// Copyright (c) 2015-2016 The Khronos Group Inc. // Copyright notice at https://www.khronos.org/registry/speccopyright.html [[renderpass]] = Render Pass A _render pass_ represents a collection of attachments, subpasses, and dependencies between the subpasses, and describes how the attachments are used over the course of the subpasses. The use of a render pass in a command buffer is a _render pass instance_. An _attachment description_ describes the properties of an attachment including its format, sample count, and how its contents are treated at the beginning and end of each render pass instance. A _subpass_ represents a phase of rendering that reads and writes a subset of the attachments in a render pass. Rendering commands are recorded into a particular subpass of a render pass instance. A _subpass description_ describes the subset of attachments that is involved in the execution of a subpass. Each subpass can: read from some attachments as _input attachments_, write to some as _color attachments_ or _depth/stencil attachments_, and do resolve operations to others as _resolve attachments_. A subpass description can: also include a set of _preserve attachments_, which are attachments that are not read or written by the subpass but whose contents must: be preserved throughout the subpass. A subpass _uses_ an attachment if the attachment is a color, depth/stencil, resolve, or input attachment for that subpass. A subpass does not use an attachment if that attachment is preserved by the subpass. The first use of an attachment is in the lowest numbered subpass that uses that attachment. Similarly, the last use of an attachment is in the highest numbered subpass that uses that attachment. The subpasses in a render pass all render to the same dimensions, and fragments for pixel (x,y,layer) in one subpass can: only read attachment contents written by previous subpasses at that same (x,y,layer) location. [NOTE] .Note ==== By describing a complete set of subpasses a priori, render passes provide the implementation an opportunity to optimize the storage and transfer of attachment data between subpasses. In practice, this means that subpasses with a simple framebuffer-space dependency may: be merged into a single tiled rendering pass, keeping the attachment data on-chip for the duration of a render pass instance. However, it is also quite common for a render pass to only contain a single subpass. ==== _Subpass dependencies_ describe ordering restrictions between pairs of subpasses. If no dependencies are specified, implementations may: reorder or overlap portions (e.g., certain shader stages) of the execution of subpasses. Dependencies limit the extent of overlap or reordering, and are defined using masks of pipeline stages and memory access types. Each dependency acts as an <>, similarly to how <> are defined. Dependencies are needed if two subpasses operate on attachments with overlapping ranges of the same sname:VkDeviceMemory object and at least one subpass writes to that range. A _subpass dependency chain_ is a sequence of subpass dependencies in a render pass, where the source subpass of each subpass dependency (after the first) equals the destination subpass of the previous dependency. A render pass describes the structure of subpasses and attachments independent of any specific image views for the attachments. The specific image views that will be used for the attachments, and their dimensions, are specified in sname:VkFramebuffer objects. Framebuffers are created with respect to a specific render pass that the framebuffer is compatible with (see <>). Collectively, a render pass and a framebuffer define the complete render target state for one or more subpasses as well as the algorithmic dependencies between the subpasses. The various pipeline stages of the drawing commands for a given subpass may: execute concurrently and/or out of order, both within and across drawing commands. However for a given (x,y,layer,sample) sample location, certain per-sample operations are performed in <>. [[renderpass-creation]] == Render Pass Creation A render pass is created by calling: include::../protos/vkCreateRenderPass.txt[] * pname:device is the logical device that creates the render pass. * pname:pCreateInfo is a pointer to an instance of the slink:VkRenderPassCreateInfo structure that describes the parameters of the render pass. * pname:pAllocator controls host memory allocation as described in the <> chapter. * pname:pRenderPass points to a sname:VkRenderPass handle in which the resulting render pass object is returned. include::../validity/protos/vkCreateRenderPass.txt[] The sname:VkRenderPassCreateInfo structure is defined as: include::../structs/VkRenderPassCreateInfo.txt[] * pname:sType is the type of this structure. * pname:pNext is `NULL` or a pointer to an extension-specific structure. * pname:flags is reserved for future use. * pname:attachmentCount is the number of attachments used by this render pass, or zero indicating no attachments. Attachments are referred to by