--- /dev/null
+Intel Surface Layout
+
+Introduction
+============
+isl is a small library that calculates the layout of Intel GPU surfaces, queries
+those layouts, and queries the properties of surface formats.
+
+
+Independence from User APIs
+===========================
+isl's API is independent of any user-facing graphics API, such as OpenGL and
+Vulkan. This independence allows isl to be used a shared component by multiple
+Intel drivers.
+
+Rather than mimic the user-facing APIs, the isl API attempts to reflect Intel
+hardware: the actual memory layout of Intel GPU surfaces and how one programs
+the GPU to use those surfaces. For example:
+
+ - The tokens of `enum isl_format` (such as `ISL_FORMAT_R8G8B8A8_UNORM`)
+ match those of the hardware enum `SURFACE_FORMAT` rather than the OpenGL
+ or Vulkan format tokens. And the values of `isl_format` and
+ `SURFACE_FORMAT` are identical.
+
+ - The OpenGL and Vulkan APIs contain depth and stencil formats. However the
+ hardware enum `SURFACE_FORMAT` does not, and therefore neither does `enum
+ isl_format`. Rather than define new pixel formats that have no hardware
+ counterpart, isl records the intent to use a surface as a depth or stencil
+ buffer with the usage flags `ISL_SURF_USAGE_DEPTH_BIT` and
+ `ISL_SURF_USAGE_STENCIL_BIT`.
+
+ - `struct isl_surf` distinguishes between the surface's logical dimension
+ from the user API's perspective (`enum isl_surf_dim`, which may be 1D, 2D,
+ or 3D) and the layout of those dimensions in memory (`enum isl_dim_layout`).
+
+
+Surface Units
+=============
+
+Intro
+-----
+ISL takes care in its equations to correctly handle conversion among surface
+units (such as pixels and compression blocks) and to carefully distinguish
+between a surface's logical layout in the client API and its physical layout
+in memory.
+
+Symbol names often explicitly declare their unit with a suffix:
+
+ - px: logical pixels
+ - sa: physical surface samples
+ - el: physical surface elements
+ - sa_rows: rows of physical surface samples
+ - el_rows: rows of physical surface elements
+
+Logical units are independent of hardware generation and are closely related
+to the user-facing API (OpenGL and Vulkan). Physical units are dependent on
+hardware generation and reflect the surface's layout in memory.
+
+Definitions
+-----------
+- Logical Pixels (px):
+
+ The surface's layout from the perspective of the client API (OpenGL and
+ Vulkan) is in units of logical pixels. Logical pixels are independent of the
+ surface's layout in memory.
+
+ A surface's width and height, in units of logical pixels, is not affected by
+ the surface's sample count. For example, consider a VkImage created with
+ VkImageCreateInfo{width=w0, height=h0, samples=s0}. The surface's width and
+ height at level 0 is, in units of logical pixels, w0 and h0 regardless of
+ the value of s0.
+
+ For example, the logical array length of a 3D surface is always 1, even on
+ Gen9 where the surface's memory layout is that of an array surface
+ (ISL_DIM_LAYOUT_GEN4_2D).
+
+- Physical Surface Samples (sa):
+
+ For a multisampled surface, this unit has the obvious meaning.
+ A singlesampled surface, from ISL's perspective, is simply a multisampled
+ surface whose sample count is 1.
+
+ For example, consider a 2D single-level non-array surface with samples=4,
+ width_px=64, and height_px=64 (note that the suffix 'px' indicates logical
+ pixels). If the surface's multisample layout is ISL_MSAA_LAYOUT_INTERLEAVED,
+ then the extent of level 0 is, in units of physical surface samples,
+ width_sa=128, height_sa=128, depth_sa=1, array_length_sa=1. If
+ ISL_MSAA_LAYOUT_ARRAY, then width_sa=64, height_sa=64, depth_sa=1,
+ array_length_sa=4.
+
+- Physical Surface Elements (el):
+
+ This unit allows ISL to treat compressed and uncompressed formats
+ identically in many calculations.
+
+ If the surface's pixel format is compressed, such as ETC2, then a surface
+ element is equivalent to a compression block. If uncompressed, then
+ a surface element is equivalent to a surface sample. As a corollary, for
+ a given surface a surface element is at least as large as a surface sample.
