skia / external / github.com / KhronosGroup / OpenGL-Registry / d15191e446614fcec3369577495dfb45b131a27a / . / extensions / APPLE / APPLE_color_buffer_packed_float.txt

Name | |

APPLE_color_buffer_packed_float | |

Name Strings | |

GL_APPLE_color_buffer_packed_float | |

Contributors | |

Alexander Rogoyski, Apple Inc | |

Serge Metral, Apple Inc | |

Contact | |

Alexander Rogoyski, Apple Inc (rogoyski 'at' apple.com) | |

Status | |

Complete | |

Version | |

Last Modified Date: February 13, 2014 | |

Version: 1.0 | |

Number | |

OpenGL ES Extension #194 | |

Dependencies | |

Requires EXT_color_buffer_half_float | |

Requires OpenGL ES 3.0 or APPLE_texture_packed_float | |

Written against the OpenGL ES 2.0.25 (Nov. 2010) Specification. | |

OpenGL ES 2.0 interacts with this extension. | |

OpenGL ES 3.0 interacts with this extension. | |

Overview | |

This extension allows two packed floating point formats | |

R11F_G11F_B10F and as RGB9_E5 defined in APPLE_texture_packed_float or | |

OpenGL ES 3.0 or to be rendered to via framebuffer objects. | |

New Procedures and Functions | |

None | |

New Tokens | |

None | |

Additions to Chapter 4 of the OpenGL ES 2.0 Specification (Per-Fragment | |

Operations and the Framebuffer) | |

Modify Section 4.3.1 (Reading Pixels), p. 104 | |

(modify first paragraph, p 104) ...Only two combinations of format and type | |

are accepted. The first varies depending on the format of the currently | |

bound rendering surface. For normalized fixed-point rendering surfaces, | |

the combination format RGBA and type UNSIGNED_BYTE is accepted. For | |

R11F_G11F_B10F surfaces, the combination RGB and | |

UNSIGNED_INT_10F_11F_11F_REV_APPLE is accepted. For RGB9_E5 surfaces, the | |

combination RGB and GL_UNSIGNED_INT_5_9_9_9_REV_APPLE is accepted. For | |

floating-point rendering surfaces, the combination format RGBA and type | |

FLOAT is accepted. The second is an implementation-chosen format... | |

(modify "Conversion of RGBA Values", p. 106) The R, G, B, and A values | |

form a group of elements. For a fixed-point color buffer, each element is | |

converted to floating-point according to section 2.1.2. For a floating- | |

point color buffer, the elements are unmodified. | |

Add to Table 4.4, p. 106: | |

type Parameter Component | |

Token Name GL Data Type Conversion Formula | |

---------------------------------- ------------- ------------------ | |

UNSIGNED_INT_10F_11F_11F_REV_APPLE uint see below | |

UNSIGNED_INT_5_9_9_9_REV uint see below | |

(modify "Final Conversion", p. 106) If type is not FLOAT, HALF_FLOAT_OES, | |

UNSIGNED_INT_10F_11F_11F_REV_APPLE or UNSIGNED_INT_5_9_9_9_REV | |

each component is first clamped to [0,1]. Then the appropriate conversion | |

formula from table 4.4 is applied to the component. | |

"Encoding of Special Internal Formats" | |

If <type> is UNSIGNED_INT_10F_11F_11F_REV_APPLE, the red, green, | |

and blue bits are converted to unsigned 11-bit, unsigned 11-bit, | |

and unsigned 10-bit floating-point values as described in | |

"Unsigned 11-BitFloating-Point Numbers" and "Unsigned 10-Bit | |

Floating-Point Numbers" | |

If <type> is UNSIGNED_INT_5_9_9_9_REV_APPLE, the red, green, and | |

blue bits are converted to a shared exponent format according to | |

the following procedure: Components red, green, and blue are | |

first clamped (in the process, mapping NaN to zero) as follows: | |

red_c = max(0, min(sharedexp_max, red)) | |

green_c = max(0, min(sharedexp_max, green)) | |

blue_c = max(0, min(sharedexp_max, blue)) | |

where: | |

sharedexp_max = (2^N - 1) / 2^N * 2^(E_max - B) | |

N is the number of mantissa bits per component (9), B is the | |

exponent bias (15), and E_max is the maximum allowed biased exponent | |

value (31). The largest clamped component, max_c, is determined: | |

max_c = max(red_c, green_c, blue_c) | |

A preliminary shared exponent exp_p is computed: | |

exp_p = max(-B - 1, floor(log2(max_c))) + 1 + B | |

A refined shared exponent exp_s is computed: | |

max_s = floor(max_c / 2^(exp_p - B - N) + 0.5) | |

/ exp_p, 0 <= max_s < 2^N | |

exp_s = | |

\ exp_p+1, max_s = 2^N | |

Finally, three integer values in the range 0 to 2^N - 1 are computed: | |

red_s = floor(red_c / 2^(exp_s - B - N) + 0.5) | |

green_s = floor(green_c / 2^(exp_s - B - N) + 0.5) | |

blue_s = floor(blue_c / 2^(exp_s - B - N) + 0.5) | |

The resulting red_s, green_s, blue_s, and exp_s are stored in the red, | |

green, blue, and shared bits respectively. | |

Add to Table 4.5, p. 117: | |

Sized Renderable R G B A D S Shared | |

Internal Format Type bits bits bits bits bits bits bits | |

-------------------- ---------------- ---- ---- ---- ---- ---- ---- ------ | |

R11F_G11F_B10F_APPLE color-renderable f11 f11 f10 | |

RGB9_E5_APPLE color-renderable 9 9 9 5 | |

(modify table description) Table 4.5: Renderbuffer image formats, showing | |

their renderable type (color-, depth-, or stencil-renderable) and the number | |

of bits each format contains for color (R, G, B, A), depth (D), and stencil | |

(S) components. The component resolution prefix indicates the internal data | |

type: f is floating-point, no prefix is unsigned normalized fixed-point. | |

Errors | |

Relaxation of INVALID_ENUM errors | |

--------------------------------- | |

RenderbufferStorage accepts the new R11F_G11F_B10F_APPLE and | |

RGB9_E5_APPLE token for <internalformat>. | |

Dependencies on OpenGL ES 3.0 | |

Replace all references to UNSIGNED_INT_10F_11F_11F_REV_APPLE and | |

UNSIGNED_INT_5_9_9_9_REV_APPLE with non _APPLE versions respectively. | |

New Implementation Dependent State | |

None | |

Revision History | |

1.0 2014/02/1 rogoyski Initial version | |