zero-based indices in the range [0,pname:attachmentCount). * pname:pAttachments points to an array of pname:attachmentCount number of slink:VkAttachmentDescription structures describing properties of the attachments, or `NULL` if pname:attachmentCount is zero. * pname:subpassCount is the number of subpasses to create for this render pass. Subpasses are referred to by zero-based indices in the range [0,pname:subpassCount). A render pass must: have at least one subpass. * pname:pSubpasses points to an array of pname:subpassCount number of slink:VkSubpassDescription structures describing properties of the subpasses. * pname:dependencyCount is the number of dependencies between pairs of subpasses, or zero indicating no dependencies. * pname:pDependencies points to an array of pname:dependencyCount number of slink:VkSubpassDependency structures describing dependencies between pairs of subpasses, or `NULL` if pname:dependencyCount is zero. include::../validity/structs/VkRenderPassCreateInfo.txt[] The sname:VkAttachmentDescription structure is defined as: include::../structs/VkAttachmentDescription.txt[] * pname:format is a elink:VkFormat value specifying the format of the image that will be used for the attachment. * pname:samples is the number of samples of the image as defined in elink:VkSampleCountFlagBits. * pname:loadOp specifies how the contents of color and depth components of the attachment are treated at the beginning of the subpass where it is first used: + -- include::../enums/VkAttachmentLoadOp.txt[] ** ename:VK_ATTACHMENT_LOAD_OP_LOAD means the contents within the render area will be preserved. ** ename:VK_ATTACHMENT_LOAD_OP_CLEAR means the contents within the render area will be cleared to a uniform value, which is specified when a render pass instance is begun. ** ename:VK_ATTACHMENT_LOAD_OP_DONT_CARE means the contents within the area need not be preserved; the contents of the attachment will be undefined inside the render area. -- * pname:storeOp specifies how the contents of color and depth components of the attachment are treated at the end of the subpass where it is last used: + -- include::../enums/VkAttachmentStoreOp.txt[] ** ename:VK_ATTACHMENT_STORE_OP_STORE means the contents within the render area are written to memory and will be available for reading after the render pass instance completes once the writes have been synchronized with ename:VK_ACCESS_COLOR_ATTACHMENT_WRITE_BIT (for color attachments) or ename:VK_ACCESS_DEPTH_STENCIL_ATTACHMENT_WRITE_BIT (for depth/stencil attachments). ** ename:VK_ATTACHMENT_STORE_OP_DONT_CARE means the contents within the render area are not needed after rendering, and may: be discarded; the contents of the attachment will be undefined inside the render area. -- * pname:stencilLoadOp specifies how the contents of stencil components of the attachment are treated at the beginning of the subpass where it is first used, and must: be one of the same values allowed for pname:loadOp above. * pname:stencilStoreOp specifies how the contents of stencil components of the attachment are treated at the end of the last subpass where it is used, and must: be one of the same values allowed for pname:storeOp above. * pname:initialLayout is the layout the attachment image subresource will be in when a render pass instance begins. * pname:finalLayout is the layout the attachment image subresource will be transitioned to when a render pass instance ends. During a render pass instance, an attachment can: use a different layout in each subpass, if desired. * pname:flags is a bitfield of elink:VkAttachmentDescriptionFlagBits describing additional properties of the attachment: include::../enums/VkAttachmentDescriptionFlagBits.txt[] include::../validity/structs/VkAttachmentDescription.txt[] If the attachment uses a color format, then pname:loadOp and pname:storeOp are used, and pname:stencilLoadOp and pname:stencilStoreOp are ignored. If the format has depth and/or stencil components, pname:loadOp and pname:storeOp apply only to the depth data, while pname:stencilLoadOp and pname:stencilStoreOp define how the stencil data is handled. [[renderpass-precision]] During a render pass instance, input/color attachments with color formats that have a component size of 8, 16, or 32 bits must: be represented in the attachment's format throughout the instance. Attachments with other floating- or fixed-point color formats, or with depth components may: be represented in a format with a precision higher than the attachment format, but must: be represented with the same range. When such a component is loaded via the pname:loadOp, it will be converted into an implementation-dependent format used by the render pass. Such components must: be converted from the render pass format, to the format of the attachment, before they are stored or resolved at the end of a render pass instance via pname:storeOp. Conversions occur as described in <> and <>. [[renderpass-aliasing]] If pname:flags includes ename:VK_ATTACHMENT_DESCRIPTION_MAY_ALIAS_BIT, then the attachment