the coverage (in the stencil buffer) for an 28entire path at the higher sample frequency, and then the cover step draws 29the path into the lower frequency color buffer using the coverage 30information to antialias path edges. 31With this two-step process, internal edges are fully covered when 32antialiasing is applied and there is no corruption on these edges. 33 34The key features of this extension are: 35 36 * It allows render pass and framebuffer objects to be created where the 37 number of samples in the depth/stencil attachment in a subpass is a 38 multiple of the number of samples in the color attachments in the 39 subpass. 40 * A coverage reduction step is added to Fragment Operations which converts 41 a set of covered raster/depth/stencil samples to a set of color samples 42 that perform blending and color writes. 43 The coverage reduction step also includes an optional coverage 44 modulation step, multiplying color values by a fractional opacity 45 corresponding to the number of associated raster/depth/stencil samples 46 covered. 47 48=== New Object Types 49 50None. 51 52=== New Enum Constants 53 54None. 55 56=== New Enums 57 58 * elink:VkCoverageModulationModeNV 59 * elink:VkPipelineCoverageModulationStateCreateFlagsNV 60 61=== New Structures 62 63 * slink:VkPipelineCoverageModulationStateCreateInfoNV 64 65=== New Functions 66 67None. 68 69=== Issues 70 71None. 72 73=== Version History 74 75 * Revision 1, 2017-06-04 (Jeff Bolz) 76 - Internal revisions 77