DirectX 10 introduced state objects to set a group of states during run time. DirectX 12 introduces pipeline state objects (PSOs) used to set an even larger group of states along with shaders. This article focuses on the changes in dealing with resources and leaves the description of how states are grouped in PSOs to future articles.
Pixel Shader 4 0 Software 12
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The first two entries in the descriptor heap description are the number of descriptors and the type of descriptors that are allowed in this descriptor heap. The third parameter D3D12_DESCRIPTOR_HEAP_SHADER_VISIBLE describes this descriptor heap as visible to a shader. Descriptor heaps that are not visible to a shader can be used, for example, for staging descriptors on the CPU or for RTV that are not selectable from within shaders.
A descriptor table offsets into the descriptor heap. Instead of forcing the graphics pipeline to always view the entire heap, switching descriptor tables is an inexpensive way to change a set of resources a given shader uses. This way the shader does not have to understand where to find resources in heap space.
The visibility of the descriptor table is restricted to the pixel shader by providing the D3D12_SHADER_VISIBILITY_PIXEL flag. The following enum defines different levels of visibility of a descriptor table:
A root signature stores root parameters that are used by shaders to locate the resources they need access to. These parameters exist as a binding space on a command list for the collection of resources the application needs to make available to shaders.
Root descriptors and root constants decrease the level of GPU indirection when accessed, while descriptor tables allow accessing a larger amount of data but incur the cost of the increased level of indirection. Because of the higher level of indirection, with descriptor tables the application can initialize content up until it submits the command list for execution. Additionally, shader model 5.1, which is supported by all DirectX 12 hardware, offers shaders to dynamically index into any given descriptor table. So a shader can select which descriptor it wants out of a descriptor table at shader execution time. An application could just create one large descriptor table and always use indexing (via something like a material ID) to get the desired descriptor.
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For earlier shader models, HLSL programming exposes only a single thread of execution. New wave-level operations are provided, starting with model 6.0, to explicitly take advantage of the parallelism of current GPUs - many threads can be executing in lockstep on the same core simultaneously. For example, the model 6.0 intrinsics enable the elimination of barrier constructs when the scope of synchronization is within the width of the SIMD processor, or some other set of threads that are known to be atomic relative to each other.
Most of the intrinsics appear in pixel shaders and compute shaders, though there are some exceptions (noted for each function). The functions have been added to the requirements for DirectX Feature Level 12.0, under API level 12.
The parameter and return value for these functions implies the type of the expression, the supported types are those from the following list that are also present in the target shader model for your app:
These intrinsics perform swap operations on the values across a wave known to contain pixel shader quads as defined here. The indices of the pixels in the quad are defined in scan-line or reading order - where the coordinates within a quad are:
These routines work in either compute shaders or pixel shaders. In compute shaders they operate in quads defined as evenly divided groups of 4 within an SIMD wave. In pixel shaders they should be used on waves captured by WaveQuadLanes, otherwise results are undefined.
The URP Deferred Rendering Path uses a rendering technique where light shading is performed in screen space on a separate rendering pass after all the vertex and pixel shaders have been rendered. Deferred shading decouples scene geometry from lighting calculations, so the shading of each light is only computed for the visible pixels that it actually affects. With this approach, Unity can efficiently render a far greater amount of lights in a scene compared to per-object forward rendering.
The High-Level Shader Language[1] or High-Level Shading Language[2] (HLSL) is a proprietary shading language developed by Microsoft for the Direct3D 9 API to augment the shader assembly language, and went on to become the required shading language for the unified shader model of Direct3D 10 and higher.
HLSL is analogous to the GLSL shading language used with the OpenGL standard. It is very similar to the Nvidia Cg shading language, as it was developed alongside it. Early versions of the two languages were considered identical, only marketed differently.[3] HLSL shaders can enable profound speed and detail increases as well as many special effects in both 2D and 3D computer graphics.[citation needed]
HLSL programs come in six forms: pixel shaders (fragment in GLSL), vertex shaders, geometry shaders, compute shaders, tessellation shaders (Hull and Domain shaders), and ray tracing shaders (Ray Generation Shaders, Intersection Shaders, Any Hit/Closest Hit/Miss Shaders). A vertex shader is executed for each vertex that is submitted by the application, and is primarily responsible for transforming the vertex from object space to view space, generating texture coordinates, and calculating lighting coefficients such as the vertex's normal, tangent, and bitangent vectors. When a group of vertices (normally 3, to form a triangle) come through the vertex shader, their output position is interpolated to form pixels within its area; this process is known as rasterization.
Optionally, an application using a Direct3D 10/11/12 interface and Direct3D 10/11/12 hardware may also specify a geometry shader. This shader takes as its input some vertices of a primitive (triangle/line/point) and uses this data to generate/degenerate (or tessellate) additional primitives or to change the type of primitives, which are each then sent to the rasterizer.
GPUs listed are the hardware that first supported the given specifications. Manufacturers generally support all lower shader models through drivers. Note that games may claim to require a certain DirectX version, but don't necessarily require a GPU conforming to the full specification of that version, as developers can use a higher DirectX API version to target lower-Direct3D-spec hardware; for instance DirectX 9 exposes features of DirectX7-level hardware that DirectX7 did not, targeting their fixed-function T&L pipeline.
Layout qualifiers are sometimes used to define various options for different shader stages. These shader stage options apply to the input of the shader stage or the output. In these definitions, variable definition will just be in or out.
The component qualifier can be used for any shader stage input/output declaration. This includes interfaces between shaders, fragment shader outputs, tessellation patch variables, and so forth. However, it may not be used on:
For Vertex Attributes and Fragment Shader Outputs, OpenGL still treats each location as though it were a single variable. So glVertexAttribPointer feeds data to all of the input variables for that location. Any components used by the shader that are not provided by the array are filled in as normal (with zeros, except for the last which gets a 1). And glDrawBuffers pulls data from all of the output variables for that location.
Buffer backed interface blocks and all opaque types have a setting which represents an index in the GL context where a buffer or texture object is bound so that it can be accessed through that interface. These binding points, like input attribute indices and output data locations, can be set from within the shader. This is done by using the "binding" layout qualifier:
Variables declared in interface blocks that get their storage from buffers (uniform blocks or shader storage blocks) have a number of layout qualifiers to define the packing and ordering of the variables defined in the block.
Calling glGetUniformLocation(prog, "modelToWorldMatrix") is guaranteed to return 2. It is illegal to assign the same uniform location to two uniforms in the same shader or the same program. Even if those two uniforms have the same name and type, and are defined in different shader stages, it is not legal to explicitly assign them the same uniform location; a linker error will occur.
Shader Subroutines use a number of resources that can be automatically assigned to each shader stage at link time. However, the user can explicitly define them within the shader text as well, to avoid having to query them.
Subroutine functions each have a specific index that identifies that particular subroutine among all subroutines in a shader stage. This subroutine can be set from within a shader using the index layout qualifier:
This sets the particular subroutine function definition to index 2. No two subroutine functions may have the same index. Also, this index is subject to the limitations on the number of subroutines in a shader stage.
The number of active subroutine uniforms for this shader stage will be the largest location + 1. This means that some "active" uniform locations may be unused. If the above example were the only subroutine uniform, then the number of active subroutine uniforms will be considered to be 2, with location 0 going unusued. 2ff7e9595c
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