is treated as if it shares physical memory with another attachment in the same render pass. This information limits the ability of the implementation to reorder certain operations (like layout transitions and the pname:loadOp) such that it is not improperly reordered against other uses of the same physical memory via a different attachment. This is described in more detail below. If a render pass uses multiple attachments that alias the same device memory, those attachments must: each include the ename:VK_ATTACHMENT_DESCRIPTION_MAY_ALIAS_BIT bit in their attachment description flags. Attachments aliasing the same memory occurs in multiple ways: * Multiple attachments being assigned the same image view as part of framebuffer creation. * Attachments using distinct image views that correspond to the same image subresource of an image. * Attachments using views of distinct image subresources which are bound to overlapping memory. Render passes must: include subpass dependencies (either directly or via a subpass dependency chain) between any two subpasses that operate on the same attachment or aliasing attachments and those subpass dependencies must: include execution and memory dependencies separating uses of the aliases, if at least one of those subpasses writes to one of the aliases. Those dependencies mustnot: include the ename:VK_DEPENDENCY_BY_REGION_BIT if the aliases are views of distinct image subresources which overlap in memory. Multiple attachments that alias the same memory mustnot: be used in a single subpass. A given attachment index mustnot: be used multiple times in a single subpass, with one exception: two subpass attachments can: use the same attachment index if at least one use is as an input attachment and neither use is as a resolve or preserve attachment. In other words, the same view can: be used simultaneously as an input and color or depth/stencil attachment, but mustnot: be used as multiple color or depth/stencil attachments nor as resolve or preserve attachments. This valid scenario is described in more detail <>. If a set of attachments alias each other, then all except the first to be used in the render pass must: use an pname:initialLayout of ename:VK_IMAGE_LAYOUT_UNDEFINED, since the earlier uses of the other aliases make their contents undefined. Once an alias has been used and a different alias has been used after it, the first alias mustnot: be used in any later subpasses. However, an application can: assign the same image view to multiple aliasing attachment indices, which allows that image view to be used multiple times even if other aliases are used in between. Once an attachment needs the ename:VK_ATTACHMENT_DESCRIPTION_MAY_ALIAS_BIT bit, there should: be no additional cost of introducing additional aliases, and using these additional aliases may: allow more efficient clearing of the attachments on multiple uses via ename:VK_ATTACHMENT_LOAD_OP_CLEAR. [NOTE] .Note ==== The exact set of attachment indices that alias with each other is not known until a framebuffer is created using the render pass, so the above conditions cannot: be validated at render pass creation time. ==== The sname:VkSubpassDescription structure is defined as: include::../structs/VkSubpassDescription.txt[] * pname:flags is reserved for future use. * pname:pipelineBindPoint is a elink:VkPipelineBindPoint value specifying whether this is a compute or graphics subpass. Currently, only graphics subpasses are supported. * pname:inputAttachmentCount is the number of input attachments. * pname:pInputAttachments is an array of slink:VkAttachmentReference structures (defined below) that lists which of the render pass's attachments can: be read in the shader during the subpass, and what layout the attachment images will be in during the subpass. Each element of the array corresponds to an input attachment unit number in the shader, i.e. if the shader declares an input variable `layout(input_attachment_index=X, set=Y, binding=Z)` then it uses the attachment provided in pname:pInputAttachments[X]. Input attachments must: also be bound to the pipeline with a descriptor set, with the input attachment descriptor written in the location (set=Y, binding=Z). * pname:colorAttachmentCount is the number of color attachments. * pname:pColorAttachments is an array of pname:colorAttachmentCount slink:VkAttachmentReference structures that lists which of the render pass's attachments will be used as color attachments in the subpass, and what layout the attachment images will be in during the subpass. Each element of the array correponds to a fragment shader output location, i.e. if the shader declared an output variable `layout(location=X)` then it uses the attachment provided in pname:pColorAttachments[X]. * pname:pResolveAttachments is `NULL` or a pointer to an array of slink:VkAttachmentReference structures. If pname:pResolveAttachments is not `NULL`, each of its elements corresponds to a color attachment (the element in pname:pColorAttachments at the same index). At the end of each subpass, the