APPLE_color_buffer_packed_float

GL_APPLE_color_buffer_packed_float

Alexander Rogoyski, Apple Inc
Serge Metral, Apple Inc

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

Complete

Last Modified Date: February 13, 2014
Version:            1.0

OpenGL ES Extension #194

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.

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.

None

None

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.

Relaxation of INVALID_ENUM errors 
---------------------------------

RenderbufferStorage accepts the new R11F_G11F_B10F_APPLE and 
RGB9_E5_APPLE token for <internalformat>.

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.

None

1.0  2014/02/1  rogoyski    Initial version