+
+Errata
+------
+ISL acquired the term 'surface element' from the Broadwell PRM [1], which
+defines it as follows:
+
+ An element is defined as a pixel in uncompresed surface formats, and as
+ a compression block in compressed surface formats. For MSFMT_DEPTH_STENCIL
+ type multisampled surfaces, an element is a sample.
+
+
+References
+==========
+[1]: Broadwell PRM >> Volume 2d: Command Reference: Structures >>
+ RENDER_SURFACE_STATE Surface Vertical Alignment (p325)
* @brief Intel Surface Layout
*
* Header Layout
- * =============
- *
+ * -------------
* The header is ordered as:
* - forward declarations
* - macros that may be overridden at compile-time for specific gens
* - enums and constants
* - structs and unions
* - functions
- *
- *
- * Surface Units
- * =============
- *
- * Intro
- * -----
- * ISL takes care in its equations to correctly handle conversion among
- * surface units (such as pixels and compression blocks) and to carefully
- * distinguish between a surface's logical layout in the client API and its
- * physical layout in memory.
- *
- * Symbol names often explicitly declare their unit with a suffix:
- *
- * - px: logical pixels
- * - sa: physical surface samples
- * - el: physical surface elements
- * - sa_rows: rows of physical surface samples
- * - el_rows: rows of physical surface elements
- *
- * Logical units are independent of hardware generation and are closely
- * related to the user-facing API (OpenGL and Vulkan). Physical units are
- * dependent on hardware generation and reflect the surface's layout in
- * memory.
- *
- * Definitions
- * -----------
- * - Logical Pixels (px):
- *
- * The surface's layout from the perspective of the client API (OpenGL and
- * Vulkan) is in units of logical pixels. Logical pixels are independent of
- * the surface's layout in memory.
- *
- * A surface's width and height, in units of logical pixels, is not affected
- * by the surface's sample count. For example, consider a VkImage created
- * with VkImageCreateInfo{width=w0, height=h0, samples=s0}. The surface's
- * width and height at level 0 is, in units of logical pixels, w0 and h0
- * regardless of the value of s0.
- *
- * For example, the logical array length of a 3D surface is always 1, even
- * on Gen9 where the surface's memory layout is that of an array surface
- * (ISL_DIM_LAYOUT_GEN4_2D).
- *
- * - Physical Surface Samples (sa):
- *
- * For a multisampled surface, this unit has the obvious meaning.
- * A singlesampled surface, from ISL's perspective, is simply a multisampled
- * surface whose sample count is 1.
- *
- * For example, consider a 2D single-level non-array surface with samples=4,
- * width_px=64, and height_px=64 (note that the suffix 'px' indicates
- * logical pixels). If the surface's multisample layout is
- * ISL_MSAA_LAYOUT_INTERLEAVED, then the extent of level 0 is, in units of
- * physical surface samples, width_sa=128, height_sa=128, depth_sa=1,
- * array_length_sa=1. If ISL_MSAA_LAYOUT_ARRAY, then width_sa=64,
- * height_sa=64, depth_sa=1, array_length_sa=4.
- *
- * - Physical Surface Elements (el):
- *
- * This unit allows ISL to treat compressed and uncompressed formats
- * identically in many calculations.
- *
- * If the surface's pixel format is compressed, such as ETC2, then a surface
- * element is equivalent to a compression block. If uncompressed, then
- * a surface element is equivalent to a surface sample. As a corollary, for
- * a given surface a surface element is at least as large as a surface
- * sample.
- *
- * Errata
- * ------
- * ISL acquired the term 'element' from the Broadwell PRM [1], which defines
- * a surface element as follows:
- *
- * An element is defined as a pixel in uncompresed surface formats, and as
- * a compression block in compressed surface formats. For
- * MSFMT_DEPTH_STENCIL type multisampled surfaces, an element is a sample.
- *
- * [1]: Broadwell PRM >> Volume 2d: Command Reference: Structures >>
- * RENDER_SURFACE_STATE Surface Vertical Alignment (p325)
*/
#pragma once
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