subpass's color attachments are resolved to corresponding resolve attachments, unless the resolve attachment index is ename:VK_ATTACHMENT_UNUSED or pname:pResolveAttachments is `NULL`. If the first use of an attachment in a render pass is as a resolve attachment, then the pname:loadOp is effectively ignored as the resolve is guaranteed to overwrite all pixels in the render area. * pname:pDepthStencilAttachment is a pointer to a slink:VkAttachmentReference specifying which attachment will be used for depth/stencil data and the layout it will be in during the subpass. Setting the attachment index to ename:VK_ATTACHMENT_UNUSED or leaving this pointer as `NULL` indicates that no depth/stencil attachment will be used in the subpass. * pname:preserveAttachmentCount is the number of preserved attachments. * pname:pPreserveAttachments is an array of pname:preserveAttachmentCount render pass attachment indices describing the attachments that are not used by a subpass, but whose contents must: be preserved throughout the subpass. The contents of an attachment within the render area become undefined at the start of a subpass S if all of the following conditions are true: * The attachment is used as a color, depth/stencil, or resolve attachment in any subpass in the render pass. * There is a subpass S1 that uses or preserves the attachment, and a subpass dependency from S1 to S. * The attachment is not used or preserved in subpass S. Once the contents of an attachment become undefined in subpass S, they remain undefined for subpasses in subpass dependency chains starting with subpass S until they are written again. However, they remain valid for subpasses in other subpass dependency chains starting with subpass S1 if those subpasses use or preserve the attachment. include::../validity/structs/VkSubpassDescription.txt[] The sname:VkAttachmentReference structure is defined as: include::../structs/VkAttachmentReference.txt[] * pname:attachment is the index of the attachment of the render pass, and corresponds to the index of the corresponding element in the pname:pAttachments array of the sname:VkRenderPassCreateInfo structure. If any color or depth/stencil attachments are ename:VK_ATTACHMENT_UNUSED, then no writes occur for those attachments. * pname:layout is a elink:VkImageLayout value specifying the layout the attachment uses during the subpass. The implementation will automatically perform layout transitions as needed between subpasses to make each subpass use the requested layouts. include::../validity/structs/VkAttachmentReference.txt[] The sname:VkSubpassDependency structure is defined as: include::../structs/VkSubpassDependency.txt[] * pname:srcSubpass and pname:dstSubpass are the subpass indices of the producer and consumer subpasses, respectively. pname:srcSubpass and pname:dstSubpass can: also have the special value ename:VK_SUBPASS_EXTERNAL. The source subpass must: always be a lower numbered subpass than the destination subpass (excluding external subpasses and <>), so that the order of subpass descriptions is a valid execution ordering, avoiding cycles in the dependency graph. * pname:srcStageMask, pname:dstStageMask, pname:srcAccessMask, pname:dstAccessMask, and pname:dependencyFlags describe an <> between subpasses. The bits that can: be included in pname:dependencyFlags are: + include::../enums/VkDependencyFlagBits.txt[] ** If pname:dependencyFlags contains ename:VK_DEPENDENCY_BY_REGION_BIT, then the dependency is by-region as defined in <>. Each subpass dependency defines an execution and memory dependency between two sets of commands, with the second set depending on the first set. When pname:srcSubpass does not equal pname:dstSubpass then the first set of commands is: * All commands in the subpass indicated by pname:srcSubpass, if pname:srcSubpass is not ename:VK_SUBPASS_EXTERNAL. * All commands before the render pass instance, if pname:srcSubpass is ename:VK_SUBPASS_EXTERNAL. While the corresponding second set of commands is: * All commands in the subpass indicated by pname:dstSubpass, if pname:dstSubpass is not ename:VK_SUBPASS_EXTERNAL. * All commands after the render pass instance, if pname:dstSubpass is ename:VK_SUBPASS_EXTERNAL. When pname:srcSubpass equals pname:dstSubpass then the first set consists of commands in the subpass before a call to flink:vkCmdPipelineBarrier and the second set consists of commands in the subpass following that same call as described in the <> section. The pname:srcStageMask, pname:dstStageMask, pname:srcAccessMask, pname:dstAccessMask, and pname:dependencyFlags parameters of the dependency are interpreted the same way as for other dependencies, as described in <>. include::../validity/structs/VkSubpassDependency.txt[] Automatic image layout transitions between subpasses also interact with the subpass dependencies. If two subpasses are connected by a dependency and those two subpasses use the same attachment in a different layout, then the layout transition will occur after the memory accesses via pname:srcAccessMask have