extensions/QCOM/QCOM_texture_foveated2.txt

Name

    QCOM_texture_foveated2

Name Strings

    GL_QCOM_texture_foveated2

Contact

    Jeff Leger - jleger 'at' qti.qualcomm.com

Contributors

    Sam Holmes
    Jonathan Wicks
    Arpit Agarwal

Status

    Complete

Version

    Last Modified Date:  October 12, 2020
    Author Revision: 1.0

Number

     OpenGL ES Extension #331

Dependencies

    This extension requires QCOM_texture_foveated.

    This extension interacts with QCOM_texture_foveated_subsampled_layout.

Overview

    This extension adds a new texture parameter that specifies a pixel density
    below which rendering can be discarded during foveated rendering.

New Tokens

    Accepted as a value for <pname> for the TexParameter{if} and
    TexParameter{if}v commands and for the <pname> parameter of
    GetTexParameter{if}v:

    TEXTURE_FOVEATED_CUTOFF_DENSITY_QCOM         0x96A0

    Add new rows to Table 8.19 (Texture parameters and their values):

        Name                               | Type | Legal Values
    ------------------------------------------------------------
    TEXTURE_FOVEATED_CUTOFF_DENSITY_QCOM | float | Any float between 0.0 and 1.0

    Add new rows to Table 21.10 Textures (state per texture object)

    Get value | Type | Get Command | Initial Value | Description | Sec
    ------------------------------------------------------------------
    TEXTURE_FOVEATED_CUTOFF_DENSITY_QCOM | R[0.0,1.0] | GetTexParameter{if}v | 0.0 | Pixel density threshold for rendering cutoff | 8.19

    This parameter defines the cutoff pixel density for a given focal
    point at the location (px,py) on a texture layer in NDC as:

    cutoff_pixel_density=TEXTURE_FOVEATED_CUTOFF_DENSITY_QCOM;
    for(int i=0;i<focalPointsPerLayer;++i){
        focal_point_density = 1./max((focalX[i]-px)^2*gainX[i]^2+
                            (focalY[i]-py)^2*gainY[i]^2-foveaArea[i],1.);
        if(focal_point_density >= cutoff_pixel_density)
            shade pixel;
    }

    The resulting contents of the buffer regions corresponding to the
    discarded pixels will be undefined.

New Procedures and Functions

    None.

Errors

    INVALID_VALUE is generated by TexParameter{if} or TexParamter{if}v
    if <pname> is TEXTURE_FOVEATED_CUTOFF_DENSITY_QCOM and <param> is a
    float less than 0.0 or greater than 1.0.

Issues

    (1)  What are the texture contents in discarded regions?

    RESOLVED: After a draw operation where the foveation density cutoff
    is applied, the contents of the discarded regions of the texture become
    undefined. It is the application's responsibility to only sample from
    the regions of the texture that are above the cutoff pixel density, as
    specified by the provided foveation parameters.

    (2)  Are any other buffers impacted other than color buffer?

    RESOLVED: Yes. Contents of the depth and stencil buffers will be
    undefined for discarded regions.

    (3)  What is the impact on primitive/geometric data for discarded regions?

    RESOLVED: For the discarded regions, primitive data is also discarded so
    the behavior of all shaders in the vertex processing stage is undefined
    for these regions (such as UAV writes and transform feedback).


Revision History

      Rev.    Date    Author    Changes
      ----  --------  --------  -----------------------------------------
      1.0   10/12/20  jleger  Initial version.