completed in all pipeline stages included in pname:srcStageMask in the source subpass, and before any memory accesses via pname:dstAccessMask occur in any pipeline stages included in pname:dstStageMask in the destination subpass. The automatic image layout transitions from pname:initialLayout to the first used layout (if it is different) are performed according to the following rules: * If the attachment does not include the ename:VK_ATTACHMENT_DESCRIPTION_MAY_ALIAS_BIT bit and there is no subpass dependency from ename:VK_SUBPASS_EXTERNAL to the first subpass that uses the attachment, then it is as if there were such a dependency with pname:srcStageMask = pname:srcAccessMask = 0 and pname:dstStageMask and pname:dstAccessMask including all relevant bits (all graphics pipeline stages and all access types that use image resources), with the transition executing as part of that dependency. In other words, it may: overlap work before the render pass instance and is complete before the subpass begins. * If the attachment does not include the ename:VK_ATTACHMENT_DESCRIPTION_MAY_ALIAS_BIT bit and there is a subpass dependency from ename:VK_SUBPASS_EXTERNAL to the first subpass that uses the attachment, then the transition executes as part of that dependency and according to its stage and access masks. It mustnot: overlap work that came before the render pass instance that is included in the source masks, but it may: overlap work in previous subpasses. * If the attachment includes the ename:VK_ATTACHMENT_DESCRIPTION_MAY_ALIAS_BIT bit, then the transition executes according to all the subpass dependencies with pname:dstSubpass equal to the first subpass index that the attachment is used in. That is, it occurs after all memory accesses in the source stages and masks from all the source subpasses have completed and are available, and before the union of all the destination stages begin, and the new layout is visible to the union of all the destination access types. If there are no incoming subpass dependencies, then this case follows the first rule. Similar rules apply for the transition to the pname:finalLayout, using dependencies with pname:dstSubpass equal to ename:VK_SUBPASS_EXTERNAL If an attachment specifies the ename:VK_ATTACHMENT_LOAD_OP_CLEAR load operation, then it will logically be cleared at the start of the first subpass where it is used. [NOTE] .Note ==== Implementations may: move clears earlier as long as it does not affect the operation of a render pass instance. For example, an implementation may: choose to clear all attachments at the start of the render pass instance. If an attachment has the ename:VK_ATTACHMENT_DESCRIPTION_MAY_ALIAS_BIT flag set, then the clear must: occur at the start of subpass where the attachment is first used, in order to preserve the operation of the render pass instance. ==== The first use of an attachment mustnot: specify a layout equal to ename:VK_IMAGE_LAYOUT_DEPTH_STENCIL_READ_ONLY_OPTIMAL or ename:VK_IMAGE_LAYOUT_SHADER_READ_ONLY_OPTIMAL if the attachment specifies that the pname:loadOp is ename:VK_ATTACHMENT_LOAD_OP_CLEAR. If a subpass uses the same attachment as both an input attachment and either a color attachment or a depth/stencil attachment, then both uses must: observe the result of the clear. Similarly, if an attachment specifies that the pname:storeOp is ename:VK_ATTACHMENT_STORE_OP_STORE, then it will logically be stored at the end of the last subpass where it is used. [NOTE] .Note ==== Implementations may: move stores later as long as it does not affect the operation of a render pass instance. If an attachment has the ename:VK_ATTACHMENT_DESCRIPTION_MAY_ALIAS_BIT flag set, then the store must: occur at the end of the highest numbered subpass that uses the attachment. ==== If an attachment is not used by any subpass, then the pname:loadOp and the pname:storeOp are ignored and the attachment's memory contents will not be modified by execution of a render pass instance. It will be common for a render pass to consist of a simple linear graph of dependencies, where subpass N depends on subpass N-1 for all N, and the operation of the memory barriers and layout transitions is fairly straightforward to reason about for those simple cases. But for more complex graphs, there are some rules that govern when there must: be dependencies between subpasses. As stated earlier, render passes must: include subpass dependencies which (either directly or via a subpass dependency chain) separate any two subpasses that operate on the same attachment or aliasing attachments, if at least one of those subpasses writes to the attachment. If an image layout changes between those two subpasses, the implementation uses the stageMasks and accessMasks indicated by the subpass dependency as the masks that control when the layout transition must: occur. If there is not a layout change on the attachment, or if an implementation treats the two layouts identically, then it may: treat the dependency as a simple execution/memory barrier. If two subpasses use the same attachment in different layouts but both uses are read-only (i.e. input attachment, or read-only depth/stencil attachment), the application does not need to express a dependency between the two subpasses. Implementations that treat the two layouts differently may: deduce and insert a dependency between the subpasses, with the implementation choosing the appropriate stage masks and access masks based on whether the attachment is used as an input or depth/stencil attachment, and may: insert the appropriate layout transition along with the execution/memory barrier. Implementations that treat the two layouts identically need not insert a barrier, and the two subpasses may: execute simultaneously. The stage masks and access masks are chosen as follows: - for input attachments, stage mask = ename:VK_PIPELINE_STAGE_FRAGMENT_SHADER_BIT, access mask = ename:VK_ACCESS_INPUT_ATTACHMENT_READ_BIT. - for depth/stencil attachments, stage mask = ename:VK_PIPELINE_STAGE_EARLY_FRAGMENT_TESTS_BIT | ename:VK_PIPELINE_STAGE_LATE_FRAGMENT_TESTS_BIT, access mask = ename:VK_ACCESS_DEPTH_STENCIL_ATTACHMENT_READ_BIT where pname:srcStageMask and pname:srcAccessMask are taken based on usage in the source subpass and pname:dstStageMask and pname:dstAccessMask are taken based on usage in the destination subpass. [[renderpass-feedbackloop]] If a subpass uses the same attachment as both an input attachment and either a color attachment or a depth/stencil attachment, reads from the input attachment are not automatically coherent with writes through the color or depth/stencil attachment. In order to achieve well-defined results, one of two criteria must: be satisfied. First, if the color components or depth/stencil components read by the input attachment are mutually exclusive with the components written by the color or depth/stencil attachment then there is no _feedback loop_ and the reads and writes both function normally, with the reads observing values from the previous subpass(es) or from memory. This option requires the graphics pipelines used by the subpass to disable writes to color components that are read as inputs via the pname:colorWriteMask, and to disable writes to depth/stencil components that are read as inputs via pname:depthWriteEnable or pname:stencilTestEnable. Second, if the input attachment reads components that are written by the color or depth/stencil attachment, then there is a feedback loop and a pipeline barrier must: be used between when the attachment is written and when it is subsequently read by later fragments. This pipeline barrier must: follow the rules of a self-dependency as described in <>, where the barrier's flags include: * pname:dstStageMask = ename:VK_PIPELINE_STAGE_FRAGMENT_SHADER_BIT, * pname:dstAccessMask = ename:VK_ACCESS_INPUT_ATTACHMENT_READ_BIT, and * pname:srcAccessMask = ename:VK_ACCESS_COLOR_ATTACHMENT_WRITE_BIT (for color attachments) or pname:srcAccessMask = ename:VK_ACCESS_DEPTH_STENCIL_ATTACHMENT_WRITE_BIT (for depth/stencil attachments). * pname:srcStageMask = ename:VK_PIPELINE_STAGE_COLOR_ATTACHMENT_OUTPUT_BIT (for color attachments) or pname:srcStageMask = ename:VK_PIPELINE_STAGE_LATE_FRAGMENT_TESTS_BIT | ename:VK_PIPELINE_STAGE_EARLY_FRAGMENT_TESTS_BIT (for depth/stencil attachments). * pname:dependencyFlags = ename:VK_DEPENDENCY_BY_REGION_BIT. A pipeline barrier is needed each time a fragment will read a particular (x,y,layer,sample) location if that location has been written since the most recent pipeline barrier, or since the start of the subpass if there have been no pipeline barriers since the start of the subpass. An attachment used as both an input attachment and color attachment must: be in the ename:VK_IMAGE_LAYOUT_GENERAL layout. An attachment used as both an input attachment and depth/stencil attachment must: be in either the ename:VK_IMAGE_LAYOUT_GENERAL or ename:VK_IMAGE_LAYOUT_DEPTH_STENCIL_READ_ONLY_OPTIMAL layout. Since an attachment in the ename:VK_IMAGE_LAYOUT_DEPTH_STENCIL_READ_ONLY_OPTIMAL layout is read-only, this situation is not a feedback loop. To destroy a render pass, call: include::../protos/vkDestroyRenderPass.txt[] * pname:device is the logical device that destroys the render pass. * pname:renderPass is the handle of the render pass to destroy. * pname:pAllocator controls host memory allocation as described in the <> chapter. include::../validity/protos/vkDestroyRenderPass.txt[] [[renderpass-compatibility]] == Render Pass Compatibility Framebuffers and graphics pipelines are created based on a specific render pass object. They must: only be used with that render pass object, or one compatible with it. Two attachment references are compatible if they have matching format and sample count, or are both ename:VK_ATTACHMENT_UNUSED or the pointer that would contain the reference is `NULL`. Two arrays of attachment references are compatible if all corresponding pairs of attachments are compatible. If the arrays are of different lengths, attachment references not present in the smaller array are treated as ename:VK_ATTACHMENT_UNUSED. Two render passes that contain only a single subpass are compatible if their corresponding color, input, resolve, and depth/stencil attachment references are compatible. If two render passes contain more than one subpass, they are compatible if they are identical except for: * Initial and final image layout in attachment descriptions * Load and store operations in attachment descriptions * Image layout in attachment references A framebuffer is compatible with a render pass if it was created using the same render pass or a compatible render pass. == Framebuffers Render passes operate in conjunction with framebuffers, which represent a collection of specific memory attachments that a render pass instance uses. An application creates a framebuffer by calling: include::../protos/vkCreateFramebuffer.txt[] * pname:device is the logical device that creates the framebuffer. * pname:pCreateInfo points to a slink:VkFramebufferCreateInfo structure which describes additional information about framebuffer creation. * pname:pAllocator controls host memory allocation as described in the <> chapter. * pname:pFramebuffer points to a sname:VkFramebuffer handle in which the resulting framebuffer object is returned. include::../validity/protos/vkCreateFramebuffer.txt[] The sname:VkFramebufferCreateInfo structure is defined as: include::../structs/VkFramebufferCreateInfo.txt[] * pname:sType is the type of this structure. * pname:pNext is `NULL` or a pointer to an extension-specific structure. * pname:flags is reserved for future use. * pname:renderPass is a render pass that defines what render passes the framebuffer will be compatible with. See <> for details. * pname:attachmentCount is the number of attachments. * pname:pAttachments is an array of sname:VkImageView handles, each of which will be used as the corresponding attachment in a render pass instance. * pname:width, pname:height and pname:layers define the dimensions of the framebuffer. include::../validity/structs/VkFramebufferCreateInfo.txt[] Image subresources used as attachments mustnot: be used via any non-attachment usage for the duration of a render pass instance. [NOTE] .Note ==== This restriction means that the render pass has full knowledge of all uses of all of the attachments, so that the implementation is able to make correct decisions about when and how to perform layout transitions, when to overlap execution of subpasses, etc. ==== [[renderpass-noattachments]] It is legal for a subpass to use no color or depth/stencil attachments, and rather use shader side effects such as image stores and atomics to produce an output. In this case, the subpass continues to use the pname:width, pname:height, and pname:layers of the framebuffer to define the dimensions of the rendering area, and the pname:rasterizationSamples from each pipeline's slink:VkPipelineMultisampleStateCreateInfo to define the number of samples used in rasterization; however, if slink:VkPhysicalDeviceFeatures::pname:variableMultisampleRate is code:VK_FALSE, then all pipelines to be bound with a given zero-attachment subpass must: have the same value for slink:VkPipelineMultisampleStateCreateInfo::pname:rasterizationSamples. To destroy a framebuffer, call: include::../protos/vkDestroyFramebuffer.txt[] * pname:device is the logical device that destroys the framebuffer. * pname:framebuffer is the handle of the framebuffer to destroy. * pname:pAllocator controls host memory allocation as described in the <> chapter. include::../validity/protos/vkDestroyFramebuffer.txt[] [[renderpass-commands]] == Render Pass Commands An application records the commands for a render pass instance one subpass at a time, by beginning a render pass instance, iterating over the subpasses to record commands for that subpass, and then ending the render pass instance. To begin a render pass instance, call: include::../protos/vkCmdBeginRenderPass.txt[] * pname:commandBuffer is the command buffer in which to record the command. * pname:pRenderPassBegin is a pointer to a slink:VkRenderPassBeginInfo structure (defined below) which indicates the render pass to begin an instance of, and the framebuffer the instance uses. * pname:contents specifies how the commands in the first subpass will be provided, and is one of the values: + -- include::../enums/VkSubpassContents.txt[] If pname:contents is ename:VK_SUBPASS_CONTENTS_INLINE, the contents of the subpass will be recorded inline in the primary command buffer, and secondary command buffers mustnot: be executed within the subpass. If pname:contents is ename:VK_SUBPASS_CONTENTS_SECONDARY_COMMAND_BUFFERS, the contents are recorded in secondary command buffers that will be called from the primary command buffer, and fname:vkCmdExecuteCommands is the only valid command on the command buffer until fname:vkCmdNextSubpass or fname:vkCmdEndRenderPass. -- include::../validity/protos/vkCmdBeginRenderPass.txt[] After beginning a render pass instance, the command buffer is ready to record the commands for the first subpass of that render pass. The sname:VkRenderPassBeginInfo structure is defined as: include::../structs/VkRenderPassBeginInfo.txt[] * pname:sType is the type of this structure. * pname:pNext is `NULL` or a pointer to an extension-specific structure. * pname:renderPass is the render pass to begin an instance of. * pname:framebuffer is the framebuffer containing the attachments that are used with the render pass. * pname:renderArea is the render area that is affected by the render pass instance, and is described in more detail below. * pname:clearValueCount is the number of elements in pname:pClearValues. * pname:pClearValues is an array of slink:VkClearValue structures that contains clear values for each attachment, if the attachment uses a pname:loadOp value of ename:VK_ATTACHMENT_LOAD_OP_CLEAR. The array is indexed by attachment number. Only elements corresponding to cleared attachments are used. Other elements of pname:pClearValues are ignored. include::../validity/structs/VkRenderPassBeginInfo.txt[] pname:renderArea is the render area that is affected by the render pass instance. The effects of attachment load, store and resolve operations are restricted to the pixels whose x and y coordinates fall within the render area on all attachments. The render area extends to all layers of pname:framebuffer. The application must: ensure (using scissor if necessary) that all rendering is contained within the render area, otherwise the pixels outside of the render area become undefined and shader side effects may: occur for fragments outside the render area. The render area must: be contained within the framebuffer dimensions. [NOTE] .Note ==== There may: be a performance cost for using a render area smaller than the framebuffer, unless it matches the render area granularity for the render pass. ==== The render area granularity is queried by calling: include::../protos/vkGetRenderAreaGranularity.txt[] * pname:device is the logical device that owns the render pass. * pname:renderPass is a handle to a render pass. * pname:pGranularity points to a slink:VkExtent2D structure in which the granularity is returned. include::../validity/protos/vkGetRenderAreaGranularity.txt[] The conditions leading to an optimal pname:renderArea are: * the pname:offset.x member in pname:renderArea is a multiple of the pname:width member of the returned slink:VkExtent2D (the horizontal granularity). * the pname:offset.y member in pname:renderArea is a multiple of the pname:height of the returned slink:VkExtent2D (the vertical granularity). * either the pname:offset.width member in pname:renderArea is a multiple of the horizontal granularity or pname:offset.x+pname:offset.width is equal to the pname:width of the pname:framebuffer in the slink:VkRenderPassBeginInfo. * either the pname:offset.height member in pname:renderArea is a multiple of the vertical granularity or pname:offset.y+pname:offset.height is equal to the pname:height of the pname:framebuffer in the slink:VkRenderPassBeginInfo. Subpass dependencies are not affected by the render area, and apply to the entire image subresources attached to the framebuffer. Similarly, pipeline barriers are valid even if their effect extends outside the render area. After recording the commands for a subpass, an application transitions to the next subpass in the render pass instance by calling: include::../protos/vkCmdNextSubpass.txt[] * pname:commandBuffer is the command buffer in which to record the command. * pname:contents specifies how the commands in the next subpass will be provided, in the same fashion as the corresponding parameter of flink:vkCmdBeginRenderPass. include::../validity/protos/vkCmdNextSubpass.txt[] The subpass index for a render pass begins at zero when fname:vkCmdBeginRenderPass is recorded, and increments each time fname:vkCmdNextSubpass is recorded. Moving to the next subpass automatically performs any multisample resolve operations in the subpass being ended. End-of-subpass multisample resolves are treated as color attachment writes for the purposes of synchronization. That is, they are considered to execute in the ename:VK_PIPELINE_STAGE_COLOR_ATTACHMENT_OUTPUT_BIT pipeline stage and their writes are synchronized with ename:VK_ACCESS_COLOR_ATTACHMENT_WRITE_BIT. Synchronization between rendering within a subpass and any resolve operations at the end of the subpass occurs automatically, without need for explicit dependencies or pipeline barriers. However, if the resolve attachment is also used in a different subpass, an explicit dependency is needed. After transitioning to the next subpass, the application can: record the commands for that subpass. After recording the commands for the last subpass, an application records a command to end a render pass instance by calling: include::../protos/vkCmdEndRenderPass.txt[] * pname:commandBuffer is the command buffer in which to end the current render pass instance. include::../validity/protos/vkCmdEndRenderPass.txt[] Ending a render pass instance performs any multisample resolve operations on the final subpass.